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A slab of silicon that turns daylight — not just sunshine — into current
A panel is a sandwich of silicon cells. Silicon is doped into two layers — one with spare electrons, one with spaces for them — creating a one-way electrical "slope" at the junction. When a photon of light strikes a cell, it knocks an electron loose; the slope sweeps it one way, and billions of these per second add up to a usable DC current. No moving parts, nothing consumed — which is why panels last 25+ years and degrade only ~0.5% annually.
Two honest physics notes: output scales with light *intensity*, so a panel still works on overcast British days (typically 10–25% of rated output), and panels actually perform slightly *better* cold than hot — a crisp bright January day beats a heatwave, watt for watt.
Panels are sold by rated wattage — output under ideal test conditions. The DIY landscape: 5–30W trickle-chargers (keep a battery topped up), 50–100W small-system panels (~£40–80), 150–200W the shed/campervan workhorses (~£75–160), and 400–550W residential-class panels (~£90–200) — astonishing value per watt, but physically large (≈2m × 1.1m) and higher-voltage, so check your controller can accept them.
Monocrystalline (black, ~20–23% efficient) has effectively won over polycrystalline (blue, cheaper, less efficient). Rigid glass panels are durable and cheap per watt; flexible/semi-flexible panels (~2–3× the price per watt) suit curved van roofs but live shorter lives. Used ex-farm panels on eBay can be genuine bargains — degradation is slow.
The panel is your generator — the only part that makes energy rather than moving or storing it. Everything else is sized from it and your loads: panel wattage determines the controller rating, daily harvest, and how fast batteries recover after grey spells. In the UK, you'll oversize panels relative to sunny-country advice, because the system must survive a 0.8-sun-hour December day, not flourish in July.
From EcoPowerful — plain-English DIY solar & wind guidance for UK homes, with a free instant system plan builder. Guidance is general; 230V fixed wiring always needs a qualified electrician. Last updated 2026-06-13.