Solar hydrogen

The intermittance and the geographical distribution of solar energy require means of storing and transporting it to the user's place. An ideal means of doing this is to split water in order to obtain hydrogen.Hydrogen is a carbon-free fuel which oxidizes to water as combustion product. The generated water becomes, together with renewable primary energy for splitting it, a source of clean and abundant energy in a carbon-free, natural cycle.Hydrogen is a fuel which can be transported over long distances and stored so that solar energy can be transported from energy rich countries over long distances in ships to Europe, stored underground or in containers and used in gaseous or liquid form in industry, households, power stations, motor cars and aviation.Solar energy as primary energy is discussed. A special form of it, the cheapest and by now largely available hydropower, is stressed.Techniques of hydrogen production, vectorisation and end use are discussed as well as safety aspects, costs and strategy for its implementation.     

Hydrogen pathways for massive solar energy utilization

Two characteristic features of solar radiation, though beneficial and even essential for plant and animal life, are serious handicaps to the large-scale commercial utilization of solar energy. These are: (1) its diffuse nature and relatively low level of intensity, and (2) its diurnal intermittency and periodic variations. The first-mentioned factor implies a need for large collecting and concentrating devices and vast land areas, which may not always be available, especially in densely populated and industrialized localities, where the energy need will be most. Location of the collectors far removed from the centers of demand will engender the problems of energy transmission. The obvious solution to these problems is to provide an effective means by which sunshine energy can be stored in a form that can be transported and used subsequently when and where required. Conversion to hydrogen through the highly endergonic dissociation of water provides a very capacious and versatile means for solar energy storage and distribution. More importantly, it ‘decouples’ the primary energy source completely from its end-uses and thus enables it to subserve all the energy needs of industrialized society, unhampered by the constraints characteristic of the prime source and indeed, as efficiently as petroleum fuels. The paper discusses the merits of this proposal and the methods by which it may be achieved in the near term and long term.     

Monitoring and control of a hydrogen production and storage system consisting of water electrolysis and metal hydrides

Renewable energy sources such as wind turbines and solar photovoltaic are energy sources that cannot generate continuous electric power. The seasonal storage of solar or wind energy in the form of hydrogen can provide the basis for a completely renewable energy system. In this way, water electrolysis is a convenient method for converting electrical energy into a chemical form. The power required for hydrogen generation can be supplied through a photovoltaic array. Hydrogen can be stored as metal hydrides and can be converted back into electricity using a fuel cell. The elements of these systems, i.e. the photovoltaic array, electrolyzer, fuel cell and hydrogen storage system in the form of metal hydrides, need a control and monitoring system for optimal operation. This work has been performed within a Research and Development contract on Hydrogen Production granted by Solar Iniciativas Tecnológicas, S.L. (SITEC), to the Politechnic University of Valencia and to the AIJU, and deals with the development of a system to control and monitor the operation parameters of an electrolyzer and a metal hydride storage system that allow to get a continuous production of hydrogen.     

A solar-hydrogen economy for U.S.A.

For the post-fossil fuel era, there are two main options. One is well known: a fusion hydrogen combination, in which fusion is the primary energy source and hydrogen is the energy carrier. The other option, the solar-hydrogen alternative, is less widely discussed, though it is far more likely to succeed in a reasonable time-scale. It is envisioned that the solar energy will be collected in the highly insolated regions, where it will be used to produce hydrogen from water. Hydrogen would then be transported to consumption centres to meet the energy requirements. There are many ways through which hydrogen can be used in homes and buildings, in cars, in airplanes, in industry, in chemistry and metallurgy, in synthetic food production and in military, more efficiently than any other known fuel. Economically it would not be feasible to replace the fossil-based energy structure all at once, but it would be prudent to start phasing in the solar-hydrogen system by limiting the change to new energy conversion plants. Such a change would be most cost-effective and could be completed in ca 40–60 years—the average life span for energy conversion and distribution systems. To achieve this conversion, a National Energy Resources Executive is recommended.     

