Integrating Solar Energy into Fossil Fuel Power Plant with CO₂ Capture and Storage: A Bibliographic Survey

Abstract

There is an urgent need to reduce greenhouse gas emissions, particularly carbon dioxide (CO₂). Currently, numerous research initiatives are underway to develop CO₂ Capture and Storage (CCS) technologies aiming for net-zero emissions, especially in sectors that are difficult to decarbonize, such as fossil fuel power generation. Integrating solar thermal energy into CO₂ capture facilities (CCFs) for fossil fuel-based power plants offers a promising approach to reduce the high operational costs associated with CO₂ capture processes. However, a comprehensive systematic review focusing on the integration of solar thermal energy with CCFs in fossil fuel power generation is currently lacking. To address this gap, this study systematically evaluates the technological frameworks involved, including (a) various generation technologies such as coal-fired Rankine cycle plants, natural gas combined cycle plants, and cogeneration units; (b) concentrated solar power (CSP) technologies, including parabolic trough collectors, linear Fresnel reflectors, solar power towers, and Stirling dish systems; and (c) post-combustion CO₂ capture systems. Additionally, this research analyzes relevant projects, patents, and scholarly publications from the past 25 years that explore the coupling of CSP technologies with fossil fuel power plants and post-combustion CO₂ capture systems. This literature review encompasses diverse methodologies, such as innovative patents, conceptual models, evaluations of solar collector performances, thermal integration optimization, and various system configurations. It also investigates technical advancements aimed at improving efficiency, reliability, and flexibility of fossil fuel power plants while mitigating the inherent challenges of CO₂ capture. Beyond the energy-focused aspects, we explore complementary circular economy strategies—such as by-product valorization and material substitution in sectors like mining, cement, and steel manufacturing—that can reduce embodied emissions and enhance the overall system benefits of solar-assisted CO₂ capture. The review employs a bibliometric approach using digital tools including Publish or Perish, Mendeley, and VOSviewer to systematically analyze the scholarly landscape.

1. Introduction

According to the Intergovernmental Panel on Climate Change (IPCC), greenhouse gas emissions over the past decade have reached the highest levels in human history, highlighting the urgent need for action. CO₂ is a long-lived greenhouse gas, and its emissions come from burning coal, oil, and natural gas. In 2022, the CO₂ concentration in the atmosphere reached 417.9 ± 0.2 ppm [1]. Without immediate and substantial reductions in emissions across all sectors, it will be impossible to limit global warming to 1.5 °C. A key outcome of the United Nations Climate Change Conference (COP 28) is the stocktake, which encompasses all previously negotiated elements and can now assist countries in crafting more robust climate action plans for 2025. The stocktake emphasizes that global greenhouse gas emissions must be reduced by 43% by 2030 compared to 2019 levels to limit warming to 1.5 °C. However, it notes that the Parties are not currently on track to meet the objectives outlined in the Paris Agreement. The stocktake urges Parties to take action to achieve a threefold increase in renewable energy capacity and to double energy efficiency improvements by 2030 [2].

Conversely, the Global Carbon Capture and Storage Institute states that climate change is the most pressing challenge currently facing humanity and the scientific community. It is clear that all available tools must be employed to mitigate its impact. Notable institutions addressing energy issues, such as the Intergovernmental Panel on Climate Change (IPCC) and the International Energy Agency (IEA), have highlighted the vital role of Carbon Capture and Storage (CCS) in reaching net-zero emissions by 2050 [3]. Furthermore, experts agree that CCS will be especially crucial for removing CO₂ already present in the atmosphere and for industries that are difficult to decarbonize, such as cement and steel production [3].

Within CCS Technologies’ extensive portfolio, chemical and physical absorption emerge as the most closely related methods, particularly with a market focus on industrial-scale applications in the electricity generation sector that utilizes fossil fuels [4]. According to Henry’s law, the physical absorption of CO₂ depends on its solubility in a solvent without undergoing any chemical reaction. In contrast, chemical absorption involves a reaction between CO₂ and specific solvents, resulting in the formation of a weak bond [5].

The primary challenge associated with implementing this technology is its significant energy consumption, which can reduce the overall efficiency of the combined cycle by approximately 6 to 9% [6,7]. This efficiency reduction (caused by the energy consumption in CCP) is called the efficiency penalty. To mitigate this efficiency penalty, various technological applications have been developed, including

• Renewable energy in Power Generation Plants, e.g., coal power plant and Natural Gas Combined Cycle (NGCC) [7,8,9,10,11];
• Exhaust Gas Recirculation (EGR) in NGCC [12,13], which consists of returning part of the flue gas to replace part of the air inflow in the combustor;
• Selective Recirculation in NGCC [14,15];
• Sequential Combustion in Gas Turbine [16];
• Sequential supplementary firing in NGCC [17,18];
• Integration of Renewables Energy Technologies [19,20].

Renewable energy sources, including photovoltaic, solar thermal, wind, bioenergy, hydropower, geothermal, and ocean energy, face challenges such as intermittency and low-capacity factors [21]. Intermittency and low plant factor in various technologies are caused by different factors. For example, in photovoltaic and solar thermal energy, it results from limited sunlight availability. For wind, hydro, biomass, and ocean energy, it is due to weather unpredictability. Additionally, for geothermal energy, it stems from long maintenance periods. One proposed solution to mitigate these issues is the integration of renewable energies into existing power plants [22].

This article presents a bibliographic overview of research focused on integrating Solar Thermal Energy into CO₂ Capture Plants utilizing post-combustion processes in power plants. It specifically concentrates on solar thermal energy and discusses two options for supplying thermal energy during periods of low irradiance. Furthermore, it includes alternatives for enhancing the flexibility of generating plants integrated into a CCS unit, which will become increasingly important as solar energy is incorporated. The main findings in this review are that CSP technologies are technically viable for supplying the thermal energy required for the CCP. The integration of CSP with CCP is most economically feasible in regions with high solar irradiance; however, the high cost of CSP fields could be a critical barrier. This review additionally emphasizes that there exists substantial research concerning individual technologies (CSP, CCP, Fossil Fuel Power Plants) in comparison with the integration of dual technologies (CSP-Fossil Fuel Plants, Fossil Fuel Plants-CCP, CSP-CCP), whereas research involving the integration of all three technologies (CSP-Fossil Fuel Plants-CCP) remains scarce.

2. Description of Evaluated Power Plant Technologies

This bibliographic survey will systematically examine power plant technologies, focusing on the following key areas: (a) conventional power plants, (b) CO₂ capture technologies utilizing post-combustion methods, and (c) solar thermal technologies employing concentration techniques. Each of these domains will be detailed to elucidate their operational principles, applications, and advancements in the field.

2.1. Fossil Fuel Power Plant Technology

It is well-established that the primary types of fossil fuel-powered central plants include (a) the Rankine Cycle (RC) and (b) the Natural Gas Combined Cycle (NGCC). Within these technologies, various configurations exist, primarily distinguished by the type of fuel used and the specific arrangements employed [23,24]. Figure 1 illustrates the fundamental configurations of these technologies.

In Cycle Rankine Power Plants, superheated steam is produced in a steam generator and then directed to expand in a steam turbine. This turbine is connected to an electrical generator that converts the turbine’s mechanical energy into electrical energy, which is subsequently supplied to the electrical grid. After the steam expands in the turbine, the exhaust steam is condensed.

In the realm of Cycle Rankine Power Plants, several variants are recognized. Coal remains the most widely utilized energy source globally, with its various classifications regarding fuels. Additionally, natural gas is acknowledged as a significant alternative fuel. The configurations of these power plants are predominantly determined by their size. For instance, small power plants, typically ranging from 5 to 50 MW, operate under low pressures and temperatures, approximately 20–60 bar and 380–490 °C. Conversely, larger power plants, with capacities from 50 to 500 MW, are designed to function at higher pressures and temperatures, specifically around 60–180 bar and 490–620 °C. Furthermore, the required power output influences the number of extractions, varying from 1 or 2 up to 8 or 10 extractions [23].

Additionally, various types of equipment contribute to the diversity of Rankine Cycle plants, including different configurations of steam generators, types of steam turbines, and cooling system designs. Another significant aspect of these plants is their ability to cogenerate, which enables the simultaneous production of electrical energy and processed steam [24].

Various equipment options are available, including different types of steam generators, steam turbines, and cooling systems. Additionally, it is essential to highlight that a significant variant of Rankine Cycle plants is their ability to operate in cogeneration, facilitating the simultaneous production of electrical energy and steam.

The Natural Gas Combined Cycle (NGCC) integrates two thermodynamic cycles: the Rankine Cycle and the Brayton Cycle. In this system, a gas turbine produces hot gases at about 600 °C, a temperature that can vary depending on the turbine’s size, technology, and manufacturer. These exhaust gases are used in a Heat Recovery Steam Generator (HRSG), which recycles the heat to generate steam, then utilized in the Rankine Cycle to produce additional electrical energy. This process boosts the overall efficiency of power generation beyond the capabilities of each cycle independently.

Moreover, the NGCC system features various operational variants. Typically, natural gas serves as the primary fuel source; however, in certain exceptional cases, diesel fuel may be utilized. Another variation involves the deployment of internal combustion engines instead of gas turbines while maintaining the integrity of the overall process [27]. Additionally, NGCC systems can be transformed into cogeneration plants, also known as combined heat and power (CHP) plants. This modification is achieved by extracting steam from either the steam turbine or the HRSG to supply thermal energy for other processes [28].

Combined Heat and Power (CHP) systems are widely recognized for their efficiency in utilizing fossil fuel technology. CHP is defined as the simultaneous generation of heat and electrical power from a single energy source. In these systems, thermal energy that would otherwise be wasted is captured and repurposed. This energy typically comes from electricity-producing devices such as heat engines, including steam turbines, gas turbines, and internal combustion engines. The captured thermal energy can be used for various applications, such as space heating, water heating, or industrial processes, and can also serve as thermal energy for other components of the system [29]. A basic configuration of CHP is illustrated in Figure 2.

The primary advantage of combined heat and power (CHP) systems is their ability to enhance fuel efficiency in generating both electrical and thermal energy. A CHP unit requires significantly less fuel to produce a given amount of electrical and thermal energy compared to traditional technologies, such as turbine-generator sets and steam boilers. This increased efficiency results from the effective use of heat generated by the turbine, which is converted into valuable thermal energy, like process steam, instead of being wasted within a cogeneration system. Different types of cogeneration units exhibit varying fuel consumption patterns and yield diverse ratios of electricity to steam. The electricity-to-heat ratio reflects the balance of electrical and thermal energy produced by a specific cogeneration unit [30].

2.2. Concentrated Solar Power

Solar concentrating technologies use complex mirror or lens systems to focus solar irradiation onto a designated receiver, facilitating the conversion of sunlight into thermal energy. This concentrated solar energy can generate superheated vapor from water or organic fluids, enabling indirect electricity generation or providing heat for industrial applications [31]. In the context of this analysis, the thermal energy harvested can serve two primary functions: it can supply the necessary heat for the CO₂ Capture Plant (CCP) during the re-boiling process, or it can offset the electrical energy needs by transferring thermal energy to a Fossil Energy Power Plant. These systems can typically achieve efficiency levels exceeding 20%, making them a viable option for enhancing energy infrastructure while reducing carbon emissions.

The primary types of Concentrated Solar Power (CSP) plants include (a) Parabolic Trough Collectors (PTC), (b) Linear Fresnel Collectors (LFC), (c) Solar Power Towers (SPT), and (d) Stirling Dish Collectors (SDC). PTC and LFC technologies are classified as linear focusing systems because they concentrate solar heat along the length of the collector. In contrast, SPT and SDC technologies focus heat at a single point, either at the top of the tower or at the center of the parabolic dish [31,32].

Concentrated solar plants can be paired with thermal storage systems (Figure 3) to use the stored heat for electricity generation during cloudy periods or when sunlight is unavailable. This ability to store solar energy increases the flexibility and dispatchability of concentrated solar power as a renewable energy source [32,33].

