An assessment of the impacts of renewable and conventional electricity supply on the cost and value of power-to-gas

Power-to-gas (P2G) is a promising enabling technology for more cross-sector integration but its high cost has so far been a key barrier to implementation. Electricity supply is the greatest contributor to the levelised cost therefore it is important to understand which technologies and strategies can minimise the cost and accelerate the deployment. In this study, a method is devised to evaluate the cost and value of combined systems comprising P2G and renewable energy technologies such as solar photovoltaics, wind and hydro as well as comparing to traditional electricity supply via the wholesale market. The proposed models are based on a temporal resolution of 1 h and include partial operation and ageing throughout the system's lifespan. Our analysis covers both distributed and centralised P2G systems producing hydrogen or methane as well as various value-adding services across different geographies. It is found that the capacity factor of a P2G system drives the economic case and therefore the electricity supply from hydropower plants is economically more attractive than electricity from wind and solar photovoltaic plants in this order. Under today's market conditions, it is highly advisable to combine local renewable supply with wholesale-based supply but interestingly, a 20% capital cost reduction in wind technology or a P2G system efficiency of 80% are break-even points for P2G systems producing hydrogen and connected to wind plants.     

System-level power-to-gas energy storage for high penetrations of variable renewables

According to outlooks by the IEA and the U.S. EIA, renewables will become the largest source of electricity by 2050 if global temperature rise is to be limited to 2 °C. However, at penetrations greater than 30%, curtailment of wind and solar can be significant in even the most flexible systems. Energy storage can reduce curtailment and increase utilisation of variable renewables. Power-to-gas is a form of long-term storage based on electrolytic production of hydrogen. This research models the co-sizing of wind and solar PV capacity and electrolyser capacity in a jurisdiction targeting 80% penetration of variable renewable electricity. Results indicate that power-to-gas can reduce required wind and solar capacity by as much as 23% and curtailment by as much as 87%. While the majority of charging events last less than 12 h, the majority of the total annual stored energy comes from longer-term events. Additional scenarios reveal that geographic diversity of wind farms reduces capacity requirements, but the same benefit is not found for distributing solar PV.     

Sizing and operating power-to-gas systems to absorb excess renewable electricity

Various configurations of power-to-gas system are investigated as a means for capturing excess wind power in the Emden region of Germany and transferring it to the natural gas grid or local biogas-CHP plant. Consideration is given to producing and injecting low concentration hydrogen admixtures, synthetic methane, or hydrogen/synthetic methane mixtures. Predictions based on time series data for wind generation and electricity demand indicate that excess renewable electricity levels will reach about 40 MW and 45 GW h per annum by 2020, and that it is desirable to achieve a progression in power-to-gas capacity in the preceding period. The findings are indicative for regions transitioning from medium to high renewable power penetrations. To capture an increasing proportion of the growing amount of excess renewable electricity, the following recommendations are made: implement a 4 MW hydrogen admixture plant and hydrogen buffer of 600 kg in 2018; then in 2020, implement a 17 MW hybrid system for injecting hydrogen and synthetic methane (with a hydrogen storage capacity of at least 400 kg) in conjunction with a bio-methane injection plant. The 17 MW plant will capture 68% of the available excess renewable electricity in 2020, by offering an availability to the electricity grid operator of >97% and contributing 19.1 GW h of ‘green’ gas to the gas grid.     