On the potential of solar energy conversion into hydrogen and/or other fuels

Solar energy, when used together with water for the production of hydrogen, forms an inexhaustible source of transportable primary energy. Hydrogen is also a potential means of storing solar energy. In this paper the thermodynamic and energetic conditions for the splitting of water are established. The different water decomposition techniques are discussed.Electrolysis. Electrolysis is a proven and convenient way of producing hydrogen. If the very high temperature electrolysis (80–1000°C) development is successful, heat-assisted electrolysis with electric efficiencies of 100% and more looks attractive in connection with thermo-mechanical helio-electricity conversion.Thermal conversion. Highest temperature (≈ 3000°C) direct decomposition (thermolysis) is thermodynamically interesting, but is, for the time being, technologically not feasible. Use of thermochemical cycles is mainly a question of economics and of adaptation to the high temperatures, attainable with solar concentrating devices.Quantum conversion. The thermodynamic potential of light makes quantum conversion highly attractive, requiring much basic research, though.Bioconversion. Biosystems are already operating in nature but with low and lowest efficiencies. With successful R & D to increase efficiencies, bio-energy systems seem to become a convenient way of fuel production.Economics are considered when it seems reasonable to do so, otherwise educated guesses are made as to the economics of the different decomposition techniques and their implications for the possible large-scale hydrogen production by solar energy.Some considerations are made on the influence of large-scale solar power plants on the climate.     

Hydrogen the fuel for 21st century

Non-Conventional Energy Sources, such as solar and hydrogen energy will remain available for infinite period. One of the reasons of great worry for all of us is reducing sources of conventional energies. The rate of fossil fuel consumption is higher than the rate of the fossil fuel production by the nature. The results will be the scarcity of automobile fuel in the world which will create lot of problems in transport sector. The other aspect is pollution added by these sources in our environment which increases with more use of these sources, resulting in the poor quality of life on this planet. There is constant search of alternate fuel to solve energy shortage which can provide us energy without pollution.Hence most frequently discussed source is hydrogen which when burnt in air produces a clean form of energy. In the last one decade hydrogen has attracted worldwide interest as a secondary energy carrier. This has generated comprehensive investigations on the technology involved and how to solve the problems of production, storage and transportation of hydrogen. The interest in hydrogen as energy of the future is due to it being a clean energy, most abundant element in the universe, the lightest fuel, richest in energy per unit mass and unlike electricity, it can be easily stored. Hydrogen gas is now considered to be the most promising fuel of the future. In future it will be used in various applications, e.g. it can generate Electricity, useful in cooking food, fuel for automobiles, hydrogen powered industries, Jet Planes, Hydrogen Village and for all our domestic energy requirements.Hydrogen as a fuel has already found applications in experimental cars and all the major car companies are in competition to build a commercial car and most probably they may market hydrogen fuel automobiles in near future but at a higher cost compared to gasoline cars but it is expected that with time the cost of hydrogen run cars will decrease with time. Long lasting, light and clean metal hydride batteries are already commercial for lap top computers. Larger capacity batteries are being developed for electrical cars. Hydrogen is already being used as the fuel of choice for space programmes around the world. It will be used to power aerospace transports to build the international space station, as well as to provide electricity and portable water for its inhabitants. Present article deals with the storage and applications of hydrogen in the present energy scenario.     

