Solar Thermal vs Solar PV: Which Wins?
Solar thermal heats water; solar PV makes electricity — two different jobs. But in 2026, a PV system heats your water too, as a free byproduct of powering your whole home. Here’s the honest comparison.
The short answer
Solar thermal and solar PV do different jobs: thermal heats water, PV generates electricity. Thermal is genuinely more efficient at making hot water (converting 70–80% of captured sun to heat, versus PV’s ~20% to electricity) — but that’s the only thing it does. PV’s electricity is far more versatile: it powers your home, charges an EV, stores in a battery, earns export income, and — with a cheap immersion diverter (£200–£400) — heats your water too.
That’s why, in 2026, PV has largely replaced standalone solar thermal for UK homes. A PV-plus-diverter setup delivers thermal’s hot-water benefit as a free byproduct while doing everything else — and the money case sealed it: the RHI subsidy that used to pay for thermal closed in 2022, the Boiler Upgrade Scheme doesn’t cover it, so new thermal must pay for itself on hot-water savings alone (15–25 year payback), while PV keeps 0% VAT and SEG income. Thermal still suits a few homes (very high hot-water demand, tight roofs) — but for most, PV wins. The full comparison below.
What this guide covers
“Solar thermal vs solar PV” is one of the most sensible questions to ask before going solar — and the honest 2026 answer is more clear-cut than it used to be. These are genuinely different technologies solving different problems, but a shift in how PV works (and how it’s subsidised) has changed which one most homes should choose. Here’s the complete, honest comparison.
The core difference: two different jobs
Everything about this comparison flows from one fact: solar thermal makes hot water, solar PV makes electricity. They’re not competing versions of the same thing — they’re two different technologies with different outputs. Solar thermal panels (collectors) capture the sun’s heat and use it to warm the water in your cylinder. Solar PV panels convert the sun’s light into electricity that powers your home. The reason this matters so much is that electricity is far more versatile than heat. Hot water is one useful thing; electricity is many useful things — it runs your appliances, charges an EV or heat pump, stores in a battery, earns you money via export, and can heat your water. Solar thermal can only ever do the single job. Hold that distinction in mind and the rest of the comparison — including why PV has become the default — follows naturally.
How each one works
Solar thermal uses roof-mounted collectors, of which there are two types: flat plate collectors (cheaper, dark rectangles that look like panels, best in direct sun) and evacuated tube collectors (rows of insulated glass tubes, more expensive but better in the diffuse, cloudy light typical of UK weather). A heat-transfer fluid — usually a water-glycol mix — circulates through the collectors, warms up, and passes through a coil inside your hot water cylinder, heating your domestic hot water. A controller runs a small circulation pump (costing just £10–£20 a year in electricity) whenever the collectors are hotter than the cylinder. Note: if you have a combi boiler with no cylinder, you’d need a cylinder added. A thermal system typically provides 50–70% of a home’s annual hot water.
Solar PV works completely differently: the panels use the photovoltaic effect to convert sunlight into direct-current (DC) electricity, an inverter converts it to the alternating current (AC) your home uses, and that electricity powers everything — with any surplus either exported to the grid for payment or, crucially, diverted to heat your water (below).
The efficiency truth (thermal wins one battle)
Thermal is more efficient at hot water — but that’s the only war it wins
You’ll often see solar thermal called “more efficient” than PV, and it’s technically true — for the one job of making hot water. Solar thermal converts roughly 70–80% of captured solar energy directly into heat, while solar PV converts only about 20% of sunlight into electricity. So square-metre for square-metre, thermal is genuinely far more efficient at heating water — a real fact, and the honest answer to “solar thermal efficiency vs PV.” But efficiency at one task isn’t usefulness overall. PV’s 20%-efficient electricity is worth vastly more because you can do so much more with it — power the home, charge an EV, fill a battery, sell to the grid, and heat water. Thermal’s 70–80%-efficient heat can only ever heat water. So read the efficiency figures honestly: thermal wins the narrow efficiency battle but loses the versatility war. A “less efficient” technology that does five useful things beats a “more efficient” one that does exactly one — which is precisely why PV has become the default despite thermal’s superior heat efficiency. Don’t let the headline efficiency stat, true as it is, mislead you about which system is the better buy.
How solar PV now heats your water too
This is the development that changed everything, and the single biggest reason PV has overtaken standalone thermal. An immersion diverter (or “solar power diverter”) — a device costing around £200–£400 fitted to your existing immersion heater — automatically detects when your PV panels are generating more electricity than your home is using, and redirects that surplus to heat your hot water cylinder rather than exporting it to the grid for a few pence. Popular models include the myenergi Eddi. The effect is that your PV system heats your water essentially for free, as a byproduct of generating electricity it was producing anyway — delivering the exact hot-water benefit that used to be solar thermal’s exclusive selling point, while the same panels also power your home and earn export income. It’s genuinely the best of both worlds, and it’s why installers increasingly recommend PV-with-a-diverter over a dedicated thermal system. In effect, PV now does thermal’s job too — which reframes the entire comparison. (A heat pump paired with PV is another highly efficient route to hot water, further reducing the need for standalone thermal.)
