They need to store an order of magnitude more than anything yet seen
By Vaclav Smil
It would be a lot easier to expand our use of solar and wind energy if we had better ways to store the large quantities of electricity we’d need to cover gaps in the flow of that energy.
Even in sunny Los Angeles, a typical house roofed with enough photovoltaic panels to meet its average needs would still face daily shortfalls of up to about 80 percent of the demand in January and daily surpluses of up to 65 percent in May. You can take such a house off the grid only by installing a voluminous and expensive assembly of lithium-ion batteries. But even a small national grid—one handling 10 to 30 gigawatts—could rely entirely on intermittent sources only if it had gigawatt-scale storage capable of working for many hours.
Since 2007, more than half of humanity has lived in urban areas, and by 2050 more than 6.3 billion people will live [PDF] in cities, accounting for two-thirds of the global population, with a rising share in megacities of more than 10 million people. Most of those people will live in high-rises, so there will be only a limited possibility of local generation, but they’ll need an unceasing supply of electricity to power their homes, services, industries, and transportation.
Think about an Asian megacity hit by a typhoon for a day or two. Even if long-distance lines could supply more than half of the city’s temporarily lowered demand, it would still need many gigawatt-hours from storage to tide it over until intermittent generation could be restored (or use fossil fuel backup—the very thing we’re trying to get away from). Li-ion batteries, today’s storage workhorses in both stationary and mobile applications, are quite inadequate to meet those needs. The largest announced storage system, comprising more than 18,000 Li-ion batteries, is being built in Long Beach for Southern California Edison by AES Corp. When it’s completed, in 2021, it will be capable of running at 100 megawatts for 4 hours. But that energy total of 400 megawatt-hours is still two orders of magnitude lower than what a large Asian city would need if deprived of its intermittent supply. For example, just 2 GW for two days comes to 96 gigawatt-hours.
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