Thermochemical Water Splitting Cycle Research Articles

Chemical Potential Analysis as an Alternative to the van't Hoff Method: Hypothetical Limits of Solar Thermochemical Hydrogen.

The van't Hoff method is a standard approach for determining reaction enthalpies and entropies, e.g., in the thermochemical reduction of oxides, which is an important process for solar thermochemical fuels and numerous other applications. However, by analyzing the oxygen partial pressure pO2, e.g., as measured by thermogravimetric analysis (TGA), this method convolutes the properties of the probe gas with the solid-state properties of the examined oxides, which define their suitability for specific applications. The "chemical potential method" is here proposed as an alternative. Using the oxygen chemical potential ΔμO instead of pO2 for the analysis, this method does not only decouple gas-phase and solid-state contributions but also affords a simple and transparent approach to extracting the temperature dependence of the reduction enthalpy and entropy, which carries important information about the defect mechanism. For demonstration of the approach, this work considers three model systems; (1) a generic oxide with noninteracting, charge-neutral oxygen vacancy defects, (2) Sr0.86Ce0.14MnO3(1-δ) alloys with interacting vacancies, and (3) a model for charged vacancy formation in CeO2, which reproduces the extensive experimental TGA data available in the literature. The reduction behavior of these model systems obtained from the chemical potential method is correlated with simulated results for the thermochemical water splitting cycle, highlighting the exceptional behavior of CeO2, which originates from defect ionization. The theoretical performance limits for solar thermochemical hydrogen within the charged defect mechanism are assessed by considering hypothetical materials described by a variation of the CeO2 model parameters within a plausible range.

Thermocatalytic Hydrogen Production from Water at Boiling Condition.

Thermochemical water-splitting cycles are technically feasible for hydrogen production from water. However, the ultrahigh operation temperature and low efficiency seriously restrict their practical application. Herein, one-step and one-pot thermocatalytic water-splitting process is reported at water boiling condition catalyzed by single atomic Pt on defective In2O3. Water splitting into hydrogen is verified by D2O isotopic experiment, with an optimized hydrogen production rate of 36.4 mmol·h-1·g-1 as calculated on Pt active sites. It is revealed that three-centered Pt1In2 surrounding oxygen vacancy as catalytic ensembles promote the dissociation of the adsorbed water into H, which transfers to singlet atomic Pt sites for H2 production. Remaining OH groups on adjacent In sites from Pt1In2 ensembles undergoes O─O bonding, hyperoxide formation and diminishing via triethylamine oxidation, water re-adsorption for completing the catalytic cycle. Current work represents an isothermal and continuous thermocatalytic water splitting under mild condition, which can re-awaken the research interest to produce H2 from water using low-grade heat and competes with photocatalytic, electrolytic, and photoelectric reactions.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

Solar photovoltaic–thermal hydrogen production system based on full-spectrum utilization

Full-spectrum high-temperature water electrolysis enables efficient conversion from solar to hydrogen. However, the supply of electric and thermal energy derived from solar energy does not match the demand for electric and thermal energy in high-temperature water electrolysis, resulting in significant energy losses within the system. In this study, a solar photovoltaic-thermal hydrogen production system based on full-spectrum utilization is proposed. The concentrated sunlight is divided into two parts based on wavelength. Longer-wavelength sunlight is directed to the reactor, where it is converted into thermal energy to directly supply the endothermic water electrolysis reaction. Shorter-wavelength sunlight is directed to photovoltaic cells to generate electrical power for the reaction. To achieve a match between the supply and demand of electric and thermal energy, system parameters are optimized for the proposed system. The results demonstrate that the mismatch losses of the proposed system are reduced by 42.8 percentage points compared to a conventional photovoltaic water electrolysis system. The proposed system achieves a solar-to-hydrogen efficiency of 39.0% under optimum conditions with a cutoff wavelength of 1000 nm, surpassing that of photovoltaic water electrolysis and water-splitting thermochemical cycle systems by 19.0 and 21.6 percentage points, respectively. Based on the proposed method, the solar-to-hydrogen efficiency can be improved.