A comprehensive review on power-to-gas with hydrogen options for cleaner applications

This review presents the power-to-gas concept, particularly with hydrogen, from renewable energy sources to end-use applications in various sectors, ranging from transportation to natural gas distribution networks. The paper includes an overview of the leading related studies for comparative evaluation. Due to the intermittent/fluctuating phenomena of most renewables, power-to-hydrogen appears to be a promising option to offset any mismatch between demand and supply. It is a novel concept to increase the renewability of fuels and reach a sustainable energy system for future transportation, power and thermal process sectors. Comparisons of different hydrogen production methods fed by several energy sources are made regarding environmental impact, cost and efficiency. The present results show that hydrogen production (with power-to-hydrogen concept) via polymer electrolyte membrane electrolyser has lower environmental effects than other traditional methods, such as coal gasification and reforming and steam methane reforming. The geothermal energy-based system has the lowest levelized cost of electricity during hydrogen production, while natural gas has the highest value. The best option for the plant efficiency is found for high-temperature steam electrolysis fed from biogas, while the lowest efficiency value belongs to polymer electrolyte membrane electrolyser driven by solar photovoltaics, respectively.     

Dynamic analyses of regenerative fuel cell power for potential use in renewable residential applications

A model of a solar-hydrogen powered residence, in both stand-alone and grid parallel configurations, was developed using Matlab/Simulink^®$\mathrm{Matlab}/{\mathrm{Simulink}}^{\circledR }$. The model assesses the viability of employing a regenerative fuel cell (RFC) as an energy storage device to be used with photovoltaic (PV) electrical generation. Other modes of energy storage such as batteries and hybrid storage were also evaluated. Analyses of various operating conditions, system configurations, and control strategies were performed. Design requirements investigated included RFC sizing, battery sizing, charge/discharge rates, and state of charge limitations. Dynamic load demand was found to be challenging to meet, requiring RFC and or battery sizes significantly larger than those required to meet average power demand. Employing a RFC with batteries in a hybrid configuration increased PV utilization and both battery efficiency and power density. Grid parallel configurations were found to alleviate many of the difficulties associated with energy storage costs and meeting peak demand.     

Hydrogen as a long-term,large-scale energy storage solution when coupled with renewable energy sources or grids with dynamic electricity pricing schemes

One of the key challenges that still facing the adoption of renewable energy systems is having a powerful energy storage system (ESS) that can store energy at peak production periods and return it back when the demand exceeds the supply. In this paper, we discuss the costs associated with storing excess energy from power grids in the form of hydrogen using proton exchange membrane (PEM) reversible fuel cells (RFC). The PEM-RFC system is designed to have dual functions: (1) to use electricity from the wholesale electricity market when the wholesale price reaches low competitive values, use it to produce hydrogen and then convert it back to electricity when the prices are competitive, and (2) to produce hydrogen at low costs to be used in other applications such as a fuel for fuel cell electric vehicles. The main goal of the model is to minimize the levelized cost of energy storage (LCOS), thus the LCOS is used as the key measure for evaluating this economic point. LCOS in many regions in United States can reach competitive costs, for example lowest LCOS can reach 16.4¢/kWh in Illinois (MISO trading hub) when the threshold wholesale electricity price is set at $25/MWh, and 19.9¢/kWh in Texas (ERCOT trading hub) at threshold price of $20/MWh. Similarly, the levelized cost of hydrogen production shows that hydrogen can be produced at very competitive costs, for example the levelized cost of hydrogen production can reach $2.54/kg-H₂ when using electricity from MISO hub. This value is close to the target set by the U.S. Department of Energy.     

An integrated system for ammonia production from renewable hydrogen: A case study

This study presents an analysis and assessment study of an integrated system which consists of cryogenic air separation unit, polymer electrolyte membrane electrolyzer and reactor to produce ammonia for a selected case study application in Istanbul, Turkey. A thermodynamic analysis of the proposed system illustrates that electricity consumption of PEM electrolyzer is 3410 kW while 585.4 kW heat is released from ammonia reactor. The maximum energy and exergy efficiencies of the ammonia production system which are observed at daily average irradiance of 200 W/m² are found as 26.08% and 30.17%, respectively. The parametric works are utilized to find out the impacts of inlet air conditions and solar radiation intensity on system performance. An increase in the solar radiation intensity results in a decrease of the efficiencies due to higher potential of solar influx. Moreover, the mass flow rate of inlet air has a substantial effect on ammonia production concerning the variation of generated nitrogen. The system has a capacity of 0.22 kg/s ammonia production which is synthesized by 0.04 kg/s H₂ from PEM electrolyzer and 0.18 kg/s N₂ from a cryogenic air separation unit. The highest exergy destruction rate belongs to PEM electrolyzer as 736.2 kW while the lowest destruction rate is calculated as 3.4 kW for the separation column.     

