A Comprehensive Review of Integrated Energy Systems Considering Power-to-Gas Technology

Abstract

Integrated energy systems (IESs) considering power-to-gas (PtG) technology are an encouraging approach to improve the efficiency, reliability, and elasticity of the system. As the evolution towards decarbonization is increasing, the unified coordination between IESs and PtG technology is also increasing. PtG technology is an option for long-term energy storage in the form of gas, but, compared to other technologies, it is economically expensive at the present time to optimize the technology. This article presents a comprehensive review of the state-of-the-art research and of the developments regarding integrated energy systems considering PtG technology. This presented review emphasizes planning and economic analysis, including system integration enhancements focusing on optimization, conversion technologies, and energy storage to improve the operation and stability and to enhance the facilities for consumers. The role of a PtG system in generation, transmission, distribution, and consumption is discussed. By emphasizing planning, integration, and the role, this paper aims to guide researchers, scientists, engineers, and policy makers towards effective research and broad strategies that sustain an IES-PtG.

1. Introduction

Electricity is an important energy in the daily life of humans to fulfil their needs in different sectors, and advanced technology connects many objects with electricity. The demand for electricity is increasing due to substantial economic development, industrialization, and consumers’ demands [1]. More demand for electricity needs the maximum amount of power generation, and there are many sources of power generation, such as hydropower, solar energy, wind energy, fossil fuels, biomass, thermal, coal, nuclear energy, etc. Renewable energy sources have the ability to generate excess electricity, but, due to a lack of proper planning, the excess electricity is wasted. To utilize the excess electricity from renewable energy sources, researchers introduced a technology to convert excess electricity to gas, which they called power-to-gas (PtG) technology. PtG technology converts electricity to gas (hydrogen), which can be stored for a long time and can be utilized in the case of required demand for power generation and gas consumption.

The energy sector is affected by climate change, which plays an active role in the development of the energy market, and seeks to increase efficiency and to minimize cost and energy waste [2,3]. Conventional power systems are decreasing and being replaced by renewable energy sources to decrease emissions from fossil fuels and to provide a long-term success plan for clean energy production [4,5]. It is very risky and dangerous to store high-voltage power, and forecasting renewable energy is difficult due to weather conditions, which result in fluctuations [4,6]. Utilizing renewable energy is increasing and playing an important role in fulfilling consumers’ demands, and the target of renewable energy in Europe is at least 32% by 2030. Energy can be stored in a variety of ways, but the best option relies on a number of factors, including location, performance (efficiency, energy density, and so on), and cost [4,7,8,9,10,11]. Different energy storage technologies are shown in Figure 1, which shows their storage capacities. In Figure 1, the short- and long-term storage of energy is shown with the possibility of storage from hours to years.

An integrated energy system entails connecting various sources of multi-energy grids via the internet and physically connected devices through efficient and proper management. It is a viable alternative in terms of the environment and energy supply. It is a system made up of several renewable energy sources, with concentrated energy serving as the system’s focal point. It is a carbon-free and environmentally friendly technology that is expected to be an economical source of energy in the future. It might be an add-on to the existing energy system based on consumers’ needs [12]. To remain aware of potential challenges, energy infrastructures and their integration with conversion technologies, from utilizing surplus electricity to gas storage, are the model of integrated energy systems [13]. This model of an energy system, in the case of a smart grid, smart cities, and energy management and coordination, as well as cost savings, encourages energy system integration [14]. Multiple energy sources can be regulated and coordinated through integrated energy systems. Converted electricity is at the heart of various energy carrier transformations, and increased economic performance can be achieved through better management and coordination [15]. For better energy flow without fluctuations, integrated energy systems necessitate a powerful transmission grid. An integrated energy system is an effective strategy for increasing the energy system with a better balance and fewer fluctuations across the power system. In the universe, carbon emissions and energy problems are two challenges that must be solved, and IESs were introduced to address these issues. An IES is a notion of energy system integration with power generation that evolved from the smart grid. The IES architecture is exemplified by the future renewable electric energy delivery and management system (FREEDM). It connects the electricity grid to distributed and alternative generating sources, as well as storage devices [16].

The power-to-gas system is a new research work, which has been in the development stages for a few years, that facilitates the integration of electricity and natural gas, utilizes surplus electricity to convert it to gases as an option for long-term energy storage, and provides an economical operation. A PtG system is attracting attention in research areas and is already being discussed in many studies, such as in [17], where electrolyzer-based PtG systems were studied in support of an electric grid and a comparison was made with a BESS, which shows the advantages of PtG technology based on a reliability and planning perspective. In [18], a rolling dispatch model was applied to an integrated electricity–gas system considering the PtG model, which indicated an improvement in system flexibility with enhanced security and an economical system operation. In [19], the uncertainties associated with a wind PV system were investigated for the integrated electricity and natural gas system associated with a PtG system. The study results indicated that the economy will be improved and the decision makers will get guidance in case of operation risk due to uncertainty. The authors of [20] researched the organic Rankine cycle and power-to-gas systems to solve the issue of an energy mismatch between the supply and load sides in integrated energy systems. The system was compared with and without a power-to-gas system and the one considering it with a power-to-gas system showed the best results. In [21], the advantages, disadvantages, and real behavior of configurations used in the dynamic analysis of chemical methanation in a power-to-gas plant were studied. Figure 2 is the schematic of PtG technology, which shows the role of PtG technology and its integration with different sectors.

