Researchers at DTU Chemistry and DTU Energy have found a new chemical method that can convert electricity, water, and CO₂ into methane gas. The method can be used to store energy from the sun and wind.
As wind and solar become increasingly important sources of energy in the goal of making Denmark independent of fossil fuels, interest from business and politicians is increasing in how we can store the green power.
Today, about half of Denmark's electrical energy comes from solar and wind, and when there is excess of electricity, it is crucial to be able to store the energy. One of the ways is to convert the excess of electricity into methane gas, which can then be stored in the existing natural gas pipes in the ground.
The conversion can be done by first producing hydrogen from water and electricity. This process is called electrolysis and separates the water into its two constituents: hydrogen and oxygen. Thereafter, CO₂ can be reacted with hydrogen by means of a catalyst and methane gas is produced.
Now, researchers from DTU have found a new method in the field of electrolysis to produce methane gas directly in one step.
“It is a well-known case that methane can be produced by split water and linked to CO₂. Now it is all about finding the most effective method to avoid as much heat loss as possible during the process. And here we have succeeded in finding a new combination of experimental conditions, where the heat loss is extremely reduced”, says Professor Niels J. Bjerrum from DTU Energy.
A new combination
The new method is to use a certain electrically conductive material (CsH2PO4) – a so-called electrolyte that allows the current to be charged to a nickel electrode at a temperature of about 350 degrees Celsius and a pressure of 8 bar (and higher). In this way, methane can be efficiently produced when CO₂ is added.
“The special thing about our method is the combination of the electrolyte, the electrode metal, the heating, and the pressure. That is why we have also filed a patent application”, says Associate Professor and Emeritus, Rolf W. Berg from DTU Kemi, who is involved in the project.
He explains that the researchers at DTU Chemistry and DTU Energy have been working on and testing the method over the past few years. He hopes that it can help strengthen the work on finding the best methods for storing the surplus energy from wind turbines and solar farms.
Hydrogen based solutions are important for the future
Several electricity storage projects have already been initiated in Denmark, where efforts are being made to transform the excess green electricity into methane. And here biogas plants play a special role because they can contribute the CO₂ needed to produce the methane gas.
“After all, biogas consists of methane and CO₂, and in the biogas plants, the CO₂ content of the biogas is removed to produce the pure methane, that can be used in our natural gas supply network. Therefore, biogas is an optimal source of CO₂, and at the same time, it has the advantage of being connected to the natural gas grid where we can store the energy“, says Professor Niels J. Bjerrum.
He continues:
“It is important that we continue our research and that society invests in hydrogen-based solutions so we can build some optimal plants where the green energy is fully utilized. By using the CO₂ from our biogas plants together with energy from excess of green electricity, we get to utilize all the carbon in the biogas and at the same time store our green energy in the form of methane production. It can hardly get more optimal, and may well be Denmark's next growth adventure. Finally, it is a crucial step if we are to achieve a 70 percent reduction in CO₂ emissions by 2030”.