We are frequently asked why we at Kyon Energy are focusing on Large-scale battery storage as a key technology for the energy transition and not on the production of green hydrogen, when the German government published a comprehensive hydrogen strategy in June 2020. A huge investment package of 9 billion euros is supposed to drive the production of green hydrogen and ensure an electrolysis capacity of 10 GW by 2040. But if hydrogen really is the panacea of the energy transition, why do both studies by the Fraunhofer Institute and government grid development plans indicate a large-scale expansion of large-scale battery storage as necessary to meet the challenges of the energy transition?
Hydrogen and battery storage are by no means competitors. Both systems bring advantages for the energy transition. In each case, it is necessary to examine for which application the respective technology can be used most sensibly. In order to master the energy transition, it is necessary to promote both systems and expand them nationwide. Why this is the case and in which areas hydrogen and in which large-scale battery storage systems make sense are answered in this article.
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:
The battery or accumulator
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 production of green hydrogen: the electrolysis
The electrolysis process has existed for more than 100 years, but has still not been used much for hydrogen production, as hydrogen is still largely obtained from natural gas by means of so-called steam reforming. Since this type of hydrogen production is veryCO2-intensive and thus anything but sustainable, hydrogen produced by steam reforming is also called "gray hydrogen". With the increasing demand for green hydrogen, i.e. hydrogen with noCO2 footprint in its production, electrolysis takes on a 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 hydrogen and oxygen by applying an electrical voltage. Electricity is converted into hydrogen in the electrolyzer, which is then available as an energy carrier and for other hydrogen applications. The electricity grid and the hydrogen infrastructure or rather the gas grid are coupled by electrolysis, which is why the term "sector coupling" is often used, or also "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, efficiencies of 70 to 80% (energy content of the hydrogen produced in relation to the electricity used) can be achieved with the electrolysers.
From hydrogen to electric power: fuel cells or gas turbines
For chemical energy stored in hydrogen to be made electrically usable again, two processes for reconversion to electricity have become established:
In principle, the fuel cell works in reverse to 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 current flow. Fuel cell efficiencies can now reach around 60%.
Gas turbines are the current industry standard for converting natural gas into electricity by burning the gas and converting it into kinetic energy, which a generator then uses to produce electricity. Modern gas turbines can also burn hydrogen instead of natural gas, producing only water vapor as exhaust gas, just as in a fuel cell. The efficiencies of modern plants are 45-50%, which is slightly lower than the efficiency of fuel cells. However, they are less expensive and in some cases can also be operated with a mixture of natural gas (or biogas) and hydrogen, making them more flexible in their application.
Energy storage using hydrogen or batteries - The advantages and disadvantages
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 its fast response time. Within milliseconds, battery storage systems can draw and store or release electrical energy, thus offering enormous flexibility for the power grid.
Due to the combination of high efficiency and very fast response time, large-scale battery storage systems therefore offer an optimal storage system for balancing short-term differences between supply and demand. A common use case is, for example, balancing day/night fluctuation of PV systems. With minimal losses, the storage systems can store the excess PV power during the day and make it available again in the evening.
The exact application areas for battery storage are described in our article "Large-scale battery storage as a key technology for the energy transition".
But what happens during periods of extended absence of wind and sun, as is often the case in winter? Battery storage systems are considered an effective Short-term energy storagebut not for supplying heat pumps for household heating and industry over these long-term periods. Hydrogen offers enormous potential here, because like natural gas today, hydrogen can be stored in large quantities underground in caverns and transported between different regions via pipelines.
So where large-scale battery storage is an ideal short-term energy store, hydrogen storage makes it possible to compensate for longer-term fluctuations, even though higher losses occur due to lower efficiency.
In addition, hydrogen can be used in an extremely versatile way 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 application areas can be directly electrified. Hydrogen can help out here and also power these applications via detours with renewable energies, so that decarbonization becomes 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 will have to be built and hydrogen storage facilities converted and expanded.
In addition to its use as a long-term energy storage hydrogen can also be used to decarbonize sectors where electrification is only possible to a limited extent and to supply them with green energy.