Solar Panels & Underfloor Heating: Do They Work Together?

Electric underfloor heating + solar: - Electric UFH uses 100–200W per m² - A 20m² room needs 2–4kW of heating power - Running 8 hours/day in winter: 16–32kWh per room per day - A 4kW solar system generates ~3kWh/day in December - Solar covers only 10–20% of electric UFH demand in winter - Summer: solar covers heating easily (but you do not need heating)

Wet underfloor heating + heat pump + solar: - Heat pump COP of 3–4 means 1kWh electricity = 3–4kWh heat - Same 20m² room needs 2–4kW of heat, but only 0.5–1.3kW of electricity - Running 8 hours/day in winter: 4–10kWh of electricity per room - A 4kW solar system generates ~3kWh in December - Solar covers 30–75% of heat pump electricity for UFH in winter - With a battery + overnight cheap tariff: near-complete coverage

The verdict: Electric UFH is too electricity-hungry for solar alone. Wet UFH with a heat pump is the efficient combination.

Source: UFH manufacturer power consumption data; heat pump COP data.

The optimal combination for solar-powered underfloor heating:

1. Solar panels (5–8kW) — generate electricity year-round 2. Air source heat pump — converts 1kWh electricity into 3–4kWh heat 3. Wet underfloor heating — distributes heat evenly at low temperature (ideal for heat pumps) 4. Hot water cylinder — stores heat for later use 5. Battery (optional) — stores solar for evening heating 6. Smart tariff (Octopus Go) — cheap overnight electricity supplements solar in winter

Why this combination works: - Heat pumps are most efficient at low flow temperatures (30–40°C) - UFH operates at exactly these temperatures (vs radiators which need 55–70°C) - Solar provides free electricity during the day when the heat pump preheats the house - The thermal mass of the floor stores heat — acting like a heat battery - In spring/autumn, solar can cover nearly all heating electricity

Annual heating costs with this setup: - Gas boiler + radiators: £1,400–£1,800/year - Heat pump + UFH (grid only): £600–£900/year - Heat pump + UFH + solar: £300–£600/year - Heat pump + UFH + solar + battery + smart tariff: £150–£400/year

Source: Energy Saving Trust; heat pump performance data.

Underfloor heating's thermal mass (the concrete or screed in the floor) can store heat for hours:

Strategy: - 10am–3pm: Solar is generating strongly. Heat pump runs, warming the floor to 2–3°C above target temperature. - 3pm–10pm: Solar drops off. The heated floor slowly releases stored warmth. No heating needed. - Result: The floor acts as a free heat battery — storing solar energy as warmth.

This works because UFH responds slowly (takes 2–3 hours to heat up, 4–6 hours to cool down). By pre-heating during solar peak hours, you reduce or eliminate evening grid electricity for heating.

Smart thermostats (Nest, Hive, Tado) can automate this — scheduling heating during solar generation hours and letting thermal mass carry through the evening.

Source: UFH thermal mass research; smart thermostat guidance.

If you already have wet UFH + heat pump: Adding solar panels is straightforward — the panels reduce the electricity cost of running the heat pump. - 5kW solar: £6,500–£9,500 - Annual heating electricity saved: £200–£400 - Plus home electricity saved: £500–£700 - Total annual savings: £700–£1,100 - Payback: 7–10 years

If you already have electric UFH: Solar helps but cannot cover winter heating. Options: - Accept partial coverage (10–20% in winter, 100% in summer) - Switch to wet UFH + heat pump (major renovation) - Use solar diverter to pre-heat a buffer tank for UFH (if your system supports it)

If you are building new / major renovation: Install all three together: solar + heat pump + wet UFH. This is the most cost-effective approach — shared installation costs and optimal system design.

Source: Renovation cost estimates; system integration guidance.