Many promoters of large-scale energy storage argue that the main case for it is to store excess renewable electricity for use during times of undersupply; for instance, when the wind does not blow or the sun fails to shine. The $64 thousand question lies in determining how much actual energy storage capacity is necessary to ensure secure back-up energy supplies.

This choice is both a strategic leadership decision as well as an operational one. Who will be held responsible when renewable energy fails to contribute its share after a long lull or calm spell and the lights go out?

For example, suppose a country had 40 GW of offshore wind that was connected to the National Grid. In addition, this country had 10 GW of grid connected energy storage. The country’s energy leadership would face several questions and decision points.

1.      The first is would it be safe to switch off 10 GW in generating capacity from its existing nuclear, coal and gas power plants?

2.      The second question is how much energy storage would such a country need to ensure security of supply; would it be 10 GW hours (sufficient to cover for lack of wind for one hour), or 480 GW hours (sufficient to cover for no wind for two days).

Currently, for example, the UK has approximately 20 GW hours of energy storage capacity.

It is becoming clear that, given the costs of the technology involved, that it is unlikely that large-scale energy storage, used in conjunction with renewable energy generation assets, can ever meet the base load without significant overbuild of storage capacity to cover the widest statistical possibilities of calm weather.

This means in effect, that the case for large-scale energy storage shifts from that of security of energy supplies to that of energy trading. Large-scale energy storage should be regarded as a method of storing cheaply generated electricity for the purposes of selling such power at a much higher price at peak times. In effect, large-scale energy storage increases the profitability of renewables for investors.

Image of 288 MW Dinorwig plant supplied by First Hydro Company

http://www.fhc.co.uk/dinorwig.htm