Costs — and the subsidy change that sealed it
| Solar thermal | Solar PV (+ diverter) | |
|---|---|---|
| Typical cost | £3,000–£5,000 | £6,000–£8,000 (+£200–£400) |
| What it does | Hot water only | Electricity + hot water + export |
| Government subsidy | None (RHI closed 2022) | 0% VAT + SEG income |
| Hot water provided | 50–70% | Varies (surplus-dependent) |
| Typical payback | 15–25 years | Faster + ongoing income |
Solar thermal has the lower sticker price — £3,000–£5,000 installed, saving roughly £110–£200 a year on hot-water bills. But the decisive financial fact is what happened to subsidies. Thermal used to be paid for through the Renewable Heat Incentive (RHI) — but the RHI closed to new applications in March 2022, and the Boiler Upgrade Scheme does not cover solar thermal. So a new thermal system in 2026 has no government support and must justify itself on hot-water savings alone, stretching payback to 15–25 years. Solar PV, by contrast, keeps 0% VAT until 2027 and earns ongoing Smart Export Guarantee income — a far stronger financial case. So although thermal is cheaper upfront, PV (which does everything thermal does and more) typically delivers the better return. It’s no coincidence that thermal, which peaked around 2021, has since largely fallen out of fashion — around 43,000 UK homes have it, and installations have slowed markedly.
When solar thermal still makes sense
This guide isn’t anti-thermal — it’s a genuinely good technology, and there are specific cases where it still wins. Very high hot-water demand: large families, houses of multiple occupancy, B&Bs and guesthouses with big, constant hot-water loads — here thermal’s superior heat efficiency pays off, because there’s always demand to absorb the heat. Very limited roof space: because thermal is so efficient at heating water, it needs less roof area to meet hot-water needs than PV would need to generate the equivalent via a diverter — so where roof space is tight and hot water is the priority, thermal can be the more space-efficient choice for that one job (our guide to fitting panels to your roof helps you judge available space). Replacing existing thermal: if you already have a working thermal system needing like-for-like repair or replacement, switching technologies may not be worth the disruption. Outside these cases, though, PV’s versatility, better payback, export income and subsidy availability make it the better choice for the large majority of homes.
Frequently asked questions
What’s the difference between solar thermal and solar PV?
Solar thermal makes hot water (it captures the sun’s heat); solar PV makes electricity (it converts sunlight to power). PV’s electricity is far more versatile — it runs your home, charges an EV, stores in a battery, earns export income, and heats water via a diverter. Thermal only heats water.
Is solar thermal more efficient than PV?
Yes, but only at making hot water — it converts 70–80% of captured sun to heat vs PV’s ~20% to electricity. But that’s its only job; PV’s electricity does far more. Thermal wins the narrow efficiency battle but loses the versatility war, which is why PV is the default.
Can solar PV heat my water?
Yes — an immersion diverter (£200–£400, e.g. myenergi Eddi) sends surplus PV electricity to your hot water cylinder instead of exporting it, heating water essentially free. This is the main reason PV has replaced standalone thermal. See our diverter guide.
How much does each cost?
Thermal £3,000–£5,000 (hot water only). PV £6,000–£8,000 for a 4kW system (+£200–£400 diverter) but does everything. Thermal lost its RHI subsidy in 2022 (payback now 15–25 years); PV keeps 0% VAT and earns SEG income — a better return.
When is thermal still better?
Very high hot-water demand (large families, B&Bs), very limited roof space where hot water is the sole priority, or replacing an existing thermal system. Outside these, PV with a diverter wins for most UK homes in 2026.
Which should I get?
For most UK homes, solar PV — it powers everything, earns export income, pairs with batteries/EVs, and heats water via a diverter. Choose thermal only for the high-demand or limited-roof exceptions. PV does thermal’s job plus much more.
PV does thermal’s job — and everything else
The bottom line: Solar thermal heats water more efficiently, but that’s all it does — and in 2026 a solar PV system with a £200–£400 immersion diverter heats your water as a free byproduct while also powering your home, charging EVs, pairing with batteries and earning export income. With thermal’s RHI subsidy gone (and PV keeping 0% VAT and SEG payments), PV also has the better financial case. Thermal still suits very high hot-water demand or very limited roof space — but for the large majority of UK homes, solar PV is the clear winner.
Get my free quotes →The verdict
The “solar thermal vs solar PV” question had a genuinely different answer a decade ago, when thermal was the sensible standalone route to solar hot water. But 2026 has settled it for most homes: PV panel costs collapsed, batteries and diverters arrived, and the RHI subsidy that propped up thermal disappeared — and the result is that a PV system now does thermal’s one job (hot water, via a cheap diverter) as a byproduct of doing everything else. Thermal remains more efficient at heating water in the narrow technical sense, and it still earns its place in high-demand homes and on tight roofs — but versatility, economics and future-proofing have moved the mainstream decisively to PV.
So for the large majority of UK homeowners weighing the two, the honest recommendation is solar PV — ideally with an immersion diverter if hot water matters to you — giving you electricity, export income, battery and EV compatibility, and hot water from a single system. The way to see the real numbers for your home is a couple of free, no-obligation quotes from MCS-certified installers, who can price a PV system (with or without a diverter) and, if your household genuinely has the high hot-water demand that suits thermal, advise honestly on that too.
Important
Going Solar UK is an introduction service, not an installer. This guide is general 2026 information comparing two technologies: costs, savings, efficiency and subsidy availability vary by system, home, roof and household hot-water demand – the figures here are typical estimates, not guarantees. Solar thermal and solar PV suit different needs; always get a professional survey and honest advice for your specific property before deciding. Grant and subsidy rules change; confirm the current position via gov.uk or the Energy Saving Trust.
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