Concentrated Solar Power (CSP) systems can improve the efficiency of Natural Gas Combined Cycle (NGCC) power plants, creating Hybrid Power Plants. These hybrid plants can also integrate with thermal power facilities that use coal, natural gas, or biofuels, providing complementary support. Additionally, CSPs can incorporate fossil fuels to supplement solar energy during periods of low solar radiation. In such instances, a boiler powered by natural gas or any available fuel source is utilized [34,35].

Figure 3. Conceptual layout of a Concentrated Solar Power (CSP) plant with thermal energy storage. Solar radiation is concentrated in a solar field and transferred via a receiver/heat-transfer-fluid loop to both (i) a thermal storage unit and (ii) a power block (steam turbine and generator) that exports electricity to the grid. Stored thermal energy enables dispatch when solar irradiance is low and can also supply heat to downstream processes such as solvent regeneration in post-combustion CO₂ capture (elaborated from reference [36]).

Figure 3. Conceptual layout of a Concentrated Solar Power (CSP) plant with thermal energy storage. Solar radiation is concentrated in a solar field and transferred via a receiver/heat-transfer-fluid loop to both (i) a thermal storage unit and (ii) a power block (steam turbine and generator) that exports electricity to the grid. Stored thermal energy enables dispatch when solar irradiance is low and can also supply heat to downstream processes such as solvent regeneration in post-combustion CO₂ capture (elaborated from reference [36]).

2.3. Post-Combustion CO₂ Capture Plants

Conversely, post-combustion CO₂ capture technology has been implemented in power plants, primarily those powered by coal, natural gas combined cycle (NGCC) plants, and, to a lesser extent, combined heat and power (CHP) systems. As noted earlier, integrating CO₂ capture technology in power plants often presents challenges related to power and efficiency losses. One proposed strategy to alleviate these drawbacks is to supplement technology with solar thermal energy. These configurations are illustrated in Figure 4, Figure 5 and Figure 6.

The following sections examine the key research, projects, and publications developed over the past 25 years concerning the integration of Concentrated Solar Power technology with fossil fuel power plants, and post-combustion CO₂ capture. Fossil fuel power plants are classified as coal-based power plants, combined cycle plants, and combined heat and power (CHP) systems.

3. Bibliographic Survey Method

According to the reviewed literature, three primary methods are employed in conducting bibliographic surveys: (a) bibliometric analysis, (b) meta-analysis, and (c) systematic review [37]. This study initially adopted a bibliometric analysis, followed by a systematic review, ultimately leading to the proposed taxonomy review. The methodology implemented is described in Figure 7.

3.1. Bibliometric Review (Step 1)

In step 1, the Google Scholar database was used as a data source for the Publish or Perish software release 8.17 [38]. The search used all the keywords listed in the methodology, and the output was saved in a RIS (Research Information System) file.

3.2. Filter Publications (Step 2)

The RIS format files obtained in step 1 were exported to the Mendeley software release 2.138.0 [39] to filter publications. Manual debugging was conducted, removing duplicate publications and disaggregating publications clearly unrelated to the research topics, e.g., CO₂ related to biomass, photovoltaics. Other eligibility criteria were indexed journal papers and patents published in English between 1995 and 2025. These eligibility criteria were chosen due to the rigorous process for publication or obtaining patents.

Figure 8 shows the results of the filtering of articles and patents. Filtering of the keyword set determined a total of 3692 publications, including patents. Regarding the journals, the first group, with a range between 200 and 300 published articles, includes Energy Conversion and Management and Energy, with 579 published articles, equivalent to a 15.7% share. The second group, with a range of 150 and 200 published articles, includes Renewable Energy, Renewable and Sustainable Energy Reviews, Applied Energy, and Solar Energy. Patents were also found in this group, with 185 grants. This group shows 895 published articles, equivalent to a 24.2% share. The third group, between 100 and 150, is Energy Procedia, Applied Thermal Engineering, Journal of Cleaner Production and International Journal of Greenhouse Gas Control. This group shows 486 articles equivalent to a share of 13.2%. In the fourth group, in a range between 25 and 100 published articles, are International Journal of Hydrogen Energy, Energy Policy, Journal of Energy Storage, Sustainable Energy Technologies and Assessments, Environmental Science & Technology, Energy & Fuels, Fuel and Environmental Science, and Pollution Research, with 319 published articles equivalent to a share of 8.6%. The fifth group is a set of 24 journals that have between 10 and 25 publications. This group shows 369 publications, equivalent to a share of 10.0%. In the last group, there are 514 journals ranging from 1 to 9 articles, with 1044 articles and a share of 28.3%. It is important to mention that to facilitate the visualization of Figure 9, only Journals with a minimum of 10 publications were included.

Figure 9 shows the articles published annually, including patents. This analysis shows a mixed trend: from 1995 to 2000, production remained flat, averaging 12 articles per year. From 2001 to 2011, production continued to increase, rising from 17 to 175 articles published yearly, with an average growth rate of around 10%. From 2012 to 2022, it increased from 158 to 316 publications per year, showing a growth rate lower than the previous period, equivalent to 1%. From 2022 to 2024, there was a decrease from 316 to 258 published articles, comparable to an average annual rate of −9.1%. It is important to note that in 2025, the publications considered are only up to 15 May 2025, so they are not considered for comparison purposes due to their incompleteness. A more detailed analysis is required to determine the reasons for these variations in growth rates over the different periods.

3.3. Bibliometric Analysis (Step 3)

To clarify step 3 of the methodology, it is important to explain how VOSviewer works. VOSviewer software (version 1.6.1) [40] categorizes keywords into clusters based on relevance. The words within each cluster determine the cluster type on the map. Each node represents a keyword, and the arcs between nodes indicate relationships between the keywords. The size of the nodes shows their importance; larger nodes represent more relevant words, reflecting their frequency and the amount of research in that area. Links between nodes also have a weight, with higher weights used to examine the strength of the connection and its significance. As the weight increases, it indicates more research has been conducted on the relationship between the two nodes [41].

• Set 1: Analysis of the topic “Carbon Capture in Coal Power Plants Utilizing Thermosolar Energy”

Figure 10 displays three clusters: (a) Energy (red), (b) Renewable energy (blue), and (c) CO₂ capture (green). In the first cluster, the word energy is clearly linked to solar energy and fossil fuels such as oil and natural gas. The second cluster is related to renewable energy and similar themes like global warming, CO₂ emissions, wind energy, and others. The third cluster focuses on CO₂ capture and related topics such as coal-fired power plants, CO₂ capture through post-combustion and pre-combustion methods, and so on. Because the connections between the three technologies—Coal Fuel Power Plant, Solar Energy, and CO₂ Capture—appear weak, it suggests that little research has been done on integrating CO₂ capture systems with power plants and solar energy.

• Set 2: Analysis of the topic Carbon Capture in Natural Gas Combined Cycle using thermosolar energy

Figure 11 displays three clusters: (a) Carbon Dioxide Capture (green), (b) CO₂ Storage (blue), and (c) Solar Energy (red). The first cluster focuses on Carbon Dioxide Capture, mainly including topics related to integrated gasification combined cycle, natural gas combined cycle, and Postcombustion Carbon Capture, showing extensive research on Combined Cycles integrated with gasification and CO₂ capture, as well as CO₂ Capture coupled to NGCC, with emphasis on the Postcombustion technology domain for CO₂ capture. The second cluster relates to CO₂ storage and the topic of CO₂ Capture and Storage (CCS), along with hydrogen production and renewable energies. The third cluster centers on solar energy, primarily related to solar power generation and integrating solar energy into combined cycles. Of the three technologies—Natural Gas Combined Cycle, Solar Energy, and CO₂ Capture—the strongest connection is between Carbon Dioxide Capture and Natural Gas Combined Cycle, indicating the need for extensive research into their integration. The other two links show weaker connections, suggesting significant potential for future research.

• Set 3: Analysis of the topic “Carbon Capture in Combined Heat and Power utilizing thermosolar energy”

Figure 12 shows four clusters: (a) Capture technology (green), (b) Solar energy (blue), (c) Combined Heat and Power (CHP) (red), and (d) Cogeneration system (light green). The first cluster focuses on Capture technology, followed by absorption, solvent, and post-combustion capture, suggesting extensive research on CO₂ capture systems through post-combustion technology, which is identified by using absorption processes and solvents such as MEA. The second cluster centers on Solar energy, followed by hydrogen production, methanol, water, and renewable energy systems, indicating substantial research in solar thermal systems aimed at generating so-called green hydrogen. The third cluster emphasizes CHP, followed by coal capture systems and coal capture and storage (CCS), indicating a dominance of studies in these areas. In the fourth cluster, the predominant term was cogeneration system, followed by performance analysis, solar power plants, and exergy, pointing to a trend in research related to optimizing these types of systems. Four clusters emerged, producing six links shown in Figure 13. Three of these have a significant number of co-occurrences: (a) Capture technology-solar energy, (b) Capture technology-CHP, and (c) Solar energy-cogeneration system. The other three links—(d) Capture technology-cogeneration system, (e) CHP-cogeneration system, and (f) CHP-solar energy—indicate promising research opportunities.

3.4. Systematic Review (Step 4)

• After conducting the bibliometric analysis in Step 3, it was determined that the research topics addressed in this study were emerging but presented significant opportunities. A more targeted analysis is recommended to achieve a comprehensive review of research papers and patents. This review was carried out using the taxonomy shown in Figure 14.

Figure 14. Taxonomy of the reviewed literature on solar-assisted post-combustion CO₂ capture integrated with fossil and cogeneration power systems.

Figure 14. Taxonomy of the reviewed literature on solar-assisted post-combustion CO₂ capture integrated with fossil and cogeneration power systems.

Table 1. List of the 20 most cited articles in this bibliometric analysis.

#	Article Title	Journal	Accumulated Citations
1	A comprehensive review of state-of-the-art concentrating solar power (CSP) technologies: Current status and research trends [42]	Renewable and Sustainable Energy Reviews	992
2	Simulation of CO2 capture using MEA scrubbing: A flowsheet decomposition method [43]	Energy Conversion and Management	477
3	Historical development of concentrating solar power technologies to generate clean electricity efficiently—A review [32]	Renewable and Sustainable Energy Reviews	459
4	A solar-driven combined cycle power plant [44]	Solar energy	293
5	Comparison of two CO2 removal options in combined cycle power plants [45]	Energy Conversion and Management	273
6	A review of concentrated solar power hybrid technologies [34]	Applied Thermal Engineering	218
7	A novel methodology for comparing CO2 capture options for natural gas-fired combined cycle plants [46]	Advances in Environmental Research	206
8	Does circular economy mitigate the extraction of natural resources? Empirical evidence based on analysis of 28 European economies over the past decade [47]	Ecological Economics	189
9	A review of integrated solar combined cycle system (ISCCS) with a parabolic trough technology [48]	Renewable and Sustainable Energy Reviews	180
10	Solar-assisted Post-Combustion Carbon Capture feasibility study [49]	Applied Energy	160
11	Evaluation of natural gas combined cycle power plant for post-combustion CO2 capture integration [50]	International Journal of Greenhouse Gas Control	134
12	An integrated combined cycle system driven by a solar tower: A review [31]	Renewable and Sustainable Energy Reviews	131
13	Natural gas combined cycle power plants with CO2 capture—Opportunities to reduce cost [51]	International Journal of Greenhouse Gas Control	112
14	Feasibility of integrating solar energy into a power plant with amine-based chemical absorption for CO2 capture [52]	International Journal of Greenhouse Gas Control	111
15	Optimal integration of solar energy with fossil fuel gas turbine cogeneration plants using three different CSP technologies in Saudi Arabia [53]	Applied Energy	104
16	Integrating mid-temperature solar heat and post-combustion CO2-capture in a coal-fired power plant [54]	Solar Energy	98
17	Performance evaluation of PACT Pilot-plant for CO2 capture from gas turbines with Exhaust Gas Recycle [55]	International Journal of Greenhouse Gas Control	92
18	Redesign, Optimization, and Economic Evaluation of a Natural Gas Combined Cycle with the Best Integrated Technology CO2 Capture [56]	Energy Procedia	85
19	Technical and economic analysis of integrating low-medium temperature solar energy into power plant [57]	Energy Conversion and Management	79
20	Potential for solar-assisted post-combustion carbon capture in Australia [58]	Applied Energy	78

shows the 20 most cited publications in this systematic review, which display the publication title, journal name, and accumulated citations. Regarding the journals, “Renewable and Sustainable Energy Reviews” and “International Journal of Greenhouse Gas Control” have 4 publications in the 20 most cited articles, followed by the “Energy Conversion and Management” and “Applied Energy” journals, which have 3 publications in the top cited publications, and “Solar Energy”, which has only 2 publications, while the rest of the journals have only 1 publication.

