One of the most quietly transformative changes in modern technology has been happening for three decades without most people noticing, and the numbers are almost hard to believe. The price of lithium-ion batteries has fallen by 97 percent since 1991. A battery with one kilowatt-hour of capacity that cost 7,500 dollars in 1991 could be purchased for around 181 dollars by 2018, and prices have continued dropping since. To put that in everyday terms: the battery pack alone in a popular electric car model would have cost 300,000 dollars in 1991. Today it costs a few thousand. This kind of price collapse, combined with batteries that are simultaneously getting smaller and lighter, has opened doors that were economically impossible to walk through just a generation ago, from affordable electric vehicles to large-scale grid storage that can hold renewable energy until it is needed.
The pattern behind this decline follows what engineers call a learning curve: for every time the total installed capacity of lithium-ion batteries worldwide doubled, the price dropped by nearly 19 percent. The same pattern held true for solar panels and wind turbines, and the three forces together have quietly rewritten what a clean energy future is allowed to cost. This matters enormously because the biggest obstacle to switching away from fossil fuels was never a shortage of sun or wind: it was the expense of capturing and storing that energy reliably. That obstacle has now been largely removed. Electric vehicles are becoming cost-competitive with traditional cars. Renewable energy now regularly outcompetes coal and gas on price alone. The falling cost of batteries is not a niche story for engineers. It is one of the central reasons that a cleaner world has moved from a distant hope to something that is actively under construction.
