The Danish firm behind the initiative is Eltra, the Independent System Operator of the electricity grid for the Jutland peninsula and island of Funen. The project involves the fifth generation of a technology -- in essence an enormous fuel cell -- developed by Britain's National Power. Dubbed Regenesys, it is destined for a site at Vester Hassing. Here it will store power from the Laesø offshore wind plant from 2004 or 2005.
Eltra's involvement in Regenesys attracted attention last year when an EC grant was approved to support the Danish research. Project leader at Eltra, Kent Søbrink, says National Power would not accept the loan because it would have to publish details of how the system works. Instead the company has formed a subsidiary bearing the same name as the storage facility, Regenesys, to market the technology.
"What is new about National Power's invention is that it is a further development of known chemical processes, involves simple chemicals and is characterised by simplicity, also if it is greatly upscaled. Last but not least it is rechargeable," says Søbrink. "It's right that it's been possible to store electricity in very large batteries, but it hasn't been economically realistic. It looks as if this facility will be. The Danish project's start point is to research its economic viability compared with, for example, buying electricity on an electricity exchange."
Wind power cannot be controlled so that it matches demand at all times and the alternative to storage is making up shortfalls from offshore plant through the Nordic power exchange. Regenesys will store electricity in two tanks with electrolytes of dissolved salt. These will be pumped through fuel cells where they will be charged or discharged as a result of the chemical reaction between the two. A converter changes direct current to alternating current as electricity is drawn from the facility, or from AC to DC when electricity is sent via the fuel cells for storage within the system. A transformer ensures the AC current matches the grid voltage.
Søbrink says Regeneys is particularly suited to wind plant because it can store electricity for a few hours or days. Its capacity can be increased by expanding the tanks.
National Power is keeping quite about the price of Regenesys, but Eltra director Georg Styrbro has previously said that a 200 MWh storage facility will cost about DKK 130 million (EUR 40.2 million). Detailed information is not available about how it functions or about the two-way electronic process that makes it rechargeable. The system has an effectivity of 70-75% with losses of 35-30%, says National Power. During the past three to four years, three smaller tests of Regenesys have been undertaken in Wales. This month an announcement is due on a fourth and larger test facility. Preliminary research in preparation for the Danish project is also to start in the autumn, says Søbrink. Information about the application side of the project will be publicly available.