Concentrated Solar Thermal Power Technology and Its Thermal Applications

Abstract

The industrial sector accounts for approximately 65% of global energy consumption, with projections indicating a steady annual increase of 1.2% in energy demand. In the context of growing concerns about climate change and the need for sustainable energy solutions, solar thermal energy has emerged as a promising technology for reducing reliance on fossil fuels. With its ability to provide high-efficiency heat for industrial processes at temperatures ranging from 150 °C to over 500 °C, solar thermal power generation offers significant potential for decarbonizing energy-intensive industries. This review provides a comprehensive analysis of various solar thermal technologies, including parabolic troughs, solar towers, and linear Fresnel reflectors, comparing their effectiveness across different industrial applications such as process heating, desalination, and combined heat and power (CHP) systems. For instance, parabolic trough systems have demonstrated optimal performance in high-temperature applications, achieving efficiency levels up to 80% for steam generation, while solar towers are particularly suitable for large-scale, high-temperature operations, reaching temperatures above 1000 °C. The paper also evaluates the economic feasibility of these technologies, showing that solar thermal systems can achieve a levelized cost of energy (LCOE) of USD 60–100 per MWh, making them competitive with conventional energy sources in many regions. However, challenges such as high initial investment, intermittency of solar resource, and integration into existing industrial infrastructure remain significant barriers. This review not only discusses the technical principles and economic aspects of solar thermal power generation but also outlines specific recommendations for enhancing the scalability and industrial applicability of these technologies in the near future.

1. Introduction

As the world pursues a low-carbon future, solar energy technologies are central to global clean energy strategies [1]. Concentrated solar thermal (CST) is a key solar technology that uses mirror-based optical systems to focus sunlight onto a small-area receiver, converting it into high-temperature heat. This high-grade thermal energy can then drive steam turbines for power generation or supply heat for industrial processes and heating/cooling applications [2]. Unlike photovoltaics, CST inherently supports thermal energy storage by storing hot fluids or materials, enabling a stable energy supply even when the sun is not shining. This ability to dispatch solar energy on demand makes CST especially suitable for large-scale, high-temperature applications that require reliability, such as around-the-clock power generation or continuous industrial heating [3].

Recent years have seen remarkable advancements in CST technology, driven by innovations in materials, optics, and thermal storage. Solar receiver materials have greatly improved; researchers have developed nano-engineered selective absorber coatings (including multilayer “tandem” structures) that significantly increase solar absorption while withstanding higher temperatures [4]. These advanced coatings reduce radiative heat losses and maintain efficiency at operating temperatures well above 600 °C. In addition, high-temperature alloys are being explored for receiver components; for example, high-entropy alloys (HEAs) offer excellent creep strength and corrosion resistance at elevated temperatures. A recent study demonstrated that a Fe-Mn-Ni-Al-Cr HEA can serve as a durable receiver tube material, with its oxide layer acting as a high-efficiency solar absorber coating. Such materials enable higher operating temperatures (≥700 °C), which in turn boost the thermal-to-electric conversion efficiency of CST systems [5].

Parallel progress in optical design and control has enhanced the solar collection efficiency. Modern CST plants employ improved concentrator configurations (e.g., refined heliostat field layouts and reflector designs) alongside smart control systems. Notably, artificial intelligence (AI) and advanced wireless communications are being integrated into heliostat control, dramatically improving solar tracking accuracy and reducing operation costs. AI-driven calibration and predictive tracking can increase the overall reflectance efficiency and reliability of heliostat fields [6]. These optical innovations ensure more sunlight is delivered to the receiver throughout the day, even under wind or alignment disturbances, thereby raising heat collection efficiency and system stability.

Advances in thermal energy storage (TES) are equally vital, since storage extends CST operation beyond sunny hours. State-of-the-art CST plants use sensible heat storage in molten salts (typically a nitrate salt mixture) to store several hours’ worth of thermal energy at high efficiency [7]. Research continues to improve molten salt formulations for higher thermal stability and lower melting points. Beyond sensible heat, new latent heat storage systems using phase change materials (PCMs) are being developed to exploit the high latent heat during solid–liquid transitions, allowing compact storage of large energy quantities. Meanwhile, thermochemical storage is an emerging frontier; high-temperature reactions (reversible chemical cycles) can store solar heat in chemical bonds and release it on demand, offering very high energy densities. Each of these TES approaches—sensible, latent, and thermochemical—has seen significant R&D progress, and hybrid systems are being designed to achieve both short-term and long-duration storage for CST. Efficient TES integration has led to today’s CST plants providing up to 10–15 h of dispatchable power after sunset. This progress in storage, coupled with incremental improvements in turbines and heat transfer fluids (e.g., adoption of supercritical CO₂ cycles), has steadily increased the overall efficiency and capacity factor of CST plants [8].

Crucially, CST is no longer limited to power stations in deserts; its application footprint has broadened. Industries are increasingly adopting concentrated solar thermal systems to provide process heat for manufacturing, mining, food processing, chemical production, and other sectors [9]. High-temperature solar heat can drive processes like steam generation, drying, and calcination, directly substituting for fossil-fuel boilers in some cases. This use of CST for industrial process heat (also known as “solar heat for industrial processes”) not only helps decarbonize heavy industry but is opening new commercial markets for CST technologies [10]. The expansion into industrial heat and other thermal applications is expected to increase production volume and bring economies of scale, further reducing the costs of CST components. Additionally, CST systems have been demonstrated in building heating and cooling contexts, for example, in solar-driven air conditioning or district heating, underscoring their versatility beyond electricity generation [11]. The growing interest and deployments in these non-traditional sectors have accelerated CST’s path toward wider commercialization and integration in the global energy mix.

This paper provides a comprehensive review of the current state of CST technology and its thermal applications, highlighting recent progress and persisting challenges. We begin by outlining the basic principles of CST and the main types of concentrator systems (parabolic trough, central tower, linear Fresnel, and parabolic dish). We then examine the latest developments in key technical areas—solar receivers and materials, heat transfer and energy storage techniques—and discuss how these innovations are enhancing performance and expanding CST capabilities. The current applications of CST in power generation, industrial processes, and other sectors are surveyed to evaluate its commercial status. Finally, we discuss future research directions and emerging opportunities, considering what advances are needed to fully unlock CST’s potential. Through this review, we aim to clarify CST’s role in a sustainable energy future and provide insights for researchers, industry practitioners, and policymakers. Ultimately, continued innovation and deployment of CST technology will help foster the wider use of solar thermal energy in the global energy transition.

2. Composition of Solar Thermal Power Generation Systems

CST technology focuses sunlight through reflectors, collectors convert light energy into high-temperature heat energy, thermal storage systems store heat to ensure a stable supply, and ultimately heat energy is converted into electricity through a power generation system. The four work in tandem to achieve efficient and sustainable energy output.

2.1. Reflector

In a solar thermal power generation system, reflectors play a crucial role in capturing and concentrating solar radiation onto the receiver, thereby improving the system’s energy collection efficiency. Their primary function is to focus sunlight, generating high-density thermal energy on the receiver’s surface. The efficiency and performance of the entire solar thermal system are directly influenced by factors such as the reflector material and the arrangement of the mirror field.

Reflectors can be categorized into four main types based on their material composition: silver-coated glass mirrors, silver-coated polymer mirrors, aluminum mirrors, and stainless steel mirrors. Figure 1 provides a visual representation of the classification of so-lar mirrors according to their fundamental materials.

Glass mirrors are among the most commonly used reflectors in solar thermal power systems. When sunlight strikes the mirror, it reflects both heat and light to a designated location. The glass surface can function as both the substrate and the protective cover layer.

There are two types of glass mirrors based on the placement of the reflective coating. A first-surface mirror is created by applying a highly reflective coating directly onto the glass to enhance its optical performance. In contrast, a second-surface mirror has the reflective material applied to the backside of the glass, which is then protected by a paint coating [13]. An experimental study on silver-plating processes was conducted to enhance the mechanical properties and environmental durability of glass mirrors. The study found that a tantalum oxide coating provided excellent protection for silver reflectors. In 1979, the glass division of the Ford Motor Company developed thin glass for heliostats in concentrated solar power plants, where the silver-plated backside achieved a solar reflectivity of 89.3% [14].