4. Thermosolar Plants Integrated into a Coal Power Plant with Post-Combustion CO₂ Capture

4.1. Patents

In 2010, Wibberley introduced the first chemical absorption system powered by solar energy through a patent in the United States. This innovative system combines solar energy with the traditional steam extraction method to meet the energy needs for solvent regeneration. However, due to its intermittent availability, the patented design did not include energy storage, which limits solar energy’s contribution to the overall thermal energy needs. The patent is reported as abandoned [59].

4.2. Evaluation of Solar Thermal Collectors

In 2011, Cohen et al. conducted a preliminary feasibility study on solar thermal technologies for powering CO₂ Capture Plants (CCPs) in conjunction with coal-fired power plants, specifically examining Parabolic Trough Collectors (PTC), Solar Dish Collectors (SDC), and Solar Power Towers (SPT). The study concluded that both PTC and SPT are technically capable of supplying energy for CO₂ capture through heat in the reboiler. However, the initial capital costs of the solar systems are estimated to be about half of those of the coal power plant with CO₂ capture (CC). Additionally, high electricity prices are necessary to offset the operating costs associated with the solar thermal system. Furthermore, the research indicates that for high-temperature solar thermal systems, directly generating electricity or using steam turbines to power the compression system offers a more efficient way to harness solar energy as a substitute for the energy lost during CO₂ capture. Conversely, low-temperature solar thermal systems could be more effectively integrated with solvent extraction equipment [8].

Qadir et al. (2013) [58] conducted a techno-economic assessment of a 660 MW coal-fired power plant retrofitted with carbon capture and storage (CCS). This system is partially supported by solar thermal energy (STE), utilizing various types of collectors, including Flat Plate Collectors (FPC), Compound Parabolic Track Collectors (CPTC), Linear Fresnel Collectors (LFC), Evacuated Tube Collectors (ETC), and Parabolic Trough Collectors (PTC). The findings were compared to those of a conventional carbon capture plant, which supplies all thermal energy through steam extracted from the steam cycle to support the CCS. The overall system comprises three subsystems: the power plant, the CCS plant, and the solar collector field. The results indicated that the ETC configuration performed best among the solar collectors when the three subsystems were thermally integrated. In contrast, the PTCs emerged as the most effective when heat integration was not utilized.

Parvareh et al. (2014) [60] conducted a comprehensive review of the integration of solar energy within modern coal-fired power plants equipped with CO₂ capture technologies. The study examined various process integration approaches, discussing their advantages and disadvantages concerning both technical and climatic factors. Furthermore, the paper highlights the potential benefits of this hybridization between energy capture and solar power plants as a transitional solution for generating low-CO₂ emissions in the future. The authors concluded that the studies reviewed suggest low-temperature solar thermal systems are well-suited for providing heat to the reboiler of the amine recovery system. In contrast, medium-temperature systems, such as parabolic collectors, can be employed for both the reboiler and auxiliary needs of the CO₂ capture plant. High-temperature systems, on the other hand, are recommended for direct power generation to recover energy lost due to the integration of the CO₂ capture plant.

Wang et al. (2016) [57] proposed six configurations for integrating Solar Thermal Energy (STE) with a coal power plant, utilizing either Parabolic Trough Collectors (PTC) or Evacuated Tube Collectors (ETC). A 300 MWe subcritical coal plant served as the reference model, and Monoethanolamine (MEA) was used as the solvent for carbon capture. Both technical analyses and economic evaluations were performed. The findings indicate that integrating STE with Carbon Capture (CC) can significantly enhance power generation and reduce the electrical efficiency penalty associated with CC. Among the configurations examined, Configurations 2 and 6, which use medium-temperature STE to replace the high-pressure feedwater—with and without CC, respectively—exhibit the highest net incremental solar efficiency. For new plants, incorporating solar energy can substantially lower the levelized cost of electricity (LCOE). Configuration 6 has the lowest LCOE at 99.28 USD/MWh, based on a parabolic trough price of 185 USD/m². Conversely, when retrofitting existing power plants, Configuration 6 also yields the highest net present value (NPV), while Configuration 2 offers the quickest payback time, even with a carbon tax of $50/tonne CO₂. Additionally, both LCOE and NPV/payback time are influenced by factors such as the proportion of solar load, the cost of solar thermal collectors, and the carbon tax. Notably, the impact of the carbon tax is more pronounced in configurations involving CO₂ capture than those without it.

In 2017, Wang et al. developed a pilot solar thermal-assisted chemical absorption system to assess its performance. They evaluated two types of solar thermal energy collectors: Parabolic Trough Collectors (PTC) and Linear Fresnel Collectors (LFC). The results indicated that the performance values met the designed parameters, and the solar collectors effectively supplied the thermal energy required by the reboiler. It was also determined that solar irradiation played a crucial role in the system’s effectiveness [61].

4.3. Solar Thermal Technologies for Powering the CO₂ Capture Plant (CCP)

Cohen et al. (2010) [8] concluded that solar thermal technologies can effectively power carbon capture processes (CCP). The compression of CO₂ requires superheated steam temperatures above 350 °C at a pressure of 900 kPa. In contrast, the solvent-stripping process depends on saturated steam for effective operation.

In 2012, Zhao et al. proposed a hybrid power system that integrates mid-temperature solar heat with a 600 MW coal-fired power plant designed for CO₂ capture. In this innovative system, solar heat at approximately 300 °C is used to replace the steam extractions of the Rankine cycle, thereby preheating the feedwater. As a result, the extracted steam can be expanded more efficiently in the high-pressure turbine. This approach presents a promising solution for mitigating the CO₂ capture penalty associated with carbon capture and storage (CCS), while also providing a cost-effective means of harnessing mid-temperature solar energy [54].

In 2012, Mokhtar et al. conducted a technical and economic feasibility study for a CO₂ capture plant that utilized solar thermal energy with Fresnel technology, specifically designed for a 300 MW coal-fired power plant located in New South Wales, Australia. The study considered thermal storage using sensible solids and monoethylamine (MEA) as the solvent for the carbon capture process. The findings indicated that the levelized cost of carbon (LFC) could be economically viable if the solar collector costs are around US$100/m² at 2012 retail prices, with an optimal solar load fraction of 22% [49].

Other researchers have proposed hybrid systems integrating renewable energy sources, such as biomass and solar thermal. Carapellucci et al. (2015) [62] explored two primary approaches: (a) the utilization of biomass in an auxiliary boiler to enhance power capacity and meet the heat demands for CO₂ capture and (b) the implementation of a Combined Heat and Power (CFL) system to partially supply the regeneration heat service, rather than extracting steam from the main power plant or generating steam through a biomass boiler. The study assessed how the availability of renewable resources and energy conversion efficiency influenced the design of the auxiliary power unit, as well as the overall energy performance of the retrofitted coal-fired power plant with CO₂ capture. The coal power plant in question had a capacity of 100 MW, employed MEA, and did not include a Thermal Storage System. The findings indicated a 14% increase in net power for the first case, along with a minimal reduction in net efficiency. However, the second case yielded unsatisfactory results, primarily due to the intermittent availability of solar resources.

In 2017, Khalilpour et al. introduced a novel approach that eliminates the costly desorption system by utilizing solar collector tubing, specifically parabolic trough tubing, to directly heat the rich solvent and break the CO₂ solvent bonds. This innovative technology aims to decrease both the capital expenditure of the process and the energy required for solvent regeneration, thereby aligning it more closely with theoretical efficiency values. Furthermore, the removal of the desorption column enhances the operational flexibility of power plants (PP) in adapting to market dynamics. A case study conducted in Sydney, Australia, demonstrates that, compared to the SPCC methodology, this approach could significantly enhance process economics while minimizing the required size of the solar thermal collector (STC) field [27].

4.4. Solar Thermal Technologies for Powering the Fossil Plant

In 2012, Zhao et al. introduced a hybrid power system that combines mid-temperature solar heat with a 600 MW coal-fired power plant for CO₂ capture. One case examined involved an independent CO₂ capture system powered by thermosolar energy for direct solvent regeneration. This scenario was compared to a system integrated with the 600 MW coal-fired power plant for CO₂ capture. The findings indicated that the annual cost of the solar field was significantly reduced to $10.8 per ton of CO₂, compared to $25.8 per ton of CO₂ in the system utilizing solar heat for direct solvent regeneration [54].

Parvareh et al. (2016) [20] proposed and evaluated three configurations for integrating solar energy into power generation: (a) parallel power generation using solar energy, (b) thermal integration of solar energy with the power plant in high-pressure feedwater heaters, and (c) combined thermal and power mode integration of solar energy with both the PCC and power plant subsystems. Each option was evaluated based on the size requirements of the solar installation, the engineering and operational challenges it presented, and its potential to maintain and/or improve the original production of the power plant when the PCC is operational. A baseline scenario was established for this benchmark, featuring a 660 MWe CCP power plant functioning at 100% capacity with a 90% capture rate in Australia. The findings indicated that option 1 incurs the least disruption and achieves 100% of the CCP penalty, despite having the second-highest investment cost. Option 2 involves moderate disturbances, carries the lowest investment cost, but does not meet the full penalty for the CCP. Option 3 also results in moderate disturbances and provides 100% of the CCP penalty yet has the highest investment cost.

Wang et al. (2017) [61] developed a pilot plant for a solar thermal-assisted chemical absorption CO₂ capture system. This initiative aimed, among other objectives, to demonstrate that the solar thermal system could meet the thermal requirements of the CO₂ capture process. The evaluation confirmed that the system satisfies the thermal demands of the capture plant, thereby helping to maintain capacity at the retrofitted coal-fired power plant.

In 2017, Zhai et al. assessed the incorporation of solar energy to enhance the performance of CO₂ capture systems and reduce energy penalties. The paper proposed three integration strategies for a 1000 MW coal-fired power plant utilizing solar energy and a post-combustion CO₂ capture system. In the first integration, solar energy substitutes for the initial extraction to heat the feedwater, enabling the steam from the extraction to generate electricity through expansion in the High Steam Turbine. The second integration directs solar energy to the stripper reboiler to aid in the recovery of MEA. In the third integration, a combined approach is employed where one portion of the solar energy is supplied to the boiler as feedwater, while another portion is sent to the stripper reboiler to assist with MEA recovery. All three integrations leverage a portion of the intermediate-pressure turbine exhaust to meet the heat demand of the reboiler. The performance of these three integrations was compared against a conventional 1000 MW coal-fired power plant, a solar-aided coal-fired power system, and a coal-fired power plant equipped with post-combustion CO₂ capture. The findings indicated that the optimal strategy involves integrating solar energy to replace the first high-pressure extraction and utilizing a portion of the intermediate-pressure turbine exhaust for the reboiler’s heat demand. Additionally, the paper analyzed the variation in evaluation indicators concerning changes in CO₂ removal rates, solar collector field area, direct normal irradiance (DNI), solar collector field costs, coal costs, and carbon taxes [63].