To furnish profound perceptions into the distinctions, future utilization, and present status of IES-PtG technology, more comprehensive research is required. This review paper aims to collect the information that is currently available about IES-PtG technology in terms of planning, integration, and its role. This article addresses the fundamental concepts about IES-PtG technology, including planning, economic analysis, optimization, conversion, energy storage, and its role. The technical aspects of IES-PtG technology, such as conversion technologies and energy storage, are studied. In order to deploy IES-PtG technology cost-effectively, the economic analysis is evaluated. Finally, the role of PtG technology is studied in terms of generation, transmission, distribution, and consumption.

Furthermore, this article is organized as follows. Section 2 concerns planning and economic analysis discussing planning models and economic analysis. Section 3 concerns system integration enhancements, which include optimization, conversion technologies, and energy storage. Section 4 concerns the role of PtG technology including generation, transmission, distribution, and consumption. The last section is the conclusion and discussion.

2. Planning and Economic Analysis

2.1. Planning Models of IES with PtG Technology

The planning models of the system consist of external and internal stages. The external stage in the planning of a system specifies the location and capacity of the units. The internal stage schedules the operation of the system to get the optimal output based on the planning of the external stage. The planning of an IES-PtG system can be both single- and multi-objective. Cost is a major obstacle in the planning stage, and in IES-PtG planning it is mostly used as a single objective in different research. Different costs are involved in IES-PtG planning, which could include construction and operation costs [22,23,24,25]. An IES-PtG engages in high energy efficiency, and improving the efficiency is also a task in the planning. In IES-PtG planning, considering the cost and efficiency in the planning models is an objective that is important, and the efficiency calculation is possible during the operation and integration of the units. In [26], the authors studied efficiency calculations and the annual performance of PtG systems, focusing on the development of efficiency variations of different levels, integrating the electrolyzer and methanation system. In [27], the authors worked on power-to-gas technologies and CO₂ emission reduction to remove the barriers to integration and to improve the efficiency to a high level in the development of the technology. In [28], the researchers focused on the efficiencies of power-to-gas-to-liquid-to-power systems, with a comparison of each technology and improvements in the efficiencies of each system. Figure 3 shows the model of PtG technology.

In the planning stages, a PtG system consists of three technologies that can play a key role in the development of the technology. The first technology is the power system, which is focused on the power generation from renewable energy sources. The second technology is the electrolyzer, which gets the surplus renewable energy and converts it to gases. An electrolysis process take place, where the water molecules are split in a chemical reaction to produce hydrogen and oxygen. The third technology is gas production, which we get from the water electrolysis, and the produced gases are stored in a tank, which is a hydrogen storage tank. The development of the planning of electricity and natural gas integration was studied, focusing on the issues of demand uncertainty and hydrological levels. This validated the analysis, which may be used to accurately determine the nominal and economic benefits delivered by the integration of installed system components [29]. Researchers used the IES optimal planning technique in a research study that focused on future energy systems and their related issues in comparison with the conventional system and PtG system integration using conversion technologies [13]. A planning algorithm was developed for the transportation system using an integrated electricity and natural gas system to improve power grid flexibility in extreme scenarios. The relationships between power grid development circumstances and severe events, as well as the most effective approach to increase power grid flexibility, were defined by a variable ambiguity set [30]. Natural gas integration into the electricity grid is becoming increasingly significant as a result of its economic and ecological advantages over fossil fuels, which minimize the expenses and operation costs [31,32]. In [33], the research revealed that in a multi-period planning scenario, new nodal generation supplies, transmission lines, and natural gas pipelines are gained instantly, solving the problems.

In [32,34], the research work presented a modeling methodology for combining coordination and inconsistencies in the growth of energy (power and gas) demand. Short-term uncertainty, such as an inconsistency in renewable energy supplies, and long-term uncertainties, such as strategy or skill fluctuations, are among the uncertainties. The long-term planning study showed that the investment and operation budgets are reduced for generators and pipes [35]. The electricity and natural gas network planning model demonstrated that demand ambiguity provides an accurate strategy, particularly for utilities that must evaluate various extension plans in a variety of economic scenarios that influence the consumption of gas and electricity. The results suggested that a low-cost solution can be found that can meet the needs of various power and natural gas consumption scenarios [34,36,37,38,39].

2.2. Economic Analysis of IES with PtG Technology

The concept of a power-to-gas system provides a financially economical system and clean energy in the future from renewable energy sources. Different countries are putting forth their best efforts to put PtG technology into economical operation. PtG converts excess energy into gas that can be conveniently stored in tanks and can be utilized according to demand. A research study indicated that PtG technology can play a significant role in saving energy, which is estimated to be 41.7 % and saving USD 1.77 million, in comparison with isolated production, on the annual cost of operation [40]. In a power-to-gas system, the energy market serves as a link that connects the heating, transportation, and electrical sectors. In terms of cost, the comparison of hydrogen and methane use in the transportation industry, as well as their conversion to electricity, is highlighted in [8]. Power-to-gas technology can gradually help to reduce dispatch plant uncertainty and play an important role in balancing the electric grid. Different economic analyses, such as approximated generation, forecasting errors, and load circumstances, are statistically employed to determine the best balance of the system. In terms of performance, a hybrid system with balancing technology is the most cost-effective solution [11,41]. A macroeconomic analysis of predictive data shows that the economical operation of PtG technology is not possible until 2030, according to a research study. In 2040, a PtG system may be economical to consumers for load hours [5]. According to the research study that focused on the economic and environmental significance of a power-to-gas system’s applications, along with other storage systems, it was shown that the use of high-level energy storage systems is the most cost-effective, which can minimize the cost of the electricity [42]. The authors of [43] studied the energy planning model, which shows the capacity investment, dispatch, and demand. The model focused on reducing the investment and operation price of the system.

