What do you do if the wind is blowing hard and the Danish wind turbines generate more electricity than the consumers have need for? You can try to export it, but as the countries around us increase their own share of renewables this becomes increasingly difficult: They will most likely have a surplus supply of electricity at the same time as Denmark. As Europe transitions to a sustainable energy system, there will be a sharply increased demand for storage of electricity. One may think that the obvious solution is to use batteries, but conventional batteries with the required – for example seasonal – storage capacity would be prohibitively expensive. A more promising option is to store the surplus electricity in the form of chemical energy in a compound, and at a later time re-convert the chemical energy into electricity again.
“The concept of the ECo project can become one of the key solutions for a future fossil-free Danish energy system with large shares of fluctuating wind energy.”
Electrolysis is precisely such a technology for converting electricity into chemical energy. Traditional electrolysis starts with water and use electricity to split it into hydrogen and oxygen. If you store the hydrogen, it can later be used to generate power in a gas turbine or a fuel cell. However, water electrolysis is typically performed at an operation temperature below 100 °C which inherently limits the efficiency of the process. Solid oxide electrolysis cells (SOECs) by contrast operate at very high temperature, 650-850 °C, with an efficiency approaching 100%. Furthermore, such cells can not only electrolyze water but also CO2 at the same time. This means that they can produce a mixture of hydrogen and CO which can easily be converted to hydrocarbons such as methane (the main constituent of natural gas).
The new European research project ECo (Efficient Co-Electrolyser for Efficient Renewable Energy Storage) coordinated by DTU Energy will develop and validate the SOEC technology for storage of sustainable energy. The project will focus on methane production, as it has a significant advantage over comparative storage options: it readily integrates with the existing natural gas grid and storage facilities. Already now, approx. 50% of the total electricity produced from renewable sources could be accommodated as methane in existing underground storage facilities in Europe, thus saving significant investments. The comprehensive natural gas network also makes it a system of transport for bringing power from production to consumption areas. The project partners, which include both research institutions and industry from across Europe, will bring the technology from proof-of-concept to validation in a relevant environment, making it ready for prototype demonstration.