In 2023, A. Alzhrani, C. E. Romero, and J. Baltrusaitis developed a comprehensive methodology to evaluate the feasibility and sustainability of solar-assisted CO₂ capture processes using amine solutions. The model combines steady-state simulation, dynamic controllability analysis, transient inventory estimation, and environmental assessment through life cycle analysis. Applied to a pilot plant in Al-Ahsa (Saudi Arabia), the system successfully removed over 90% of CO₂ from the flue gas by integrating a parabolic trough collector with ethylene glycol at 153 °C to feed the reboiler. The results showed that using the parabolic trough collector (PTC) resulted in a reduction of 328 kg CO₂ eq per 1000 kg avoided emissions, compared to 175 kg without the PTC. PTC was used for steam consumption in a CO₂ stripper reboiler. The two scenarios considered and compared were the steam-based MEA solvent regeneration and the PTC integrated. The dynamic model investigated the process control effects on CO₂ capture, including external disturbance handling. Solar irradiance contributed to steam consumption during the day, where the specific reboiler energy decreased to ~0.5 GJ/tonne CO₂ in the summer. The captured CO₂ amount and all the utilities used were integrated for January and July from the dynamic results and scaled to one year to be used in the comparative economic evaluation. Although the capital cost increased in the PTC-based case, the operating cost decreased. The total capital cost for a steam-based case was $5.2 million, and for the PTC combination case, it was $6.8 million. On the other hand, the operational cost for the steam-based case is $1.11 million/year to $1 million/year for the PTC combination case for ~20,000,000 kg CO₂ captured annually [64].

4.5. Assessment of Site Conditions

In 2012, Li et al. conducted a feasibility study on integrating solar energy into post-combustion CO₂ capture systems. This research emphasizes using parabolic and evacuated tube technologies and examines their performance under diverse environmental conditions. The operation of a coal-fired electricity generation plant that incorporates a solar-assisted post-combustion CO₂ capture (SPCC) system is greatly influenced by the site’s climatic factors, including solar irradiation, the number of sunlight hours, dry bulb temperature, type of solar collector, and CO₂ recovery rate. The evaluation results reveal that the costs of electricity generation and CO₂ avoidance are mainly determined by local climatic conditions. In regions with higher solar irradiation, more sunlight hours, and warmer ambient temperatures, SPCC-equipped power plants tend to have a lower Cost of Electricity (COE) and Cost of CO₂ Avoided (AOC). Furthermore, COE and AOC are particularly sensitive to the prices of Solar Thermal Collectors (STC) [52].

Qadir et al. (2013) [58] conducted a technical-economic evaluation of three sites in Australia, focusing on the locations of existing coal-fired power plants. The selected sites included Sydney, Townsville, and Melbourne. They evaluated a 660 MW coal-fired power plant as the baseline case, comparing various types of solar collectors: FPC, CPTC, LFC, and ETC. Among the sites assessed, Townsville yielded the most favorable results, showcasing the highest annual net benefits. This outcome was primarily attributed to its optimal characteristics for solar energy utilization, including impressive figures for average daily direct normal irradiation, average global horizontal irradiation, yearly sunshine hours, and ambient temperature. These findings underscore the critical importance of site conditions in the performance of solar thermal technology.

4.6. Quantitative Comparison

Table 2. Comparison of the main parameters of the integration of CPP with post-combustion CO₂ capture plant and Solar Thermal Energy.

Refs.	Technologies								Total Gross Power [kWe]	Efficiency [%]	CO2 Emission [tons/yr]	LCOE USD/MWh	Solvent	Solar Thermal Heat Input
	CPP	PCC	PTC	LFC	SPT	EGR	SSF	TES
[58] Qadir, et al.	X								660,000	30	4,430,370
	X	X							621,000	24	443,037		MEA
[57] Wang et al.	X								299,800	37.50	2,476,552
	X			X					312,740	39.22	2,368,151			LP feedwater preheaters
	X			X					343,000	43.23	2,148,330			HP feedwater preheaters as shown
	X			X					379,800	48.11	1,930,557			To Steam turbine
	X	X	X						299,760	34.15	271,935		MEA	to the striper reboiler
	X	X	X						254,910	28.20	329,264		MEA	LP feedwater preheaters
	X	X	X						292,400	33.17	279,942		MEA	HP feedwater preheaters
	X	X	X						329,250	38.06	244,000		MEA	To Steam turbine
[63] Zhai et al.	X								1000,000	48.95	6,689,249	34.94
	X		X						1057,850	51.78	6,689,249	39.41
	X	X							839,500	41.10	1,337,850	66.10	MEA
	X	X	X						896,670	43.89	1,337,850	70.94	MEA	HP feedwater preheaters as
	X	X	X						878,500	43.01	1,337,850	71.49	MEA	to the striper reboiler
	X	X	X						886,900	43.42	1,337,850	71.23	MEA	HP feedwater preheaters and striper reboiler
[64] Li et al.	X								520,000 (Net Power)	44.5	2,769,562	42.9
	X	X							408,000	34.9	414,593	70.9
	X	X	X					X	450,600	37.1	414,593	71.2		to the striper reboiler
	X	X	X					X	482,000	41.5	414,593	79.8		to the striper reboiler
	X	X	X					X	482,000	44.5	414,593	87.2		to the striper reboiler

summarizes the main results of the different integration options for Coal Power Plants. We will focus on three primary parameters: (a) Total Gross Power, (b) Efficiency, and (c) CO₂ emissions. First, we will analyze the power plant without the incorporation of any technology, and then we will analyze it with the CO₂ capture plant incorporated, and finally with the solar thermal plant incorporated.

The gross power in Coal Power Plants varies widely, ranging from approximately 300 to 1000 MW, and efficiency ranges between 30% and 48%. When the CO₂ capture plant is incorporated, the power and efficiency decrease by between 6% and 21.5%. When the solar thermal plant is incorporated into power plants with its CO₂ capture plant, the power generally tends to recover to the original capacity, as does the efficiency. Regarding other parameters, the predominant solar technology is the PTC, the CO₂ capture rates predominate at 90%, the predominant solvent is the MEA, and there is an interconnection between the solar thermal plant, the power plant, and the CO₂ capture plant, in which the striper reboiler predominates, followed by the high- and low-pressure preheaters, and finally the steam turbine.

4.7. Conclusions of the Section

Integrating thermosolar energy into coal power plants with CCPs is a key strategy to reduce CO₂ emissions without affecting electric output. Different thermosolar setups, using PTC, SDC, or SPT, have varying impacts on cost and efficiency depending on the power cycle design, thermal integration, and financial factors like carbon taxes and thermosolar field costs. In regions with high solar irradiance, thermosolar energy is a competitive choice for CCPs. Areas with the highest solar radiation, sunshine hours, and dry bulb temperatures yield the greatest technical advantages and economic benefits. The main challenge for these technologies is their high investment costs, making the impact on LCOE especially significant.

5. NGCC Coupled with Carbon Capture CO₂ and Thermosolar Energy

Only three publications concerning the integration of Natural Gas Combined Cycle (NGCC) with Carbon Capture and thermosolar energy were identified [10,65,66]. However, numerous studies exist on (a) NGCC with Carbon Capture and (b) NGCC with thermosolar energy. Initially, references [9,28] were examined as they concern NGCC with Carbon Capture and NGCC with thermosolar energy.

5.1. Papers Integrating Three Technologies

In 2011, Ordorica et al. introduced a proposal that integrates solar thermal concentrating technology with fossil fuel energy systems. This initiative aims to address the limitations of both technologies while leveraging their respective benefits. Solar thermal technology suffers from intermittency, low plant factor, and unpredictability, while fossil fuel systems contribute to high CO₂ emissions. Conversely, solar thermal energy has zero CO₂ emissions, whereas fossil fuels provide higher plant factors. This solar-fossil hybrid system would ensure a reliable energy supply even in the absence of sunlight or when stored solar energy is depleted. Additionally, the paper explores incorporating carbon capture (CC) technologies into these systems, which could potentially reduce their carbon intensity to nearly zero. The authors present three significant solar-fossil hybrid energy systems: (1) Integrated Solar Combined Cycle System (ISCCS), (2) Solar-assisted Post-Combustion CO₂ Capture (SPCC), and (3) Solar Gasification with CO₂ Capture [65].

With respect to reference [10], a Natural Gas Combined Cycle (NGCC) plant integrated with Post-Combustion Capture (PCC) was simulated using Aspen Plus and validated against models developed by the National Energy Technology Laboratory (NETL). This validation was subsequently tailored to align with the operational parameters of a facility located in Poza Rica, Mexico. Various heat integration strategies were assessed following the successful validation of the NGCC model coupled with PCC. These strategies utilized waste heat from flue gas coolers, CO₂ dryers, and CO₂ compressor intercoolers to preheat feedwater or generate low-pressure (LP) steam within the steam cycle. Further modifications to the model incorporated Solar-Assisted Carbon Capture (SACC) to mitigate the adverse effects of PCC on plant performance. Specifically, the simulation explored the application of parabolic trough solar thermal collectors to provide heat for the stripper reboiler within the PCC system. The findings indicated that harnessing solar thermal energy for the reboiler could decrease the flow rate of LP steam extraction or eliminate its requirement altogether, depending on the availability of solar thermal energy. The analysis revealed a significant increase in net plant power when 100% of the reboiler’s thermal duty was met through solar thermal energy, compared to scenarios without solar thermal collectors. Additionally, the solar resource availability for the target location in Mexico was forecasted using the System Advisor Model (SAM), developed by the National Renewable Energy Laboratory (NREL). By integrating the output data from SAM with those obtained from Aspen Plus, the annual energy production of the NGCC plant equipped with PCC utilizing solar thermal energy for reboiler heating was evaluated. A final case study was conducted where solar thermal energy was employed for heating LP steam. This particular case demonstrated slightly improved performance over the case that applied solar thermal energy directly to the reboiler. However, this system’s added complexity outweighed the marginal increase in net annual power generation. Overall, this modeling initiative illustrated that solar thermal heating of the stripper reboiler in an NGCC plant with PCC significantly offsets the negative impact of carbon capture on operational efficiency and power generation, providing a viable pathway for renewable energy integration in carbon mitigation strategies for NGCC plants.

In 2024, Y. A. H. Al-Elanjawy and M. Yilmaz analyzed the integration of solar thermal power into an NGCC plant at the Besmaya plant in Baghdad, Iraq, using Aspen Plus simulations and SAM for solar potential estimation. A solar-assisted post-combustion capture (PCC) plant was simulated and integrated into the existing NGCC plant infrastructure. The baseline simulation without carbon capture revealed a robust total power generation capacity of 751 MW, achieving a net plant efficiency of 49.8%. However, with post-combustion capture (PCC) integration, the total power capacity experienced a modest reduction to 698 MW, accompanied by a slight decline in efficiency to 48%. Crucially, the environmental impact assessment showcased a remarkable achievement in CO₂ emissions reduction. Without solar-assisted PCC, the NGCC plant emitted 2,119,318 tonnes of CO₂ annually. Through integration with solar assistance, emissions were slashed by an impressive 99%, reaching a minimum of 18,064 tonnes/year. The solar potential analysis for Baghdad indicated an annual solar energy availability of approximately 984,018,688 kWhth. The designed solar power system demonstrated its efficacy by generating 350,000 kW during the summer months, highlighting the feasibility and seasonal adaptability of solar integration [66].

5.2. Publications About NGCC with Carbon Capture

5.2.1. Patents

In 2013, Li et al. submitted Patent No. US 8,365,537 B2, titled “Power Plant with CO₂ Capture.” This patent proposes a method for operating a natural gas combined cycle (NGCC) power plant equipped with a carbon capture plant (CCP). The technique involves exhaust gas recirculation (EGR) of a first partial flow from the heat recovery steam generator (HRSG). Additionally, it incorporates carbon capture (CC) of a second partial flow from the HRSG, along with supplementary firing to enhance the plant’s net power output and partially offset the energy consumption of the CCP. This patent has expired. At the time of writing, there is no commercial CO₂ capture implemented in natural gas combined cycle (NGCC) power plants. However, although this patent has expired, it is important to note that the method could be useful once CO₂ capture is integrated into NGCC systems [67].

In 2020, Gulen [68] was awarded patent No. US 10,641,173 B2 for a technology titled “Gas Turbine Combined Cycle Optimized for Post-combustion CO₂ Capture.” This patent introduces a method to optimize a natural gas combined cycle (NGCC) system with an integrated carbon capture plant (CCP). Specifically, it involves diverting a portion of the combustion gases from the heat recovery steam generator (HRSG) to a second gas turbine that has been previously cooled. The exhaust from this second turbine is then mixed with the gases from the first turbine. Additionally, the system uses sulfur dioxide (SO₂) to enhance carbon monoxide (CO) concentration, thereby optimizing the overall NGCC-GT-CCP configuration. This patent has expired.

