For the grid to work, supply must match demand – all the time. “There are already times when we produce so much green electricity, we don’t know what to do with it,” says Hartman. “That can be in the middle of the day when the sun is shining, or in the middle of the night when we are not using so much electricity, but we are producing a lot from wind turbines.” At certain times, energy goes to waste; producers are paid to take capacity offline.
On the other hand, the vagaries of the weather mean generation can fall short of expectations as well. For instance, on rare occasions both Germany and the UK have experienced ‘not much sun’ and ‘not much wind’, so respective energy outputs slumped at the same time. Hence the hive of research activity around energy storage. Behind it is a key idea: if storage can be made cheap enough, dense enough and extensive enough, it becomes viable to operate an energy mix with a much higher percentage of renewables.
This is driving deployment of grid-scale storage; something companies like Tesla, LG Chem and Samsung are anticipating as they construct battery megafactories around the world15 (see Figure 4). Combining renewables with large, preassembled battery units to store excess power, with energy fed back into the grid when demand requires it, has taken off.
The relative attractiveness of this has shifted “seismically” recently, according to energy consultancy Wood MacKenzie.17 Producing energy using solar and wind power already undercuts natural gas on a levelised cost basis (see Figure 5) and recent discoveries suggest further efficiency gains are possible.
Henry Snaith, professor of physics at the University of Oxford, describes solar “being in 1965 in silicon technology terms,” for example, with “lots of room to improve”. (In Search of Wild Solutions has more details.) Now battery costs have fallen rapidly as well, so ‘solar PV + large-scale battery storage’ are cheaper than ‘solar PV + natural gas’ as back-up to meet peak demand.
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