Design and optimum energy management of a hybrid renewable energy system based on efficient various hydrogen production

Utilizing renewable energy resources is one of the convenient ways to reduce greenhouse gas emissions. However, the intermittent nature of these resources has led to stochastic characteristics in the generation and load balancing of the microgrid systems. To handle these issues, an energy management optimization for microgrids operation should be done to urge the minimization of total system costs, emissions, and fuel consumption. An optimization program for decreasing the operational cost of a hybrid microgrid consisting of photovoltaic array, wind unit, electrolyzer, hydrogen storage system, reformer, and fuel cell is presented. Two different methods of producing hydrogen are considered in this study to ensure the effectiveness of the developed methodology. In the microgrid system with high penetration of renewable energy resources, using storage technologies to compensate for the intermittency of these resources is necessary. To evaluate the functioning of the microgrid system, a mathematical model for each source is developed to coordinate the system operation involving energy conversion between hydrogen and electricity. Particle Swarm Optimization Algorithm is utilized to determine the optimum size and operational energy management within the system. It is evident from the results that there is about a 10% reduction in the amount of CH₄ consumption in reformer when the electrolyzer was employed in the system. It is observed that the CH₄ reduction in summer and fall is higher than other seasons (10.6% and 11.5%, respectively). The reason is that the highest RES production occurs in these seasons during a year. It is also worth mentioning that the electrolyzer technology would play a significant role in decreasing the CH₄ consumption in the microgrid system.     

Modeling and performance analysis of renewable hydrogen energy hub connected to an ac/dc hybrid microgrid

This paper proposes a system modeling and performance analysis of a renewable hydrogen energy hub (RHEH) connected to an ac/dc hybrid microgrid (MG). The proposed RHEH comprises a photovoltaic (PV)-based renewable energy source (RES) as the primary source, a proton exchange membrane fuel cell (PEMFC) as the secondary power source, and a proton exchange membrane electrolyzer (PEMELZ) that can generate and store hydrogen in a hydrogen tank. All these resources are directly connected at the dc bus of the ac/dc microgrids. The PEMFC operates and utilizes the hydrogen from the hydrogen tank when the energy generated by RES cannot meet the load demand. A coordinated power flow control approach has been developed for the RHEH to mitigate the mismatch between generation and demand in the ac/dc microgrid and produce renewable hydrogen when renewable power is in excess. The paper also proposes a modified hybrid Perturb & Observe-Particle Swarm Optimization (Hybrid PO-PSO) algorithm to ensure the maximum power point tracking (MPPT) operation of the PV and the PEMFC. The operation of the proposed RHEH is validated through simulations under various critical conditions. The results show that the proposed RHEH is effective to maintain the system power balance and can provide power-to-hydrogen and hydrogen-to-power when required.     

Feasibility study of large scale hydrogen power-to-gas applications and cost of the systems evolving with scaling up in Germany,Belgium and Iceland

The use of hydrogen to store electricity is no longer utopian nor merely theoretical. Hydrogen applications such as Power-to-Gas systems are entering the market and some of them are ready to compete with other options in the near future. This means they have indeed a potential for profitability, especially if seen as large-scale storage solutions for the electricity surplus produced by variable renewable energy sources.In this study Power-to-Industry, Power-to-Mobility and Power-to-Power applications are chosen to be investigated and compared through levelized cost of hydrogen to identify the main cost drivers and consequently understand the possible solutions to reduce costs. The feasibility of the applications is discussed and analyzed in Germany, Belgium and Iceland, with mid and long-term perspectives, focusing the analysis on the advantage of scaling up.     