5.2.2. Conceptual Proposals

In 1998, Bolland and Mathieu compared two concepts for CO₂ capture. The first concept, developed under the European Joule II program, utilizes a semi-closed gas turbine cycle with CO₂ as the working fluid and combustion powered by oxygen produced in an Air Separation Unit (ASU). This system boasts zero emissions since any excess CO₂ generated during combustion is fully captured without the need for costly and energy-intensive devices. The second concept involves partial recirculation of flue gas from the heat recovery steam generator (HRSG) outlet of a natural gas combined cycle (NGCC). The remaining flue gas is directed to a CO₂ capture process (CCP), where ninety percent of the CO₂ is removed through an absorber/separator. The two concepts were evaluated alongside a state-of-the-art NGCC employing the latest technology (gas turbine type 9FA) and a three-pressure level HRSG. The findings indicate that the performance of the NGCC semi-closed CO₂ cycle is largely independent of the HRSG configuration, while the NGCC with recirculation shows slight sensitivity to the recirculation rate. A higher recirculation rate significantly reduces the size and, consequently, the cost of the CCP. From a performance perspective, the results show that the efficiency of the system with exhaust gas recirculation (EGR) and carbon capture (CC) consistently exceeds that of the NGCC with a CCP without EGR by approximately 2 to 3 percentage points [45].

In 2000, Undrum et al. conducted a technical and economic assessment of CO₂ capture and storage in Norway, sponsored by Statoil and several contracting firms. The central concept of this study revolves around capturing CO₂ from the exhaust gases of a Natural Gas Combined Cycle (NGCC) using an amine solution absorption method. The captured CO₂ is then compressed, transported via pipeline, and stored in offshore deep saline aquifers. The findings are contrasted with an alternative method for CO₂ capture based on a Hydrogen Combined Cycle. The study compares the costs of CO₂ capture from an NGCC with other greenhouse gas reduction strategies. The primary outcome indicates that post-combustion CO₂ capture for a 1400 MW NGCC is more efficient, achieving an efficiency of 49%, while the hydrogen cycle attains an efficiency of 46.5%. Economically, the costs associated with post-combustion capture are $ 1235/kW installed, compared to $ 1291/kW for the hydrogen cycle [69].

In 2003, Bolland and Undrum conducted a study that evaluated and compared three concepts for capturing CO₂ in Natural Gas Combined Cycle (NGCC) systems. The first concept involves capturing CO₂ from exhaust gases through chemical absorption using amine solutions. The second concept focuses on a semi-closed gas turbine employing near-stoichiometric combustion with oxygen from an Air Separation Unit (ASU), producing CO₂ and water as combustion products. The third concept entails natural gas reforming with an Auto Thermal Reactor (ATR) that utilizes catalytic partial oxidation, after which the reformed hydrogen-rich fuel gas is combusted within the combined cycle. The calculations for CO₂ removal, including CO₂ compression, yielded efficiencies of (a) 49.6%, (b) 47.2%, and (c) 45.3%. However, the study is deemed inconclusive due to the lack of an economic evaluation [46].

In 2011, Ordorica et al. introduced a proposal integrating solar thermal concentrating technology with fossil fuel energy systems. The aim of this proposal is to address the limitations of each technology while leveraging their respective advantages. Its intermittency, lower plant factor characterizes solar thermal technology, and, to some extent, unpredictability. In contrast, fossil fuel technologies are associated with high CO₂ emissions. On a positive sidenote, solar thermal energy generates zero CO₂ emissions, while fossil fuels typically provide higher plant factors. This hybrid solar-fossil system would ensure a reliable energy supply during periods without sunlight or when stored solar energy is depleted. Additionally, the paper explores the incorporation of carbon capture (CC) technologies into these systems, which could significantly reduce their carbon intensity to nearly zero. The paper outlines three notable solar-fossil hybrid energy systems: (1) Integrated Solar Combined Cycle System (ISCCS), (2) Solar-assisted post-combustion CO₂ capture (SPCC), and (3) Solar Gasification with CO₂ Capture [65].

5.2.3. Integration Optimization Proposals

In 2005, Alie et al. conducted an analysis of the carbon capture (CC) process to minimize implementation costs. Since large-scale CC operations can be expensive, employing process simulation and modeling is essential for evaluating alternative approaches. Specifically, for amine-based carbon capture processes, achieving convergence in the process flowsheet presents a significant challenge due to the complex non-linear characteristics of the process and the various recirculation cycles involved. This study introduced a flowsheet decomposition method aimed at facilitating the convergence of the process flowsheet and optimizing key operational variables, particularly the amine loadings and the temperature of the monoethanolamine (MEA) entering the desorber. The method was applied to three different CO₂ concentrations (expressed as molar fractions on a wet basis): 3% (simulating flue gas from a gas turbine), 14% (flue gas from a coal plant), and 25% (flue gas from a cement plant). The results obtained from the decoupled and integrated flowsheets were similar. It was found that the minimum reboiler load occurred at a lean MEA loading of 0.25 for all studied CO₂ concentrations [43].

In 2009, Botero et al. assessed the Best Integrated Technology (BIT) concept for a 400 MW combined cycle developed by the CO₂ Capture Project Consortium, which includes British Petroleum, Texaco, and Petrobras. This concept incorporates carbon capture and storage with 40% gas recirculation and an amine regeneration boiler integrated into the heat recovery steam generator (HRSG). The evaluation considered a 90% carbon capture rate and a 30% weight solution of monoethanolamine (MEA). Compared to state-of-the-art solutions for conventional CO₂ capture in 2009, the BIT demonstrated technical performance very similar to traditional methods while also requiring smaller equipment for the CO₂ capture island, thereby enhancing its competitiveness relative to conventional capture schemes [56].

In 2011, Sander et al. assessed the impact of Exhaust Gas Recirculation (EGR) on gas turbines (GT), Natural Gas Combined Cycle (NGCC), and Combined Cycle Power (CCP) systems. The flue gas fraction reintroduced to the gas turbine requires additional cooling before mixing with ambient air. The following conclusions were drawn in the paper: (a) The outlet temperature of the recirculated gas fraction is the most significant parameter influencing the performance of NGCC and CCP; (b) EGR decreases the regeneration steam requirements in CCP; (c) For the reference cycle (NGCC with CCP), EGR enhances net power and cycle efficiency by 3.6% and 2.1%, respectively; (d) It also lowers the Cost of Energy (COE) by 5%, subsequently reducing the minimum price necessary for making Combined Cycle (CC) systems viable [70].

In 2011, Sipöcz et al. conducted a thermodynamic and economic evaluation of a 440 MWe natural gas combined cycle (NGCC) system equipped with a carbon capture process (CCP) using monoethanolamine (MEA). In this study, the CCP was optimized through internal absorber cooling and Lean Vapor Recompression (LVR), along with the application of Exhaust Gas Recirculation (EGR) to the gas turbine. The first scenario analyzed involved EGR at approximately 40%, while the second scenario included both internal absorber cooling and LVR. The first case demonstrated a net efficiency of 50.73%, a total installed cost of €352.34 million, a levelized cost of electricity (LCOE) of €58.56 per MWh, and a cost of abatement (COA) of €62.20 per ton. In contrast, the second case revealed a net efficiency of 51.04%, a total installed cost of €371.43 million, a LCOE of €59.40 per MWh, and a COA of €62.20 per ton [51].

In 2013, Biliyok and Yeung developed an evaluation of a 440 MW capacity natural gas combined cycle (NGCC) power plant integrated with CO₂ capture and compression at a rate of 90%. This integration resulted in a 15% decrease in power generation and a 33% increase in cooling water requirements. They also analyzed a scenario featuring exhaust gas recirculation (EGR) at 40%, which led to a power recovery of 10 MW; however, this option also resulted in higher water demands. The addition of Supplementary Fire (SF) to this scenario enhanced the combustion section’s performance. The economic analysis indicated that the overnight costs of the integrated plant are 58% higher than those of the conventional power plant, posing a challenge for adopting carbon capture technology. The impact of EGR was found to be marginal, while including SF nearly doubled the overnight costs. Consequently, the cost of electricity increased by 30% for the integrated plant, compared to a 26% rise with EGR and a 24% increase with SF [50].

In 2013, Canepa et al. conducted a thermodynamic analysis of a combined cycle natural gas power plant (NGCC) using simulations. Both the NGCC and the carbon capture process (CCP) were modeled in Aspen Plus, with the CCP model validated against experimental data from the pilot plant at the University of Texas at Austin. The study scaled the CCP from pilot plant operations to a commercial level to process flue gas from 250 MWe NGCC. It proposed implementing exhaust gas recirculation (EGR) to enhance the CO₂ concentration in the flue gas while reducing the overall flow rate. The study examined the impact of EGR on the performance of the NGCC and the sizing of the CCP. The results indicated that EGR could decrease the performance penalty by 1.8 MW without significantly altering the original plant parameters [71].

In 2016, Akram et al. conducted an experimental study at the UK Carbon Capture and Storage Research Centre (UKCCSRC). This study featured a 100 kWe Turbec PH turbine equipped with a post-combustion carbon capture (PCC) system capable of capturing one ton of carbon per day. The primary aim was to assess the effects of exhaust gas recirculation (EGR). The evaluation was carried out using various proportions of EGR and a concentration of 30% monoethanolamine (MEA). The results indicated that for each unit increase in CO₂ concentration, the specific thermal load of the reboiler decreased by 7.1%. Overall, a trend emerged showing that higher CO₂ concentrations correlated with lower specific thermal loads of the reboiler at a constant capture rate. Additionally, both the rich and lean solvent loadings increased as flue gas CO₂ concentration rose. The energy balance within the stripping process revealed that the rates of steam generation and condenser work intensified with increasing CO₂ concentrations [55].

In 2016, González et al. conducted a study evaluating sequential supplementary firing in the heat recovery steam generator of a natural gas combined cycle (NGCC) power plant. This approach presents an appealing alternative for markets with access to competitively priced natural gas and where carbon dioxide supply for Enhanced Oil Recovery (EOR) is critical. Sequential combustion leverages the excess oxygen in gas turbine exhaust to produce additional CO₂. Unlike conventional supplementary firing, this method maintains gas temperatures in the heat recovery steam generator (HRSG) below 820 °C, thereby avoiding significant increases in capital costs. Additionally, it offers a slight reduction in the relative energy requirements for solvent regeneration and minimizes amine degradation. Models of power plants integrated with capture and compression processes for Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units indicate that the efficiency penalty is 8.2 percentage points lower heating value (LHV) compared to an NGCC utilizing the same capture technology. However, the marginal thermal efficiency of natural gas firing in the HRSG can improve with supercritical steam generation, reducing the efficiency penalty to 5.7 percentage points of LHV. Although the efficiency of this setup is lower than that of the conventional configuration, the increase in power output from the combined steam cycle allows for a reduction in the number of gas turbines needed to achieve a similar overall power output. This positively affects the number of absorbers and lowers the capital costs of the post-combustion capture system by reducing the total volume of flue gas by half on a normalized basis. The relative decrease in overall capital costs is 15.3% for subcritical and 9.1% for supercritical combined cycle configurations with capture, in comparison to a conventional setup [17].

In 2017, Alcaraz et al. conducted an evaluation of the part-load operation of a natural gas combined cycle (NGCC) power plant utilizing exhaust gas recirculation (EGR) alongside a CO₂ capture facility. According to the authors, while several studies have highlighted the advantages of EGR at full load, part-load operation is equally significant, as it is a common scenario when NGCC power plants serve as backup for renewable energy sources. The findings indicated that EGR reduces the number of absorber trains from four to three. At full load, the efficiency of the NGCC plant with EGR was 0.5 percentage points higher than that of a conventional NGCC, attributed to a higher concentration of CO₂ in the flue gas. However, this efficiency advantage diminished as the load decreased from 100% to 50%, with both configurations exhibiting identical efficiency at the 50% load level. This suggests that the benefits of EGR are negligible at lower loads. The efficiency of the NGCC plant with EGR and CO₂ capture dropped from 52.6% to 45.9% when the load was reduced from 100% to 50%, whereas the conventional NGCC saw a decline from 52.1% to 45.9%. The study concluded that an NGCC plant incorporating EGR and CO₂ capture is a viable option, resulting in reduced capital costs due to fewer absorber trains while providing marginally higher efficiencies for operation at part-load down to 50% [13].