Table 1. Hydrogen production costs estimations.

Year	2016	2030	2050	Reference
Definite investment in €/kWel	1500	900	500	[5,44]
Efficiency (LHV)	70%	75%	80%	[4,5,7,8,45]
Electricity cost in €/MWhel	0 or 70	0 or 70	0 or 70	[5,10]
Rate for natural gas in €/MWhth	15	34	50	[5,44]
Rate for CO2 budgets in €/t	5	50	130	[5,44]

shows the future forecasted estimated production cost of hydrogen based on the recent development of the technology.

In [46], the research study presented a daily integrated forecast model for dealing with generation and hourly loads, as well as handling renewable energy system fluctuations and organizing flexible provisioning. The examples show how the cost of power system operating, flexible ramp arrangements, and hourly load forecasts can affect the real-time natural gas distribution. According to the results of the conducted research, PtG technology can reduce the cost of energy system integration and promote renewable energy generation [47]. According to the research, a gas system can save costs, while also improving the reliability of the electrical system [29]. Multi-energy arrangements can work together to share existing capabilities in integrated systems like electricity to gas, improving economics, sustainability, safety, resilience, and reliability. In order to improve power grid flexibility in severely disrupted conditions, the study conducted integrated electricity and natural gas planning [30]. To promote a healthy and ecological energy-based environment, moderate energy crises, and reduce carbon emissions, the study depicted the architecture for a future electric power distribution system that is well organized and integrates distributed and effective generating sources and storage with current power systems. Various energy transporters with suitable topological facts have been built, as well as energy conversion links between electrical and gas systems. The goal is to reduce the integrated system’s investment and operation expenses through economizing the system [22,48]. A study was carried out to manage and store the gas load in order to optimize the PtG operation in the day-ahead market (electricity and gas) and to lower costs [49]. In [50], the authors studied multi-energy microgrids, which focus on the challenges of the uncertainties associated with renewable energy, loads, and the integration of energy systems in the context of operation. The results of the case study show that multi-energy microgrids can reduce carbon emissions and the cost of a multi-energy supply.

Many sources are getting benefits from the integration of the energy system, such as microgrid design, energy sources, consumers, national grid infrastructure, and education institutes. In [38], the generation expansion planning method was used, which can help in risky environments that increase the investment. In [51], according to a forecast, by 2050, 80 percent of electrical energy consumption would be met by renewable energy sources, necessitating large-scale energy storage, and PtG is the greatest choice for achieving this goal. In [52], gas tariffs replicate natural gas flow direction transit costs, which is inefficient commercially. The parameters employed have an impact on the combined operation of the natural gas and electrical system optimization. In [53], the authors assessed the economic viability of energy and electricity costs considering a feasibility analysis of a PtG system in the future, with the result that PtG technology needs more research to economize and provide profits to consumers in the future. In [54], the authors investigated the issues of the day-ahead market co-optimization related to integrated electricity–gas systems, which focused on uncertainties in renewable power generation and the demand for gas and electricity. Furthermore, this study also focused on PtG price formation, economic efficiency, and locational marginal value. The result showed that the expected locational marginal value can properly accept the role of PtG technology and can deal with uncertainties.

3. System Integration Enhancement

3.1. Optimization of IES with PtG Technology

In [55], the integration of energy systems increased the demand of PtG systems, and the expanding generation capacities were strengthened. These energy systems were faced with expansion planning issues. To reduce the costs of energy system integration, including reliability, operation, and investment costs, a linearized model of an IES and an optimal expansion planning model with natural gas supply stations (NGSSs), natural gas-fired generation plants (NGFPs), gas pipelines, natural gas, and transmission lines was presented. From an economic standpoint, the scheme for optimal investment in a collaborative growth planning model of an integrated energy system with limits was developed to minimize the costs. In [56], according to the research, the integration of the energy system improves reliability and reduces reliance on a single source. As a result, in comparison to a single generation technique, an attempt was made to increase the system’s performance.

An investigated study demonstrated that utilizing the TIMES-VVT model, Nordic nations could achieve 100% renewable energy sources by examining the viability of PtG technology from 2010 to 2050. PtG utilization, as a substitute for the energy storage of excess renewable electricity, is primarily driven by the industrial sector and the provision of synthetic gas transportation. In the generation of synthetic gas, PtG must compete with biomass gasification [57,58]. PtG technology can increase system flexibility and connect electrical and different energy systems with each other [45]. PtG technology has the potential for a significant role in the expansion of energy systems with high efficiency and flexibility. It has the potential for sustainability in the future, and hydrogen gas can boost the market for automobile fuel cells [4].

