Currently, Germany stores excess electricity by pumping water uphill into reservoirs. When electricity demand increases, the water is released through turbines to generate hydroelectric power. But there are limits to expanding this type of storage. With 30 pump facilities already in operation, Germany has run out of suitable options to build more.
As a result, one of the country’s main aims is to improve and build more storage systems. The government is currently investing over €1.5-bn each year in energy research and about €200-m is being spent on the development of storage technologies.
Power to Gas Research Project
As recently reported on Engerati’s Power to gas-the new kid on the block? , P2G shows great potential and adoption. The energy storage challenge has led Germany to urgently carry out the next phase of the Energiewende: a power-to-gas research project. The aim of the project is to create a long-term storage system, able to handle a grid consisting of only renewable power. The project is set to begin from January 2014 and is expected to run for two years. Key players include Etogas, juwi technologies, the Centre for Solar Energy and Hydrogen Research or ZSW, the Reiner Lemoine Institute, and RWE Germany.
In order to assess how Power to Gas storage technology handles a 100% renewable energy scenario, a model region has been elected and will be analyzed by a research team. The test facility, located in Morbach im Hunsrück, in Rhineland-Palatinate, will be operating under “real-world” conditions and will provide backup capacity for gas-powered stations.
The aim is for large quantities of renewables-generated power to be stored in a gaseous state for long periods of time. This allows for a quick release when there is sufficient demand. Through this process, the country’s current natural gas network will become the basis for the renewable energy system, providing storage and transport capacities which are not currently available in the power grid.
Germany’s Power to Gas Pilot Plants
There are currently two operational P2G plants in Germany which are designed to store excess electricity, generated by renewable sources. The first, with 250KW of electrolysis stacks, is located in Stuttgart and was inaugurated in 2012. The latest is situated in Werlte-with a capacity of 6MW, it is the largest P2G facility in the world. Both were developed by ZSW and Etogas (formerly Solarfuel).
Several demonstration Power to Gas plants are currently being analyzed for their smart grid potential.
The Niederraussem project
RWE Power began testing a proton exchange membrane (PEM) electrolyzer to store renewable electricity in a facility at its coal innovation centre in Niederaussem. This runs at a normal capacity of 100 kW with a peak capacity of 300 kW for limited periods. The PEM separates the areas in which oxygen and hydrogen emerge with metal electrodes connected to the positive and negative sides at the front and back of the membrane. The membrane manufactured from polymer foil is able to provide ionic conductivity while keeping the oxygen and hydrogen gases separate.
In our recent article, ITM Power reports a fast response time of less than 2 seconds. In this case, response is achieved by combining the properties of the PEM electrolyser with Siemens’ industrial control technology. In the system tests conducted in 2013, the PEM module is being analysed for its behaviour as power is ramped up to assess its performance under various load cycles and to test the quality of the hydrogen produced.
250 kW demonstrator
Pressurized alkaline electrolyzers represent a very mature technology-it is the current standard for large-scale electrolysis. This technology is the core of a P2G demonstration plant which launched in December 2012. The 250 kW plant has been developed by German Center for Solar Energy and Hydrogen Research (ZSW) with partners Fraunhofer IWES and Solarfuel, which plans to commercialize the technology. It expands upon an earlier smaller 25 kW system. The plant is able to produce hydrogen up to 11 bar. The advantage is that it uses a commercially available and proven technology. However, compared to Proton Exchange Electrolysers which uses water as a medium, these plants use potassium hydroxide solution which raises environmental concerns.
Thüga Group - Power to Gas Pilot
This pilot plant is under construction in Frankfurt using ITM Power’s proton exchange membrane technology. The self-pressurising electrolyser from ITM power operates at 80 bar which is well above other systems,. Its key advantage is that it operates at the same pressure as the gas grid . As a result, no additnional energy is required to add the hydrogen. An analysis by Thüga has shown that the storage requirements could be 17 terawatt hours (TWh) in 2020 and could even reach 50 TWh in 2050. They are looking to Power to Gas as the “Battery of the Future”
Applications for hydrogen
Solarfuel is already constructing a 6 MW power-to-gas plant for automaker Audi in Werlte, Lower Saxony. The knowledge gained from ZSW’s 250 kW research plant will be incorporated into Audi’s facility, which should be operational by the end of 2013. Power from four 3.6 MW offshore wind turbines will be used to produce fuel for 1,500 turbo-compressed natural gas (TCNG) Audi A3 vehicles for a year. Audi plans to begin serial production in 2014.
In addition to this, as intoned from the Thüga Group pilot, there is hope that Power to Gas can become the “Battery of the Future” through the utilisation of existing municipal gas distribution networks to store energy from renewable sources. Barriers to this exist, however, in terms of the legal frameworks to run energy storage systems. Germany is currently looking into the framework of a sustainable market model to foster innovation and investment in this technology. In addition, the restrictions on the amount of hydrogen allowed into the gas grid may need to be reviewed - this currently stands at 3% in Germany.
PEM v alkaline
Despite it being a less mature technology, there are several benefits of PEM technology over classical alkaline electrolyser devices. These include the absence of corrosive electrolytes, good chemical and mechanical stability, high protonic conductivity and high gas-impermeability. PEM electrolysers achieve excellent gas separation for high quality hydrogen production and high current density at higher efficiency. The reduced number of moving parts in PEM electrolyser devices also allows for easier maintenance. PEM systems can also achieve an excellent partial-load range and respond rapidly to fluctuating power inputs.
For countries or regions seriously committed to renewable generation, Power to Gas offers a real storage solution. This is provided that the right legal and economic frameworks are in place. The pragmatic German approach will ensure this happens. However, it may be a bigger challenge in other countries. The two large P2G facilities and the growing number of pilots, indicate that Germany is serious about power storage. If Germany reaches its P2G goals, the country will move one step closer to achieving a 100% sustainable energy economy.