Silver-coated polymer reflectors are lightweight and offer greater design flexibility. However, they have a shorter lifespan due to poor adhesion with silver when exposed to water [15]. An aluminum-coated first surface polymer mirror was fabricated by depositing an aluminum layer on a polycarbonate substrate. The focus of the research has been on creating lightweight and durable reflectors. The study also demonstrated that these plastic mirrors are resistant to extreme outdoor conditions, with a long-term reflectivity of up to 88%.

Aluminum oxide is a commonly used reflective material in concentrated solar power plants. Aluminum is the most abundant metal, relatively inexpensive, and widely used as a non-ferrous metal. The solar reflectivity of aluminum reflectors typically ranges from 85% to 91% [16]. A composite mirror for parabolic solar concentrators was developed using a magnetron sputtering technique. Efforts were made to enhance the reflectivity and longevity of the mirror by applying a bilayer reflective coating of aluminum (Al) and silicon dioxide (SiO₂). The study also demonstrated high mirror-like solar reflectivity and excellent protection against harsh environmental conditions by providing multiple protective layers.

Stainless steel is tough and does not require substantial thickness; however, its main limitation is its low solar reflectivity. Although aluminum has a higher reflectivity than stainless steel, aluminum mirrors require a minimum thickness of 4 mm to be self-supporting [17]. A reflector material was designed and fabricated that combined the beneficial properties of steel and aluminum. The reflective layer was created by directly evaporating aluminum onto the backside of a polyethylene terephthalate (PET) protective layer. A 9 μm aluminum foil substrate was then provided to support the reflectivity. To prevent aluminum damage, an additional PET layer was applied, and a stainless steel plate was pressed onto the back to enhance the strength of the reflector. A schematic diagram of the aluminum-steel reflector manufacturing process is shown in Figure 2.

Reflectors are key components in solar thermal power stations, responsible for reflecting sunlight and concentrating it onto the receiver. The design of the reflector must adapt to the position of the sun, ensuring that the solar rays are reflected as vertically as possible onto the receiver. Additionally, to enhance reflection efficiency, the surface of the reflector should be appropriately treated for reflectivity. This can be achieved through the choice of materials for the reflector, such as glass mirrors, ceramic mirrors, metal mirrors, self-cleaning high-reflectivity solar film materials, and sputtering targets.

2.2. Collector

A solar collector is a special type of heat exchanger that converts solar radiation into the internal energy of a transport medium. Solar collectors are the primary components of any solar energy system. They absorb incoming solar radiation, convert it into heat, and transfer this heat to a fluid (usually air, water, or oil) that flows through the collector. The collected solar energy is then directly transferred to hot water or space conditioning systems or stored in a thermal storage tank, from which it can be extracted for use during the night and/or on cloudy days. This chapter will introduce flat-plate collectors, compound parabolic concentrators, and vacuum tube collectors, starting with their types.

A typical flat-plate solar collector is illustrated in Figure 3. When solar radiation passes through the transparent cover and reaches the high-absorption blackened surface of the absorber, most of the energy is absorbed by the plate and then transferred to the heat transfer medium within the fluid pipes. This medium carries the absorbed heat away for storage or direct use. To minimize conductive heat losses, the bottom surface of the absorber plate and the sides of the housing are well insulated. The fluid pipes, responsible for transporting the heat transfer medium, can either be welded to the absorber plate or integrated directly into it. At both ends of the fluid pipes, a large-diameter manifold is in-stalled to ensure efficient fluid circulation [18].

The transparent cover plate serves to reduce convective losses from the absorber plate by restricting the stagnant air layer between the absorber plate and the glass. It also minimizes radiation losses from the collector, as the glass is transparent to the short-wave solar radiation received by the sun, while being almost opaque to the long-wave thermal radiation emitted by the absorber plate.

Flat-plate collectors are made with various designs and different materials. They have been used to heat fluids such as water, water with antifreeze additives, or air. Their primary goal is to collect as much solar energy as possible at the lowest total cost.

Glass has been widely used as a glazing material for solar collectors because it can transmit up to 90% of incident short-wave solar radiation, while being almost opaque to the long-wave radiation emitted by the absorber plate. Standard window glass and greenhouse glass have normal transmission rates of about 0.87 and 0.85, respectively. For direct radiation, the transmission rate varies significantly with the angle of incidence. Reflective coatings and surface texturing can also significantly improve the transmission rate. Dirt and dust have minimal impact on the collector glass, and occasional rainfall is usually sufficient to keep the transmission rate within 2–4% of the maximum.

Compound parabolic concentrators (CPCs) are non-imaging concentrators. They are capable of reflecting all incident radiation onto an absorber over a wide range [20]. Winston [21] noted their potential as solar collectors. The use of two parabolically orientated slots reduces the need to move the concentrator to accommodate changes in solar orientation, as shown in Figure 4. Composite parabolic concentrators can accept incoming radiation over a relatively wide range of angles. Through multiple internal reflections, any radiation entering the aperture within the collector’s acceptance angle reaches the surface of the absorber located at the bottom of the collector [22]. The absorber is available in a variety of configurations. It can be cylindrical or flat, as shown in Figure 4. In the CPC shown in Figure 4, the lower part of the reflector (AB and AC) is circular while the upper part (BD and CE) is parabolic. Since the upper part of the CPC has little effect on the radiation reaching the absorber, it is often truncated, resulting in a shorter CPC, which is also cheaper. The CPC is usually covered with glass to avoid dust and other substances from entering the collector, which reduces the reflectivity of the collector walls. These collectors are more useful as linear or trough concentrators. The acceptance angle is defined as the angle at which the light source can move and still converge on the absorber. The orientation of a CPC collector is related to its acceptance angle (θc; in Figure 4) [19]. The way the collector moves depends on its acceptance angle, which determines whether it can be stationary or needs to track the sun. The long axis of a CPC collector can be orientated either in a north–south direction or an east–west direction, with the aperture tilted at an angle equal to the local latitude, pointing towards the equator [19]. When the long axis is orientated in a north–south direction, the collector must face the sun continuously by rotating its axis, as the collector receives a larger angle along the long axis and therefore does not require seasonal tilt adjustment. If kept stationary, the collector will only receive radiation during the periods when the sun is within the receiving angle. When the collector’s long axis is orientated east–west, a slight adjustment of the seasonal tilt angle will allow the sun to be captured efficiently through the larger acceptance angle. In this case, the minimum acceptance angle should be equal to the maximum angle of incidence in the north–south vertical plane when the collector needs to output.

Traditional simple flat-plate solar collectors were developed for use in sunny and warm climates. However, their benefits are greatly diminished under conditions of cold, cloudy, and windy days. Additionally, weathering effects such as condensation and moisture can lead to the premature degradation of internal materials, resulting in performance deterioration and system failure. Vacuum tube solar collectors (tubes) operate differently from other collectors on the market. These collectors consist of heat pipes sealed in vacuum tubes, as shown in Figure 5.

The vacuum tube collector primarily consists of heat pipes housed within vacuum-sealed tubes. There are numerous variations of vacuum tube absorbers available on the market [23]. Recently, a manufacturer has introduced a fully glass evacuated tube collector (ETC), which could represent a significant advancement in reducing costs and extending the system’s lifespan. Another variation of this collector is the Dewar tube, which uses two concentric glass tubes, with the space between them evacuated to create a vacuum jacket. A key advantage of this design is that it is entirely constructed from glass, allowing heat to be extracted from the tube without the need to penetrate the glass shell, thereby eliminating the potential for leakage losses. This design is also more cost effective compared to single-shell systems [24].