Energy and exergy analysis of a novel solar-hydrogen production system with S–I thermochemical cycle

A novel hydrogen production system based on a sulfur-iodine (S–I) thermochemical water-splitting cycle driven by 100% solar energy is proposed in this paper. A solar power tower (SPT) with thermal energy storage (TES) is used to supply heat stably. Considering the large heat recovery potential in the S–I cycle, a supercritical carbon dioxide (S–CO2) Brayton cycle is used to improve the system performance. A complete thermodynamic model and detailed description of the energy and exergy flow from the sun to SPT, TES, S–I cycle, S–CO2 Brayton cycle and hydrogen is obtained. The system performance in the base case and actual weather conditions are obtained. The influence of major parameters on the system performance is investigated. The results show that the hydrogen production rate is 3.52 mol s−1 in the base case. Using the S–CO2 Brayton cycle, the overall energy and exergy efficiency can be increased from 10.6%, 11.1% to 30.5%, 32.4%, respectively. The solar part accounts for 48.2% of the total energy loss and 76.1% of the exergy destruction. In addition, increasing DNI, the maximum reaction temperature, the regeneration ratio of the S–CO2 Brayton cycle (RR) can improve the system performance, and the system efficiency is more sensitive to RR.

Investigation of the hydrogen production of the PACER fusion blanket integrated with Fe–Cl thermochemical water splitting cycle

In order to meet the energy demand, energy production must be done continuously. Hydrogen seems to be the best alternative for this energy production, because it is both an environmentally friendly and renewable energy source. In this study, the hydrogen fuel production of the peaceful nuclear explosives (PACER) fusion blanket as the energy source integrated with Fe–Cl thermochemical water splitting cycle have been investigated. Firstly, neutronic analyzes of the PACER fusion blanket were performed. Necessary neutronic studies were performed in the Monte Carlo calculation method. Molten salt fuel has been considered mole-fractions of heavy metal salt (ThF4, UF4 and ThF4+UF4) by 2, 6 and 12 mol. % with Flibe as the main constituent. Secondly, potential of the hydrogen fuel production as a result of the neutronic evaluations of the PACER fusion blanket integrated with Fe–Cl thermochemical cycle have been performed. In these calculations, tritium breeding (TBR), energy multiplication factor (M), thermal power ratio (1−ψ), total thermal power (Phpf) and mass flow rate of hydrogen (m˙H2) have been computed. As a results, the amount of the hydrogen production (m˙H2) have been obtained in the range of 232.24x106 kg/year and 345.79 x106 kg/year for the all mole-fractions of heavy metal salts using in the blanket.

Advancing production of hydrogen using nuclear cycles - integration of high temperature gas-cooled reactors with thermochemical water splitting cycles

The usage of heat from the nuclear cogeneration plant and hydrogen production technologies based on thermochemical water splitting was analyzed. Two most promising ones – copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles have been studied. The main advantage of the two analyzed thermochemical technologies is that they can be completely or partially independent from the electricity required for the process. The Cu–Cl method has a high ability to reduce the enthalpy of technological heat even to temperatures of up to 120 °C, enabling high output of the produced hydrogen. It is not demonstrated by the S–I technology, which can reduce the temperature of the working medium to approximately 380 °C, although it exhibits the limited demand for electricity. Considering the working conditions of the planned demonstration plant it is recommended to install Cu–Cl cycle due to its high level of utilization of the available heat and no requirement for additional medium heating.

Hydrogen production by isothermal thermochemical cycles using La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites

Solar-driven thermochemical water splitting has the potential to transform concentrated solar energy into green hydrogen and other solar fuels. In this work, La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites have been synthesised by a modified Pechini method and evaluated as materials for hydrogen production by two step thermochemical water splitting cycles. Performing the thermal reduction at temperatures of 1200 and 1000 °C, while the oxidation is done at 800 °C, allows a remarkable and stable hydrogen production after 5 consecutive cycles. However, the perovskites suffer changes in the structure after each redox cycle, with potential effects in the long-term cyclic operation. On the contrary, the isothermal thermochemical cycles at 800 °C produce a stable amount of hydrogen with each consecutive cycle maintaining the perovskite structure. This hydrogen production ranges from 3.60 cm3 STP/gmaterial·cycle for the material with the lowest productivity (La0.8Ca0.2FeO3±δ) to 5.02 cm3 STP/gmaterial·cycle for the one with the highest activity (La0.8Ca0.2NiO3±δ). Particularly the Ni-based material shows the highest H2 productivity accompanied by very good material stability after 15 consecutive cycles, being possible to combine with current solar thermal facilities based on concentrated solar power technologies like plants with central receivers.

