How much hot water can solar thermal provide?

A well-sized solar thermal system typically provides 50-70% of a household's annual hot water demand. In summer it can provide close to 100%, while in winter it may only pre-heat the water. The annual solar fraction depends on collector size, orientation and household demand.

Flat plate vs evacuated tube collectors?

Flat plate collectors are cheaper, more durable and integrate well with roofs. Evacuated tubes perform slightly better in cold/overcast conditions and produce more per m², but cost more and can be fragile. For most UK domestic installations, flat plates are the best value.

How much does solar thermal cost in the UK?

A typical domestic solar thermal system costs £3,500-£5,500 including collector panel, twin-coil cylinder, controls and installation. Evacuated tube systems cost 10-20% more than flat plate. A new twin-coil cylinder adds £500-£800 if not included.

What cylinder do I need for solar thermal?

Solar thermal requires a twin-coil cylinder (or a thermal store) with a dedicated solar coil. Size should be approximately 50 litres per person, minimum 150 litres. The solar coil must be at the bottom of the cylinder with the boiler coil above. Unvented cylinders are preferred.

Is solar thermal worth it compared to solar PV?

Solar PV is generally considered better value now because surplus electricity can be exported (SEG payments), used for other appliances, or stored in batteries. Solar thermal only heats water. However, solar thermal produces more energy per m² of roof and is efficient for homes with high hot water demand.

TradeCalculator.co.uk

Solar Thermal Calculator

Size a solar thermal hot water system for your household. Calculate collector area, annual yield, solar fraction and financial savings versus gas, oil or electric heating.

Collector TypeFlat plate is the standard choice

UK RegionAffects annual solar yield

Household Size

Number of occupants

System Price

Supply and install (excl. cylinder)

Existing FuelFuel being displaced

How We Calculate This

This calculator sizes solar thermal systems based on household demand and UK regional yield.

The formula

Collector area = Household size × Area per person (0.9-1.2 m²)

Flat plate yield: 400-500 kWh/m²/year
Evacuated tube: 500-600 kWh/m²/year
Cylinder: 50 litres per person (min 150L)
Solar fraction: typically 50-70% of annual hot water

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.