A study contrasted the system models to highlight the problems of future energy systems considering the integration of energy systems and the PtG system, focusing on the optimized technologies used for conversion [13]. The researcher discussed multiple energy systems and their integration with a PtG system for the optimal scheduling using wind energy [59]. In [33,39], transmission expansion planning (TEP), natural gas grid expansion planning (NGGEP), and generation expansion planning (GEP) were discussed for a bulk system in an integrated energy system. According to a study, the PtG system is a choice to accommodate renewable energy excess generation, and the prediction to economize the system will see a step-wise improvement till 2050 [60]. In [61], the authors studied fuel cell vehicles as a hydrogen power transportation system and focused on the operation and distributed hydrogen supplies. The purpose was to decarbonize the transport system and maximize the total profits. This involved hydrogen production, utilization, dispensation, and storage. The results showed that hydrogen power transportation systems improve the total profit.

3.2. Conversion Technologies

PtG technology holds an important position in integrated energy systems utilizing renewable energy sources. PtG technology offers a way to accommodate the surplus electricity from renewable energy sources and convert it into chemical energy in the form of gases such as hydrogen and synthetic natural gas (SNG). These gases can be easily stored in storage tanks, transported through vehicles and transmission pipelines, and utilized according to consumers’ demands in different energy sectors. The applications of this power-to-gas conversion help in balancing the grid when renewable energy sources are generating surplus electricity and also contribute to the decarbonization of the energy system. Figure 4 shows the conversion infrastructure of PtG technology from renewable generation to storage, regeneration, and utilization in different technologies.

Electric power can be converted to gas via water electrolysis. The electrolysis procedure takes place in an electrolyzer, which includes different types such as a high-temperature electrolyzer, a proton exchange membrane, and an alkaline electrolyzer. The process of electrolysis starts when electricity is connected to electrodes in a electrolyzer and gas production takes place. An electric isolator diaphragm that keeps the gas isolated to avoid a flammable mixture is used to conduct the electrolysis [8,9,62]. In the electrolysis process, water is divided into hydrogen and oxygen (2H₂O → 2H₂ + O₂). Any electrolysis technique can be utilized; however, for the PtG process, a PEM is the best option. Apart from carbon dioxide (CO₂ + 4H₂ → CH₄ + 4H₂O), which requires the Sabatier reaction, the methanation process requires H₂ from the electrolysis [9,63,64]. In a research study, a biogas system was modified, and an anaerobic digester was integrated with a PtG plant to produce CO₂, using the Sabatier reaction to develop a techno-economic analysis of the PtG process. The results show that for the production of methane in the Sabatier reaction 1000 kW_el at 10 kmol/h are needed; 4.6 kmol/h and 22 kmol/h are the flow rates of CO₂ and hydrogen [65]. A research study showed that the efficiency is 54–77% for the power-to-gas conversion from renewable generation [4].

Table 2. Technical data of electrolyzers.

Technical Data	AEC		PEMEC		SOEC		Reference
	Mid-Term	Long-Term	Mid-Term	Long-Term	Mid-Term	Long-Term
Chemical reaction at anode	2OH− → 0.5O2 + H2O + 2e−		H2O → 2H+ +0.5O2 + 2e−		O2− → 0.5O2 + 2e−		[8,9]
Chemical reaction at cathode	2H2O + 2e− → H2 + 2OH−		2H+ +2e− → H2		H2O + 2e− → H2+ O2−		[8,9]
Production rate (m3 h−1)	<760 <1000		<40 <500		<5 >5		[9]
Min. part load (%)	30–40 10–20		0–10 0–5		N/a N/a		[4,8,9]
Max. part overload (%)	<150 <150		<200 <200		N/a N/a		[9]
Pressure (bar)	<30 <60		<200 <200		<25 <40		[4,7,8,9,45]
Temperature (C)	60–80 60–90		60–80 60–100		700–1000 500–700		[4,7,8,9,45]
Electricity demand (system) (kWh m−3)	>4.6 >4.4		>4.8 >4.4		>3.2 >3.2		[9]
Current density (A cm−2)	<0.5 <0.8		<1.0 <2.0		<0.3 <1		[9]
Cell voltage (V)	>1.9 >1.8		>1.8 >1.6		>1.0 >1.0		[9]
Lifetime system (a)	20 30		6–15 30		N/a N/a		[9]
Lifetime stack (h)	<100,000 <100,000		<50,000 <100,000		<5000 >5000		[9]
Development status	Commercial		Commercial		Under development		[9]

shows the technical data for the electrolyzers.

