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Cruachan - Double or Quits?

The reports that the Scottish Government is encouraging a doubling of the installed generating capacity at the Cruachan pumped storage station in the expectation that this will increase our hydro output does not suggest that Scotland's energy policy is getting back on the rails. There seems to be no limit to the additional burdens the Scottish administration is prepared to load on the electricity consumer while denying him a secure electricity supply.

The point needs to be made that a pumped storage station does not produce energy; it consumes it and over 20% of the energy used in pumping is lost. At Cruachan only a small percentage of the output, of the order of 5%, comes from natural run off from the catchment area. Therefore by putting energy through the pumped storage scheme there is an immediate increase of some 25% in the energy costs. And this is before taking account of the capital costs of building the scheme.

Pumped storage has three possible roles:- ( a) providing  quick response ( a few seconds ) to meet rapid changes in system  demand , (b) using low cost energy for pumping when demand is low at night in order to generate higher value energy when demand is high during the day  and (c) ( to a very limited extent) smoothing out variations in intermittent energy such as wind.

As regards fast response there is already sufficient pumped storage existing and in prospect on the UK system to cater for the sudden loss of the largest generating set and clearly, even with 1000MW of generation capacity, Cruachan could make only a minimal contribution to smoothing the output from the 35,000 MW of  wind generation  proposed by  Government as its target for year 2020. And since low wind output can persist for weeks, any pumped storage station would soon run out of water so additional capacity at Cruachan would not allow any reduction in the amount of thermal back up generation required.  This leaves only (b) as a possible justification.

Cruachan was designed in the 1960's with 400MW (since uprated to 440 MW)  generating capacity with  sufficient water storage to generate at the equivalent of full load for 20hours. This enables it to operate on a weekly cycle, pumping when there is low cost energy available at night and weekends and generating at times of peak loads during the day. The cost of this pumping energy is the marginal fuel and operating costs of base load plant such as Longannet where generation would otherwise have had to be shut down at times of low system loads. And because, when operated in this mode, the output can be relied on, it reduced the amount of other generation required on the system.

Compared with the present  price of  bulk power of £50/MWhr in the electricity market, each MWhr of wind output costs the consumer £100 (£150 for offshore)  and this is before taking into account the costs of additional long distance transmission and of back up thermal plant for when the wind does not blow.  Because of the energy losses, if passed through a pumped storage scheme these costs would increase by at least 25%, so pumped storage output from wind would become prohibitively expensive for consumers.

And with base load generation not being replaced in Scotland, this pumping energy could only be provided by importing from England with the consequent transmission losses. Perhaps  the real reason behind this proposal to increase Cruachan’s capacity, apart from making a minimal contribution to smoothing  variations in wind output, is the prospect of Government  offering  guaranteed high prices for 35 years under the Energy Bill now going thorough Parliament- all to be paid for by the poor electricity consumer.

The Scottish Government (just like the Spanish Government with its concentration on wind power) has reason to be concerned at the way its energy policies are harming the Scottish economy and the electricity consumer, but introducing still further unnecessary costs in a futile attempt to compensate for the weaknesses in its energy policy is certainly not the answer. The urgent requirement now is to plan for new base load generating plant to replace existing plant as it approaches the end of its useful life.


Sir Donald Miller FREng, FRSE.

Chief Engineer  Hydroboard 1966-74.  Chairman Scottish Power 1982-92.

Scientific Alliance Scotland

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