Production of hydrogen for export from wind and solar energy,natural gas,and coal in Australia

Hydrogen production for export to Japan and Korea is increasingly popular in Australia. The theoretically possible paths include the use of the excess wind and solar energy supply to the grid to produce hydrogen from natural gas or coal. As a contribution to this debate, here I discuss the present contribution of wind and solar to the electricity grid, how this contribution might be expanded to make a grid wind and solar only, what is the energy storage needed to permit this supply, and what is the ratio of domestic total primary energy supply to electricity use. These factors are required to determine the likeliness of producing hydrogen for export. The wind and solar energy capacity, presently at 6.7 and 11.4 GW, have to increase almost 8 times up to values of 53 and 90 GW respectively to support a wind and solar energy only electricity grid for the southeast states only. Additionally, it is necessary to build-up energy storage of actual power >50 GW and stored energy >3000 GW h to stabilize the grid. If the other states and territories are considered, and also the total primary energy supply (TPES) rather than just electricity, the wind and solar capacity must be increased of a further 6–8 times. It is concluded that it is extremely unlikely that hydrogen for export could be produced from the splitting of the water molecule by using excess wind and solar energy, and it is very unlikely that wind and solar may fully cover the local TPES needs. The most likely scenario is production hydrogen via syngas from either natural gas or coal. Production from natural gas and coal needs further development of techniques, to include CO₂ capture, a way to reuse or store CO₂, and finally, the better energy efficiency of the conversion processes. There are several challenges for using natural gas or coal to produce hydrogen with near-zero greenhouse gas emissions. Carbon capture, utilization, and storage technologies that ensure no CO₂ is released in the production process, and new technologies to separate the oxygen from the air, and in case of natural gas, the water, and the CO₂ from the combustion products, are urgently needed to make sense of the fossil fuel hydrogen production. There is no benefit from producing hydrogen from fossil fuels without addressing the CO₂ issue, as well as the fuel energy penalty issue during conversion, that is simply translating in a net loss of fuel energy with the same CO₂ emission.     

Potential importance of hydrogen as a future solution to environmental and transportation problems

Air pollution is a serious public health problem throughout the world, especially in industrialized and developing countries. In industrialized and developing countries, motor vehicle emissions are major contributors to urban air quality. Hydrogen is one of the clean fuel options for reducing motor vehicle emissions. Hydrogen is not an energy source. It is not a primary energy existing freely in nature. Hydrogen is a secondary form of energy that has to be manufactured like electricity. It is an energy carrier. Hydrogen has a strategic importance in the pursuit of a low-emission, environment-benign, cleaner and more sustainable energy system. Combustion product of hydrogen is clean, which consists of water and a little amount of nitrogen oxides. Hydrogen has very special properties as a transportation fuel, including a rapid burning speed, a high effective octane number, and no toxicity or ozone-forming potential. It has much wider limits of flammability in air than methane and gasoline. Hydrogen has become the dominant transport fuel, and is produced centrally from a mixture of clean coal and fossil fuels (with C-sequestration), nuclear power, and large-scale renewables. Large-scale hydrogen production is probable on the longer time scale. In the current and medium term the production options for hydrogen are first based on distributed hydrogen production from electrolysis of water and reforming of natural gas and coal. Each of centralized hydrogen production methods scenarios could produce 40 million tons per year of hydrogen. Hydrogen production using steam reforming of methane is the most economical method among the current commercial processes. In this method, natural gas feedstock costs generally contribute approximately 52–68% to the final hydrogen price for larger plants, and 40% for smaller plants, with remaining expenses composed of capital charges. The hydrogen production cost from natural gas via steam reforming of methane varies from about 1.25 US$/kg for large systems to about 3.50 US$/kg for small systems with a natural gas price of 6 US$/GJ. Hydrogen is cheap by using solar energy or by water electrolysis where electricity is cheap, etc.     

The hydrogen economy: technology,logistics and economics

Abstract

There is much current discussion on the contribution the 'hydrogen economy' can make to a 'sustainable energy system', centring around the environmental and supply advantages that may accrue from use of hydrogen as a secondary energy carrier. Whether generated by electrolysis or reforming, or even produced locally at filling stations, the hydrogen must be packaged by compression or liquefaction, transported by surface vehicles or pipelines, stored and transferred to the end user. Hydrogen may represent an option for clean energy use if produced using reduced carbon or carbon-free primary energy sources, e.g. renewable, biomass or nuclear energy. To date, hydrogen has competed with direct use of clean primary energy and/or electrical energy produced without CO₂ emissions. However, to succeed as a secondary energy carrier, hydrogen must demonstrate advantages over established systems, especially electricity.     