Two types of grid connections are used for the PtG system design modelling. One is on-grid, which connects with the national grid, and the other is off-grid, which is not connected with the national grid and could possibly be installed in remote isolated locations [4]. Water electrolysis is used to convert power to gas, and the equations are as follows:

$${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)={\mathrm{H}}_2\left(\mathrm{g}\right)+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2\left(\mathrm{g}\right)$$

(1)

As the electricity produces gases in the electrolyzer, the performance characteristic equation is as follows:

$$H{y}_{el}\left(t\right)=\left\{\begin{array}{l}{E}_{el}\left(t\right){\eta }_{el}if{E}_{el}\left(t\right)\ge \underset{¯}{E_{el}}\\ 0if{E}_{el}\left(t\right)<\underset{¯}{E_{el}}\end{array}\right.$$

(2)

where Hy_el (t) and E_el (t) indicate the amount of hydrogen produced and the amount of electricity used by the electrolyzer. The electrolyzer’s operational efficiency is measured in η_el, because efficiency drops abruptly at low loads, and an electrolyzer has the lowest power energy limit. In a methanation device, a Sabatier catalyst is utilized, where a chemical reaction take place to convert hydrogen and carbon dioxide to methane and water [59]. Equation (3) shows the chemical reaction.

$$\left\{\begin{array}{l}4{\mathrm{H}}_2{+\mathrm{CO}}_2\to {\mathrm{CH}}_4{+2\mathrm{H}}_2\mathrm{O}\\ \Delta H_R^o=-165.12\mathrm{kJ}/\mathrm{mol}\end{array}\right.$$

(3)

$$Q_{fuel\_m}\left(t\right)=H{y}_m\left(t\right){\eta }_m$$

(4)

Fuel cells generate electricity by a chemical reaction involving hydrogen and oxygen, as shown below:

$$E_{fc}\left(t\right)=H{y}_{fc}\left(t\right){\eta }_{fc}$$

(5)

$$\underset{¯}{E_{fc}}\le E_{fc}\left(t\right)\le \overline{E_{fc}}$$

(6)

where E_fc (t) and Hy_fc (t) represent the amount of hydrogen consumed and the amount of electricity generated by a fuel cell [59]. Hydrogen can be stored in tanks and used during peak hours while also being kept during off-peak hours. In [40], the electrolyzer’s energy efficiency was defined as follows:

$${\eta }_{el}={\displaystyle \frac{n{H}_2\cdot HH{V}_{H_2}}{P_{el}}}$$

(7)

where nH₂, P_el, and HHV_H2 stand for nominal capacity, electrolyzer installed power, and higher hydrogen heating value. In [63], the authors described a methanation method that requires hydrogen (H₂) and carbon dioxide (CO₂) during electrolysis, with the following chemical reaction:

$$\mathrm{C}{\mathrm{O}}_2\left(\mathrm{g}\right)+4{\mathrm{H}}_2\left(\mathrm{g}\right)=\mathrm{C}{\mathrm{H}}_4\left(\mathrm{g}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$$

(8)

3.3. Energy Storage

Energy storage technologies are essential, because of the intermittent nature of renewable energy sources, in order to increase overall grid reliability. Different varieties of energy storage technologies have been developed, which include cutting-edge options like lithium-ion batteries, flow batteries, compressed air storage, and pumped hydro storage [66]. These energy storage technologies are short-term energy storage and can store energy from hours to days and weeks. Each of these technologies have their advantages in terms of scalability, efficiency, and suitability. As a result of the intermittent nature of renewable energy sources, energy storage contributes significantly by storing excess energy during low demand and releasing it during peak demand. PtG technology is an option for long-term energy storage in the form of gases amongst these energy storage technologies [7,67].

As surplus power generation is used for conversion to gases, power-to-gas technology has received more interest recently in the context of long-term energy storage and utilizing renewable energy. The gas is stored in tanks and can be used in industries for commercial use and in homes for residential use. According to a study, a natural gas company purchased the excess power that is generated from renewable energy sources, e.g., wind farms, and installed a power-to-gas system, which transported synthetic natural gas from storage tanks to demand centers via gas pipes [40]. In [68], the essential elements utilized in the installation of the power-to-gas system, such as fuel cells and generators, as well as energy storage, were discussed. The efficiency improves while changing the load, but, for power-to-gas conversion, the efficiency decreases when the load is increased.

According to a study, PtG technology can boost the utilization of renewable generation for electricity while also storing extra energy. The methane gas generated from the PtG system and stored in a tank can be utilized for commercial, industrial, and electricity generation [69,70]. The researchers anticipated the data for 2025 energy storage using a power-to-gas system, which solves the challenging concerns of CO₂ and energy storage. In [71], the authors studied the integrated energy system and hydrogen production, storage, and utilization for the purposes of marketing and scheduling the amount of storage to buy or sell to consumers. In [72], the authors discussed energy storage that acts as a bridge to provide energy during low power events to consumers. The financial advantage of energy storage is realized in many research papers, which go beyond grid stability. Large-scale storage projects are more financially feasible due to the decreasing costs of energy storage technologies, which also promote their integration into energy markets [73]. The development of energy storage is hampered by a high upfront cost, governmental restrictions, and the requirement for uniform market processes. The fact that energy problems are global challenges, and international cooperation is needed for mutual collaboration in the development of energy storage technologies [74]. The working together of research institutions, industries, and government can help create a more resilient and sustainable energy landscape by accelerating the development and implementation of energy storage technologies globally.

4. The Role of PtG Technology

PtG technology plays a very significant role in different sectors and shows development in different research studies. Figure 5 shows the role of a PtG system in different stages and the technologies adopting it.

4.1. Generation

A major change is occurring in the power generation landscape as the global energy paradigm shifts to one that is more environmentally friendly and sustainable. The most recent technology that achieved significant attention in this transformation is PtG technology.

