We are often asked why we at Kyon Energy focus on large-scale battery storage as a key technology in the energy transition and not on the production of green hydrogen, given that the German government published a comprehensive hydrogen strategy in June 2020. A huge investment package of 9 billion euros is to drive forward the production of green hydrogen and ensure an electrolysis capacity of 10 GW by 2040. But if hydrogen really is the panacea for the energy transition, why do both studies by the Fraunhofer Institute and the government's grid development plans point to a large-scale expansion of large-scale battery storage systems as necessary to meet the challenges of the energy transition?
The answer:
Hydrogen and battery storage are by no means competitors. Both systems offer advantages for the energy transition. It is important to examine in each case for which application the respective technology can be used most effectively. In order to master the energy transition, it is necessary to promote both systems and expand them nationwide. This article explains why this is the case and in which areas hydrogen and large-scale battery storage make sense.
To understand and classify both technologies, here is first a brief digression on the technologies behind batteries, electrolysers, fuel cells and gas turbines, which can also be used to convert hydrogen into electricity:
Accumulators (short "rechargeable batteries") are batteries that can be used not only once, but are rechargeable. In general, batteries and accumulators are so-called electro-chemical storage devices. The electrical energy is converted into chemical energy by a reaction taking place in the accumulator cell and can later be recycled at any time within a very short period of time.
Over time, many different technical concepts have been developed for this purpose. Because of their good specific energy (energy per mass or energy per volume), lithium-ion accumulators are most commonly used today. Thus, lithium-ion batteries can be found in almost all cell phones, notebooks, cameras and also in electric cars. We also rely on this technology for our stationary large-scale battery storage systems.
The electrolysis process has been around for over 100 years and yet has been little used for hydrogen production to date, as hydrogen is still largely produced from natural gas by means of steam reforming. As this type of hydrogen production is veryCO2-intensive and therefore anything but sustainable, hydrogen produced by steam reforming is also known as "gray hydrogen". However, with the increasing demand for green hydrogen, i.e. hydrogen withouta CO2 footprint during production, electrolysis is taking on a new relevance. However, the electrical energy required for electrolysis must come from renewable energy sources such as wind and photovoltaics in order to produce truly green hydrogen.
In hydrogen electrolysis, water is split into the components hydrogen and oxygen by applying an electrical voltage. Electricity is thus converted into hydrogen in the electrolyser, which is then available as an energy carrier and for other hydrogen applications. The electricity grid and the hydrogen infrastructure or the gas grid are coupled by electrolysis, which is why the term "sector coupling" is often used, or "power-to-gas", i.e. the coupling between electricity and gas.
There are several electrolysis processes, which differ in the electrolyte used, the temperature and the operating pressure. Depending on the process, electrolysers can achieve efficiencies of 70 to 80% (energy content of the hydrogen produced in relation to the electricity used).
For chemical energy stored in hydrogen to be made electrically usable again, two processes for reconversion to electricity have become established:
Fuel cell
In principle, the fuel cell works in reverse to an electrolyser and is used to directly convert the chemical energy stored in hydrogen into electricity. In the fuel cell, a controlled electrochemical reaction takes place with a continuous supply of hydrogen and oxygen to form water (vapor), resulting in a constant flow of electrons, i.e. a current flow. The efficiency of fuel cells can now reach around 60%.
Gas turbine
Gas turbines are the current industry standard for generating electricity from natural gas by burning the gas and converting it into kinetic energy, which is then used by a generator to produce electricity. Modern gas turbines can also burn hydrogen instead of natural gas, producing only water vapor as exhaust gas, just like a fuel cell. The efficiency of modern systems is 45-50%, which is slightly lower than that of fuel cells. However, they are cheaper and can sometimes also be operated with a mixture of natural gas (or biogas) and hydrogen, making them more flexible in their application.
Both hydrogen and batteries can be used to store electrical energy. Both technologies can thus make an important contribution to security of supply and to the success of the energy transition. The question arises: When should hydrogen and when should batteries be used?
