In 1873 Willoughby Smith (pictured) found that electricity travels through selenium when placed in light (photoconductivity). In 1877 William Adams and Richard Day discovered that sunlight actually generates electricity in selenium. In 1883 Charles Fritts made the first primitive PV cell, mounting selenium on a metal plate and coated in gold.

 

Further progress halted for a half-century as coal, oil and gas were plentiful and far better for generating electricity. In 1954 Calvin Fuller and Gerald Pearson made a PV cell with silicon, which proved 50 times more effective than selenium. In 1958 the US satellite Vanguard I was first to carry a solar–powered transmitter.

But PV was still too expensive for use on Earth: even by 1971 the price of PV power was 200 times that of standard electricity. But, as oil prices multiplied 25 times over the next decade, PV research intensified. Since the mid-1990s progress has accelerated massively, with PV cells becoming ever-cheaper and more productive. Nowadays we are using two ways to derive electricity from the sun: either huge 'solar farms' supplying towns or urban areas; or domestic systems installed in individual homes for private supply.