How Does Solar PV Actually Work?

The photovoltaic effect

Solar panels are made of semiconductor cells, usually silicon. When light hits a cell, it knocks electrons loose. An internal electric field pushes those electrons into a flow of direct current (DC) electricity. There are no moving parts, no fuel and no combustion — just a physical reaction between light and material.

From DC to AC: the inverter

Homes and businesses in the UK run on alternating current (AC). An inverter converts the DC electricity from the panels into AC that matches the grid. In a grid-connected system, the inverter also synchronises with the mains frequency, so any surplus can be exported safely.

What affects output

• Orientation: in the UK, a south-facing array generally receives the most sunlight over the year.
• Pitch or angle: roofs around 30–40° are often a good compromise between summer and winter performance.
• Shading: even partial shade from chimneys, trees or nearby buildings can reduce output disproportionately.
• Panel efficiency: this is how much of the light that hits a panel is turned into electricity. Higher-efficiency panels produce more in the same space.
• Temperature: panels lose a small amount of efficiency as they get hot, which is why ventilation behind the array matters.

Why solar still works on cloudy days

Panels do not need direct, blue-sky sunlight. They also respond to diffuse light — the scattered illumination you see on overcast days. Output is lower than in bright sun, but it is not zero, and generation continues whenever there is daylight.

On-grid and off-grid

Most UK properties use on-grid solar: the system works alongside the mains supply, importing when generation is low and exporting when it is high. Off-grid systems are standalone and need batteries to cover periods without generation. They are unusual for ordinary homes and require careful design.