Germany utility company E.ON has developed a novel technology that provides a possible answer to a pressing question: what to do with surplus wind-generated electricity when the wind is blowing strongly but demand is low? The answer it has come up with is to use the electricity to produce a flammable gas – hydrogen – that can be fed into the natural gas transmission grid.
Its first such plant – which it describes as a “power-to-gas”, or P2G, unit” – was inaugurated last month in Falkenhagen in eastern Germany, as it began injecting hydrogen into the ONTRAS/VNG high-pressure natural gas system on an industrial scale for the first time.
The plant works by using wind power to run electrolysis equipment that converts water into hydrogen and oxygen. The hydrogen is then injected into the regional gas transmission system, becoming part of the natural gas mix. The unit, which has a capacity of 2 MW, can produce 360 cubic metres/hour of hydrogen.
Managing intermittent power: Unlike most types of energy, electricity is difficult to store in large quantities, so it is generally generated at a rate that just meets demand so that the electricity system stays in balance. As the amount of renewable power increases, the electricity industry is faced with the challenge of how best to manage electricity sources, such as wind and solar power, that are inherently intermittent. P2G is one way of doing that because gas can be stored easily, as linepack in the transmission network or by injection into large gas storage facilities.
“This project makes E.ON one of the first companies to demonstrate that surplus energy can be stored in the gas pipeline system to help balance supply against demand,” said Dr. Ingo Luge, CEO of E.ON Deutschland. “This method of energy storage is considered a key technology for the transformation of Germany’s energy system. It will reduce the need to take wind turbines offline when the local grid is congested and will therefore enable us to harness more wind power.”
E.ON built and is operating the P2G unit in partnership with Swissgas, which will take some of the unit’s hydrogen output.
The inauguration ceremony was attended by around 200 guests, including Dr. Philipp Rösler, Germany’s economics minister, who commented: “One of the biggest challenges of transforming Germany’s energy system is finding ways to integrate the increasing share of intermittent, renewable-source energy. To ensure that Germany’s power system remains stable and that our economy continues to have the energy it needs, we not only have to rapidly expand energy networks. We also need innovative solutions like the P2G unit here in Falkenhagen.”
E.ON built the unit in Falkenhagen because the location is ideal. The region has a high output of wind power, the necessary power and gas infrastructure is already on hand, and E.ON has a control centre there. The region’s wind farms already produce more electricity than the local grid can handle.
Proven technology: The unit uses proven technology. “This,” says E.ON, “makes the project well suited to serve as a platform for gathering technical and regulatory experience in the construction and operation of P2G storage units. This experience will represent an important step toward making P2G technology ready for the mass market.”
There is, however, some way to go before P2G become a large-scale technology, for a number of reasons. One is that the Falkenhagen plant is very small-scale – E.ON describes it as a “pilot plant”. Its 2 MW capacity compares with the 1,000 MW capacity of a typical nuclear or gas-fired power station. Another is that hydrogen can be injected into the gas grid only in low concentrations – up to around 2%, at a maximum pressure of 55 bar(g) – because of gas regulations.
Next step: “To expand the energy storage potential,” says E.ON, “the next step is to convert hydrogen into synthetic gas. Theoretically this means that the entire storage capacity of the gas grid could be utilised.”
E.ON has not disclosed any data on the efficiency or costs of the process, so it remains to be seen how economic it will be. However, the company believes that eventually it will be possible to use P2G technology “economically and on an industrial scale”.
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