The History of Solar PV: From 1839 Discovery to UK’s 21.5 GW Network 

In 1839, French physicist Edmond Becquerel discovered the photovoltaic effect, observing that certain materials, such as silver chloride in an acidic solution connected to platinum electrodes, generated a small electric current when exposed to light. This marked the first observation of light directly producing electricity in a solid-state setup. However, the voltages and currents were minuscule, with efficiencies far below 0.1 per cent, making it impractical for meaningful power generation and limiting it to laboratory demonstrations.

In 1873, Willoughby Smith identified the photoconductivity of selenium, showing it became more conductive under light. This led to William Grylls Adams and Richard Evans Day’s 1876 experiments, where selenium bars produced electricity directly from sunlight without heat or mechanical parts. By 1883, Charles Fritts had built the first solid-state photovoltaic cell using a selenium layer coated with gold, achieving around 1 per cent efficiency and demonstrating a workable, if rudimentary, device. 

Developed by Daryl Chapin, Calvin Fuller, and Gerald Pearson at Bell Labs, the silicon cell achieved 6 per cent efficiency, far surpassing earlier selenium devices, and reliably powered small loads such as a toy Ferris wheel and a radio transmitter. Silicon’s abundance, stability, and compatibility with semiconductor manufacturing enabled scalable production, shifting photovoltaic technology from niche experiments to a technology with genuine commercial potential.

Launched in 1958, Vanguard I was the first satellite to use solar cells for primary power, operating reliably for over six years despite the harsh space environment. This demonstrated PV’s durability and low maintenance, spurring US government and industry investment in space-qualified cells. The resulting improvements in efficiency, radiation resistance and manufacturing laid the foundation for terrestrial applications.

The 1973 and 1979 oil crises prompted governments and energy firms to fund photovoltaic research and development as an alternative to fossil fuels, with the United States allocating billions to research. Efficiency doubled through advances in silicon processing, while industrial efforts led by companies such as Exxon and Mobil improved crystal growth, doping, and module assembly. These changes reduced costs from over $100 per watt in the early 1970s to around $10 by the end of the decade, making solar cells more manufacturable.

Named after SunPower founder Richard Swanson, Swanson’s Law observes that solar PV module prices fall by about 20 per cent for every doubling of cumulative global production volume. This learning curve effect stems from manufacturing efficiencies, including automation, larger wafers, thinner cells, supply chain optimisation, and ongoing process refinements. Over several decades, production scaling from megawatts in the 1970s to terawatts today has driven prices down by a factor of more than 500.

Introduced in April 2010, the Feed-in Tariff offered generous fixed payments of up to 41p per kWh for generated electricity, spurring a boom that installed over 800,000 systems by 2015 and grew the UK solar fleet from near zero to gigawatt scale. Degressions and caps, driven by scheme costs exceeding budgets, halved rates in 2011–12, causing a bust as installations plummeted and the supply chain contracted. This cycle highlighted the need for predictable policy to sustain deployment.

The Feed-in Tariff closed to new applicants in 2019 and was replaced by the Smart Export Guarantee in 2020, which pays only for exported electricity at market-driven rates, typically 5 to 20 pence per kWh depending on the supplier, rather than providing a fixed generation tariff. Without subsidies for self-generated power, the economics now depend on maximising on-site consumption, often through the use of batteries, to offset electricity bills. This makes photovoltaic systems more viable for households with high daytime demand but less attractive for those relying primarily on export income.

The 21.5 GW figure, as of late 2025, represents the UK’s total installed solar PV capacity and generates around 20 TWh annually, which is enough to meet the electricity needs of over 6 million homes under typical UK conditions with a capacity factor of about 10 to 11 per cent. Capacity is split at roughly 42 per cent rooftop, including domestic and commercial systems, and 58 per cent ground-mounted installations, with the latter dominated by large utility-scale solar farms connected to the grid.

PV’s evolution from early low-power cells to grid-scale arrays underscores the critical need for safe DC to AC integration, with inverters handling high-voltage DC arrays feeding the AC network. BS 7671 Section 712 sets requirements for PV-specific earthing, protection and array wiring to mitigate risks like arc faults, while MCS certification ensures installers meet these standards for consumer protection and scheme eligibility. Understanding this history reinforces why rigorous, standards-driven practice is essential for reliable, compliant UK installations.