Over the last decade, there has been a staggering fall in the price of solar and wind power, and of the lithium-ion batteries used to store energy. This has led to rapid expansion of these technologies, even though they are still used much less than fossil fuels: in 2017, for instance, sun and wind produced just 6 percent of the world’s electric supply, but they made up 45 percent of the growth in supply, and the cost of sun and wind power continues to fall by about 20 percent with each doubling of capacity. One analysis suggests that in the next few years, they will represent all the growth. We will then reach peak use of fossil fuels, not because we’re running out of them but because renewables will have become so cheap that anyone needing a new energy supply will likely turn to solar or wind power.