PtG technology is the latest technology in the early stages of planning and development to facilitate large-scale energy storage and power generation. The produced gas stored in the tanks can be used for different purposes, and one of these purposes is power generation. PtG technology plays a significant role in power generation, which contributes to improving grid stability and easily integrates renewable energy sources. Conventional power systems face a challenge from intermittent renewable energy sources as variations in energy output can cause grid instability. PtG serves as an essential bridge, enabling the storage of energy in the form of gases and utilizing it when renewable energy power generation is limited. In [75], the authors focused on PtG reversible action, which shows that, during peak power generation, electricity is converted to hydrogen gas and is stored in tanks and, during low power generation and high demand, the stored hydrogen is injected to fuel cells to generate electricity. This is called a reversible power-to-gas system. The authors applied this model to the market environment and concluded that a reversible PtG system is economically viable. In [76], the authors focused on the future interaction of a PtG system and power generation in China to deal with electricity demand and economical generation and operation.

PtG technology makes it possible to have a robust infrastructure for power generation to utilize the stored energy in case of energy demand and provide a continuous power supply. PtG technology provides a special type of energy storage that may be conveniently included in the processes involved in power generation. In case of demand, the produced hydrogen can be put straight into fuel cells via electrolysis or gas turbines to generate electricity. Because of its flexibility, the electricity generation system is able to respond and adapt more quickly, meeting changing demand while preserving grid stability. Furthermore, an additional source of clean and dependable power generation can be obtained by injecting the synthetic natural gas (SNG) generated by PtG technology into the current natural gas infrastructure. By integrating with the current gas grid infrastructure, the power generation system’s overall system flexibility improves.

PtG technology is becoming a more competitive option for power generation and storage as a result of its economic viability, which is a key factor in its widespread adoption in the power generation industry. Technological advancements in electrolyzers and economies of scale are also bringing down the cost of producing hydrogen through PtG technology. PtG technology is gaining traction in the market due to its economic benefits. Additionally, governments and energy market participants are increasingly acknowledging the potential of PtG technology to facilitate the shift towards a low-carbon energy system [77]. To promote the adoption of PtG technology in power generation, it is crucial to establish supportive policies, incentives, and regulatory frameworks that create a conducive environment.

PtG technology has been widely adopted by various countries for the purpose of power generation, demonstrating the technology’s usefulness and efficiency. Germany employs PtG technology to produce hydrogen on a massive scale with the goal of integrating hydrogen into power generation and other industries [78]. The USA has explored the potential of PtG technologies to store excess energy and enhance grid resilience [79]. China is attempting to provide economical projects with PtG technology and has developed an economical and large electrolyzer compared to other countries and is developing low-carbon technologies such as renewable energy generation and power-to-gas plants [80]. The projects working in promoting PtG technology exemplify the application of PtG technology for grid balancing and power generation, demonstrating the technology’s real-world viability [81]. In [82], the authors focused on the generation of electricity, hydrogen, and desalinated water. The produced hydrogen shows improvements in technical performance and helps with greenhouse gas emissions. In [83], the efficiency challenge of power generation from fuel cell integration was studied and resulted in the efficient and optimized operation of the system. The researchers in [84] developed an economical dispatch model integrated with PtG technology, which resulted in improved economic efficiency in generation. In [85], an integrated system of power generation and hydrogen production was developed for economical operation and energy management, leading to an improved result. In [86], for electricity generation, a microbial fuel cell was designed that showed a significant improvement in the development of industrial microbial fuel cell technology. In [87], a multi-generation system was developed to generate electricity, hydrogen gas, steam, and heat, with the result indicating the equivalent ratio can increase hydrogen production, system energy, and energy efficiencies.

4.2. Transmission

The major contribution and strengths of PtG technology depend on the unified integration of existing and future transmission networks. Conventional power plants encounter issues in accommodating the intermittent behavior of renewable energy sources, which create instability in power grid transmission [88]. PtG works as a supportive bridge in the instability of power transmission by utilizing stored gases for power generation in case of demand [89]. In [90], the natural gas market merger was studied, and it was shown that transmission system operators can bring about an effective merger of different market mergers, which can lead to efficient regulation and transaction cost reductions. In [91], a model of a chemical plant and a gas and power transmission network was studied to highlight the issues associated with the optimal planning, reliability, and secure operation of gas and power transmission with chemical plants. The integration of these three networks showed an improvement in the communication between decision makers, and this model could support different industries.

The integration of PtG technology into transmission networks improves power grid stability and balances the power. PtG acts as a virtual storage hub when storing surplus electricity and producing hydrogen and methane, which provides a continuous power supply and deals with fluctuations in RES generation and transmission [89]. In [92], the authors worked on coordinating the transmission, distribution, and gas systems for load restoration to solve the issue of outages in the power system. The simulation and actual result of this method in China show a progressive output and shorten the time of load restoration. In [93], the prices of gas and electricity were compared in European countries before and after the Russia–Ukraine war, and the effect was compared. The indirect effect of gas and electricity prices on each other due to affected prices based on electricity transmission or with gas were investigated. In [94], the power losses from natural gas and hydrogen transmission were analyzed. It provided knowledge to industry and consumers based on energy demand and power losses in transmission. Injecting gases produced from renewable energy sources into the gas grid provides a more flexible energy supply. This is relevant to the framework of transmission networks, where balancing supply and demand is a challenge. Research shows that PtG technology is a promising source for the future, which can minimize the curtailment of renewable energy and increase the utilization of clean energy resources [89].

