How Solar Became the Cheapest Light in History

There is a graph that energy economists pass around the way other people pass around holiday photographs. It shows the price of a watt of solar power falling from roughly a hundred dollars in the mid-1970s to a few tens of cents today. The line does not descend gently. It falls off a cliff and keeps finding new cliffs.

What makes the graph remarkable is what is missing from it: the breakthrough. There is no single year in which a laboratory changed everything. Silicon photovoltaics work today essentially as they worked in 1954. What changed was not the physics but the making.

Wright's law, patiently applied

In 1936 an aeronautical engineer named Theodore Wright noticed that every time aircraft production doubled, costs fell by a predictable fraction. Factories learn. Workers waste less. Machines are redesigned around the mistakes of the previous machine. Solar has obeyed Wright's law with almost eerie fidelity for four decades: each doubling of cumulative production has cut prices by about a fifth.

The consequence is that solar's cheapness was, in a sense, purchasable. Early subsidies in Japan and Germany — much mocked at the time — were not really buying panels. They were buying doublings.

“Every roof we paid for in 2005 made every roof in 2025 cheaper,” one veteran of the German programme said. “That was the product. The electricity was a bonus.”

What cheap light changes

When the cheapest electricity in history arrives, it does not politely replace the old kind; it starts changing the shape of the day around it. Industries drift towards noon the way mills once drifted towards rivers. Grid planners, who spent a century managing scarcity in the evening, now also manage abundance at lunchtime.

There are real problems left — storage, minerals, the grim arithmetic of winter at high latitudes. But it is worth pausing on what has already happened, because it is the largest price collapse in the history of energy and it was achieved mostly by people doing the same thing again, slightly better, several billion times.