5.3. Publications About NGCC Integrated with STC

5.3.1. Patents

In 1995, Moore filed patent No. 5444972, titled “Solar-Gas Combined Cycle Electrical Generating System,” which proposed a power plant utilizing both fossil fuels and solar energy to generate electricity. The design includes a solar power tower (SPT). The thermal energy captured from the sun produces steam that powers a steam turbine. This steam can alternatively be sourced from the exhaust of a gas turbine and can optionally be enhanced by adding fuel to a furnace. The harvested solar energy may either be stored as heated fluid in a thermal storage tank or used immediately within the power plant. Additionally, a heat shield can be implemented over the central solar receiver to insulate it, providing leak protection and safeguarding the SPT [72]. Although the patent has expired, there are some existing power plants integrated with solar technology, for example, (a) Ain Beni Mathar Integrated Solar Combined Cycle Power Plant, Morocco, which started operation in the year 2011 [73], and (b) ISCC Kuraymat CSP Project, which started operation in the year 2014 [74].

5.3.2. Conceptual Proposals

In 1995, Pak et al. introduced a power generation system designed to capture CO₂ using solar thermal energy (STE). In this system, STE generates saturated steam at approximately 200 °C, which serves as the working fluid for a gas turbine. The CO₂ produced is recovered via oxycombustion, leading to a significantly higher utilization efficiency of solar thermal energy compared to traditional solar thermal power plants that require high-temperature steam near 400 °C for steam turbines. Additionally, the demand for solar radiation is notably reduced. The proposed hybrid system integrates both fossil fuels and solar thermal energy, resulting in a very high plant factor. The system effectively utilizes the fuel, which is used to elevate the steam temperature to over 1000 °C. Oxycombustion facilitates the recovery of nearly 100% of the CO₂ generated, achieving zero NOx emissions. Simulations demonstrate that this system achieves a net power generation efficiency of 64.5% based on the fuel energy consumed, utilizing saturated steam at a temperature of 230 °C. This marks an increase of 48.3% compared to the conventional plant, which has an efficiency of 43.5% [75].

In 1995, Williams et al. proposed the hybridization of fossil energy schemes, outlining five configurations: (a) Redundant Power Generation Systems (RSH), (b) Parallel Generation Systems with matching temperatures in Solar Thermal Energy (STE) and Fossil Machine (PFHH), (c) Parallel Generation Systems where the STE temperature is lower than that of the Fossil Machine, (d) Integrated Combined Cycle System with Solar Energy (ISCCS), and (e) Preheating with Solar Energy (SPH). The RSH system consists of two redundant subsystems—one powered by solar thermal energy and the other by fossil energy. The PFHH system has two parallel systems of solar thermal and fossil energy, both operating at the same outlet temperature. The third proposed system is similar, but the exit temperature of the STE is lower than that of the fossil machine. The fourth system introduces an integrated combined cycle that incorporates solar thermal energy, which is used in the steam turbine component as steam. Lastly, the fifth system uses STE to preheat the fossil energy system [76].

In 1995, Bohn et al. evaluated an innovative SPT concept that offers significant advantages for commercializing SPT technology. This concept employs a central molten nitrate salt receiving plant to supply heat, specifically through preheating combustion air, to a conventional combined cycle power plant. The evaluation focused on initial commercial plants, analyzing three different capacities (31, 100, and 300 MWe), and compared these facilities to a 100 MWe solar plant, as well as to gas-only combined cycle plants at the same three capacities. The analysis findings underscore several benefits compared to the solar-only plant, including lower energy costs for the initial plants, reduced capital costs for these plants, diminished risks associated with commercial uncertainties, and the potential for accessing new markets. Furthermore, the concept appears to require minimal technological advancements. Notably, the results suggest that constructing a first plant based on this concept could effectively compete with existing gas-only combined cycle plants [77].

In 1997, Pak et al. proposed using saturated steam at a relatively low temperature as a working fluid for a gas turbine burning methane. This approach significantly enhances the utilization efficiency of solar thermal energy compared to conventional solar thermal power plants, which typically operate with superheated steam at approximately 670 K. The suggested hybrid system also captures the CO₂ produced during oxycombustion. The design incorporates a collection system with an area of 10,000 m², based on estimates from a simulation model. The net power output was recorded at 1.55 MW, with a capacity factor of 21.5% and an overall operating efficiency of 20.9% at a saturated steam temperature of 496 K. Considering the fuel consumed, the thermal system’s efficiency reached 63.7% [78].

5.3.3. Assessment of Different Types of Thermosolar Collector and Integration Optimization Proposals

In 1998, Kribuz et al. conducted a feasibility study on a Natural Gas Combined Cycle (NGCC) power plant fueled by highly concentrated solar energy and central receiver technology. The study integrated advancements in solar tower optics, high-performance air receivers, and the solar-to-gas turbine interface, notably the Porcupine Volumetric Absorber (PVA) and Frustum-Like High-Pressure (FLHiP) window technologies. This innovative design enables 100% solar operation at the design point, alongside hybrid operation (utilizing both solar energy and conventional fuel) to enhance dispatchability. The findings indicate that this new system design provides both cost and performance benefits compared to other solar thermal concepts and can compete with traditional fuel-fired power plants in specific markets, even without government subsidies [44].

In 2001 Kelly et al. conducted two studies on the designs of integrated plants utilizing a General Electric Frame 7 (FA) gas turbine and a three-pressure heat recovery steam generator (HRSG). The findings are as follows: (1) the most efficient use of solar thermal energy (STE) involves producing high-pressure saturated steam to supplement the HRSG; (2) the capacity for transferring high-pressure steam generation work from the HRSG to the solar steam generator is limited, defining the maximum practical solar contribution; (3) minimal annual solar thermal contributions to an integrated plant can be converted into electrical energy more efficiently than using a parabolic trough plant alone, thereby enhancing the overall thermal-to-electrical conversion efficiency of the Rankine cycle; and (4) annual solar contributions of up to 12 percent in an integrated plant can provide economic benefits compared to a conventional solar-only parabolic plant [79].

In 2014, Gunasekaran et al. proposed and analyzed four distinct integration schemes for the Advanced Zero Emissions Power (AZEP) cycle utilizing parabolic trough technology: vaporization of the high-pressure stream, preheating of the high-pressure stream, heating of the inlet stream to the intermediate pressure turbine, and heating of the inlet stream to the low-pressure turbine. The power outputs of these integration schemes were compared both among themselves and against the power output of the standalone AZEP cycle when coupled with Concentrated Solar Power (CSP). Among the proposed integration schemes, the vaporization of the high-pressure stream resulted in the highest power output. Furthermore, both the vaporization and the heating of the intermediate pressure turbine inlet stream integration schemes yielded power outputs that surpassed those of the corresponding autonomous AZEP cycle and its CSP integration. When comparing the proposed vaporization scheme to existing hybrid technologies that do not incorporate carbon capture and storage (CCS), it was found to have a greater annual incremental solar efficiency than most of these technologies. Additionally, it offered a higher solar share compared to hybrid technologies with superior incremental efficiency. Consequently, AZEP cycles emerge as a promising option for consideration in solar thermal hybridization [80].

In 2014, Behar et al. conducted a comprehensive review of publications regarding Combined Cycle Systems Integrated with Solar Energy utilizing parabolic trough technology (ISCCS). The review assessed the status of operational, under-construction, and planned power plants. Key findings from the study include (a) enhanced solar field performance results in higher operating temperatures and, consequently, improved efficiency; (b) smaller solar fields yield greater energetic efficiency; (c) higher steam pressure levels and a greater number of feedwater heaters contribute to better steam cycle performance; (d) larger power plants generally lead to lower electricity production costs; and (e) rising fossil fuel prices increase the competitiveness of ISCCS. The review also highlighted that rapid advancements in research and development within ISCCS have enabled the emergence of highly efficient and profitable configurations. Given the continuous decline in fossil fuel reserves and the corresponding increases in their prices, ISCCS is becoming a more competitive option compared to traditional combined cycle power plants, positioning it as a potential technology of choice in the near future [48].

In 2015, Baharoon et al. reviewed the historical development of solar concentration technologies for generating electrical energy. The document outlined the evolution of Concentrated Solar Power (CSP) technologies and highlighted current global projects to demonstrate that these technologies are both technically sound and commercially viable. Moreover, it emphasized the potential for hybridization with fossil fuels or integration with storage systems to enable continuous operation like conventional power plants. The parabolic trough system stands out as the most technical and commercially established among various solar thermal technologies. It has been successfully hybridized in numerous commercial projects over the past 28 years, showcasing a high level of maturity. This technology can efficiently deliver the necessary operational thermal energy—either independently or as part of hybrid systems—at a competitive cost with minimal economic risks. Consequently, it remains the predominant choice in operational and construction projects. However, advancements in performance have sparked a trend toward adopting other CSP technologies in future initiatives. Currently, parabolic trough technology comprises 95.7% of operational CSP projects, which has decreased to 73.4% for projects currently under construction. In contrast, the use of Linear Fresnel Collectors (LFC), Solar Power Towers (SPT), and Solar Dish Collectors (SDC) in operational projects stands at 2.07%, 2.24%, and 0%, respectively. In comparison, those percentages have risen to 5.74%, 20.82%, and 0.052% for under-construction projects. Additionally, in the realm of development projects, the utilization of Solar Power Tower technology has reached 71.43%, compared to 28.57% for parabolic trough systems [32].

In 2016, Okoroigwe and Madhlopa conducted a review of articles discussing the integration of solar power tower (SPT) systems into combined cycle (NGCC) power plants. This publication examined advancements in the development of SPT-NGCC integration. The findings revealed significant attention has been given to the research surrounding SPT technology, with some commercial power plants successfully operating in various regions worldwide. This technology holds substantial promise for integration with NGCC from both thermodynamic and economic perspectives. However, the maturity level of SPT technology remains lower than that of parabolic trough concentrators (PTC). Limited research has been directed toward the development of SPT-NGCC systems, and to date, most operational NGCC power plants utilize PTC technology, with no commercial SPT-NGCC power plants existing as of 2015. This situation suggests that several barriers to the advancement of SPT-NGCC technology exist, categorized into three areas: (a) technological maturity, (b) financial and political considerations, and (c) technical challenges. It is concluded that the solar thermal integrated solar combined cycle systems (ST-ISCCS) are still in an immature state, highlighting the need for further efforts to enhance their technological readiness [31].

In 2017, Pramanik and Ravikrishna conducted a comprehensive review of hybrid power generation technologies that utilize concentrated solar energy. This article examines hybrid power generation technologies involving concentrated solar power (CSP) along with several renewable and non-renewable resources, including biomass, wind, geothermal energy, coal, and natural gas. The technologies are classified into high, medium, and low renewable hybrids based on their renewable energy components. Highly renewable hybrids demonstrate the lowest specific CO₂ emissions (less than 100 kg/MWh), followed by medium hybrids (less than 200 kg/MWh) and low renewable hybrids (greater than 200 kg/MWh). These hybrids are compared based on their plant characteristics and performance metrics, drawing from both literature and data from actual hybrid power plants. Technologically mature low-renewability hybrids, such as Integrated Solar Combined Cycle (ISCC), Brayton solar, and solar-assisted coal-fired Rankine systems, exhibit superior performance compared to their high- and medium-renewability counterparts. Medium renewable hybrids, like natural gas-supported solar plants, offer a high solar share but encounter challenges related to low efficiency and high costs, which impede market acceptance. Highly renewable hybrids, including CSP wind, CSP biomass, and CSP geothermal energy, have minimal negative environmental impacts. Nevertheless, several factors, such as energy efficiency, solar-to-electricity efficiency, capacity factor, and cost-effectiveness, require enhancement for these systems to achieve competitive viability [34].

