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Storing offshore wind power

The author writes: For several days now southern Britain has had a great demand for heat and its main airport at Heathrow a demand for light. Yet if the much vaunted Thames Estuary wind farms had been operational they would have contributed nothing to aid this situation. Why? Because as things are at present, wind energy must be used as soon as it is generated. There is no "energy storage" for wind power in the system, as there is in conventional energy generation: the coal bunker, the oil tank, the nuclear hot core, the wood stack. Wind energy systems having no inherent energy storage.

For several days now southern Britain has had a great demand for heat and its main airport at Heathrow a demand for light. Yet if the much vaunted Thames Estuary wind farms had been operational they would have contributed nothing to aid this situation. Why? Because as things are at present, wind energy must be used as soon as it is generated. There is no "energy storage" for wind power in the system, as there is in conventional energy generation: the coal bunker, the oil tank, the nuclear hot core, the wood stack. Wind energy systems having no inherent energy storage.

It seems likely that this lack of wind energy storage had some bearing on the recent widespread blackout in Europe, the necessary backup for a sudden cold, windless "snap" being either too late or insufficient. The Irish in a small way are dealing with the situation with the use of a new type of battery system, the VRB-ESS. But there is another, simpler approach.

For the past decades I have advocated primary wind energy being collected as "random" frequency and voltage to improve energy collection efficiency, with the resulting current stored at very high temperature heat in "Cowper stoves" (blast furnace regenerators) with energy extraction as heat (steam) for combined heat and power generating units. There is often as great an energy demand for plain heating as there is for electricity, if not a greater one.

Alongside the Thames Estuary is the Isle of Grain power station. High temperature heat could be fed into its system, possibly in the "superheat" section, as well as being stored alongside in heat stores of some sort. The possible interference of sudden changes of energy supply from wind farms, which might disturb a grid network, would be eliminated, wind energy collection might be improved, and the problems of maintaining constant frequency and voltage offshore eliminated.

Further, if contra rotation wind turbines were re-developed for offshore wind energy collection, further energy collection efficiency improvements could be anticipated, together with much reduced foundation costs for wind stations, which could be mounted on barges. Discussions have started among German, British and American organisations about a possible program of re-development for the contra rotation concept, based on axial flux alternators.

Just as buildings are kept warm and the lights stay on when a large conventional power plant or interconnector trips out, so they would if wind turbines stopped producing. No grid operator, anywhere, relies on a single power plant or, indeed, on any one generating technology, to meet demand. The output from wind plant, just as for nuclear, is sometimes below the long term average, sometimes above. There is only a minor economic penalty associated with wind's variable supply until it is supplying more than 20% of electricity, or even a good deal more, as our recent close examination of markets with a theoretical high wind penetration revealed (Windpower Monthly, September 2006).

As for storage, it rarely makes economic sense to "level" the output from wind plant. In most cases, the process of storage costs more than any economic gains that might be achieved. Electric utility companies the world over who have studied the impact of wind's variability agree. They have unanimously concluded that wind can be accommodated, without storage, at very modest cost to the system.

Utility investigations of the recent blackout in Europe concluded that wind was not to blame. It was caused by operator error in a control room during a routine power re-routing (Windpower Monthly, December 2006). Lastly, the VRB-ESS project you refer to in Ireland is part of a proposal for a possible wind farm extension and is not an operational system. Furthermore, the economic claims for the device have yet to be proved in practice, as we report in this issue (page 62)

David Milborrow, Windpower Monthly Technical Consultant

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