An analysis of hydrogen production from renewable electricity sources

Three aspects of producing hydrogen via renewable electricity sources are analyzed to determine the potential for solar and wind hydrogen production pathways: a renewable hydrogen resource assessment, a cost analysis of hydrogen production via electrolysis, and the annual energy requirements of producing hydrogen for refueling. The results indicate that ample resources exist to produce transportation fuel from wind and solar power. However, hydrogen prices are highly dependent on electricity prices. For renewables to produce hydrogen at $2 kg⁻¹, using electrolyzers available in 2004, electricity prices would have to be less than $0.01 kWh⁻¹. Additionally, energy requirements for hydrogen refueling stations are in excess of 20 GWh/year. It may be challenging for dedicated renewable systems at the filling station to meet such requirements. Therefore, while plentiful resources exist to provide clean electricity for the production of hydrogen for transportation fuel, challenges remain to identify optimum economic and technical configurations to provide renewable energy to distributed hydrogen refueling stations.     

A multi-model method to assess the value of power-to-gas using excess renewable

Power-to-Gas (P2G) is a process that produces a gas from electricity, which is most commonly hydrogen via electrolysis. While some studies have considered hydrogen as a power-to-power storage vector, it could also be used as a fuel across the energy system, for example for transport or heat generation. Here, two energy models are used to explore the potential contribution of P2G as a cost-effective source of hydrogen, particularly for future energy systems with high variable renewable energy (VRE) in which there are occasional periods when electricity supply exceeds demand. A detailed electricity system model is iterated with a multi-vector energy system model using a soft-linking approach. This iterative approach addresses shortcomings in each model to better understand the optimal capacity of P2G and the potential economic capture rate of excess VRE. The modelling method is applied to Great Britain in 2050 as a case study. A substantial proportion of excess VRE in 2050 can be captured by P2G, and it is economically competitive compared with alternative sources. Moreover, the effectiveness and economic viability of P2G for reducing excess renewable is robust at even very high levels of renewable penetration.     

Design and analysis of a combined floating photovoltaic system for electricity and hydrogen production

The current study deals with a potential solution for the replacement of fossil fuel based energy resources with a sustainable solar energy resource. Electrical energy demand of a small community is investigated where a floating photovoltaic system and integrated hydrogen production unit are employed. Data are taken from Mumcular Dam located in Aegean Region of Turkey. PvSyst software is used for the simulation purposes. Furthermore, the obtained results are analyzed in the HOMER Pro Software. Photovoltaic (PV) electricity provides the required load and excess electricity to be used in the electrolyzer and to produce hydrogen. Saving lands by preventing their usage in conventional PV farms, saving the water due to reducing evaporation, and compensating the intermittent availability of solar energy are among the obtained results of the study for the considered scenario. Stored hydrogen is used to compensate the electric load through generating electricity by fuel cell. Floating PV (FPV) system decreases the water evaporation of water resources due to 3010 m² shading area. FPV and Hydrogen Systems provides %99.43 of the electricity demand without any grid connection or fossil fuel usage, where 60.30 MWh/year of 211.94 MWh/year produced electricity is consumed by electric load at $0.6124/kWh levelized cost of electricity (LCOE).     

Thermodynamic analysis of a multigeneration system using solid oxide cells for renewable power-to-X conversion

A hybrid renewable-based integrated energy system for power-to-X conversion is designed and analyzed. The system produces several valuable commodities: Hydrogen, electricity, heat, ammonia, urea, and synthetic natural gas (SNG). Hydrogen is produced and stored for power generation from solar energy by utilizing solid oxide electrolyzers and fuel cells. Ammonia, urea, and synthetic natural gas are produced to mitigate hydrogen transportation and storage complexities and act as energy carriers or valuable chemical products. The system is analyzed from a thermodynamic perspective, the exergy destruction rates are compared, and the effects of different parameters are evaluated. The overall system's energy efficiency is 56%, while the exergy efficiency is 14%. The highest exergy destruction occurs in the Rankine cycle with 48 MW. The mass flow rates of the produced chemicals are 0.064, 0.088, and 0.048 kg/s for ammonia, urea, and SNG, respectively.     