In addition to the flat-plate, evacuated tube, and compound parabolic collectors discussed earlier, concentrated solar collectors form the core of modern concentrated solar thermal (CST) and concentrated solar power (CSP) technologies. These collectors use optical devices to focus direct normal irradiance (DNI) onto a small receiver area, thereby achieving very high operating temperatures (typically between 250 °C and 1000 °C). Depending on the optical geometry and tracking configuration, concentrated collectors are categorized into four main types (Figure 6): Parabolic trough collectors (Figure 6a) use linearly curved mirrors that focus sunlight onto an absorber tube located at the focal line. A heat transfer fluid (HTF), typically synthetic oil or molten salt, circulates through this tube to absorb the concentrated thermal energy. PTC systems usually operate at temperatures between 300 °C and 400 °C, although advanced molten salt designs can reach 550 °C [25]. Central receiver (tower) systems (Figure 6b) employ a field of heliostats (flat, sun-tracking mirrors) that reflect sunlight to a central receiver atop a tower. The concentrated energy heats a working fluid—such as molten salt or air—circulated through the receiver. CRS systems are known for achieving very high operating temperatures up to 1000 °C, suitable for advanced thermodynamic cycles like supercritical CO₂ [26]. Regarding parabolic dishes (Figure 6c), these collectors are composed of a parabolic dish that focuses sunlight onto a receiver at its focal point, often integrated with a Stirling engine or Brayton cycle for direct power generation. Parabolic dishes offer the highest optical efficiency among all CSP technologies and are ideal for modular and distributed applications [27]. And regarding linear Fresnel reflectors (Figure 6d), LFR systems consist of long rows of flat or slightly curved mirrors that focus sunlight onto a fixed receiver positioned above the mirror field. Although the concentration ratio and thermal efficiency are generally lower than PTCs, the simpler design and reduced structural requirements make LFR systems more cost effective [28]. They are often used where land constraints and cost optimization are critical. These systems are key enablers for high-efficiency solar thermal power generation and high-temperature industrial heat supply.

2.3. Heat Storage System

To address the need for on-demand power generation under variable solar conditions, energy storage is essential. It enhances the reliability of renewable energy and helps manage peak demand for solar power generation [30]. Thermal energy storage (TES) is one of the key advantages of concentrated solar power (CSP); compared to battery storage, TES is more cost effective and better suited for integration into the electrical grid [31]. Studies have shown that CSP systems with energy storage can offer over twice the value of photovoltaic power generation in certain contexts [32].

TES technologies include sensible heat storage, which raises the temperature of a medium to store heat but has lower density, latent heat storage (PCM), which stores heat through phase changes and offers higher density, and thermochemical storage, which stores heat via reversible chemical reactions and has the highest potential for heat density, although it is still in early development (Figure 7).

With technological advancements, CSP plants are expected to transition from sensible heat storage to latent heat storage, and eventually to thermochemical storage, in order to achieve higher efficiency and greater energy storage capacity.

2.3.1. Sensible Heat Storage

Sensible heat exchangers can generally be divided into two types: solid and liquid. There are also systems that combine both solid and liquid, such as fluid flowing through a packed bed made of solid particles. The working principle of both solid and liquid sensible heat exchangers is the same; heat is stored by raising the temperature of the material.

Molten salts are an ideal choice for high-temperature energy storage due to their high energy density and low cost. The operational temperature of molten salts is limited by their freezing point and corrosion issues, with freezing being the primary concern as it can damage pipes and pumps. Therefore, auxiliary heaters are typically required. Common molten salts include nitrates, nitrites, and carbonates, with mixed salts improving performance, particularly by lowering the melting point. For example, NaNO₃-NaNO₂-KNO₃ (Hitec) and Ca(NO₃)₂-NaNO₃-KNO₃ (HitecXL) are common commercial salt mixtures [34]. Ongoing research is focused on developing better molten salts, such as the quaternary salt mixture (K, NaNO₂, Cl, and NO₃) designed by Peng et al., and low-melting-point salts (80 °C) presented by Zhao and Wu [35].

When using solid materials, packed bed structures are typically employed, with heat storage and discharge occurring via a heat transfer fluid (HTF). If the HTF is gas (e.g., air), it is used solely for heat transfer; if it is a fluid, its heat capacity is comparable to that of the solid material and can act as an auxiliary storage medium. Inexpensive options include sand, gravel, or concrete. Sand and gravel are generally used as packing materials, with some proposals for using a fluidized bed structure [36]. Concrete can be formed into bricks to create a packed bed or can be used with heat transfer tubes running through large concrete blocks [37]. To enhance the thermal performance of concrete and to be compatible with finned HTF heat exchangers, concrete and castable ceramics with volumetric heat capacities greater than 0.7 kWhth/m³/K have been developed [38]. For high-temperature applications, silica bricks, alumina bricks, and magnesia bricks are recommended, often paired with molten salts as HTFs [39]. Graphite has also been proposed as a sensible heat storage material due to its excellent stability at high temperatures and high specific heat capacity.

2.3.2. Latent Heat Storage

In latent heat storage systems, thermal energy is stored by inducing phase changes in the storage material. The most common phase change is from solid to liquid, while sol-id-to-solid transitions are occasionally used. Liquid-to-gas phase changes are rarely employed due to the significant expansion and the need for strict pressure containment.

Metals and metal alloys are often proposed as Phase Change Materials (PCMs) due to their high thermal conductivity and latent heat. While metals exhibit excellent properties, their high cost can be a drawback. Alloying metals with cheaper materials, such as aluminum–silicon alloys, can reduce costs while maintaining good thermal performance [40].

To enable the widespread use of PCM-based thermal storage, cost-effective and high-performance materials must be developed. Additionally, low-cost containers, heat exchangers, and encapsulating materials compatible with PCM are needed to support efficient charging and discharging processes. High-performance PCMs, suitable materials, and efficient system design are crucial for the practical application of latent heat storage.

2.3.3. Thermochemical Heat Storage

Thermochemical TES stores thermal energy via reversible chemical reactions, where heat input drives internal reactions, storing energy in chemical bonds [41]. The reverse exothermic reactions are used for heat recovery and power generation. Common energy storage processes include the following:

Metal hydroxide dehydration: energy is stored by dehydration, but the low thermal conductivity of the materials limits the reaction rate [15].

Metal hydride dehydrogenation: Energy is stored by removing hydrogen, although issues with poor heat transfer and slow reaction kinetics exist. However, doping elements such as iron or nickel can increase the reaction rate [42].

Metal carbonate decarbonation: Energy is stored by removing carbon dioxide, typically requiring high temperatures (>450 °C), making it suitable for future high-temperature power plants [43].

Metal oxide redox: Energy is stored by reducing metal oxides. Although this process is less studied, it holds significant potential for high energy density.

Thermochemical storage materials offer high energy density and, in theory, virtually unlimited storage duration. However, challenges related to reaction reversibility, rates, conversion efficiency, and economic feasibility must be addressed. Overcoming these obstacles will improve CSP system performance and advance their integration into global renewable energy networks.

2.4. Power Generation Systems

Power generation systems convert thermal energy into electricity, with traditional plants using steam generators to produce high-temperature steam that drives turbines. A key area of research is the development of technologies that directly convert thermal energy into electricity, eliminating the need for intermediate mechanical conversion. Efficient, low-cost direct conversion technologies could improve the scalability of solar thermal systems.

2.4.1. Thermal Engine Systems

A thermal engine is the system in a CSP plant that converts collected heat into electrical energy. The traditional approach involves converting thermal energy into mechanical energy via a thermodynamic cycle, which is then used to drive a generator for electricity production. The main characteristics, advantages, and challenges of various traditional power generation systems are summarized in

Table 1. Key features, advantages, and challenges of various traditional power generation systems.

Technology Type	Description	Advantages	Challenges
Parabolic Trough Solar Power	Mirrors focus sunlight onto pipes, heating a fluid to produce steam that drives a turbine for power generation.	Mature technology, suitable for large-scale power generation.	Requires large land area, highly weather dependent.
Solar Power Tower	Mirrors focus sunlight onto pipes, heating a fluid to produce steam that drives a turbine for power generation.	High efficiency, capable of generating power around the clock.	High initial construction cost, large land requirements.
Parabolic Dish Solar Power	Flat mirrors concentrate sunlight onto a collector to generate steam that drives a turbine for power generation.	Low cost, suitable for medium- to small-scale projects.	Lower efficiency, performance not as good as trough and tower systems.
Carbide Concentrated System	Parabolic dish mirrors concentrate sunlight to drive a Stirling engine for power generation.	High efficiency, suitable for distributed generation.	High maintenance, large initial investment.
Solar Multi-Receiver Collection System	Multiple heliostats focus sunlight onto a high tower receiver, and heat transfer drives a turbine for power generation.	High efficiency, suitable for large-scale generation, and peak load management.	High cost, complex technology, requires precise tracking.