In 2018, Islam et al. conducted a comprehensive review of the current state of Concentrated Solar Power (CSP) technologies. The Parabolic Trough Collector (PTC) and the Solar Power Tower (SPT) are the two primary CSP systems that are either operational or under construction. The United States and Spain are recognized as global leaders in CSP electricity generation, while developing countries such as China and India are making significant investments to advance in this field. The PTC collector with direct steam generation (DSG) technology represents an evolving area of research that holds potential for hybrid integration with other CSP technologies for both electricity and thermal heat production. Additional promising research topics in CSP include optimizing solar fields with multiple solar collectors, estimating the levelized cost of electricity through sensitivity analysis, applying the System Advisor Model (SAM) in the development of CSP plants, and implementing organic Rankine cycle engines for heat and energy production. Furthermore, research on the Supercritical CO₂ Energy Cycle in CSP plants, performance analysis of thermochemical energy storage and calcium looping methods in CSP systems, desalination processes, life cycle assessments, hydrogen production, and the use of phase change materials (PCM) should also be explored in future studies [42].

5.4. Quantitative Comparison

Table 3. Comparison of the main parameters of the integration of NGCC with post-combustion CO₂ capture plant and Solar Thermal Energy.

Refs.	Technologies								Total Gross Power [kWe]	Efficiency [%]	CO2 Emission [tons/yr] *	LCOE USD/MWh	Solvent	HTF	SC	Solar Thermal Heat Input
	NGCC	PCC	PTC	LFC	SPT	EGR	SSFC	TES
[10] Bravo et al.	X								547,874	49.7	1,452,281
	X	X							485,861	41.3	145,262		MEA
	X	X	X						547,923	46.8	145,262	45.7	MEA	Dowtherm Q	PTC, Siemens SunField 6	to the striper reboiler
[66] Elanjawy and M. Yilmaz	X								751,340	49.8	2,119,318
	X	X	X						751,340	48.0	18,064	18	MEA	Dowtherm Q	PTC, Siemens SunField 6	to the striper reboiler
[69] Undrum et al.	X								400 000	58	363 g/kWh
	X	X							338 000	49	60 g/kWh	90	MEA
[56] Botero et al.	X								413 000	50.71	363 g/kWh
	X	X							367 000	50	60 g/kWh	80	MEA
[50] Biliyok and Yeung	X								440,600	59.62	354.5 (kg CO2/MWh)
	X	X							376,000	49.38	40.1 (kg CO2/MWh)		MEA
[43] Alie et al.	X	X				X			386,100	50.71	39.5 (kg CO2/MWh)		MEA
[13] Alcaraz et al.	X	X							674,000	52.5			MEA
	X	X				x			672,800	51			MEA
[17] González et al.	X								835,000	51.3
	X						X		840,000	43.1
	X	X					X supercritical		884,000	45.6			MEA
	X	X					X subcritical		834,000	43.1			MEA

* If the units are not indicated, they are tons/yr.

summarizes the main results of the different integration options for the Natural Gas Combined Cycle. We will focus on three main parameters: (a) Total Gross Power, (b) Efficiency, and (c) CO₂ emissions. First, we will analyze the NGCCC without the incorporation of any technology, and then we will analyze it with the CO₂ capture plant incorporated, and finally with the solar thermal plant incorporated.

The gross power in NGCC varies widely, ranging from approximately 350 to 850 MW, and the efficiency between 50% and 59%. When the CO₂ capture plant is incorporated, the power and efficiency decrease by 11.1% and 15.5%. When the solar thermal plant is incorporated into power plants with its CO₂ capture plant, the power generally tends to recover to the original capacity, as does the efficiency. Regarding other parameters, the predominant solar technology is the PTC, the CO₂ capture rates predominate at 90%, the predominant solvent is the MEA, and the interconnection between the solar thermal plant, the NGCC, and the CO₂ capture plant, the striper reboiler predominates.

5.5. Conclusions of the Section

In this section, only three publications were found to analyze the integration of three technologies: NGCC combined with Carbon Capture CO₂ and thermosolar energy. The findings show that integrating these three technologies effectively addresses the disadvantages of each—such as the intermittency of solar thermal energy, CO₂ emissions from power plants, and the energy consumption of the CCP. The other two trends examined were the integration of CO₂ capture with NGCC and the integration of solar thermal energy with NGCC. Concerning publications that incorporate carbon capture with the combined cycle, the optimization approach is prominent, employing strategies like flue gas recirculation, supplementary firing, sequential supplementary firing, sequential combustion, as well as comparisons with oxy-combustion, pre-combustion, and hydrogen combustion schemes. Optimization primarily aims to increase CO₂ concentration in the exhaust gases to lessen the energy penalty caused by the CCP. Regarding the integration of solar thermal energy with NGCC, the focus has been on exploring various types of low- and high-temperature solar energy integrations, such as (a) steam integration in the gas turbine combustor; (b) high-pressure steam integration in the HRSG; (c) medium-pressure steam heating; and (d) low-pressure steam heating. These evaluations concluded that the best option is to generate high-pressure, high-temperature steam to feed the steam turbine. Another approach involved evaluating different solar concentration technologies, with the parabolic trough identified as the most suitable due to its technological maturity costs.

6. Thermosolar Plants Integrated into Combined Heat and Power with Postcombustion CO₂ Capture

6.1. Combined Heat and Power with CO₂ Capture Incorporated

In 1995, Gelowitz et al. conducted a technical-economic study that assessed five cogeneration systems utilizing gas and steam turbines. The gas turbines examined included (a) Typhoon with a capacity of 4.56 MWe, (b) Mars T14000 with a capacity of 10 MWe, (c) MF111B with a capacity of 14.57 MWe, (d) FT8 with an electrical capacity of 25.42 MWe, and (e) 251b12 with a capacity of 49.1 MWe. These systems were analyzed for their potential in CO₂ capture and storage for enhanced oil recovery (EOR). The study illustrates how cogeneration concepts, coupled with optimization design strategies, can help reduce CO₂ production costs by employing low-pressure vapors and waste heat from various stages of the power generation process to extract CO₂. The economic and technical feasibility of these concepts is explored, along with discussions on their practical implications given the resources available in Western Canada for EOR applications [81]

In 2011, Leduc et al. conducted a technical and economic evaluation focusing on cogeneration plants designed to be “Carbon Capture Ready” (CCR). A plant built or retrofitted with the CCR concept includes provisions for future implementation of Post-Combustion Carbon Capture (PCC) [82]. Their study examined both oxy-combustion and post-combustion capture as promising technologies. The primary objective was to assess the potential of each technology in addressing carbon capture within the two main types of thermomechanical converters found in cogeneration plants: turbines and boilers, while also identifying their limitations. The evaluation considered alternative cogeneration plant designs, including those with and without combined cycles. The findings indicate a close competition between oxy-combustion and post-combustion capture technologies. Additionally, the study highlights that the optimal CO₂ emissions reduction achievable with these technologies ranges from 40% to 60% of the original emissions, resulting in an avoided cost of CO₂ emissions between $100 and 150 USD/ton [83].

6.2. Combined Heat and Power with CO₂ Capture and Thermosolar Energy Incorporated

In 2017, Mokheimer et al. conducted a study to assess the technical and economic feasibility of integrating concentrating solar power (CSP) technologies with gas turbine cogeneration systems, which are increasingly being adopted in Saudi Arabia. Various designs of hybrid solar and fossil fuel gas turbine cogeneration systems have been proposed, exploring the potential integration of Solar Tower (ST), Parabolic Trough Collector (PTC), and Linear Fresnel Reflector (LFR) systems with conventional gas turbine cogeneration systems. The study evaluated these three CSP technologies for integration with a gas turbine cogeneration system capable of generating steam at a consistent flow rate of 81.44 kg/s, under conditions of P = 45.88 bar and T = 394 °C throughout the year, in addition to electricity generation. The performance of the Integrated Solar Gas Turbine Cogeneration Plant (ISGCP) for various gas turbine sizes was assessed using THERMOFLEX simulation software with PEACE, considering the climatic conditions of Dhahran. Comparative thermoeconomic analyses determined the optimal levelized electricity cost (LEC) and CO₂ emissions mix for each ISGCP configuration associated with the three CSP technologies, compared to the integration of CO₂ capture technology in a conventional plant. The simulation results indicated that the optimal configuration involves integrating LFR with the steam side of a 50 MWe gas turbine cogeneration plant, achieving an LEC of 5.1 US/kWh and reducing annual CO₂ emissions by 119 k tons [53].

In 2019, Pérez et al. evaluated the integration of solar-assisted post-combustion carbon capture into an experimental cogeneration system. At the National Institute of Electricity and Clean Energy (INEEL), a cogeneration system modeled on Thermoflex^® was installed, featuring a 200 kW Capstone microturbine and a thermal oil recovery system. Three optimized systems were considered for the economic analysis: a microturbine cogeneration system (COGEN), a microturbine cogeneration system with a post-combustion carbon capture plant (COGEN-CCS), and a microturbine cogeneration system with solar-assisted post-combustion carbon capture (COGEN-CCS+SOLAR). The cogeneration system was modeled using natural gas (NG) as fuel, incorporating typical characteristics of Mexico to determine the exhaust gas (EG) composition and simulate the CO₂ capture system in Aspen Hysys V8.6^®, utilizing monoethanolamine (MEA) as a solvent. The results indicated that implementing carbon capture and storage (CCS) significantly increased the levelized cost of electricity (LCOE) by approximately 86%, while achieving near-zero emissions and lacking the capability to supply energy to the process.

Furthermore, the COGEN-CCS+SOLAR system demonstrated improved overall performance. CO₂ emissions per kilowatt increased by 0.2% compared to COGEN-CCS, with LCOE rising by 230% in comparison to the COGEN case, also with nearly zero emissions. The incorporation of solar energy enhances cogeneration efficiency when combined with CO₂ capture [84].

In 2023, Alcaraz et al. conducted an evaluation of various design configurations for a combined heat and power (CHP) plant equipped with post-combustion CO₂ capture. Three distinct cases were analyzed: Case 1 comprised three trains, each featuring a configuration of one gas turbine paired with a heat recovery steam generator (HRSG); Case 2 included three trains along with a steam turbine; and Case 3 consisted of only two trains. Notably, Case 3 exhibited the highest CHP efficiency at 72.86%, yielding a net power generation of 511.8 MW. After identifying the optimal configuration, a parabolic-trough collector (PTC) was integrated to produce additional saturated steam at 3.5 bar for the capture plant, enhancing the flexibility of the CHP by allowing for greater availability of steam. Consequently, the efficiency of the cycle improved from 72.86% to 80.18%. Although Case 2 demonstrated lower efficiency compared to Case 3, its inclusion of a steam turbine offers the potential to increase electricity generation rather than steam production. With the integration of the PTC in Case 2, the power generated by the steam turbine rose from 23.22 MW to 52.6 MW, resulting in an increase in the net efficiency of the cycle from 65.4% to 68.21% [11].

6.3. Circular Carbon Synergies Across Hard-to-Abate Sectors

While most solar-assisted PCC/CCUS evaluations focus on thermal integration and power-cycle coupling, material flows across industrial systems can further enhance decarbonization efforts. Framed within a circular economy (CE), three key levers are particularly important: (i) valorization of by-products through industrial symbiosis, (ii) material substitution aimed at reducing clinker and cement intensity and embodied CO₂, and (iii) closed-loop recovery of critical minerals and reagents. Recent research in the mining and processing sectors highlights how metallurgical slags—by-products of steelmaking and non-ferrous metallurgy—can partially replace cement in applications such as mine backfilling and binders. This substitution can reduce process-related CO₂ emissions from clinker production and lower the overall life-cycle emissions of mining operations ([85] and [86]). From a systems perspective, such industrial symbioses can be co-optimized with solar-assisted PCC in fossil-fuel-powered assets (coal, NGCC, CHP) by (a) lowering site-level embodied emissions (Scope 3/embodied), (b) decreasing net avoided-CO₂ costs when material avoidance is credited, and (c) improving the dispatchability of low-carbon supply chains that incorporate thermal storage with material circularity. We propose a comprehensive assessment framework that reports, alongside energy metrics (Δη, GJ·tCO₂⁻¹ for reboilers, solar share, TES hours), circular economy (CE) metrics such as the avoided clinker factor, slag substitution ratio (%), and material circularity indicators. Including these metrics enables portfolio comparisons in regions where mining, cement, and steel industries co-locate with high Direct Normal Irradiance (DNI) solar resources. Additionally, it reveals opportunities where interdisciplinary collaboration—spanning process design, materials science, and mining engineering—can maximize overall system benefits. We cite Born, (2025) [85] and Ghorbani (2024) [86] as exemplary pathways within the CE framework for mining and metallurgy. Our review remains neutral regarding site-specific performance values and advocates for standardized reporting protocols.