Experimental results for hybrid energy storage systems coupled to photovoltaic generation in residential applications

An experimental solar-hydrogen powered residence simulator was built and tested. The system consisted of a solar photovoltaic array connected to an electrolyzer which produced hydrogen as a means of energy storage. The hydrogen was used to produce electricity in a fuel cell that operated in parallel with a battery to meet dynamic power demand similar to that found in residential applications. The study demonstrated the technical feasibility of operating such a system under the simultaneous dynamics of solar input and load. Limitations of current fuel cell and electrolyzer designs, as they pertain to both power delivery and energy storage, were identified. The study also established the need to understand and address dynamic performance in the design and application of solar-hydrogen reversible fuel cell hybrid systems. An economic analysis found that major cost reductions would need to be achieved for such systems to compete with conventional energy storage devices.     

Overview of energy storage systems for storing electricity from renewable energy sources in Saudi Arabia

Renewable power (photovoltaic, solar thermal or wind) is inherently intermittent and fluctuating. If renewable power has to become a major source of base-load dispatchable power, electricity storage systems of multi-MW capacity and multi-hours duration are indispensable. An overview of the advanced energy storage systems to store electrical energy generated by renewable energy sources is presented along with climatic conditions and supply demand situation of power in Saudi Arabia. Based on the review, battery features needed for the storage of electricity generated from renewable energy sources are: low cost, high efficiency, long cycle life, mature technology, withstand high ambient temperatures, large power and energy capacities and environmentally benign. Although there are various commercially available electrical energy storage systems (EESS), no single storage system meets all the requirements for an ideal EESS. Each EESS has a suitable application range.     

Electrolytic hydrogen based renewable energy system with oxygen recovery and re-utilization

The Hydrogen Research Institute (HRI) has developed a stand-alone renewable energy (RE) system based on energy storage in the form of hydrogen. When the input devices (wind generator and photovoltaic array) produce more energy than is required by the load, the excess energy is converted by an electrolyzer to electrolytic hydrogen, which is then stored after stages of compression, purification and filtration. Conversely, during a time of input energy deficit, this process is reversed and the hydrogen produced earlier is reconverted to electrical energy through a fuel cell. The oxygen which has been produced by the electrolyzer during the hydrogen production is also stored at high pressure, after having gone through a purification and drying process. This stored oxygen can be re-utilized as oxidant in place of compressed air in the fuel cell. The modifications of the electrolyzer for oxygen storage and re-utilization of it as oxidant for the fuel cell are presented. Furthermore, the HRI has designed and developed the control system with power conditioning devices for effective energy management and automatic operation of the RE system. The experimental results show that a reliable autonomous RE system can be realized for such seasonal energy sources, using stored hydrogen as the long-term energy buffer, and that utilizing the electrolyzer oxygen by-product as oxidant in the fuel cell increases system performance significantly.     

Hydrogen for heat: Using underground hydrogen storage for seasonal energy shifting in northern climates

To determine if a power-to-gas pilot-scale plant would be possible in Oregon, a feasibility study was conducted that assessed the technical, political, economic, environmental, safety, and policy aspects of a potential project in the region. The results of this study were submitted as part of Oregon State University – Cascades' entry to the Hydrogen Education Foundation's 2018 student design competition. The Pacific Northwest has a need for long term energy storage (seasonal energy shifting) due to seasonally available low-priced, low-carbon electricity. There appears to be the political motivation and the technical feasibility to install a demonstration-scale power-to-gas plant in the region to assess the technical and economic performance of the system when exposed to real-world boundary conditions. However, preliminary economic analyses show the system will be challenged by low capacity factor operation resulting in a levelized cost of hydrogen of $121.81/kg_H2 when only using otherwise curtailed electricity, or $8.84/kg_H2 when running continuously for 6 months per annum. To fund a pilot scale plant a renewable gas development surcharge of $0.18/therm is proposed as a way for willing customers to support the decarbonization mission. There is precedent within the utility for such an incentive, indicating that it would be approved by the utility commission and could be a viable path forward for a pilot-scale plant.     

