An electrolysis cell uses electricity to split, e.g., water molecules (H2O) into hydrogen (H2) and oxygen (O2). In this way, surplus electricity generated by, e.g., wind turbines can be transformed into chemically bound energy in the hydrogen molecules and stored as a gas for later use.
In the research project “Towards Solid Oxide Electrolysis Plants in 2020”, funded by the Danish transmission system operator energinet.dk, DTU Energy joined forces with the company Haldor Topsoe A/S, DTU Electrical Engineering and Aalborg University to test state-of-the-art cell and stack designs in a “close-to-lifelike” simulation based on very detailed wind data from a wind farm on the Danish island of Bornholm in the Baltic Sea.
“We always talk about the benefits of electrolysis cells to convert surplus energy from renewable energy sources like wind turbines into gas, and now we did so in a real state-of-the-art stack”, says Ming Chen, senior researcher at DTU Energy.
The Bornholm distribution system is part of the Nordic interconnected system and fully integrated in the power market “DK2” and it is connected to the Sweden main grid via a sea cable. The system comprises about 28,000 electricity customers (55 MW peak load) and has very high penetration of a variety of low-carbon energy resources, including wind power from four windmill farms totaling 38 windmills = approx. 30 MW. The project used data based on the wind profile from one of the four wind farms.
Ming Chen, senior researcher, DTU Energy
“We had all wind data from 2013 from that wind farm, broken down in five-minute resolutions. This gave us opportunity to create some very accurate simulations on our cells and stacks based on realistic data”, explains senior researcher Ming Chen. “It was just like the real world, except that we scaled the wind data down by a factor of 1000 to allow us to test a single stack instead of an entire facility.”
The project team created two different test scenarios based on wind data from December 2013 as December has lots of wind fluctuations and these fluctuations are very hard on the cells and stacks. This gave the researchers the possibility to test a 7.5 kW stack under the harshest working environment possible.
The first scenario simulated steady state constant flow of gas, while the second simulated variable flow according to the needs. In total the 7.5 kW electrolysis cell stack was tested for 2000 hours. In both cases the stack behaved the same and was able to handle the variations.
“We have now successfully demonstrated that the state-of-the-art cell and stack designs are robust and that they can handle dynamic operation under fluctuating steam supply and/or power load”, says Principal Scientist at Haldor Topsoe, Peter Blennow. “We still have to test them under real conditions in full scale, where other variables will influence the results, but we have proven that the technology works and is robust.”
Senior researcher at DTU Energy, Ming Chen, agrees. “The cells and stack did well under harsh conditions in both scenarios. This bodes well for using the electrolysis cells and stacks for energy storage in full-scale plants.”
The researchers of DTU Energy now work on further improving the electrolysis cells.
Facts on electrolysis cells
Solid Oxide Electrolysis Cell’s (SOEC’s) and SOEC-stacks uses electricity to split, e.g., water molecules (H2O) from steam into hydrogen (H2) and oxygen (O2) and in this way transform electrical energy into chemically bound energy in the hydrogen molecules. The same cell-technology can be used to produce carbon monoxide (CO) from CO2 and a combination of H2 and CO when both CO2 and H2O are supplied to the cells/stacks. H2 and CO have many uses in the chemical industry and can be made into green fuels.
A Solid Oxide Electrolysis Cell (SOEC) is basically the corresponding fuel cell (Solid Oxide Fuel Cell – SOFC) run in ‘reverse’. Such a cell operates at relatively high temperatures (700-1000 °C), which makes the efficiency very high. The electrolysis products, carbon monoxide/hydrogen and oxygen, are formed on each side of the cell. SOECs may be used for the production of H2 and CO from surplus electricity generated by, e.g., wind turbines. The H2 and CO can be stored and – using a fuel cell – reconverted into electricity again when the demand arises. This allows the storage of electricity when production exceeds demand.
The SOEC/SOFC technologies are proven technologies and Haldor Topsoe already offers several commercial products for converting CO2 to CO with high efficiency. These technologies make it possible to produce green chemicals and fuels in the future.
Source : Technical University of Denmark