PtG technology has been widely adopted by several countries in their transmission networks, demonstrating the usefulness and efficiency of this technology. Germany has carried out a number of PtG projects as a part of its Energiewende program [95]. The INGRID projects show how PtG technology can be used for grid stabilization and storage, enhancing the transmission system’s overall stability [96]. Power utilities in the USA are investigating the potential of PtG technology to solve the issues related to the variability of renewable energy sources [79]. Utilizing PtG technology for large-scale energy storage, initiatives such as the Advanced Clean Energy Storage (ACES) program promote grid resilience and reduce greenhouse gas emissions [97].

4.3. Distribution

A paradigm change is occurring in power distribution as societies work to move toward cleaner and more sustainable energy sources. PtG technology has surfaced as a viable technology within this revolutionary path, having the potential to change power distribution networks [79]. The role of PtG technology in power distribution highlights how important it is to improving grid flexibility, facilitating the integration of renewable energy sources, and assisting in the creation of a resilient and sustainable energy distribution infrastructure [98].

PtG technology acts as a bond between the irregular behavior of renewable energy sources and the reliable demand of electricity in power distribution networks. In PtG technology, the produced gases that are stored in tanks can be used for different purposes and utilized for various applications, such as power distribution, providing a flexible and adaptable way to deal with the issues brought on by a changing energy landscape. In [99], a model was used for restoration purposes in the case of disasters in which the power–gas transportation distribution network was considered to provide assistance in case of emergency. In [100], the measurement and definition of a distributed system operator were studied, in which management and enabling activities for different technologies were adopted, and the methodology was applied to electricity and distributed system operators in the UK. This shows many challenges in the electricity and gas sector, which are noticed after the applied methodology and will be improved with further research. In [101], the role of PtG technology was analyzed at the distribution network level for electricity and gas systems; the purpose of the system was used for the optimization of renewable energy sources. In [102], under variable load operations, a method was used to decompose the energy consumption to reveal and track the internal energy consumption distribution.

The potential of PtG technology to improve grid flexibility and enable demand response mechanisms is one of its main contributions to power distribution. The demand for adaptable solutions grows as power distribution networks change to accommodate a large amount of renewable energy sources. A model of PtG technology is developed and integrated with the distribution network for planning and operations. The algorithm used for the development set the demand of the conversion system for a passive load and RES generation [103]. PtG technology enables the construction of smart grids that can dynamically respond to changing conditions. This type of dynamic response minimizes transmission losses, maximizes energy utilization, and improves the overall efficiency of power distribution networks. Hydrogen produced through PtG technology can be injected into existing natural gas networks or utilized directly in fuel cells, providing a clean and flexible energy source for power distribution. This integration not only addresses the intermittent nature of renewable energy but also helps to reduce greenhouse gas emissions in the distribution sector. PtG technology is essential to the integration of renewable energy into power distribution networks. To deal with uncertain generation and load demand, a model was used for hydrogen production with a distribution system considering the microgrid. The model showed that this model in a distributed network results in an optimized cost rather than using a single system [104].

Power distribution networks are vulnerable to a range of disturbances such as equipment malfunctions, cyberattacks, and natural disasters. PtG technology provides quick system restoration and backup power, which can improve grid resilience. Stored gases can be utilized to maintain essential services during a power outage and minimize the effect on consumers [105]. The distributed nature of PtG technology enables the development of robust microgrids, which can function independently or are connected with the main grid to supply localized power generation and distribution capacities. This distributed approach improves the overall resilience of the power distribution network and minimize outages [89]. In [106], the authors showed that the coupling of power-to-hydrogen technology with the gas and electricity sector decreases the mismatch of distributed solar generation based on local production and consumption. The issues of power distribution systems that cause reverse power flow during lower demand was discussed. The authors found out that PtG technology is the best choice to provide a definite solution to stop reverse power flow in distributed generation [107]. The impact of PtG technology in the distribution system is a good choice to promote the technology to deal with reverse power flow in the integrated energy system with renewable energy sources [108]. In [109], the voltage regulation issue in the distribution network was highlighted, and the solution to regulate the voltage without any disturbance to the distribution energy network was integrated with the power and gas grid. The results indicated that the integrated energy system of power distribution and the gas and electricity network shows a beneficial result.

The flexibility and efficacy of PtG technology have been demonstrated by their practical applications in power distribution networks across the globe. The Power to Hydrogen project in the USA focuses on utilizing PtG technology for grid balancing and storage to improve the stability of the power distribution system [110]. The HyBalance project in Denmark integrates PtG technology with an electrolyzer to produce hydrogen gas for utilization in different energy sectors, including power distribution [111]. PtG technology has been applied in real-world power distribution network challenges by the National Renewable Energy Laboratory (NREL) in the USA, which has been conducting research projects examining PtG technology’s potential to improve the resilience and reliability of power distribution systems [79].