.

2.4.2. Direct Thermoelectric Conversion

The most active research areas in direct solar thermoelectric conversion are Solar Thermoelectric Generators (STEGs) and Solar Thermophotovoltaic (STPV). A brief overview of these two fields is provided below.

STEGs convert thermal energy into electrical energy through thermoelectric generators. Due to the Seebeck effect, thermoelectric materials generate a voltage gradient under the influence of a temperature gradient, which in turn produces a current and generates electricity [44]. Thermoelectric generators are typically used for waste heat recovery, but when coupled with solar energy absorbers, they can generate power from solar energy. A typical configuration of a STEG is illustrated in Figure 8.

Solar Thermophotovoltaic (STPV) systems absorb solar radiation to generate heat, which is then converted into thermal radiation. This radiation is directed to a single-junction thermophotovoltaic (TPV) cell, where it is converted into electricity. STPV’s advantage lies in using frequency-dependent thermoelectric converters to achieve an ideal spectral irradiation, resulting in higher conversion efficiency than direct solar irradiation. The challenge is ensuring an effective intermediate absorption/re-emission process, so that the spectral enhancement outweighs its negative impacts. A typical STPV system configuration is shown in Figure 9.

The main challenge faced by STPV systems is the high-temperature requirement, as they rely on converting thermal radiation into electrical energy. Even with the semiconductors that have the lowest bandgap (around 0.5 eV), a blackbody spectrum temperature of over 1000 °C is needed to achieve efficient conversion. Although 1000 °C is below the melting point of many materials, constructing a highly efficient and reliable STPV system remains a significant engineering challenge [33].

3. Types of Solar Thermal Power Generation

3.1. Trough Solar Power System

Among the various concentrated solar power (CSP) technologies, parabolic trough solar power systems stand out as the most widely utilized solution. While CSP systems encompass different types of concentrating collectors, the parabolic trough configuration has garnered significant attention due to its proven effectiveness in large-scale power generation. In this section, we focus on the parabolic trough solar power system, which represents a key approach to harnessing solar energy in an efficient and scalable manner.

Parabolic trough solar power systems are currently the most widely utilized concentrated solar power (CSP) technology. The full name of this system is the parabolic trough solar thermal power system, which typically consists of a concentrating collector, a heat storage unit, a heat engine power generation device, and auxiliary energy systems (such as boilers). It primarily comprises several parabolic trough-type concentrating collectors arranged in series and parallel. These collectors harness solar energy to heat the working fluid within the heat pipe, generating high-temperature steam that drives a turbine, which in turn powers a generator to produce electricity [45]. The medium used (typically heat transfer oil or a nitrate mixture) is enclosed within a vacuum glass cover in the heating tube. The concentration ratio generally ranges from 10 to 100. When oil is employed as the heat transfer fluid, the maximum heat collection temperature can reach 400 °C. Conversely, when a nitrate mixture is used, the maximum heat collection temperature can reach 700 °C. The latter maintains superior thermal efficiency at high temperatures, resulting in a higher power generation efficiency [46,47,48].

Parabolic trough concentrating collectors (Figure 10) are linear focusing collectors. A large number of trough-type concentrators are typically connected in series and parallel to form a concentrating collector array. One-dimensional tracking of solar radiation is employed. The advantages of the trough system include its relatively simple structure, low maintenance costs, potential for mass production, and compact size, which enables easy installation and maintenance when arranged on the ground. However, due to the low geometric concentration ratio of the parabolic concentrator and the relatively low collector temperature, the thermal-to-power efficiency of the power subsystem in the parabolic trough solar thermal power generation system remains relatively low. Consequently, it is challenging for a pure parabolic trough solar thermal power generation system to further enhance thermal efficiency and reduce power generation costs.

To enhance the efficiency of the system and reduce costs, new materials and technologies are continuously being explored and implemented. In parabolic trough concentrated solar power (CSP), the selection of collector materials is crucial. In recent years, studies [50,51] have highlighted the development of highly efficient nano-functionalized absorber materials that can effectively utilize most of the radiation in sunlight. Despite the nanoscale manipulation of the material, its photothermal conversion efficiency can be significantly enhanced, thereby improving the overall system performance. Due to the variability of light during the day and night, as well as under sunny and cloudy conditions, existing parabolic trough CSP systems are increasingly being integrated with thermal energy storage technology. By employing molten salt energy storage and other technologies [52], excess thermal energy collected during periods of optimal sunlight can be stored for use during the night or on cloudy days, ensuring a continuous supply of electricity.

3.2. Tower Solar Power System

Applying solar power generation technology in the form of a tower provides a novel method for generating electricity. Not only can it efficiently store thermal energy, but it can also operate at high temperatures. A solar power generation system primarily consists of a power generation unit, a main control system, a heat storage tank, a receiver, and a heliostat array. A specific number of heliostats (spherical mirror groups that automatically track the sun) are positioned on the ground, with a solar collector tower constructed at an optimal location within the heliostat array. The heliostats reflect solar energy into the collector at the top of the tower, heating the working fluid to produce high-temperature steam that drives a turbine for electricity generation [47]. The SDIC Gansu Akesai Huidong “Solar Thermal + Photovoltaic” Project has a total installed capacity of 750 MW, with 110 MW allocated to solar thermal power generation and 640 MW to photovoltaic power generation [29]. As illustrated in Figure 11, the solar thermal section includes 11,960 pentagonal heliostats and a collection tower approximately 200 m high. Each heliostat is capable of rotating to track the sun and reflect solar radiation onto the absorber at the top of the heat collection tower.

Due to the large number of heliostats in a tower power generation system, its concentration ratio can reach 1500. Compared to a parabolic trough solar power generation system, the concentration ratio of a tower solar power generation system is significantly higher. The unique design allows the cavity temperature of its collector to exceed 1000 °C [53,54]. Due to its advantages in high concentration and high thermal conversion efficiency, a tower solar power system can achieve high power generation capacity. This makes it highly suitable for large-scale, high-capacity commercial applications. However, a tower solar thermal power system requires a significant one-time investment, has a complex device structure and control system, and incurs high maintenance costs [55].

Similarly, several emerging technologies are anticipated to be applied to tower power generation systems. Göttsche et al. proposed a novel design utilizing a mini-mirror array (10 × 10 cm), with each mirror mounted on a ball joint driven by a stepper motor (Figure 12) [56]. The purpose of this design is to mitigate the adverse effects that strong winds may have on the mirrors while reducing costs. However, the final optical performance was not satisfactory.

The hydraulic tracking system [58] utilizes a hydraulic structure to track the movement of the sun, ensuring that the device is always positioned to receive the maximum amount of sunlight. Additionally, the incorporation of a dual-axis tracking system and a high-precision solar tracking algorithm will enhance both the efficiency and reliability of the CSP system. Due to the higher temperatures in tower power generation systems, the application of materials with high thermal conductivity and thermal stability has become essential. High-entropy (HE) materials [59] have garnered widespread attention in recent years. These materials possess excellent light-to-heat conversion capabilities and broadband light absorption characteristics, enabling selective absorption of the solar spectrum, reducing infrared light absorption, and minimizing heat loss.

3.3. Dish Stirling Solar Power Generation System

The dish Stirling solar power generation system is a solar energy system that uses parabolic mirrors to concentrate sunlight for power generation. It primarily consists of a parabolic dish, a receiver, a Stirling engine, and a generator. When sunlight hits the parabolic mirror, the light is focused onto the receiver, heating the working fluid inside the receiver to a high temperature. This, in turn, drives the Stirling engine to generate electricity. This system can operate independently, serving as a small power source for off-grid remote areas, or multiple units can be connected in parallel to form a small-scale solar thermal power plant. The dish Stirling system is known for its high efficiency, modularity, and ability to operate independently.