Hydrogen quantum yields in the 360 nm photolysis of Eu solutions and their relationship to photochemical fuel formation

Water decomposition by a cyclic photoredox process is discussed in general terms. Thermodynamics determines the wavelength of the charge transfer band corresponding to electron transfer to or from water of hydration of a cation. These relationships indicate that it is unlikely that a photoreduction reaction resulting in water decomposition will occur in the sea level solar range of wavelengths. Such is not the case for photo-oxidation, and an example is known: the photolysis of Eu²⁺ in aqueous solution. Hydrogen quantum yields have been determined for this reaction. They are sufficiently high ( 0.3) as to offer encouragement for the further exploration of photoredox reactions as a means of solar energy conversion.     

Hydrogen from solar energy,a clean energy carrier from a sustainable source of energy

Solar energy is going to play a crucial role in the future energy scenario of the world that conducts interests to solar-to-hydrogen as a means of achieving a clean energy carrier. Hydrogen is a sustainable energy carrier, capable of substituting fossil fuels and decreasing carbon dioxide (CO₂) emission to save the world from global warming. Hydrogen production from ubiquitous sustainable solar energy and an abundantly available water is an environmentally friendly solution for globally increasing energy demands and ensures long-term energy security. Among various solar hydrogen production routes, this study concentrates on solar thermolysis, solar thermal hydrogen via electrolysis, thermochemical water splitting, fossil fuels decarbonization, and photovoltaic-based hydrogen production with special focus on the concentrated photovoltaic (CPV) system. Energy management and thermodynamic analysis of CPV-based hydrogen production as the near-term sustainable option are developed. The capability of three electrolysis systems including alkaline water electrolysis (AWE), polymer electrolyte membrane electrolysis, and solid oxide electrolysis for coupling to solar systems for H₂ production is discussed. Since the cost of solar hydrogen has a very large range because of the various employed technologies, the challenges, pros and cons of the different methods, and the commercialization processes are also noticed. Among three electrolysis technologies considered for postulated solar hydrogen economy, AWE is found the most mature to integrate with the CPV system. Although substantial progresses have been made in solar hydrogen production technologies, the review indicates that these systems require further maturation to emulate the produced grid-based hydrogen.     

Transient simulation and comparative assessment of a hydrogen production and storage system with solar and wind energy using TRNSYS

This paper uses the TRNSYS software to investigate the hourly energy generation potential, storage, and consumption via an electrolyzer and a fuel cell in the Canadian city of Saskatoon, which is a region with high solar and wind energy potential. For this purpose, a location with an area of 10,000 m² was considered, in which the use of solar panels and vertical-axis wind turbines (VAWTs) were simulated. In the simulation, the solar panels were placed at specific distances, and the energy generation capacity, amount of produced hydrogen, and the energy available from the fuel cell were examined hourly and compared to the case with wind turbines placed at standard distances. The results indicated energy generation capacities of 1,966,084 kWh and 75,900 kWh for the solar panels and the wind turbines, respectively, showing the high potential of solar panels compared to wind turbines. Moreover, the fuel cells in the solar and wind systems can produce 733,077 kWh and 22,629 kWh of energy per year, respectively, if they store all of the received energy in the form of hydrogen. Finally, the hourly rates of hydrogen production by the solar and wind systems were reported.     