Heat transfer characteristics and design aspects of thermolysis reactor in copper-chlorine thermochemical water splitting cycle

Thermolysis of copper oxychloride is the highest temperature reaction step of Copper–Chlorine cycle which forms cuprous chloride and oxygen gas as products. In the present study, important design aspects of thermolysis reactor have been investigated experimentally and a mathematical model has been developed to understand the effect of critical parameters on conversion. Experiments were conducted in tubular reactors with three different diameters of 25 mm, 50 mm and 100 mm to study the effect of reactor geometry on heat transfer and conversion. Modelling of batch thermolysis reactor has been carried out using governing heat transport equations coupled with reaction kinetics and validated against experimental data. As per the experimental and modelling results, enhancement in conversion could be achieved with increasing aspect ratio and heat transfer. The studies provide clear insights into the design and scale-up of thermolysis reactor to address the issues of low conversion observed during the multi-step thermal decomposition reaction.

Simulation and optimization of an innovative thermochemical water splitting cycle for the production of greenhydrogen

Highly efficient and cost-effective green Hydrogen production is a crucial challenge in a future sustainable economy. The innovative Nickel–Iodine-Sulphur (NIS) thermochemical cycle is a potential candidate for this purpose. For the first time in literature, this paper provides a complete Aspen Plus V10 simulation of the closed NIS cycle. Whitin the cycle, the Bunsen reactor was simulated as a PFR with a kinetic constant k = 1.38 m3/mol·s, while the other four reactors were considered at the thermodynamic equilibrium. A simulation of the conventional IS cycle was used as a benchmark for the NIS cycle, whose process parameters were optimized through a sensitivity study. Finally, the thermal efficiency without heat recovery of both cycles was calculated through an energy balance. The simulation results shows that the NIS cycle simulation achieves the same stoichiometric hydrogen yield as the IS cycle and a 17% higher thermal efficiency than the latter.

Potential of solar thermochemical water-splitting cycles: A review

Hydrogen fuel is a valuable tool to achieve the energy transition process, and according to the 2050 net zero emissions scenario its demand is expected to increase by more than 530 Mt H2. This article discusses several routes available to produce hydrogen fuel, with a special focus on solar thermochemical cycles for Water Splitting (WS). Solar thermochemical WS cycles are a potential technology to produce green hydrogen and CO in the future due to their great potential to become a commercial scale process. This technology is still under development and some challenges related to components and sub-processes are being addressed by several research groups in order to make green hydrogen production by this route technically and economically feasible. Specific technological aspects such as particle heating methods, suitability and properties of redox materials for two-step cycles, methods to achieve low oxygen pressure in the reduction chamber, as well as the importance of implementing heat recovery are analysed in detail, as their performance have a significant effect on the overall efficiency and economic of the whole process. Current progress indicates that the realisation of a sufficiently efficient thermochemical cycle is possible within the few years, if the mentioned limitations are overcome.

The waste heat of a biofuel-powered SOFC for green hydrogen production using thermochemical cycle; Economic, environmental analysis, and tri-criteria optimization

Biofuels are becoming more and more attractive recently due to their environmental benefits and various applications. In transport section and automotive industries, the biofuels and hydrogen energy are considered promising alternatives for decarburization. In the present research, two biofuel-driven systems for cogeneration of hydrogen and electricity, are suggested and investigated, in which biomass digestion or biomass gasification are compared to provide the required biofuel. The suggested schemes are comprised of SOFC units and thermochemical water splitting cycles, fueled with either biogas or syngas. To comprehensively compare the two schemes, thermoeconomic investigations are established to assess thermodynamic efficiencies as well as produced electricity and hydrogen costs. To examine adverse impacts on the environment, the greenhouse gas emission index is also considered. A sensitivity appraisal is presented for studying the influence of vital design/operation factors on systems’ responses and performances. Finally, triple-objective optimization is implemented to detect the best practical operation of the systems for achieving maximum efficiency and minimum emission and product costs. The obtained results under the optimum operation of the systems revealed an interesting feature. It is concluded that each of the two examined systems might be preferred to the other one regarding the desired objective. For instance, if higher hydrogen production (with lower prices) is favored over electricity production, then the gasification-derived scheme is chosen; however, the digestion-based scheme must be selected to gain more electricity.

Analysis of copper chlorine electrolysis for large-scale hydrogen production

Nuclear hydrogen production is experiencing an unprecedented momentum worldwide, in response to the increasing demand for clean large-scale hydrogen production in line with the outcomes of the UN Conference of the Parties (COP26). A seamless integration of several innovative nuclear designs including Small Modular Reactors with steam Rankine cycle and the cogeneration of Hydrogen using thermochemical water-splitting cycles (e.g., the Cu–Cl cycle) is possible for a complete solution of hydrogen, oxygen, and electric power generation. In this paper, a process and flow sheet for large-scale hydrogen production by CuCl electrolysis at 50 tonnes per day is proposed and analyzed. The scaled-up process and flow sheet is based on lab-scale experience with 50 l/h hydrogen generation. Pressurized Cu–Cl electrolysis and basic electrolysis are reported to support the scaling up parameters, assumptions, and considerations. Based on determined sizing parameters and energy analysis, the Cu–Cl cycle consumes substantially less primary energy (thermal) than water electrolysis, which makes it a serious competitor, despite its obvious higher investment cost in the hardware.