This technology converts solar thermal energy into rotational motion via the Stirling cycle, with AC generators transforming mechanical energy into electricity [60]. After accounting for power losses, the system can convert nearly 30% of the direct normal solar radiation into electricity, achieving an efficiency of about 30% [61].

As early as 1988, Roelf [62] optimized the solar application of the STM4-120 Stirling engine. The engine’s power output at 25 rpm was 1800 kW, with an efficiency of 40% from heat input to shaft output. The use of a simple variable slotted piston stroke control eliminated sealing and power control issues that previously plagued Stirling engines.

Singh et al. [63] designed, simulated, and optimized a solar Stirling engine. The study found that the maximum thermal efficiency of the dish Stirling system at an absorber temperature of 850 K was 32%. The energy and exergy efficiency of the dish Stirling system were 17% and 19%, respectively, with the majority of the losses occurring at the receiver. Mari et al. [64] addressed gaps in the mathematical modeling of the parameters of the parabolic solar dish Stirling engine system, providing numerical equations and simulations related to solar dish applications. Pheng et al. [65] reviewed the parabolic dish Stirling system based on CSP technology, considering aspects such as performance, overall efficiency, dish position, and levelized cost of electricity. They also analyzed the technical and high capital cost barriers to the practical application of parabolic dish systems.

Zayed et al. [66] developed a theoretical model based on optical geometry and thermodynamic analysis for the solar dish Stirling system, considering the optical configurations and energy balance of different system components. An optimization algorithm was implemented using multi-objective particle swarm optimization to simultaneously maximize output power and total efficiency, achieving a maximum power output of 23.46 kW and an optimal overall efficiency of 30.15%. Subsequent research [67] conducted comprehensive assessments of the following: design standards, geometric parameters’ optimization, thermal performance analysis, thermodynamic optimization, and techno-economic aspects.

Typically, a solar thermal receiver is added to a parabolic solar dish to capture the maximum concentrated solar radiation from the dish. Senthil et al. [68] experimentally analyzed the improvement of the thermal inertia balance and heat storage capacity of a solar thermal receiver using phase change materials (PCMs). The average energy and exergy efficiency of the receiver reached 66.7% and 13.8%, respectively.

3.4. Fresnel Solar Thermal Power Generation System

The Fresnel solar thermal power generation system employs arrays of flat mirrors to reflect sunlight onto a collector tube. It has a modest concentration ratio but is cost effective and suitable for large-scale applications. The advantages of the Fresnel system include its simple structure, high land utilization, ease of cleaning, and low cost.

In 1957, Baum et al. [69] first proposed modularizing parabolic trough mirrors into flat mirror arrays. A tracking system with flat glass mirrors can reflect and concentrate sunlight onto a fixed secondary concentrator. Francia et al. [70] implemented this concept practically in a linear Fresnel concentrator system, achieving pioneering work with a prototype featuring a dual-axis tracking system, laying the foundation for large-scale applications of linear Fresnel reflectors (LFRs). Since then, researchers have extensively studied the Fresnel solar thermal power generation system.

Feuermann et al. [71] introduced the concept of secondary concentrators by adding secondary mirrors to the receiver to enhance concentration efficiency and reduce thermal losses. The advent of compound parabolic secondary concentrators has significantly advanced the linear Fresnel solar thermal collection technology. Grena et al. [72] used molten nitrate salt as the heat transfer fluid in a solar Fresnel linear concentrator. They introduced a system designed to handle molten nitrate salts more effectively, with vacuum tube collectors that can tolerate temperatures up to 550 °C. Through optical and thermodynamic simulations, they found that, with an adequately precise tracking system, the efficiency loss of the molten salt Fresnel system was about 10% to 20% compared to the trough system. Taramona et al. [73] overcame the main limitations of previously proposed hyperbolic secondary concentrators by proposing a new type of secondary concentrator made up of several fixed flat mirrors at the same height. This setup established a new solar field model and achieved a concentration ratio of up to 31% and optical efficiency up to 60%. Grena [74] discussed the impact of optical geometry on linear Fresnel concentrators, the parameters required to determine the geometry, and the main optical concepts. He also summarized a ray-tracking program to simulate the mirror field and a fast calibration analysis method for optimization and real-time calculation.

An important subsystem in LFR systems is the collector system. Currently, research on the heat collection performance of linear Fresnel collectors is relatively limited, focusing mainly on two areas: new heat transfer fluids and collector tube designs. Zhai [75] conducted experimental and simulation studies on a Fresnel lens solar collector with vacuum tubes and found that for water heating, when the inlet water temperature was 80–90 °C, the heat efficiency of the collector reached 9.80%, which was 90% higher than the commonly used evacuated tube collectors. However, optical losses were the primary source of energy loss, accounting for nearly 40% of solar radiation. Khan et al. [76] studied the effect of new corrugated collector tubes with nanofluids on the energy efficiency of a novel dual-fluid heat collection system and presented an optimization model for the corrugated collector tube through simulation. Alamdari et al. [77] reviewed research on linear Fresnel solar power generation systems over the past decade, emphasizing that various types of thermal losses are key parameters affecting efficiency.

Each of the four CSP technologies mentioned above has its own set of advantages and disadvantages, which can be evaluated based on the factors in

Table 2. The technical characteristics for CSP [78,79,80,81,82,83,84,85,86].

	Capacity (MW)	Installation Cost	Power Generation Efficiency (%)	Cost of Electricity (USD/kWh)	Thermal Loss Coefficient	Optical Efficiency Attenuation Rate
Trough solar power system	10–200	Low	13–18	0.17	High (significant radiation and conduction losses)	Relatively high (affected by radiation and weather variations)
Tower solar power system	10–200	High	16–17	0.14	Low (highly efficient light concentration)	Low (precise optical design)
Dish Stirling Solar Power Generation System	0.01–0.4	High	20–30	0.15	High (large collector area and Stirling engine thermal losses)	High (significantly affected by external environmental changes)
Fresnel Solar Thermal Power Generation System	10–200	Low	8–11	0.14	Moderate (relatively high optical component efficiency)	Relatively low (influenced by dust accumulation on mirrors)

. The table presents the key technical characteristics of each technology, including their capacity range, associated costs, efficiency percentages, and electricity costs (calculated using the Levelized Cost of Electricity model). These factors play a crucial role in determining the economic viability and performance of each CSP system, and they vary depending on the system design, installation location, and solar radiation levels. For instance, systems with higher efficiency tend to have lower electricity costs, but they might come with higher initial installation costs. The comparison of these attributes allows for a comprehensive assessment of the strengths and limitations of each CSP technology.

4. Application of Solar Thermal Systems in Industrial Process Heating

4.1. Energy Demand and Challenges in Industrial Process Heating

Industrial process heating accounts for a significant portion of global energy con-sumption, with a major share of energy allocated to thermal applications across various industries. These demands range from low to high temperatures, with the majority con-centrated in the low- to medium-temperature range, particularly in sectors such as food processing, textiles, chemicals, and paper manufacturing. However, the predominant re-liance on fossil fuels, especially natural gas and oil, raises concerns about environmental pollution, greenhouse gas emissions, and resource depletion. As the world shifts toward more sustainable energy sources, renewable options, such as solar thermal energy, offer substantial potential to meet industrial heating needs, particularly in regions with abun-dant solar resources. However, the widespread adoption of solar thermal systems faces challenges, including high initial costs and the intermittent nature of solar energy, which necessitates the integration of energy storage solutions and hybrid systems for greater economic feasibility and stability.

4.1.1. Energy Demand for Industrial Process Heating

Industrial process heating constitutes a major share of global energy consumption, representing over 35% of total energy demand, with nearly 54% of industrial energy allocated to thermal applications [19]. This demand spans a wide range of applications, from low-temperature (<100 °C) to medium-temperature (100–400 °C) and high-temperature (>400 °C) needs. However, the majority of the industrial heating demand is concentrated in the low- to medium-temperature range, particularly in industries such as food processing, textiles, chemicals, and paper manufacturing. In these sectors, thermal energy is typically used for processes such as pasteurization, drying, cooking, bleaching, and dyeing. For example, the temperature range for cleaning, pasteurization, and drying in the food processing industry generally falls between 60 °C and 250 °C, while the thermal energy requirements for cooking and drying in the paper industry typically range from 90 °C to 200 °C. In the chemical and pharmaceutical industries, distillation, evaporation, and reaction processes often require higher temperatures, typically in the range of 100 °C to 400 °C [87].