The case for solar/hydrogen energy

Since sustainable, technologically-converted solar energy is the likely basis for our post-fossil-energy future, there is a basic need for solar-produced fuels. It is noteworthy that heat and electricity, solely, are being developed as solar-energy delivery means, while historically civilizations depend on fuels. Hydrogen, a clean, efficiently-used fuel, can be readily derived from water using any of a number of both proved and prospective solar-energy conversion technologies—both direct and indirect (hydropower, wind, etc.). Solar/hydrogen (and oxygen) can also extend depleting fossil-energy resources while ameliorating environmental degradation. The Hydrogen Energy System concept is overviewed as background.A recent ‘Solar/Hydrogen Systems Assessment’ delineated early-availability systems based on photovoltaic, thermal/heat-engine, wind and hydropower solar conversion, and associated water electrolysis to yield product hydrogen and oxygen as ‘hydrogen energy’. Involved technologies being highly modular, good economics of equipment manufacture and deployment are inherent, as is early availability and as-needed rates of construction (in contrast, e.g., with nuclear-plant experience). Proved technological means exist for transporting, storing and distributing hydrogen energy to end-users.Most significant, both small-scale (local, dispersed) and large-scale (central, remote) solar/hydrogen generation facilities can be established in balance with prevailing societal-selection dictates. Involving a readily storable, transportable ‘energy currency’, then-existing hydrogen-energy systems can be inter-tied as desired, providing load-management-related economic advantages to both the energy-user and the ‘energy utility’ of that era. Future solar/hydrogen-electric residences might, as is illustrated, buy and sell hydrogen and electricity in a ‘grid-cooperative’ arrangement.The salient operative question concerns the efficacy of ‘conventional wisdom’ in the energy free-market decision-making process. Will early-enough, adequate level-of-effort programmes be implemented to ensure non-disruptive meeting of tomorrow's demand worldwide? In an aura of business-as-usual, solar/hydrogen's timely contribution to ‘picking up the load’ from exhaustible fossil fuels in the face of still-escalating world energy demand is judged most problematic. Consequently, an unprecedented cooperative world effort for the research, development, demonstration and deployment of solar hydrogen energy delivery capabilities is suggested.     

Optimal heat recovery during polymer electrolyte membrane electrolysis

The severe reduction in the available fossil fuel resources highlights the need to make more use of renewable energy resources (RER), such as solar photovoltaic (PV) modules, wind turbines, hydro-turbines, etc. Hydrogen (H₂) may be seen as a possible alternative fuel which can be produced from renewable energy, as mentioned and a promising contender in the energy storage domain. A hydrogen electrolyser harnesses the energy produced by the RER, in order to produce H₂, which could be stored in its current form to be used at a later stage to generate electrical energy, by means of a fuel cell.In this paper, an optimal switching control of a solid polymer electrolyte membrane water electrolyser (PEMWE) water heating system is presented, in which actual historic exogenous data obtained from a weather station in the considered area is used as inputs for the established model.The main aim of this paper was to develop an optimal control model, which maximizes the removal of the undesired heat from the PEMWE and transferring it to the hot water storage tank (HWST), whilst ensuring sufficient hydrogen is being produced.Simulations of the optimal switching control of a PEMWE water heating system was conducted successfully with the SCIP (Solving Constrained Integer Programs) solver in the optimization toolbox in MATLAB.The optimal switching control model yields a daily energy consumption of 49.85 kWh by the PEMWE compared to an energy consumption of 48.86 kWh by the standard PEMWE system (baseline). The optimal switching control model resulted in 2.51 kg of hydrogen compared to 2.56 kg which is produced by the standard PEMWE system. Moreover, the optimal control model recovered 1.03 kWh of heat successfully which is transferred to the HWST.The optimal control model development and implementation for a PEMWE to maximize the thermal energy recovery from the PEMWE to the HWST whilst ensuring stable H₂ production are presented as one of the main contributions to the study.Secondly, by recovering the generated heat from the PEMWE, the time period for the membrane to degrade to a thickness of 50% could be prolonged by 0.68 years, after which the membrane degradation occurs non-linearly.     

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.     

