What solar can and cannot do
The match between the two looks neat on paper: a heat pump runs on electricity, and panels make it. The timing is the problem. Heating demand peaks on cold winter evenings, and panels generate most on long summer days. The Energy Saving Trust is direct about this: whatever size system you install, the heat pump is bound to use electricity when your panels are not generating, so you will need the grid to keep warm at those times.
What is possible is a balance over the year. The Trust says it may be possible to fit a solar system that generates as much electricity in a year as the heat pump uses, so total generation matches demand. That depends on your roof size and how much heating your home needs. It also describes the pattern: you sell surplus to the grid on summer days and buy electricity back to run the heat pump at night and in winter. The Trust says the average domestic solar system in the UK is about 3.5 kWp and should generate enough across a year to balance a heat pump’s needs in a typical home, though every home differs.
Where a battery and tariff help
A battery shifts solar from the afternoon to the evening. The Trust says that saves money because you are generally paid less for export than you pay for import. It does not shift summer surplus into winter. In its efficiency tips, the Trust says a battery gives most benefit when combined with a time-of-use tariff, which charges less at certain times, and it describes solar, battery and tariff together as the way to maximise savings.
Tariffs matter even without panels. A heat pump uses a lot of electricity, so the unit price drives the bill; the heat pump tariffs guide explains the types and how to compare them using Ofgem data. If you have solar and a standard tariff, the cheapest-looking choice may change, so check whether a solar export deal or a time-of-use deal suits your pattern.
Running hot water on solar
Space heating is best run steadily, so the flexible load is hot water. The Energy Saving Trust gives a simple order of preference:
- With a time-of-use tariff, set the hot water programme to the cheapest period.
- With solar and a standard tariff, set it for when the panels typically produce most.
- With a standard tariff and no solar, the middle of the afternoon is usually best, when the outdoor air is warmest.
The cylinder’s periodic high-temperature cycle, which the Trust says takes water above 60°C to prevent bacterial growth, should also run in the cheapest or sunniest window. See the cylinder guide for why that cycle exists.
Rough numbers
On the illustrative model used across this site, a home needing 12,000 kWh of heat a year at a seasonal efficiency of 3.0 would use about 4,000 kWh of electricity a year for heating, before hot water losses and anything else in the house. At the Ofgem cap rate of 26.32p/kWh for 1 October to 31 December 2026, each kilowatt-hour you generate and use yourself instead of importing avoids that rate; each kilowatt-hour you export earns an export rate that is usually lower than the import price, so the saving comes mostly from self-use. This is arithmetic from published rates, not a prediction for your roof, and the calculator lets you change the figures.
Heat pump running cost before any solar
No details needed. Change any figure to match your own quote or bills. Results are indicative — an MCS installer’s heat-loss survey and written quote are what count.
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Difference per year at these prices.
Prices: Ofgem cap 1 October to 31 December 2026 — electricity 26.32p/kWh, gas 7.97p/kWh, gas standing charge 29.68p/day (GB average, Direct Debit); heating oil 114.8p/litre including 5% VAT (109.3p before VAT; BoilerJuice UK average for 1,000 litres, read 28 September 2026); 10.35 kWh per litre assumed. No VAT on household electricity from 1 October 2026 to 31 March 2027, which flatters heat pumps in this window. LPG prices vary too much to default — use your own bills. Illustrative, not a quote.
The grant and solar
The Boiler Upgrade Scheme pays for the heat pump: £7,500 for an air source or ground source system, or £9,000 where the home has no mains gas and replaces oil or LPG heating. It is not a grant for solar panels or batteries, and it does not depend on them. Check the band with the eligibility checker and see grant amounts. VAT on heat pump installation is covered on the VAT page; ask the installer for separate lines for each technology if you buy both so the heat pump quote and the grant are clear.
Which first, and who to ask
There is no rule that one must come first. Many households have panels already; for others, the heat pump quote is the moment to ask what the electrical assessment says about the incoming supply. The Catapult trial noted that heat pump installs took longer where solar panels or batteries were already fitted, because the wiring and commissioning took more time, so allow for it. Whichever order you choose, ask the heat pump installer to design the system on heat loss and flow temperature first, and treat solar as a bill-reducer on top of a sound design. The installer guide shows how to compare firms.