At present, industrial process heating is predominantly dependent on fossil fuels, particularly natural gas and oil. While these energy sources can meet the high-temperature requirements of industrial processes, their usage is associated with environmental pollution, greenhouse gas emissions, and resource depletion [88]. In many developing countries, coal remains the primary energy source for industrial process heating due to technological and economic limitations, while more industrialized regions tend to rely on natural gas [89]. With the increasing global focus on energy efficiency, fluctuating fossil fuel prices, and the tightening of environmental regulations, governments and businesses are progressively shifting towards renewable energy sources as alternatives to conventional energy. This transition is not only aimed at alleviating environmental pressures but also at addressing the potential crisis arising from the gradual depletion of fossil fuels.

4.1.2. Potential for Application in the Industrial Sector

Solar thermal energy is the process of converting solar radiation into heat energy. As shown in Figure 13, solar thermal systems utilize solar collectors to capture solar radiation. The potential of solar thermal energy systems in industrial process heating is primarily reflected in their ability to fulfill low- and medium-temperature demands while providing substantial economic and environmental advantages. These systems employ various types of solar collectors, including flat plate collectors, evacuated tube collectors, and parabolic trough collectors, to provide thermal energy for multiple industrial applications such as food processing, textiles, chemicals, and pharmaceuticals [90]. The application of solar thermal technology is not confined to specific industries but also demonstrates notable benefits in particular regions. For example, in regions with abundant solar resources, such as India, the Middle East, and Africa, the strong solar radiation provides crucial support for the economic viability and efficiency of solar thermal systems. Industrial enterprises in these regions can substantially reduce their dependence on traditional fossil fuels, while simultaneously lowering energy costs and carbon emissions [87]. Despite the extensive potential of solar thermal systems in the industrial sector, their large-scale implementation faces considerable obstacles. High initial investment cost represent a significant barrier to widespread adoption, while the intermittent nature of solar radiation impacts system stability. As a result, the incorporation of energy storage technologies, such as phase change materials (PCMs) and molten salt storage, is of critical importance to maintaining a stable energy supply. Moreover, to enhance adaptability and economic feasibility, hybrid heating technologies that integrate solar thermal technology with conventional fossil fuel systems have emerged as a crucial area of research.

4.2. Application Scenarios of Solar Thermal Systems in Industrial Processes

Solar thermal systems have a wide range of applications in industrial processes, from low-temperature hot water to high-temperature steam, meeting the diverse needs of industries such as food processing, textiles, chemicals, and metalworking (Figure 14). These systems provide clean and sustainable energy solutions, significantly reducing dependence on fossil fuels and lowering carbon emissions. The application scenarios of solar thermal systems can be broadly classified into low-temperature, medium-temperature, and high-temperature categories, depending on the specific thermal requirements of industrial processes.

4.2.1. Low-Temperature Application Scenarios

Solar thermal systems exhibit broad applicability in low-temperature industrial processes, particularly in industries requiring low-temperature hot water or thermal energy. Low-temperature solar thermal systems, typically used for applications below 100 °C, mainly convert solar radiation into heat through solar collectors, providing sustainable energy alternatives for industrial production. Key application scenarios include food and beverage processing, textile industries, and chemical processes.

In the food industry, solar thermal systems can be utilized for cleaning, pasteurization, and disinfection, all of which require low-temperature heat. Pasteurization, a widely used technique, necessitates a constant supply of hot water at temperatures between 60 and 70 °C, a requirement efficiently met by solar thermal systems. This approach not only reduces reliance on fossil fuels but also significantly cuts energy costs and carbon emissions [91]. Additionally, the beverage industry often uses solar energy to provide the required low-temperature hot water for cleaning in bottling production lines.

In the textile industry, low-temperature solar thermal systems play an essential role. Dyeing, rinsing, and washing processes in textile manufacturing demand substantial quantities of warm water, typically within the 50–80 °C range. Solar thermal systems supply the necessary heat for these processes, reducing dependence on coal and natural gas while enhancing energy independence for enterprises [92].

Low-temperature applications in the chemical industry demonstrate considerable potential, finding extensive utilization in processes such as low-temperature evaporation, dissolution, and precision cleaning. This system reliably supplies the necessary thermal energy while mitigating cost pressures associated with fluctuations in fossil fuel prices. In industrial production processes with a continuous yet relatively low heat demand, the integration of solar thermal systems with thermal energy storage technologies significantly improves the system’s flexibility and operational stability.

Consequently, in low-temperature industrial applications, solar thermal systems serve as a low-carbon, cost-effective, and sustainable energy solution, positioning them as an essential enabler in advancing industrial energy efficiency and emission reduction objectives.

4.2.2. Medium-Temperature Application Scenarios

Solar thermal systems are also widely applied in medium-temperature industrial processes (100–250 °C), representing an important pathway for achieving industrial energy savings and sustainable development. This temperature range is commonly required in industries such as paper and pulp, dairy processing, chemicals, and pharmaceuticals. In these fields, solar thermal systems use solar collectors and moderately concentrated parabolic trough systems to provide hot water or steam to meet medium-temperature energy demands.

In the paper industry, pulp drying and thermal treatment are the main energy-consuming stages. Solar thermal systems can provide a stable heat source, reducing reliance on traditional fossil fuels. In dairy processing, such as milk powder production, a significant amount of medium-temperature steam is required for evaporation and drying. Empirical studies conducted in dairy processing facilities indicate that solar thermal systems can fulfill up to 76–94% of the thermal load demand [93], leading to a substantial reduction in both energy expenditures and carbon emissions. In the chemical and pharmaceutical industries, solar thermal energy is used for solvent evaporation, chemical reactions, and distillation, all of which require stable temperatures. By integrating solar thermal systems with thermal energy storage devices (such as phase change materials or thermal storage tanks), a continuous and stable heat supply can be ensured, overcoming the intermittent nature of solar energy [87].

Additionally, the application of solar thermal systems in medium-temperature scenarios in beverage industries, such as breweries, has been highly successful, where they are used to heat water and steam for cleaning, pasteurization, and production processes. Through the implementation of advanced solar thermal technologies, industrial facilities not only achieve significant reductions in operating costs but also substantially cut their carbon emissions, thus playing a crucial role in advancing carbon neutrality objectives [91]. To clearly illustrate the correlation between solar thermal applications and specific industrial process temperature ranges,

Table 3. Solar systems at different temperatures’ generation.

Temperature Divisione	Industrial Type	Application
Low (<100 °C)	Food industry	Wash, pasteurize, and disinfect
	Textile industry	Dyeing, rinsing, and washing
	Chemical industry	Low-temperature evaporation, dissolution, and cleaning
Medium (100–250 °C)	Paper industry	Pulp drying, heat treatment
	Beverage industry	Wash and pasteurize
	Chemical and pharmaceutical industries	Solvent evaporation, chemical reaction, and distillation
High (<250 °C)	Metalworking industry	Metal melting, heat treatment
	Chemical industry	Pyrolysis, gasification, and synthesis at high temperature

summarizes the typical industrial sectors and their representative thermal processes categorized by low-, medium-, and high-temperature requirements.

Table 3 shows typical industrial sectors and thermal process examples at different temperature levels for solar thermal systems.

Solar thermal systems demonstrate immense potential in medium-temperature industrial applications by significantly reducing fossil fuel usage and enhancing energy efficiency. When integrated with thermal energy storage technologies, they further improve reliability and adaptability. The effective deployment of these technologies offers practical and scalable solutions to enhancing industrial energy efficiency and promoting environmental sustainability.