Wind energy–hydrogen storage hybrid power generation

In this theoretical investigation, a hybrid power generation system utilizing wind energy and hydrogen storage is presented. Firstly, the available wind energy is determined, which is followed by evaluating the efficiency of the wind energy conversion system. A revised model of windmill is proposed from which wind power density and electric power output are determined. When the load demand is less than the output of the generation, the excess electric power is relayed to the electrolytic cell where it is used to electrolyze the de‐ionized water. Hydrogen thus produced can be stored as hydrogen compressed gas or liquid. Once the hydrogen is stored in an appropriate high‐pressure vessel, it can be used in a combustion engine, fuel cell, or burned in a water‐cooled burner to produce a very high‐quality steam for space heating, or to drive a turbine to generate electric power. It can also be combined with organic materials to produce synthetic fuels. The conclusion is that the system produces no harmful waste and depletes no resources. Note that this system also works well with a solar collector instead of a windmill. Copyright © 2001 John Wiley & Sons, Ltd.     

Hydrogen—The ultimate fuel

Hydrogen is regarded in certain quarters as the ultimate, non-polluting fuel and energy storage medium for future centuries. This view is based upon a scenario in which fossil fuels are reserved for chemical use, while other primary energy sources are employed to generate hydrogen from water.

This paper reviews briefly the prospects for such a future and outlines the technical and engineering problems to be solved and the economic disincentives in terms of present-day fuel prices. Likely trends in hydrogen production technology are discussed, followed by a consideration of hydrogen storage, either as liquid hydrogen or in the form of metallic hydrides.

Future uses of hydrogen are reviewed, first as a chemical in industry, then as a fuel for heating purposes and finally as a portable fuel for aircraft and road vehicles. In reaching a conclusion as to the prospects for hydrogen, the importance of timescales is emphasised, together with likely technical developments in the primary energy sectors.     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Peak power and heavy water production from nuclear electrolytic H2 and O2 in Canada

A combined energy storage-heavy water production system is presented. Off-peak nuclear energy is stored in the form of electrolytic H₂ (and O₂) from which a large fraction of the deuterium has been transferred to water in a deuterium exchange catalyst column. The main features and advantages of the Combined Electrolysis Catalytic Exchange-Heavy Water Process (CECE-HWP) are discussed. Significant quantities of D₂O could be produced economically at reasonable peak to base power cost ratios. Thirty to forty per cent of the primary electric energy should be available for peak energy via either gas-steam turbines or fuel cells.     

Impact of hydrogen energy storage on California electric power system: Towards 100% renewable electricity

Decarbonization of the power sector is a key step towards greenhouse gas emissions reduction. Due to the intermittent nature of major renewable sources like wind and solar, storage technologies will be critical in the future power grid to accommodate fluctuating generation. The storage systems will need to decouple supply and demand by shifting electrical energy on many different time scales (hourly, daily, and seasonally). Power-to-Gas can contribute on all of these time scales by producing hydrogen via electrolysis during times of excess electrical generation, and generating power with high-efficiency systems like fuel cells when wind and solar are not sufficiently available. Despite lower immediate round-trip efficiency compared to most battery storage systems, the combination of devices used in Power-to-Gas allows independent scaling of power and energy capacities to enable massive and long duration storage. This study develops and applies a model to simulate the power system balance at very high penetration of renewables. Novelty of the study is the assessment of hydrogen as the primary storage means for balancing energy supply and demand on a large scale: the California power system is analyzed to estimate the needs for electrolyzer and fuel cell systems in 100% renewable scenarios driven by large additions of wind and solar capacities. Results show that the transition requires a massive increase in both generation and storage installations, e.g., a combination of 94 GW of solar PV, 40 GW of wind, and 77 GW of electrolysis systems. A mix of generation technologies appears to reduce the total required capacities with respect to wind-dominated or solar-dominated cases. Hydrogen storage capacity needs are also evaluated and possible alternatives are discussed, including a comparison with battery storage systems.