Comparisons
Solar thermal vs solar PV: two different technologies
"Solar panels" covers two different technologies that only share a roof: solar thermal, which heats water directly, and solar PV (photovoltaic), which generates electricity. Confusing them muddles every comparison that follows.This guide separates the two and explains why PV has largely won the roof.
Written and edited by Christopher Panteli
Christopher is the founder and editor of MyPlugInSolar. He oversees the site’s research standards, data tools and editorial process. He is not an electrician or solar installer, and specialist technical claims are sourced from official documentation or reviewed by appropriately qualified professionals.
How each one works
A solar thermal system pumps fluid through roof collectors (flat plates or evacuated tubes), where sunlight heats it; the heat transfers to your hot-water cylinder. It's plumbing. A solar PV system converts light directly into electricity via the photovoltaic effect; the power runs anything in the home through an inverter. It's wiring. Thermal is the more efficient collector of raw solar energy per square metre — but everything it collects is locked into one use: hot water.
Why PV came to dominate
The decisive shift: PV panel prices collapsed, and PV electricity can *become* hot water anyway — a solar diverter sends surplus PV power to the immersion heater — while also running everything else. Combi-boiler homes (no cylinder) can't use thermal at all. Thermal still suits some high-hot-water households with cylinders and limited electrical ambitions, but it's now the specialist choice.
| Aspect | Solar thermal | Solar PV |
|---|---|---|
| Output | Hot water only | Electricity — any use |
| Surplus | Wasted once the cylinder is hot | Exported or stored |
| System | Pumps, fluid, plumbing to maintain | No moving parts |
| Requires | A hot-water cylinder | Nothing special |
| Trend | Niche and declining | Dominant and still falling in price |
Where plug-in fits
Plug-in solar is PV at its smallest: one or two panels and a microinverter offsetting your daytime electricity use. There is no plug-in equivalent of solar thermal — thermal needs plumbing into the cylinder by its nature. As throughout this site: plug-in PV is not yet legal to use in the UK, with the Government's consultation response awaited. If you're weighing any solar for your home, start from what you want more of — cheaper electricity (PV) or cheaper hot water from a cylinder you already have (possibly thermal) — and estimate the PV side with the calculator.
Frequently asked questions
- What is the difference between solar thermal and solar PV?
- Solar thermal heats water directly through roof collectors plumbed to a hot-water cylinder. Solar PV generates electricity that can power anything, be exported, or heat water via a diverter. They're different technologies solving different problems.
- Is solar thermal better than solar PV?
- Per square metre, thermal captures more energy — but only as hot water. PV's electricity is far more flexible and panel prices have fallen dramatically, so most UK homes now get more total value from PV (optionally diverting surplus to the immersion). Thermal remains sensible mainly for cylinder-equipped, high-hot-water households.
Sources
- 1. Find ways to save energy in your home — GOV.UK
Estimate your solar potential
See how much electricity a small system could generate at your postcode, and the indicative bill saving.