4.2.3. High-Temperature Application Scenarios

Solar thermal systems in industrial processes are primarily applied in fields that require high-temperature heat sources, such as metal processing, ceramic manufacturing, glass production, and high-temperature chemical reactions. High-temperature solar thermal systems primarily rely on concentrated solar power (CSP) technologies, including parabolic trough collectors, solar power towers, and Fresnel lens collectors, to achieve temperatures of approximately 250 °C or higher. These technologies focus solar radiation onto specific areas using mirrors, achieving the required high temperatures. In the metal processing industry, solar thermal systems can provide sustainable high-temperature heat sources for metal smelting and heat treatment, replacing traditional coal or gas energy sources [94]. In ceramic and glass manufacturing, where high-temperature kilns frequently operate at temperatures exceeding 1000 °C, solar power tower systems can provide the necessary thermal energy, thereby lowering production costs and mitigating environmental pollution [92].

The chemical industry presents considerable potential for high-temperature applications. In high-temperature cracking, gasification, and synthesis processes, solar thermal systems can provide high-temperature steam and heat support. These processes are inherently energy-intensive, and integrating solar thermal systems can substantially decrease fossil fuel consumption while enhancing overall energy efficiency. High-temperature solar systems can be coupled with thermal energy storage technologies to ensure a continuous supply of high-temperature heat, even during periods of insufficient sunlight. Molten salt storage technology, for example, stores solar thermal energy during the day and releases it at night, providing a stable heat source for chemical reactions or high-temperature manufacturing.

In summary, solar thermal systems hold great promise for high-temperature industrial applications. These systems serve as clean and efficient heat sources, reduce industrial dependence on conventional energy, and play a pivotal role in enhancing energy efficiency and reducing emissions.

4.3. Economic Effects of Solar Thermal Systems in Industrial Processes

As the global energy transition accelerates and industrial sustainability becomes a priority, solar thermal systems, a clean and efficient renewable energy technology, are increasingly being integrated into the industrial sector. These systems provide a sustainable source of thermal energy for industrial processes, reducing reliance on fossil fuels and mitigating greenhouse gas emissions. While the adoption of solar thermal systems in the industry is still evolving, numerous studies highlight their substantial potential to lower operational costs, meet carbon reduction targets, and foster long-term economic stability.

4.3.1. Cost Savings and Investment Return Analysis

The economic benefits of solar thermal systems in industry are primarily evident in long-term fuel cost savings and rapid return on returns. Although the initial capital investment for solar thermal systems—comprising equipment, installation, and integration—can be high, these systems significantly reduce reliance on traditional fossil fuels, resulting in notable fuel cost reductions. For example, a dairy plant in Austria installed 1000 m² of solar collectors, which saves 85,000 m³ of natural gas annually and reduces CO₂ emissions by 170 tons. This not only generates considerable environmental benefits but also shortens the payback period to under three years [91].

Life cycle cost (LCC) analysis further underscores the economic viability of solar thermal systems. Despite higher initial investments, energy cost savings during operation, combined with low maintenance costs, render these systems economically advantageous in the medium to long term [95,96]. Furthermore, the monetization of carbon reduction benefits, supported by policy incentives, further enhances the economic appeal of these systems. For example, under the European Union Emissions Trading System (EU ETS), the value of carbon emission reductions is integrated into company revenues, providing additional incentives for investors. This dual benefit—direct fuel cost savings and policy incentives—makes solar thermal systems a powerful tool for reducing industrial operating costs.

4.3.2. Regional and Industry-Specific Differential Benefits

The economic benefits of solar thermal systems vary significantly across different geographical regions and industries. The key factors influencing these benefits include local climate conditions and fossil fuel prices. In regions with abundant solar and high fossil fuel prices, such as Southern Europe and Australia, the payback period for solar thermal systems is typically shorter, and the economic benefits are particularly pronounced [96]. In contrast, regions with lower solar radiation or fuel prices, such as some developing countries, experience more limited economic benefits. These areas often require additional policy support and technological optimization to fully unlock the potential of solar thermal energy [97].

At the industry level, low-temperature processes (40–120 °C) generally show higher compatibility with solar thermal systems. Industries such as food, beverage, and textiles, where thermal energy demand is concentrated within a low-temperature range, can effectively meet significant thermal needs using flat-plate collectors or vacuum tube collectors. For instance, a dairy plant in New Zealand implemented a solar thermal system to meet part of its thermal demand, achieving additional economic benefits through heat storage and system optimization [98]. The characteristics of these industries allow for a faster realization of high investment returns.

For industries requiring medium-temperature heat (150–400 °C), such as chemical and plastic processing, economic benefits are more dependent on technological support. These sectors typically employ highly efficient collectors, such as parabolic troughs or linear Fresnel reflectors, often coupled with high-temperature storage systems to meet thermal demands. While the initial investment is higher, the gradual optimization of these technologies and their increasing deployment are demonstrating their economic feasibility [97]. However, for high-temperature processes exceeding 400 °C, such as steelmaking and glass manufacturing, the economic benefits of solar thermal systems remain relatively low due to technological and efficiency limitations. Further research and breakthroughs in these technologies are essential for future development [96].

4.3.3. Long-Term Economic Stability and Intangible Value

In addition to direct cost savings, solar thermal systems contribute to long-term economic stability and provide intangible asset value to businesses. As a renewable energy technology, they reduce a company’s reliance on fossil fuels, thereby mitigating the financial risks associated with energy price volatility. This risk avoidance benefit is especially crucial for regions dependent on imported fuels [95].

Moreover, the intangible value of carbon reduction is increasingly recognized as a key component of corporate competitiveness. As the global focus on sustainable development intensifies, the adoption of solar thermal systems can significantly enhance a company’s environmental reputation and social responsibility image [91]. These intangible assets not only help attract more investments but also increase market competitiveness, particularly in industries that place a high emphasis on green production.

Although the promotion of solar thermal systems in high-temperature industrial sectors still faces technological and economic challenges, the economic benefits in low- and medium-temperature industrial processes have been widely recognized. Future research directions should include further optimization of system designs, reducing initial investment costs and driving the global adoption of solar thermal systems through policy support and business model innovation (Figure 15). Additionally, improvements in energy storage technologies and the development of new, efficient collectors will further enhance the economic potential of solar thermal systems in high-temperature applications, providing new possibilities for achieving sustainable industrial development.

4.4. Technical Advantages and Challenges in Industrial Applications

4.4.1. Technical Advantages

Solar thermal systems represent a clean, renewable energy source that can significantly reduce carbon emissions in industrial production. This is especially true in energy-intensive industrial sectors such as metal smelting, chemical production, and food processing, where solar thermal energy can effectively replace traditional fossil fuels, thereby reducing carbon dioxide and other greenhouse gas emissions. This contributes to addressing the global challenge of climate change [99]. Moreover, with the continuous development of concentrated solar thermal technologies, such as tower systems, parabolic trough collectors, and concentrating collectors, solar energy can be efficiently converted into thermal energy. These technologies generally exhibit high heat collection efficiency, meeting industrial heat demands ranging from low to high temperatures. This is particularly beneficial in industries such as metal processing and ceramic manufacturing, which require high-temperature heat sources [100]. Solar thermal systems can also be integrated with traditional industrial energy systems to form hybrid energy supply systems. For instance, solar thermal energy can be combined with natural gas boilers or electricity systems to ensure the stability and reliability of heat supply. Especially in regions with weaker solar radiation, the combination of solar energy and traditional energy sources can provide around-the-clock energy supply [94]. With the advancement of energy storage technologies, solar thermal systems can integrate advanced thermal storage technologies (e.g., molten salt storage and phase change material storage), which allow excess thermal energy to be stored during the day and used during the night or on cloudy days. This resolves the intermittency issue associated with solar energy. The application of such storage systems makes solar thermal systems more widely applicable, particularly in industrial processes that require a stable heat source [101].

Despite the higher initial investment in solar thermal systems, their operational costs are much lower than those of fossil fuels, particularly in the context of rising energy prices. Solar thermal energy thus becomes a competitive alternative energy source. Many studies show that in some regions, the payback period for solar thermal systems typically ranges from 3 to 5 years, effectively reducing energy costs and improving economic efficiency [94].