Table 4. Mapping CE levers to solar-assisted CCS metrics.

CE Lever (Example)	Sector (s)	Mechanism	Primary Metric (s)	Interaction with Solar-Assisted PCC
Slag-based cement substitution in mine backfill	Steel → Mining	Avoided clinker production	Substitution ratio (%), kg clinker avoided·t−1, Δembodied CO2 (kgCO2·t−1)	Lowers life-cycle CO2; improves avoided-CO2 cost when credited
Reuse of waste heat in pre-processing	Mining	Thermal offset	kWhth·t−1, Δfuel	Reduces auxiliary loads; may downsize solar field
Solvent/amine reclaim via circular reagent loops	Power/CCS	Closed-loop chemicals	% solvent recovered, waste reduction	Cuts OPEX; lowers environmental footprint

summarizes the material-side interventions that can complement solar-assisted PCC and explains how they relate to reportable metrics. Each row represents a CE lever (e.g., slag-based cement substitution for mine backfill), the sectorial interface where it operates (steel → mining), and the underlying mechanism (industrial symbiosis, material substitution, or closed-loop recovery). The primary metrics column lists variables that make studies comparable across sites: substitution ratio (%), clinker avoided (kg t⁻¹), embodied-CO₂ change (kgCO₂ t⁻¹), and, when relevant, the effect on AOC/COA and LCOE once process-side metrics (capture rate, specific reboiler duty in GJ tCO₂⁻¹, and Δη) are held constant. The final column indicates the interaction with solar integration, showing whether the lever (i) reduces auxiliary energy demands (thus lowering required solar field/TES size), (ii) improves system-level net avoided CO₂ when material credits are included, or (iii) shifts the economic break-even point (e.g., under high DNI, lower CSP capex, or higher carbon prices). To improve reproducibility, we suggest that entries in the table be site-normalized—reporting DNI, storage hours, and solvent choice for the energy pathway, along with local material specifications for the CE pathway—while providing uncertainty bands (±1σ) or ranges obtained from sensitivity analyses. This format allows readers to connect material circularity outcomes with the thermal integration choices of solar-assisted PCC and to identify where cross-sector synergies generate the greatest improvements in avoided CO₂ at the portfolio level.

Figure 15 combines the energy and material aspects of the proposed setups. In the energy pathway (top), concentrated solar power (CSP) provides thermal energy via a heat-transfer-fluid (HTF) loop with thermal energy storage (TES). This solar heat is directed to the post-combustion capture (PCC) reboiler and/or to feedwater heaters (FWH), thus reducing steam extraction from the steam cycle/HRSG and lessening the efficiency penalty of capture. The central block depicts the fossil power unit (NGCC, coal, or CHP), whose flue gas is treated in the absorber–stripper PCC system. The material pathway (bottom) shows a circular-economy synergy: steel/metallurgy produces slag that, once processed, acts as a cement substitute in mining backfill, lowering embodied emissions compared to clinker-based binders. The two boxes highlight that evaluations should include both process-side metrics (capture rate, specific reboiler duty) and material-side metrics (clinker avoided, slag substitution ratio) to establish a coherent net avoided-CO₂ system

6.4. Quantitative Comparison

Table 5. Comparison of the main parameters of the integration of CHP with post-combustion CO₂ capture plant and Solar Thermal Energy.

Refs.	Technologies								Total Gross Power [kWe]	Efficiency [%]	CO2 Emission [tons/yr]	Solvent	Solar Thermal Heat Input
	CHP	PCC	PTC	LFC	SPT	EGR	SSFC	TES
[81] Gelowitz et al.	X	X							5929	39.81	23,824.28	MEA
	X	X							12,546	40.23	49,888.565	MEA
	X	X							18,832	40.53	9016.96	MEA
	X	X							28,974	43.78	105,879.2	MEA
	X	X							61,887	41.46	238,776.43	MEA
[83] Leduc et al.	X	X							150,000	55.0		MEA
[53] Mokheimer et al.	X		X						150,000	32.7	706,300.00		To process
	X			X					150,000	32.7	709,900.00		To process
	X				X				150,000	32.7	288,800.00		To Gas Turbine
[84] Jordan et al.	X	X	X						146.3	50.7	1025.05	MEA	to the striper reboiler
[11] Alcaraz et al.	X								511,800	80.07	1,997,254	MEA
	X	X							511,800	72.86	252,743	MEA
	X	X	X						511,800	80.18	229,593	MEA

summarizes the main results of the different integration options for Combined Heat and Power Plants. We will focus on three main parameters: (a) Total Gross Power, (b) Efficiency, and (c) CO₂ emissions. First, we will analyze the CHP without the incorporation of any technology, after we will analyze it with the CO₂ capture plant incorporated, and finally with the solar thermal plant incorporated.

The gross power in CHP Plants varies widely, ranging from approximately 0.146 to 511.8 MW, and the efficiency ranges between 32% and 80%. When the CO₂ capture plant is incorporated, the power and efficiency decrease by about 8%. When the solar thermal plant is incorporated into power plants with its CO₂ capture plant, the power generally tends to recover to the original capacity, as does the efficiency. Regarding other parameters, the predominant solar technology is the PTC, the CO₂ capture rates predominate at 90%, the predominant solvent is the MEA and the interconnection between the solar thermal plant, the CHP and the CO₂ capture plant, the process predominates.

6.5. Conclusions of the Section

This section has had the least research, with two main trends emerging: (1) cogeneration plants paired with CO₂ capture plants and (2) cogeneration plants paired with CO₂ capture plants assisted by solar thermal energy. It is concluded that cogeneration helps lower CO₂ production costs, but adding solar thermal energy to cogeneration plant systems with CCP improves overall system efficiency and its flexibility.

7. Conclusions

This review synthesizes 30 years of research, patents, and technological advancements, offering crucial insights into the feasibility, challenges, and future potential of integrating concentrated solar power (CSP) with coal-fired plants, natural gas combined cycle (NGCC) facilities, and combined heat and power (CHP) systems. The addition of solar thermal energy systems—operating in both thermal and power modes—alongside amine-based post-combustion CO₂ capture systems in traditional power plants has been thoroughly studied as a promising strategy for reducing greenhouse gas emissions. Research conducted over the past 30 years shows that the integration of concentrated solar technologies, such as parabolic trough collectors, linear Fresnel collectors, and solar power towers, can effectively address the operational drawbacks associated with amine CO₂ capture processes, particularly the energy-intensive compression systems. This combination not only enhances the overall sustainability of fossil fuel power plants but also offers a promising pathway for significantly reducing CO₂ emissions.

Key findings and recommendations derived from a systematic analysis of the interplay between solar thermal technologies, fossil energy systems, and carbon capture and storage (CCS) are consolidated below.

7.1. Technical Viability

The coupling of CSP technologies—such as parabolic trough collectors (PTC), solar power towers (SPT), and linear Fresnel collectors (LFC)—with CCS processes demonstrates measurable success in offsetting energy penalties (6–9% efficiency loss reduction) and enhancing operational flexibility. Solar-assisted feedwater heating, reboiler support, and sequential supplementary firing in NGCC systems exemplify configurations that improve efficiency while maintaining CO₂ capture rates. Coal-fired plants, benefiting from higher flue gas CO₂ concentrations (14–25%), achieve up to 43% emission reductions, while NGCC and CHP systems show promise through innovations like exhaust gas recirculation (EGR) and thermal storage hybridization.

7.2. Economic and Operational Challenges

Despite technical progress, economic barriers persist. Solar collector fields account for ~50% of retrofit costs, with levelized electricity costs (LCOE) for hybrid systems ranging from 99.28 USD/MWh (optimized PTC configurations) to 230% higher than conventional plants in solar-CHP integrations. Site-specific factors—solar irradiance variability, carbon taxation, and grid flexibility requirements—further complicate feasibility. Low-temperature solar systems prove to be cost-effective for solvent regeneration, but high-temperature applications demand material innovations and scaled manufacturing to compete with standalone fossil plants.

7.3. Integration Complexity

The taxonomy of hybrid systems reveals a fragmented landscape of solutions, underscoring the need for standardized frameworks to evaluate synergies and gaps. Dynamic operational challenges, such as solar intermittency and heat integration inefficiencies, necessitate advanced process simulation and adaptive control strategies to optimize performance across diverse climatic and operational settings.

To accelerate the transition toward low-carbon energy systems, the following strategic recommendations emerge:

• Cost and performance optimization:
  • Reduce capital expenditures through advancements in solar collector materials (e.g., high-reflectivity coatings, modular designs) and thermal storage systems.
  • Refine hybrid configurations using multi-objective optimization models to balance LCOE, efficiency, and scalability.
• Policy and market incentives:
  • Implement carbon pricing mechanisms, tax credits, and subsidies to offset upfront costs and incentivize private-sector adoption.
  • Foster public–private partnerships to pilot large-scale deployments, particularly in regions with high solar potential and fossil-dependent grids.
• Technological synergies:
  • Explore circular carbon economies by integrating solar-CCS systems with biomass co-firing, hydrogen production, and enhanced oil recovery (EOR). There is strong evidence that the circular economy contributes to reducing the extraction of primary resources [85]. Incorporating CO₂ capture in a circular economy frame would allow the capture of CO₂ to be converted into synthetic fuels (Methanol, Methane, or Syngas) or chemical products (carbonates, urea, ethylene, propylene, etc.) instead of being released into the atmosphere. The integration of solar energy could be incorporated, contributing to the required energy to capture CO₂ and providing energy to store and convert the CO₂ into new products.
  • Invest in digital twin technologies and AI-driven predictive maintenance to enhance hybrid plant adaptability to intermittent solar input.
• Research Priorities:
  • Address scalability gaps in pilot studies, particularly for NGCC and CHP systems, which face challenges due to low flue gas CO₂ concentrations (3–5%).
  • Validate long-term performance of solar-thermal storage hybrids under real-world operating conditions, including partial-load and transient scenarios.
  • Investigate issues of corrosion and material degradation because of solvents in the CO₂ capture plant. Also, operational flexibility due to the unpredictability of solar thermal energy requires further research.

Studies have predominantly focused on coal-fired power plants, which benefit greatly from solar thermal integration due to the high concentration of CO₂ in flue gases. However, even for natural gas combined cycle (NGCC) systems and cogeneration plants—which typically present lower CO₂ concentrations—research indicates that the incorporation of concentrated solar energy can yield encouraging results. These findings suggest that, despite inherent challenges, solar-assisted capture processes can be tailored to various operational contexts, although the degree of benefit may vary with the specific characteristics of the power plant.

Solar-assisted CCS technologies offer a critical transitional pathway for decarbonizing fossil fuel infrastructure, aligning with global net-zero targets. While technical feasibility has been demonstrated, widespread deployment hinges on resolving economic disparities, advancing integration frameworks, and securing robust policy support. Solar-thermal CCS systems can evolve from niche solutions to cornerstone strategies in the sustainable energy transition by addressing these challenges through interdisciplinary collaboration and iterative innovation.

In summary, while CO₂ capture technologies based on chemical absorption and assisted by solar thermal energy hold significant potential for decarbonizing fossil fuel-based power generation, their full-scale implementation depends on further technological development, comprehensive techno-economic studies, and robust policy support. Governmental initiatives, including fiscal incentives and regulatory frameworks, will be essential to overcome current economic barriers and to facilitate the transition toward low-carbon energy systems.