In 1956, solar power was priced at about $1,865 per watt and survived largely because spacecraft needed lightweight power. Decades later, prices fell below 50 cents per watt and solar became the cheapest new electricity

In 1956, one watt of usable solar photovoltaic capacity was an astonishingly expensive thing. Adjusted for inflation into 2019 dollars, the often-cited figure is about $1,865 per watt. A modern 400-watt module would therefore represent roughly $746,000 of capacity at that historical price. Yet today, solar modules can sell for a tiny fraction of a dollar per watt. The more surprising part is not simply that panels became cheaper. It is that an invention once practical mainly for spacecraft became one of the cheapest ways ever devised to produce electricity.

That transformation is easy to underestimate because the numbers describe different stages of the technology. The $1,865 figure refers to photovoltaic capacity in the early era of solar cells, expressed in inflation-adjusted dollars.