United Kingdom

United Kingdom

Flexible and modular

Regenesys is a reversible fuel cell, although the owner, Innogy, prefers the term "regenerative." The principle is similar to that of a car battery, but on a somewhat larger scale. When the system is charging, electrical energy is converted into chemical energy by transforming two liquid electrolyte solutions. All the energy storage takes place in the two solutions and does not involve the electrodes, as it does in the case of a car battery. Consequently, the electrodes, which are made of carbon fibre material, are very light and can easily be stacked in series to produce the required voltage output.

A typical module comprises 200 electrodes, an output voltage of 300 and an operating temperature range of 20-40 degrees Celsius. The prototype plant at Little Barford Power Station will comprise 120 such modules and will occupy less than 3000 square meters. Output from the device is fed to the electricity network through a sophisticated power conversion system which provides the interface between the alternating current network and the varying direct current voltage from the modules.

The energy storage capacity of the prototype plant is 120 MWh and would normally discharge over a ten hour period, although the maximum rated power output is 15 MW. The predicted lifetime of the plant is at least 15 years and the overall cycle efficiency between 60-65%.

Innogy claims that Regenesys can provide an impressive list of benefits, including: spinning reserve, a function normally associated with hydro or steam plant; power factor control; frequency regulation, meaning it can operate so as to increase its output when the frequency falls and vice-versa; power system stabilisation, meaning it can damp frequency oscillations; black start, meaning it can energise a "dead" system and provide essential power supplies to enable power stations to re-start.

Few of the other storage technologies can provide all these attributes, coupled with both low cost and environmental impact. The most well established technology is pumped hydro, which needs space for two large reservoirs; the technology is not really suited to small-scale applications. Compressed air storage is another possible option, but has made little headway, although there are a few operational schemes. Very large reservoirs are needed as the economics, again, are unfavourable at small sizes. Work continues on flywheel storage, which is more suited to smaller systems but none of these have the flexibility and modularity of the Regenesys system.

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