The main technical advantages of solar thermal systems in industrial applications are their clean, renewable energy characteristics, high energy conversion efficiency, low operating costs, good system integration, and ability to integrate with energy storage technologies. With continuous technological innovation and the gradual maturation of markets, solar thermal systems are expected to be more widely applied in industrial fields, providing sustainable solutions for reducing carbon emissions and lowering energy consumption.

4.4.2. Technical Challenges

Despite the significant advantages of solar thermal systems in industrial applications, there remain numerous technical challenges to their widespread implementation.

First, the initial investment for solar thermal systems is typically high, especially in large-scale industrial applications such as chemical processing, food manufacturing, and metal smelting. While the operational costs of these systems are relatively low, the initial costs for equipment purchase, installation, and system integration require substantial capital investment. This can be a major challenge for smaller and medium-sized enterprises looking to adopt solar thermal systems [101].

Second, the efficiency of solar thermal systems is heavily influenced by climate conditions and geographic location, particularly in regions with insufficient sunlight. In such areas, the heat supply capability of the system may be compromised. Although thermal storage technologies, such as molten salt storage or phase change material storage, can partially address this issue, challenges remain with the widespread adoption of efficient storage technologies and the high cost of storage equipment. Particularly in regions with long winters or frequent cloudy weather, solar thermal systems may not meet the continuous industrial heat demand [100].

Furthermore, integrating solar thermal systems into existing industrial energy systems poses another challenge. The integration design, installation, and maintenance of these systems require a high level of technical expertise, adding complexity to their deployment. Determining the optimal configuration and scale of collectors for different industrial applications and effectively storing and supplying solar heat when needed are significant technical challenges [99].

Currently, although solar thermal technology has made significant progress in certain areas, it is still in the process of gradual refinement and broader adoption. This is especially true for high-temperature industrial applications, where the maturity and reliability of the technology still need to be improved. For example, solar tower collector technology and concentrating systems require higher costs and precision, and their reliability and efficiency in actual industrial applications are still under ongoing optimization [94].

Finally, despite being seen as a clean energy solution in many countries, the promotion of solar thermal technology faces challenges in some regions due to insufficient policy support and low market demand. The lack of adequate government incentives, subsidy policies, and a general lack of corporate awareness about green development often leads to the slow adoption of solar thermal systems in industrial applications. Without policy guidance, enterprises may be reluctant to bear the high initial costs, even though solar thermal systems may offer higher economic and environmental benefits in the long term [96].

In conclusion, the application of solar thermal systems in the industry faces challenges related to technical costs, system integration complexity, weather dependency, technology maturity, and insufficient policy support. To further advance the application of solar thermal technology in industrial settings, technological innovation, policy support, and an improved market environment are urgently needed to lower costs, enhance system stability and reliability, and promote the widespread use of renewable energy in the industrial sector.

5. Emerging Technologies in Concentrating Solar Thermal Systems

5.1. Innovative Solar Collector Materials

Advances in nano-functionalized absorber materials and high-performance optical systems are expected to enhance the heat collection efficiency of CST systems. Nano-functionalized materials, such as nanostructured coatings and multi-layered absorbers, offer superior light absorption and reduced thermal losses. These innovations help to significantly improve the conversion of sunlight into thermal energy, particularly for high-temperature applications where traditional materials might not perform as well. For example, the development of selective absorbers with tailored optical properties allows CST systems to operate efficiently at temperatures exceeding 500 °C. A schematic representation of the nanocomposite-based single-layer absorber coating developed on SS 304 substrate is shown in Figure 16, which highlights the fabrication process using SiO₂ nanoparticles and the improvement in solar absorptance through nano-void textured surfaces [102].

5.2. Thermal Energy Storage (TES) Innovations

Emerging TES technologies are playing a critical role in enhancing the performance of CST systems by enabling them to provide continuous power even when sunlight is un-available. Technologies like phase change materials (PCMs) and thermochemical storage systems offer higher energy density and cost effectiveness compared to traditional methods such as sensible heat storage. PCMs, which store thermal energy through phase transitions (solid to liquid), allow for more compact and efficient thermal storage. Thermo-chemical storage systems, which store energy via reversible chemical reactions, provide even higher energy densities and longer storage durations, making them especially useful for large-scale applications. The integration of TES with CST systems has been well explained through Figure 17, which illustrates the indirect configuration using super-critical carbon dioxide (s-CO₂) as the heat transfer fluid (HTF). The integrated system in this study, which utilizes supercritical carbon dioxide (s-CO₂) as the heat transfer fluid (HTF) in a parabolic trough collector (PTC) system, operates as follows. Solar radiation is focused by the parabolic mirrors onto a receiver tube, where it heats the circulating HTF (Points 1–5). The heated HTF is transported through the PTC loop, passing through a heat exchanger (Point 8) to transfer thermal energy to a thermal energy storage (TES) system. The system includes both hot and cold TES tanks (Points 11–12), where energy is stored during the day and discharged during non-sunny periods (Point 13–15). The HTF, after being heated, flows into the hot tank for storage, while the cold tank helps maintain the temperature differential for energy efficiency. The stored thermal energy is later used to generate electricity in the power block (Point 17) through a conversion process. This process is facilitated by a secondary heat exchanger, which is specifically required for the s-CO₂ configuration (Point 9). The system’s design ensures efficient energy storage and usage, with feedback mechanisms to regulate energy flow throughout the day and night (Points 16–19). This system design shows how s-CO₂ improves thermal energy storage efficiency and reduces system costs [52].

6. Conclusions and Outlook

This review comprehensively explored the technological evolution, thermal performance, and industrial applications of concentrated solar thermal (CST) systems, emphasizing their capabilities beyond power generation. CST systems, through optical concentration and efficient thermal conversion, can generate medium- to high-temperature heat suitable for a wide range of industrial sectors such as food processing, chemical manufacturing, textiles, and metal treatment. With growing global pressure to decarbonize industrial processes, CST technologies present a critical pathway for reducing fossil fuel reliance and greenhouse gas emissions in the heat domain.

Through an extensive survey of CST configurations—including parabolic troughs, central towers, linear Fresnel reflectors, and dish Stirling systems—we highlighted their respective thermal efficiencies, temperature capacities, land requirements, and application scopes. Recent research advancements in optical design, receiver materials, and heat transfer fluids are significantly enhancing the thermal efficiency and operational stability of CST systems. Especially, the development of high-absorptance, low-emissivity coatings and high-temperature-tolerant materials such as high-entropy alloys has elevated CST systems’ ability to perform at temperatures exceeding 700 °C, opening new possibilities for energy-intensive processes.

Thermal energy storage (TES) technologies, such as molten salt storage, phase change materials, and thermochemical storage, have been shown to extend CST system performance during periods without solar radiation, allowing for continuous and dispatchable thermal energy delivery. This capability is crucial for ensuring the operational flexibility of CST systems in real industrial scenarios, especially where thermal loads are steady or require precise temperature control.

While the hybridization of CST with photovoltaic (PV) systems offers clear benefits for electricity dispatchability, it was not the core focus of this work. Our review intentionally centered on CST’s role in heat production, not electrical power generation. As such, the discussion on PV-CSP hybrid systems—although important in the context of power systems—is outside the intended scope of this study, and should not constitute a key takeaway of the conclusion. Instead, future research and industrial implementation strategies should focus on enhancing CST’s value as a sustainable heat supply solution, particularly in hard-to-electrify industrial sectors.

Looking forward, several challenges remain. These include high initial capital investment, integration complexity with existing heat infrastructure, and performance degradation in sub-optimal sunlight conditions. To overcome these, innovation should continue in areas such as smart solar tracking, AI-based operation control, durable receiver coatings, and cost-effective thermal storage materials. Meanwhile, policy incentives, industrial demonstration projects, and cost reduction through scale will play a decisive role in accelerating CST deployment in the thermal energy market.

In summary, CST systems are no longer limited to niche or experimental roles. Their ability to deliver reliable, high-grade heat makes them a promising and scalable solution for low-carbon industrial transformation. Continued advances in material science, thermal storage, and system integration will be key to realizing CST’s full potential in achieving industrial decarbonization, thermal energy security, and sustainable development goals.