We are often asked why we from Kyon Energy on Large-scale battery storage As a key technology in the energy transition and not on the production of green hydrogen, the Federal Government published a comprehensive hydrogen strategy in June 2020. A huge investment package of 9 billion euros is intended to promote the production of green hydrogen and ensure an electrolysis capacity of 10 GW by 2040. But if hydrogen is indeed the panacea for the energy revolution, why do both studies by the Fraunhofer Institute and the government's network development plans show that a large-scale expansion of large battery storage systems is necessary to overcome the challenges of the energy transition?
The answer:
Hydrogen and battery storage systems are by no means competitors. Both systems provide benefits for the energy revolution. It is important to check in each case for which application the respective technology can be used most effectively. In order to master the energy revolution, it is necessary to promote and expand both systems nationwide. Why this is the case and in which areas hydrogen and in which large battery storage systems can be used sensibly is answered in this article.
In order to understand and classify both techniques, here is a brief digression into the technologies behind batteries, electrolyzers, fuel cells and gas turbines, which can also be used to convert hydrogen into electricity:
Accumulators ("batteries" for short) are batteries that can not only be used once but are rechargeable. In general, batteries and accumulators are so-called electrochemical storage devices. The electrical energy is converted into chemical energy through a reaction taking place in the battery cell and can later be converted back into electricity 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 batteries are the most commonly used today. Lithium-ion batteries can be found in almost all mobile phones, notebooks, cameras and even electric cars. We also use this technology for our stationary large battery storage systems.
The electrolysis process has existed for over 100 years and yet has so far been little used for hydrogen production, as hydrogen is still largely obtained from natural gas by means of so-called steam reforming. Because this type of hydrogen production is veryCO2-intensive and therefore anything but sustainable, hydrogen, which is produced using steam reforming, is also known as "gray hydrogen." With the increasing demand for green hydrogen, i.e. hydrogen withoutCO2footprintin manufacturing, but electrolysis is gaining new relevance. However, the electrical energy required for electrolysis must necessarily 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 electrolyzer, which is then available as an energy carrier and for further hydrogen applications. The power grid and the hydrogen infrastructure or the gas network are linked through electrolysis, which is why there is often talk of "sector coupling," 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, electrolyzers can achieve efficiencies of 70 to 80% (energy content of the hydrogen produced based on the electricity used).
If the chemical energy stored in hydrogen is to be made electrically usable again, two methods for reconversion of electricity have been established:
fuel cell
In principle, the fuel cell functions in the opposite way as an electrolyzer 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 continuously supplied hydrogen and oxygen to form water (steam), resulting in a constant flow of electrons, i.e. a flow of electricity. Fuel cell efficiencies 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 a generator then uses to generate electricity. Modern gas turbines can also burn hydrogen instead of natural gas, which, just like a fuel cell, produces only water vapor as exhaust gas. The efficiency of modern systems is 45-50% and is therefore slightly below the efficiency of fuel cells. However, they are cheaper and can sometimes also be operated with a mixture of natural gas (or biogas) and hydrogen, meaning they are more flexible to use.
Both hydrogen and batteries can therefore be used to store electrical energy. Both technologies can therefore make an important contribution to security of supply and to the success of the energy revolution. The question is: When should hydrogen be used and when should batteries be used?
A decisive advantage of battery storage systems is their very high efficiency, as this is now over 95% for lithium-ion batteries. The entire battery storage system, including inverters and transformers, still has an efficiency of around 90%. This means that approximately 90% of the stored electrical energy can be stored again and used. By way of comparison, modern gasoline and diesel engines achieve an efficiency of 45% in the best case, but often not even 30% in everyday operation. The overall efficiency of the combination of electrolyzer and fuel cell is at least 40 to a maximum of 50% and pumped storage power plants reach up to around 70%. In order to limit conversion losses, many experts agree that all applications should be electrified as directly as possible, as long as this is technically possible and economically viable. In this way, the required expansion of renewable energy sources can be minimized, as the overall energy requirement is then lower. For this reason, among other things, there is currently a higher potential in e-mobility in battery-powered vehicles than in fuel-cell-powered vehicles.
Another important advantage of battery technology is the fast response time. Within milliseconds, battery storage systems can draw, store and release electrical energy, thus offering enormous flexibility for the power grid.
Thanks to the combination of high efficiency and very fast responsiveness, large battery storage systems thus offer an optimal storage system to compensate for short-term differences between supply and demand. A common application is, for example, the compensation of day/night fluctuations in PV systems. With minimal losses, the storage systems can store excess PV power 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 in the energy revolution".
But what happens during periods of prolonged absence of wind and sun, as is often the case in winter? Battery storage systems are considered effective short-term energy storagebut not to supply heat pumps for domestic heating and industry over these long-term periods of time. Hydrogen offers enormous potential here because, just like natural gas today, large quantities of hydrogen can be stored underground in caverns and transported between different regions via pipelines.
Where large battery storage systems therefore represent an ideal short-term energy storage device, hydrogen storage also makes it possible to compensate for longer-term fluctuations, albeit with higher losses due to lower efficiency.
In addition, hydrogen is extremely versatile 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 electrified directly. Hydrogen can help out here and also operate these applications via detours with renewable energy, so that decarbonization is possible in all sectors. However, hydrogen will require a completely new infrastructure in the near future. In addition to electrolysis plants and fuel cells, new pipelines must also be built and storage facilities for hydrogen converted and expanded.
In addition to using as long-term energy storage Hydrogen can therefore also be used to decarbonize sectors in which electrification is only possible to a limited extent and supply them with green energy.
We did it! With Europe-wide cooperation, we can cover all our energy needs through renewable energy sources. Biogas plants, onshore and offshore wind energy plants, and photovoltaics generate sufficient electrical energy. PV systems on the roofs combined with home storage systems cover the majority of domestic needs and also feed into the power grid. The further expanded power grid reliably supplies electrical energy and is stabilized for this purpose by stationary battery storage systems. Short-term fluctuations, such as between day and night or during the day due to changing weather, can be effectively compensated by stationary battery storage systems.
In regions with a continuous surplus of electrical energy, green hydrogen is also produced in large electrolyzers. Industry has largely been electrified; major industries also use green hydrogen as a process gas. The building sector can be heated with hydrogen using electrically operated heat pumps and CHP systems, or in urban areas via a district heating network using waste heat from large-scale industrial plants. Electrolyzers and large battery storage systems can also be integrated here. Mobile applications such as mobile phones, cars and short-haul trucks rely primarily on accumulators. Heavy-duty traffic and sparsely 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. Instead, a successful energy transition requires a combination of both technologies. Battery storage systems serve as short-term buffer storage and to stabilize the grid. Hydrogen serves applications that cannot be electrified and bridges long-term downturns in renewable energy sources.
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