Solar PV vs solar thermal in 2026: which still makes sense for UK homes?

The economic shift since 2022

Solar thermal had a meaningful UK market through the 2010s, funded primarily by the Renewable Heat Incentive (RHI) which paid quarterly subsidies per kWh of useful heat output for seven years. The RHI closed to new applicants in March 2022. At the same time, solar PV prices fell ~40% between 2018 and 2024, and the Boiler Upgrade Scheme (BUS) positioned heat pumps + cylinder heating as the decarbonisation pathway. The result: solar thermal’s market shrank from ~10,000 installs/year in 2015 to <500/year by 2024.

The technology still works — solar thermal in mid-summer UK conditions can supply 100% of a household’s hot water for weeks at a time. The problem is that the same roof area used for solar PV delivers more annual cash benefit because the electricity output is fungible (can offset anything), while thermal output is constrained to hot-water demand.

Why solar PV usually wins

Three structural reasons solar PV beats solar thermal on 2026 UK economics:

• Flexibility of output. 1 kWh of PV electricity can run the fridge, charge an EV, power the heat pump, or export to the grid. 1 kWh of solar-thermal heat can only warm your hot water cylinder. Once your cylinder is at temperature, additional thermal output is wasted (the system stops circulating); PV electricity beyond self-consumption gets exported under the Smart Export Guarantee for cash income.
• Coverage of summer demand.A 4 kWp PV system covers most of a UK household’s daytime electricity demand from April through September. Solar thermal covers hot-water heating in the same months but the household doesn’t need MORE hot water in summer — usage is roughly flat year-round, so summer surplus is wasted. The mismatch between thermal output (peaks in summer) and demand (flat) hurts thermal’s effective utilisation.
• Heat-pump compatibility.Solar PV + heat pump is multiplicative: the PV offsets the heat-pump’s electricity bill at no extra fuel cost. Solar thermal + heat pump is duplicative: the heat pump already heats the cylinder via its coil, so the thermal panels displace capability the heat pump already provides. Most modern UK home decarbonisation pathways end up with a heat pump; PV is the natural addition.

When solar thermal still makes sense (rare)

Two narrow scenarios where solar thermal is still defensible in 2026:

• Very high hot-water demand.Large families (5+ residents), households with a home gym + frequent showers/baths, or properties with significant live-in carer arrangements can have hot-water demand 3–4× a typical 3-bed household. Solar thermal’s direct heat-into-cylinder pathway becomes more competitive when the cylinder is being recharged constantly. Even so, PV + larger cylinder + immersion diverter often delivers equivalent benefit with more flexibility.
• Off-grid properties without grid-export option. A few rural UK properties have no grid-export path (typically remote locations with constrained connections). Solar thermal’s output is consumed at source regardless of grid status, which can simplify the off-grid setup. Solar PV with a battery + diverter system covers the same scenario and is the dominant off-grid pathway, but thermal can be a simpler retrofit.

The hybrid approach (PV + cylinder diverter)

A solar-thermal-style outcome can usually be achieved with PV alone using a cylinder diverter: when PV is generating surplus electricity (export-bound), the diverter routes it to the cylinder’s electric immersion element instead. Equivalent to solar-thermal’s hot-water displacement AND retains the option to use PV electricity for anything else when the cylinder is up to temperature.

Diverters cost £200–£500 fitted onto an existing PV system. Most modern UK PV installs include one as standard. This is why “should I add solar thermal?” usually answers itself: the PV system you’re already considering covers the same hot-water capability with more flexibility.

If you’re still considering solar thermal

Three questions worth asking an installer pitching solar thermal in 2026:

1. Why aren’t you proposing solar PV with a cylinder diverter instead?The honest answer should reference your specific hot-water demand or off-grid context. Vague answers about “thermal being more efficient” don’t hold up — PV + diverter delivers equivalent hot-water displacement with more flexibility.
2. What’s the projected payback period? Without RHI, solar thermal payback periods on a typical UK home are 15+ years. If the installer is quoting much shorter payback, ask which assumptions they’re using and how those align with current UK energy prices.
3. How does this interact with future heat-pump plans?If you’re likely to install a heat pump in the next 5–10 years, the solar thermal system may become redundant. Better to plan the heat-pump path first and add PV to support it.

Switching pathway

1. Run a free pre-survey at propertoasty.com/check to confirm your roof’s solar PV potential + indicative system size.
2. Get 2–3 PV quotes from MCS-certified installers. Ask about cylinder diverters as standard inclusion.
3. If your installer is also pitching solar thermal, ask them to quote PV with diverter as an alternative — easier to compare like-for-like.

The takeaway

Solar PV almost always wins on 2026 UK economics. The underlying reason is structural — electricity output is more flexible than heat output, and the PV market has scaled while solar thermal’s subsidy regime closed in 2022. The narrow remaining solar thermal use cases (very high hot-water demand, off-grid simplicity) are real but covered better in most homes by PV with a cylinder diverter at a fraction of the install cost.