Wind energy can be converted into methane gas and stored in a natural gas grid, eliminating carbon emissions from biogas plants which use this method, a research project carried out by the Technical University of Denmark (DTU) and Lemvig Biogas Plant has shown.
Through the MeGA-StoRE project (Methane Gas Storage for Renewable Energy), DTU and Lemvig Biogas Plant have tested a new method that basically involves using a biogas plant to convert wind energy into methane gas, which can subsequently be transferred to a natural gas grid.
The first step in the process is to convert the surplus wind turbine energy into hydrogen using electrocatalysis. In the next step, hydrogen is allowed to react with CO₂ in a reactor at the biogas plant to produce methane gas and water.
The CO₂ can be sourced from the biogas plant itself, where it would otherwise be emitted as a waste product. Biogas namely consists of methane and CO₂, and is thus an excellent source of CO₂, according to Lars Albæk Kristensen, Director at Lemvig Biogas Plant.
“Biogas contains 35 per cent CO₂ of an extremely high purity. And if we can store the surplus wind power energy in a carbon source such as methane, it’ll be just like with oil: 100 per cent of what we put into the pipe, comes out the other end.” So if we use the hydrogen (which is made from surplus wind turbine electricity, ed.) to convert CO₂ into methane, we will have a carbon-based energy storage facility. And very close to 100 per cent of the CO2 is converted into chemically pure methane. We already have access to the infrastructure in the natural gas grid where we can store the energy. That’s the brilliance of the idea,” Kristensen said.
In contrast to the typical method where biogas is cleansed of CO₂ and the methane then transferred to the natural gas grid, the Lemvig Biogas Plant project has succeeded in capturing the CO2, allowing it to react with hydrogen. Not only did this utilize all the carbon in the biogas, it also increased methane production by approximately 50 per cent, according to DTU.
“Put a little crudely, with the help of biogas we are using the Danish fields to collect carbon from the atmosphere by means of photosynthesis—and with the help of wind energy, we can increase this yield by 50 per cent. Wind energy has already come a long way in Denmark. We’ve made the world sit up and take note—we’re the ones who came up with the solution. The next goal is to store the electricity so that in the future we don’t just sell wind turbines, but the complete system,” said Professor Per Møller from DTU Mechanical Engineering, who is behind the MeGA-StoRE project.