A bifunctional electrochemical flow cell integrating ammonia production and electricity generation for renewable energy conversion and storage

Renewable energy has rapidly advanced in the global energy system, triggering the visible development of energy storage technologies in recent decades. Among them, the electricity-fuel-electricity approach is an effective way for the storage and utilization of renewable power. In this work, a bifunctional electrochemical flow cell integrating both ammonia production and electricity generation modes is developed for renewable energy conversion and storage. Ammonia, a hydrogen carrier having a high hydrogen content of 17.6 wt %, is relatively easier to convert to liquid phase for large-scale storage. The long-distance ammonia transport can reliably depend on the established infrastructure. In addition, as a carbon-free fuel beneficial for achieving the goal of carbon-neutrality, ammonia is considered as an environmentally benign and cost-effective mediator fuel. This flow cell is able to operate via two modes, i.e., an ammonia-production mode for energy storage in the form of ammonia (via nitrogen reduction reaction) and an electricity-generation mode for energy conversion in the form of electricity (via ammonia oxidation reaction). This flow cell is constituted by a PtAu/C-coated nickel-foam electrode for nitrogen and oxygen reduction reactions, a Pt/C-coated nickel-foam electrode for water and ammonia oxidation reactions, and an alkaline anion exchange membrane for charge-carrier migration. Charging this flow cell with the supply of nitrogen results in a Faradaic efficiency of 2.70% and an ammonia production rate as high as 9.34 × 10^?10 mol s^?1 cm^?2 at 23 °C. Moreover, energizing this flow cell with ammonia results in an open-circuit voltage of 0.59 V and a peak power density of 3.31 mW cm^?2 at 23 °C. A round-trip efficiency of 25.7% is realized with the constant-electrode mode.     

Hydrogen-based systems for integration of renewable energy in power systems: Achievements and perspectives

This paper is a critical review of selected real-world energy storage systems based on hydrogen, ranging from lab-scale systems to full-scale systems in continuous operation. 15 projects are presented with a critical overview of their concept and performance. A review of research related to power electronics, control systems and energy management strategies has been added to integrate the findings with outlooks usually described in separate literature. Results show that while hydrogen energy storage systems are technically feasible, they still require large cost reductions to become commercially attractive. A challenge that affects the cost per unit of energy is the low energy efficiency of some of the system components in real-world operating conditions. Due to losses in the conversion and storage processes, hydrogen energy storage systems lose anywhere between 60 and 85% of the incoming electricity with current technology. However, there are currently very few alternatives for long-term storage of electricity in power systems so the interest in hydrogen for this application remains high from both industry and academia. Additionally, it is expected that the share of intermittent renewable energy in power systems will increase in the coming decades. This could lead to technology development and cost reductions within hydrogen technology if this technology is needed to store excess renewable energy. Results from the reviewed projects indicate that the best solution from a technical viewpoint consists in hybrid systems where hydrogen is combined with short-term energy storage technologies like batteries and supercapacitors. In these hybrid systems the advantages with each storage technology can be fully exploited to maximize efficiency if the system is specifically tailored to the given situation. The disadvantage is that this will obviously increase the complexity and total cost of the energy system. Therefore, control systems and energy management strategies are important factors to achieve optimal results, both in terms of efficiency and cost. By considering the reviewed projects and evaluating operation modes and control systems, new hybrid energy systems could be tailored to fit each situation and to reduce energy losses.