What is the difference between solar PV and solar thermal panels?

Because both sit on the roof and both are called 'solar', the two are often confused. They work on entirely different principles and produce entirely different outputs — this page makes the distinction clear.

How each technology works

The two systems share a roof location but nothing else about how they operate:

• Solar PV uses semiconductor cells, usually silicon, to convert light into a flow of electrons — direct-current electricity. An inverter then converts that to the alternating current your home uses. The electricity can power appliances immediately, charge a battery, or flow to the grid.
• Solar thermal uses collectors — either flat plates or evacuated tubes — to absorb the sun's heat. A fluid circulates through the collector, picks up that heat and transfers it via a coil into a hot-water cylinder. There is no electricity involved in the output; the product is hot water.

This is the core distinction: PV makes electricity you can use for anything, while thermal makes hot water and nothing else. The hardware behind them, and what each connects to inside the home, is completely different.

The visible difference on the roof is smaller than you might expect — both look broadly like flat dark panels from the street, and evacuated-tube thermal collectors are the main giveaway, with their distinctive row of glass tubes. What sets them apart is entirely on the inside: a PV system runs cables down to an inverter and your consumer unit, whereas a thermal system runs insulated pipework carrying fluid down to a coil in your hot-water cylinder, driven by a small circulating pump. Knowing which you are looking at, or being quoted for, comes down to asking the simple question of whether the output is electricity or hot water.

The reason the two are so often muddled is partly historical and partly linguistic: both arrived on UK roofs as 'solar panels', and for a time solar thermal was the more familiar of the pair, before PV prices fell and electricity generation became the mainstream choice. Today, when most people say 'solar panels' they mean PV, but the older thermal systems are still out there and still being fitted, so the ambiguity persists. The practical consequence is that anyone researching solar should pin down which technology a guide, quote or installer is talking about, because almost every downstream question — cost, payback, export payments, battery compatibility — depends entirely on that first distinction.

What each one can power

Because electricity is so flexible, solar PV is the more versatile of the two. The electricity it generates can run lights, appliances, an immersion heater (so PV can heat water too, indirectly), an electric vehicle charger, or be stored in a battery. Any surplus can be exported to the grid and paid for under the Smart Export Guarantee.

Solar thermal is more specialised. It is efficient at the single job it does — heating water — and can supply a large share of a household's hot water over the year, more in summer than winter. But it cannot run appliances, charge a car or earn an export payment, and it needs a hot-water cylinder, so it does not suit homes with a combi boiler and no cylinder.

Comparison for guidance only. Source: Energy Saving Trust.

Which suits a UK home?

For most UK households, solar PV is the more useful technology because electricity can be put to so many uses and surplus can be exported for payment. It is also the more widely installed, so installers, inverters and batteries for PV are easy to source.

Solar thermal makes most sense for homes with consistently high hot-water demand — a larger household, for example — and an existing or new hot-water cylinder to store the heat. Some homeowners weigh the two and conclude that PV with a solar diverter gives them most of the hot-water benefit of thermal while also generating electricity, which is why standalone solar thermal has become less common on UK rooftops than it once was. The decision ultimately rests on what you most want from your roof: electricity for the whole home, or dedicated hot water.

Roof space, efficiency and lifespan

A few practical points often decide between the two beyond their basic outputs. Roof space is shared: each technology needs its own area, so on a typical roof you usually choose one rather than both. Efficiency at the task differs in kind — solar thermal converts a high proportion of the sun's heat it captures into hot water, while PV converts a smaller share of light into electricity but produces a far more flexible output, so the two figures are not directly comparable.

On seasonal pattern, both produce most in summer and least in winter, following UK daylight and sun height. Solar thermal can supply a large share of summer hot water but contributes much less in the depths of winter, when a boiler or immersion makes up the difference; PV similarly generates strongly in summer and modestly in winter. In terms of lifespan and upkeep, both are durable roof technologies with no major moving parts on the collector or panel itself, though solar thermal systems include a pump and fluid that need occasional checks, and PV has an inverter that is typically replaced after around 10 to 15 years. None of this changes the headline: PV makes electricity for the whole home, thermal makes hot water, and most UK homeowners pick PV — increasingly with a diverter — for its versatility.

Frequently asked questions

Sources & further reading

• Energy Saving Trust — Solar water heating
• Energy Saving Trust — Solar panels (PV)

Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.