A decisive advantage of battery storage systems is their very high efficiency, because today this is over 95% for lithium-ion accumulators. The entire battery storage system, including the inverters and transformers, still has an efficiency of about 90%. This means that about 90% of the electrical energy stored can be retrieved and used again. By comparison, modern gasoline and diesel engines achieve an efficiency of 45% in the best case, but often not even 30% in everyday operation. The combination of electrolyzer and fuel cell achieves an overall efficiency of 40 to a maximum of 50%, and pumped-storage power plants reach up to around 70%. To limit conversion losses, many experts agree that all applications should be electrified directly as long as this is technically possible and economically viable. In this way, the required expansion of renewable energies can be minimized, as the total energy requirement is then lower. For this reason, among others, battery-powered vehicles are currently seen as having greater potential in e-mobility than fuel cell-powered vehicles.
Another important advantage of battery technology is the fast response time. Battery storage systems can draw, store and release electrical energy within milliseconds, thus offering enormous flexibility for the electricity grid.
Thanks to the combination of high efficiency and very fast response times, large-scale battery storage systems are therefore an ideal storage system for balancing out short-term differences between supply and demand. A common application is, for example, the balancing of day/night fluctuations in PV systems. With minimal losses, the storage systems can store the surplus PV electricity during the day and make it available again in the evening.
The exact areas of application for battery storage systems are described in our article "Large-scale battery storage as a key technology for the energy transition".
But what happens in times of prolonged absence of wind and sun, as is often the case in winter? Battery storage systems are regarded as effective short-term energy storagebut not for supplying heat pumps for domestic heating and industry over these long-term periods. Hydrogen offers enormous potential here because, like natural gas today, hydrogen can also be stored in large quantities underground in caverns and transported between different regions via pipelines.
Where large-scale battery storage systems therefore represent ideal short-term energy storage, hydrogen storage also makes it possible to compensate for longer-term fluctuations, albeit with higher losses due to lower efficiency.
Furthermore, hydrogen is extremely versatile and can be used in almost all sectors. In the chemical industry for the production of fertilizers and synthetic fuels, in the steel industry for process heat or for CO2-neutral steel production via "direct reduction" and with the gas turbine or fuel cell as electrical energy for the power grid or for mobile and transport applications. Not all of these areas of application can be directly electrified. Hydrogen can help out here and also operate these applications via detours with renewable energies, making decarbonization possible in all sectors. However, a completely new infrastructure will be needed for hydrogen in the near future. In addition to electrolysis plants and fuel cells, new pipelines must be built and storage facilities for hydrogen must be converted and expanded.
In addition to its use as a long-term energy storage hydrogen can also be used to decarbonize sectors in which electrification is only possible to a limited extent and to supply them with green energy.
We have made it! Thanks to Europe-wide cooperation, we can cover our entire energy requirements with renewable energies. Biogas plants, onshore and offshore wind turbines and photovoltaics generate sufficient electrical energy. Rooftop PV systems in combination with home storage systems cover the majority of our domestic demand and also feed into the electricity grid. The expanded electricity grid provides a reliable supply of electrical energy and is stabilized by stationary battery storage systems. Short-term fluctuations, such as between day and night or during the course of the day due to changing weather, can be effectively balanced out by the stationary battery storage systems.
In regions with a continuous surplus of electrical energy, green hydrogen is also produced in large electrolysers. Industry has been largely electrified, and large-scale industries also use green hydrogen as a process gas. The building sector can be heated with hydrogen using electrically powered heat pumps and CHP plants or, in urban areas, via a district heating network using waste heat from large-scale industrial plants. Electrolysers and large battery storage systems can also be integrated here. Mobile applications such as cell phones, cars and short-distance trucks rely predominantly on rechargeable batteries. Heavy goods vehicles and less frequented regional trains can also be powered by hydrogen fuel cells.
In this possible future scenario, battery storage and hydrogen storage are therefore by no means competing technologies. Rather, a combination of both technologies is needed for a successful energy transition. Battery storage serves as short-term buffer storage and for grid stabilization. Hydrogen serves the applications that cannot be electrified and bridges long-term lulls in renewable energies.
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