New flow batteries provide just the right energy storage for intermittent renewables such as solar and wind to guarantee constant supply throughout the grid Prof Peter Saunders
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The art of going electric
Electricity is a very convenient form of energy but it has the big disadvantage that it is hard to store. We cannot pile it into heaps like coal or keep it in tanks like oil or gas. Unless the amount is so small that it can be held in a capacitor (a charge-storage device), we have to turn it into another kind of energy and then back to electricity when we want it. There are a number of ways of doing this, such as turning it into gravitational potential energy by pumping water up hill and then letting it flow back down and drive a turbine when the electricity is needed, but by far the most common is to convert it into electrochemical energy, i.e. to store it in a battery. That works well for many applications, which is why batteries are so common, but not if there is a lot of energy to be stored. Think how large a battery you need to give a car a range of a hundred miles, compared with the much smaller petrol tank that will take it two or three times as far.
There has recently been a lot more interest in whether electricity can be stored efficiently because many countries are planning to generate more of their energy from wind and solar. Neither of these produces energy at a constant rate, still less at a rate that responds to changes in the demand for electricity. That’s not a fatal problem, of course, because there are other sources of energy such as biogas that can be used to fill the gaps. It is, however, still a serious issue, and forecasts of the cost of solar energy have built in the need for backup supplies. The Department of Energy and Climate Change, in predicting that 11.3GW of solar could be available in the UK as early as 2017, explains that that a key limiting factor is that the grid would need a substantial upgrading [1].