A Comparative Assessment of Thermodynamic and Exergoeconomic Performances of Three Thermochemical Water-Splitting Cycles of Chlorine Family for Hydrogen Production

Hydrogen production processes utilizing hydrocarbon-based sources as feedstocks have severe environmental implications (when not incorporating carbon capturing and storage technology) in addition to resulting in depletion of non-sustainable naturally occurring fuel sources. In this regard, thermochemical water-splitting is an extremely environmentally benign pathway for obtaining sustainable hydrogen. Thus, this paper studies and comparatively evaluates three different thermochemical cycles of the chlorine family for hydrogen production which include iron-chlorine, copper-chlorine, and magnesium-chlorine cycles. Each cycle is first modeled and simulated in Aspen-plus and then analyzed from thermodynamic and exergoeconomic viewpoints. A thermodynamic and exergoeconomic performance comparison of the three thermochemical cycles is further performed in terms of their overall efficiencies, net heat input and rejection rates, exergy destruction rates, unit costs of hydrogen, hourly levelized cost rates, and cost rates of exergy destruction. All cycles are modeled and simulated by considering the incorporation of waste heat recovery from a steel plant and internal heat recovery within each cycle to improve the process efficiencies by reducing the overall thermal energy consumption. According to the performed analyses, the copper-chlorine cycle has the highest energy (79.7%) and exergy (81.1%) efficiencies followed by the iron-chlorine cycle (energy and exergy efficiencies of 48.8% and 49.6%, respectively) with the magnesium-chlorine cycle exhibiting the lowest overall energy (19.8%) and exergy (20.2%) efficiencies. Moreover, the iron-chlorine cycle demonstrates the lowest unit cost of hydrogen (0.7 $/kg) followed by the copper-chlorine cycle (4 $/kg) with the magnesium-chlorine cycle exhibiting an extremely high unit hydrogen cost (8.9 $/kg). This study also identifies certain key factors that largely impact the cost of hydrogen and comprehensively discusses the influence and extent of each factor on the cost of hydrogen.

Thermodynamic analysis of an epitrochoidal rotary reactor for solar hydrogen production via a water-splitting thermochemical cycle using nonstoichiometric ceria

An epitrochoidal rotary reactor for solar hydrogen production via a water-splitting thermochemical cycle using nonstoichiometric ceria is proposed. The reactor performs solid-phase heat recovery in the form of mechanical energy via isentropic compression and expansion of the sweep gas. A thermodynamic analysis for a system consisting of the epitrochoidal rotary reactor and two exchangers is presented. Under typical conditions with a solar concentration ratio of 3000, reduction temperature of 1773K, oxidation temperature of 1073K, gas-phase heat recovery effectiveness of 0.9, mechanical energy recovery effectiveness of 0.85, and the ratio of the molar flow rates of sweep gas and ceria of 10, the solar-to-fuel efficiency is 13.2%. The thermodynamic analysis demonstrates the potential of using an epitrochoidal rotary reactor for convenient solid-phase heat recovery without sacrificing the solar-to-fuel efficiency.

Screening Ruddlesden-Popper (n=1) Oxide Materials for Thermochemical Water Splitting By Density Functional Theory

