A BATTERY of 1MWh connected to Hywind's 30 MW of offshore wind turbinesdoes not represent a landmark in making wind generation reliable. These two numbers tell the whole story. The turbines can produce 30 MWh of electricity in one hour. The battery will store 1MWh, a mere two minutes of the turbines' maximum output.
The real wind intermittency issue is when there are several days of low, sometimes near zero wind generation. As I write this on 28th June 2018 we have had five days in which Britain's wind generation has seldom reached 10% of its nominal capacity and for much of the time has been between 1% and 2%. No likely reduction in battery costs would make storage over this sort of time remotely affordable.
The best that battery storage is likely to provide is a supplement to STOR - Short Term Operational Reserve, the National Grid's emergency generation which is kept available to meet sudden increases in demand or loss of supply. This is currently mostly met by diesel generators. The much publicised Tesla battery installation in South Australia is essentially for this purpose. The costs of this to the Grid, and thus to consumers are significant. STOR providers are paid to keep capacity available even if it is not used and when it is they can receive four or five times the normal wholesale price. The developer of a solar plus battery installation in the UK has stated that this is how he expects to make it pay.
It is possible that in time battery storage could become competitive with pumped storage, currently the only way of storing relatively large amounts of electricity. The key word however is 'relatively'; our four existing pumped storage sites can provide only about 45 minutes of average UK demand. Furthermore, they were built for a very specific purpose, to complement nuclear generation. Nuclear reactors cannot be turned up when demand is high and down when it falls. (They can be turned off rapidly in an emergency but then take several days to restart.) So at night when demand drops, low cost nuclear electricity can be used to pump water to an upper reservoir, and at peak evening demand time it can be released through turbines and sold at a higher price. The operators will thus receive a regular income from selling electricity every day.
However, the situation with wind is quite different. The recent five day wind lull was preceded by about a week of high winds when a storage facility, after being charged, would sit idle and unprofitable. Wind highs and lows are irregular and unpredictable. It is noticeable that although a number of new pumped storage developments have been proposed in Britain, none have in fact been built. And in Germany, with a huge amount of wind and solar power, pumped storage plants are losing money and having their operation cut back. The capital cost of any known storage technology to cover several days demand in an electricity system based primarily on wind power would be astronomical and could be recovered only by astronomical prices to consumers.
There is a place for battery storage as and when its price is right. STOR needs to kick in fast, for which batteries are ideal, but may only be required for a short time. In tropical countries, or in Britain in summer, solar panels could generate enough to store for use overnight. However in December and January here solar panels will produce less than 2% of their nominal output, insufficient to meet daytime needs, let alone enough to store for use after dark.
Jack Ponton is an Emeritus Professor of Engineering, a Fellow of the Royal Academy of Engineering and the Institution of Chemical Engineers.