The Solar Energy Revolution

Nineteen-year-old Edmond Becquerel, working in his father's laboratory, observes that light striking an electrolytic cell generates a small electric current — the photovoltaic effect. The finding had no practical use at the time but laid the physical foundation for all later solar cells.

Location: Paris, France

William Grylls Adams and Richard Day demonstrate that selenium, a solid element, produces electricity when exposed to light — the first photovoltaic effect observed without a liquid. The cells were far too weak to be useful, but they proved sunlight could be converted to power directly.

Location: London, England

Albert Einstein publishes his paper explaining light as quantized packets of energy, solving the photoelectric effect that underlies photovoltaic conversion. The work — not relativity — wins him the 1921 Nobel Prize in Physics.

Location: Bern, Switzerland

Daryl Chapin, Calvin Fuller, and Gerald Pearson demonstrate the first practical silicon solar cell, converting sunlight to electricity at about 6 percent efficiency. The New York Times called it potentially "the beginning of a new era" — though at first the cells were far too expensive for anything but specialty uses.

Location: Murray Hill, New Jersey, USA

The U.S. launches Vanguard 1, the first satellite powered by solar cells, which continue transmitting for years. Space became solar's first reliable market, funding the industry's early decades and driving steady efficiency gains.

Location: Cape Canaveral, Florida, USA

After the 1973 oil embargo exposed import dependence, the United States founds the Solar Energy Research Institute — today the National Renewable Energy Laboratory — and President Carter installs solar water-heating panels on the White House roof in 1979. The panels were removed by the Reagan administration in 1986, an emblem of stop-start policy support.

Location: Golden, Colorado, USA

Japan launches a generous subsidy program for residential rooftop solar systems, creating the world's first mass consumer solar market and making it the decade's largest PV installer. The program demonstrated that solar could be a household product rather than just an industrial or space technology.

Location: Japan

Germany's Renewable Energy Act (EEG) guarantees solar producers above-market rates for decades, creating the first policy-driven mass market for photovoltaics. German demand industrializes global manufacturing and pulls costs down the learning curve; by the 2010s the model is copied in dozens of countries.

Location: Berlin, Germany

China, already the world's largest photovoltaic manufacturer, becomes its largest installer too, as domestic capacity targets absorb its enormous factory output. Combined with economies of scale and improved silicon processing, module prices fall roughly 90 percent over the 2010s, turning solar from a subsidized novelty into a mainstream energy source.

Location: China

195 countries adopt the Paris Agreement, committing to hold warming well below 2 degrees Celsius. Solar deployment becomes the centerpiece of most national decarbonization plans, tying the technology's future to global climate politics — a linkage that would shape trade disputes as well as energy markets.

Location: Paris, France

The International Energy Agency's World Energy Outlook declares solar "the cheapest electricity in history" for sun-rich regions, noting policies more than economics now drive investment. The judgment marked a reversal for an agency long accused of underestimating renewables.

Location: Paris, France

Solar photovoltaics account for roughly three-quarters of all new renewable generating capacity added worldwide in 2023, with annual installations approaching 440 gigawatts — more than the total installed solar base of just four years earlier. Once a physics curiosity, solar had become the largest single source of new electricity generation on the planet.