Why this combination works so well
Three separate technologies each have their own merits in isolation. But the reason the Agile-plus-heat-pump-plus-solar combination outperforms any single technology is that each one compensates for the weaknesses of the others.
Solar generation peaks in the middle of the day, in spring and autumn, when outdoor temperatures are moderate and the heat pump is most efficient. Agile provides cheap overnight electricity for the heating demand that solar cannot cover in winter or at night. The heat pump multiplies every unit of cheap electricity into three to four units of heat, amplifying the value of both solar and Agile electricity more than any resistive heating system can.
The synergies are multiplicative, not additive. A household with all three technologies does not simply add up three separate savings. It benefits from interactions that individually would not be possible. A heat pump running on free solar electricity delivers heating at effectively zero cost. A battery charged at negative Agile pricing runs the heat pump during morning peak hours at a negative fuel cost. These are not edge cases. They happen regularly across the UK.
Heat pump: the electricity-to-heat efficiency multiplier
A gas boiler converts one unit of gas energy into approximately 0.9 units of heat, an efficiency of around 90%. A heat pump converts one unit of electricity into three to four units of heat by moving heat from the outdoor air rather than generating it. This is the coefficient of performance, or CoP.
At a CoP of 3.5 and an Agile overnight rate of 4p per kWh, the effective cost of delivering one unit of heat is 4p divided by 3.5, roughly 1.1p per kWh of heat delivered. Gas costs approximately 6.24p per kWh, delivering 0.9 kWh of heat at an effective cost of 6.9p per kWh of heat.
Even at the standard electricity price cap of 26.11p, the heat pump delivers heat at around 7.5p per unit at a CoP of 3.5, competitive with gas. At overnight Agile rates of 3-4p, it is the cheapest form of heating available anywhere in the country.
Modern air source heat pumps from manufacturers such as Mitsubishi, Vaillant, Daikin, and Samsung maintain strong CoP figures in UK winter temperatures. A well-sized heat pump in a well-insulated home will achieve CoP of 3 or above even on cold nights.
Solar: covering daytime heat pump operation
The most expensive period for heating in the UK is not winter nights. It is the shoulder seasons, when heating demand is moderate and gas or electricity costs for top-up heat add up steadily across October to April.
In spring and autumn, solar generation aligns almost perfectly with this moderate heating demand. A 3.5 kWp system generates 6-14 kWh on a typical spring day. A heat pump in mild weather may need 3-5 kWh of electricity to provide comfortable heating. The solar fully covers daytime heat pump operation with surplus left over.
In winter, shorter days and higher heating demand mean solar can supply perhaps 20-30% of heat pump electricity in December and January. But the combination of solar-generated electricity plus cheap Agile overnight rates means the average cost per unit of heating electricity across the full year falls sharply.
Running a heat pump on solar electricity costs, in practical terms, nothing. The marginal cost of that solar generation is zero once the panels are installed. Every hour of solar-powered heat pump operation is an hour that does not draw on the grid.
Agile: covering overnight heating and hot water
Heat pumps can and should run at night. In mild weather, their CoP remains high. The strategy used by experienced Agile-plus-heat-pump households is called pre-heating: warming the thermal mass of the building overnight using cheap Agile electricity, so that the heat released through the morning requires little or no additional input.
A four-bedroom house with reasonable insulation (EPC band C or above) retains heat well enough that pre-heating to 20-21 degrees at 2am keeps the house comfortable until 9-10am with minimal top-up. At Agile prices of 3p overnight, the entire heating cycle costs roughly £0.30-0.50 in electricity.
Hot water is similarly valuable. A 200-litre cylinder heated by the heat pump during the 1am-4am Agile window costs around £0.15-0.25. The same cylinder heated at peak time would cost £0.80-1.00. Checking tonight's prices on AgileAlert takes 30 seconds and guides the precise timing of this overnight hot water cycle.
Homes with a smart thermostat, such as Nest, Hive, or tado, can link the heat pump schedule to Agile price data via Home Assistant, automating the overnight pre-heat without any daily manual input.
The annual bill: a realistic worked example
Consider a four-bedroom semi-detached house in England, EPC band C, with a family of four:
| System | Annual energy bill |
|---|---|
| Gas boiler + standard electricity tariff | £2,400-2,800 |
| Heat pump only (standard electricity tariff) | £1,600-2,000 |
| Heat pump + Octopus Agile (no solar) | £900-1,300 |
| Heat pump + solar 3.5 kWp (no Agile) | £1,000-1,400 |
| Heat pump + solar + Agile (no battery) | £400-700 |
| Heat pump + solar + Agile + 10 kWh battery | £200-500 |
The full triple-win system delivers annual electricity bills of £200-500 for a home that previously spent £2,400-2,800 per year on gas and electricity combined. The saving is £1,700-2,300 per year, every year, for the life of the equipment.
These are not theoretical figures. They reflect actual data from households that have shared consumption statistics in the Octopus Energy community forums and Home Assistant user groups. The numbers are attainable for any home with reasonable insulation that makes this investment.
What this system costs to set up and what grants are available
The upfront cost is the obvious challenge. Here is a realistic breakdown for a UK installation in 2026:
| Component | Installed cost | Grant available | Net cost |
|---|---|---|---|
| Air source heat pump (ASHP) | £8,000-15,000 | BUS grant: £7,500 | £500-7,500 |
| Solar panels 3.5 kWp | £6,000-8,000 | None in 2026 | £6,000-8,000 |
| Home battery 10 kWh | £8,000-12,000 | None in 2026 | £8,000-12,000 |
| Total system | £22,000-35,000 | £7,500 | £15,000-28,000 |
The Boiler Upgrade Scheme grant of £7,500 for air source heat pumps reduces the heat pump cost substantially. With this grant, a competitively priced heat pump installation can cost as little as £500-2,000 net. The solar and battery elements receive no grant in 2026, though VAT is zero-rated on both.
Annual savings of £2,000+ against a net system cost of £15,000-28,000 gives a payback of 8-14 years. For households at the lower end of the installation cost range, 8-10 year payback is achievable. Given the 25-year lifespan of solar panels and heat pumps, the investment case is strong.
Carbon impact: near-zero heating from near-zero-carbon electricity
The financial case is compelling. The environmental case is even cleaner.
A heat pump running on overnight Agile electricity is predominantly powered by UK wind generation. Overnight grid carbon intensity regularly falls to 50-100g CO2 per kWh during periods of high wind output, the same periods when Agile prices are cheapest. A heat pump with a CoP of 3.5 running on 80g/kWh electricity delivers heat at an effective carbon intensity of 23g per kWh of heat. That is 97% cleaner than a gas boiler.
A typical UK gas boiler produces approximately 2 tonnes of CO2 per year for home heating. The full triple-win system reduces that to approximately 100-200 kg per year, a reduction of roughly 1.8 tonnes annually. Across 20 years of operation, that is 36 tonnes of CO2 avoided from a single household.
There is no single home energy investment available in the UK today that delivers a larger carbon reduction. The money saving and the planet saving are aligned. That is genuinely rare.