4.4. Consumption

PtG technology signifies a vital connection between energy production and consumption, offering a flexible way to store and use excess electricity. The primary purpose of PtG technology has previously been explained: typically utilizing electricity from renewable energy sources for gas production. The stored gases, such as hydrogen and methane, in PtG technology can be utilized in a variety of applications, including power consumption, which makes a bridge between RESs and energy demand. Due to the intermittent nature of renewable energy sources and the high demand for clean energy, the conventional model of energy consumption faces challenges. In PtG technology, the produced gases, such as hydrogen, can be utilized for power generation in fuel cells, which provide clean electricity for various consumption needs [89]. In [112], the authors focused on the issue deployed, with distributed generation having a limited injection of electricity into power grids. PtG technology shows a significant role in maximizing energy self-consumption in the integration of hydrogen with the local grid.

A dynamic dimension to power consumption patterns is introduced by PtG technology providing flexibility in terms of energy storage and utilization. Stored gases can be utilized to optimize energy consumption in a sustainable way and contribute to grid stability during times of high demand or the low generation of renewable energy [113]. An important feature of PtG technology in terms of power consumption is its ability to support decentralized energy production and consumption models. PtG technology enables communities to become independent in meeting their energy demands by facilitating the local production of hydrogen or synthetic natural gas (SNG). This decentralized approach eliminates the demand for long-distance energy transmission and centralized power generation, which improves energy security [114]. Decentralized energy consumption is in line with the more general trend of distributed energy resources (DERs) and microgrids. When PtG technology is incorporated into these systems, clean energy can be produced, stored, and consumed locally, promoting sustainability and resilience at the community level.

PtG technology plays a significant role in power consumption that goes beyond the conventional consumption of energy to encompass environmentally friendly transportation options. Fuel cell vehicles can utilize the hydrogen produced by PtG technology as a clean fuel substitute for traditional fossil fuels. This application of PtG technology in the transportation industry decreases greenhouse gas emissions and encourages an eco-friendly approach to energy consumption [115]. The integration of PtG technology in the transportation industry facilitates the economy, which supports renewable energy sources to produce hydrogen for consumption in vehicles to power the vehicle. This method focuses on resource efficiency, minimizing environment impact, and providing a circular economy.

PtG technology has shown practical applications in different countries, which have demonstrated its potential and radical power consumption. The Badenove PtG plant in Germany used for transportation purposes demonstrates how PtG technology can be used to support sustainable energy consumption beyond conventional power grids [116]. The HyStock project in the Netherlands focuses on PtG technology, storing renewable energy and providing grid services [117]. China’s contribution is developing PtG technology based on size, optimization, and the lower cost of equipment compared to other countries. This shows the diverse application of PtG technology in energy consumption.

5. Conclusions and Discussion

The integration of energy systems is a configuration of various renewable resources, with concentrated energy serving as the system’s focal point. It connects diverse sources of multi-energy grids with each other via the internet and physically connected devices. The rising demand for electricity and the need to dispose of extra energy has prompted the shift from electricity to gas, which can be stored economically. The process of converting electrical energy into gas is crucial for the growth of technology in the integration of energy systems. Water electrolysis is a method of converting electrical energy into gases, which are then transported via pipelines and stored in tanks.

This review paper studied the integrated energy system considering power-to-gas technology. Power-to-gas technology will be a more cost-effective technology in the future than a single system, because of the long-term storage of gases and the regeneration of electricity from gases. PtG technology also plays a role in clean energy production, which can decrease carbon emissions.

The planning models and economic analysis of an integrated energy system with PtG technology were studied in this paper with different reference papers that focused on this topic. Economic analysis, which focused on the cost and investment of the integrated energy system for economical future operation and utilization, focusing on cost reduction and economic issues, was discussed. System integration enhancements, which are very important for technologies, were discussed, focusing on optimization, conversion technologies, and the energy storage of the system. The optimization issues were elaborated and discussed for the development of IES PtG technology. The conversion technologies that use types of electrolyzers for converting electricity to gas were discussed and compared based on their operation and efficiency. Energy storage issues, which need proper sites and an energy conversion capacity and demand that is economical and available to consumers with an economical cost, were discussed in this review paper. The role of PtG technology in generation, transmission, distribution, and consumption was discussed, with proper examples of the projects working for the development of PtG technology in the world.

This study concluded that power-to-gas technology is expensive technology in the present era, and there are many issues regarding its integration to make it economical. The planning models describe the integration of technologies from the surplus electricity of a power system to gas storage and their economical impact on consumers. In the integration of the system for power-to-gas conversion, a reliable and economical electrolyzer operation is important, which can convert electricity to gases with good efficiency, but electrolyzers are expensive and conversion is not very efficient. Energy storage needs proper security to save the environment from any fault event and leakage. A location that is easily available to consumers is important. The key outcomes of an integrated energy system with PtG technology are providing an economical and reliable operation to consumers and prosumers. An integrated energy system plays a role in providing energy to consumers from both electricity and gas systems. Power-to-gas technology plays a role in climate change, by focusing on cleaner energy production, which will decrease the dependency on coal power plants in the future. Another role of power-to-gas systems is providing long-term energy storage to consumers in the form of gases. The role of PtG technology in generation, transmission, distribution, and consumption is very important in all aspects, because it can provide balanced energy to consumers and minimize outages.

Future work needs to pay proper attention to the optimization of the system, efficiency improvements, cost minimization, and the economical operation of PtG technology. These are important and need further research to improve the technology.