Thermochemical redox reactors store concentrated solar power by thermally inducing an oxygen deficiency within a metal oxide structure. The metal oxide’s affinity for reoxidation allows it to facilitate the splitting of H2O or CO2 to produce H2 or CO for syngas formation.[1] Typically, high temperatures (>1400 °C) are used to drive the reduction of the benchmark material, CeO2, [2] however there is motivation to lower this temperature and investigate new metal oxides capable of larger fuel productions. Perovskite materials have been thoroughly investigated due to their crystallographic stability and ability to accommodate relatively large oxygen deficiencies. Emery et al. [3] conducted a wide computational screening of this family of materials based on a few simple thermodynamic parameters originally proposed by Meredig and Wolverton. [4]Herein, we extend these previous studies and investigate the A2BO4 Ruddlesden-Popper (RP) oxides family [5], layered perovskites, that have previously demonstrated fast redox kinetics and large oxygen storage as solid oxide fuel cell cathodes.[6] A combination of screening parameters based on charge neutrality, Goldschmidt tolerance and computed defect formation energy, identified 38 possible RP candidate materials. One of which - Ca2MnO4-δ – was taken forward to experimental testing due to its Earth abundant elements. The powder was synthesized via a modified Pechini method and thermal analysis experiments demonstrated thermally driven oxygen evolution from 800 to 1200 °C equating to a non-stoichiometry of δ=0.18. High-temperature X-ray diffraction alluded to the formation of a CaMn2O4 secondary phase above 1075 °C, therefore consequent thermochemical water splitting cycles were carried out at a maximum of 1000 °C. Oxidation under steam at 800 °C demonstrated good hydrogen production volumes, although gas production on further cycles was limited by particle sintering observed by scanning electron microscopy. Further investigations aim to understand and improve the cyclability and kinetics under different reaction temperatures and humidity. This study outlines, with experimental validation, how computational screening can be used to find future suitable RP candidates for thermochemical water splitting whose performance can be further improved with doping strategies and morphological adaptation.

Introduction and preliminary testing of a 5 m3/h hydrogen production facility by Iodine–Sulfur thermochemical process

The Iodine–Sulfur (IS) or Sulfur–Iodine (SI) thermochemical water-splitting cycle is considered as one of the most promising hydrogen production methods through thermal chemical cycle process with heat. This paper introduces the new built hydrogen production testing facility of IS process made by industrial structural material (IS-5m3 facility). The TC4, Hastelloy C276 and SiC materials were chosen in this pilot-scale testing facility for different modules. The new designed structure of Bunsen reactor, HI decomposer and H2SO4 decomposer are described particularly, and the corresponding individual tests are successfully executed to verify the function of each section. Based on testing, a preliminary continuous experimental run was carried out in September of 2021 for about 4 h with the hydrogen production capacity of 80 L/h. The problems such as slight corrosion, lower hydrogen gas yield and shorter operation time faced in this experiment will be modified in the near future. A longer time operation and higher H2 production rate test will be carried out soon.

Which thermochemical water-splitting cycle is more suitable for high-temperature concentrated solar energy?

The manuscript reviews the thermochemical water-splitting cycles not in general (many other works have covered this topic) but specifically for producing hydrogen coupled with high temperature concentrated solar energy which is available at temperatures of 1000 to 1100 °C. This is important to benefit from synergies with near future dispatchable concentrated solar power, simply replacing the power cycle with the thermochemical hydrogen production plant. The review shows as three-step cycles are those benefiting the most from the synergy with higher solar flux dispatchable concentrated solar power with thermal energy storage, also profiting in terms of technology readiness level from past experiences in thermochemical water-splitting cycles for nuclear power plants, and the affordable complexity of the cycle. From preliminary evaluations, three-step cycles may permit CO2-free hydrogen production within a decade at a competitive cost with green hydrogen as well as the current prevailing production of hydrogen from hydrocarbons at less than $1 per 1 kg. The thermochemical pathway has the same minimum energy requirement as electrolysis, despite the conversion efficiencies achieved so far have been much less because of the reduced development. Since the collection of solar thermal energy is much easier and more efficient than solar photovoltaic conversion, the thermochemical pathway has the potential to deliver a cost of hydrogen smaller than green hydrogen from solar photovoltaic electricity and electrolyzers.

Process modeling of a hybrid-sulfur thermochemical cycle combined with solid oxide fuel cell/gas turbine system

This work proposes a novel design of the hybrid sulfur (HyS) thermochemical water-splitting cycle for hydrogen production. The hydrogen production plant is combined with a solid oxide fuel cell/gas turbine (SOFC/GT) system to satisfy the demand for the high-temperature heat from the HyS cycle by exploiting the heat loss of the SOFC stack and the demand for electric power for SO2-depolarized electrolysis. A detailed thermodynamic analysis of the HyS cycle and the SOFC/GT system was conducted on a flowsheet basis to determine the energy requirement and to estimate the effects of the operating conditions on the overall efficiency. As a result, it was found that the LHV efficiency of the combined HyS-SOFC/GT system can reach > 29% (34.32% HHV efficiency), with a net electric efficiency of the SOFC/GT system of 38.83% and consumption of 340.3 kJ molH2-1 high-temperature heat, 148.77 kJ molH2-1 low-temperature heat, and 134.35 kJ molH2-1 electric power.