Free Eco Home Calculators

Energy Mix Planner

1 min read Last updated 20 May 2026
Quick answer For a typical 3-bed semi spending £15,000, a balanced mix is: 4 kWp solar PV (£4,400), 5 kWh battery (£2,500), insulation top-up (£3,000), and an air source heat pump (£12,000 less £7,500 grant = £4,500). Total £14,400, saving £900-£1,400 a year.

The Renewable Energy Mix Planner suggests the optimal combination of solar PV, battery storage, heat pump and insulation for your home given your budget, roof space and current consumption. It applies grants where eligible (BUS for heat pumps), prioritises insulation first (it always pays back fastest), and gives a total investment, total annual saving, payback per technology and combined CO2 reduction.

Renewable Energy Mix Planner

Plan the optimal combination of renewable technologies for your home.

UK average is ~3,100 kWh. Check your annual bill.
UK average is ~12,000 kWh. Enter 0 if you have no gas.
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See 20 real-world examples

Each link below runs this calculator with real UK city and property inputs and publishes the exact computed savings, payback time, install cost and CO2 figures.

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How this calculator works

We model technologies in efficiency-first order: insulation always comes first (best ROI), then solar PV (no fuel cost), then battery (improves solar self-use), then heat pump (replaces gas). Each step checks against remaining budget. Solar size is roof-area / 6 m² per kWp, capped at 8 kWp. Battery is sized to ~50% of typical daily import. Heat pump sizing uses gas-demand / 2,500 to estimate kW. BUS grant of £7,500 applies to heat pumps where homeowner-occupier or landlord.

Sources & references

Frequently asked questions

Why does insulation always come first?

It costs less per kWh saved than any other measure and works whatever heating system you fit afterwards. There's also no point sizing a heat pump or solar system for a leaky home — you'll pay more for kit you don't need once the demand drops.

Should I get a battery without solar?

Sometimes. If you have a smart tariff like Octopus Go or Cosy, a battery can cost-shift cheap overnight electricity to peak hours and save £200-£400 a year. Without time-of-use tariff differences, a stand-alone battery rarely makes financial sense.

Can I afford all of this on £15,000?

For a typical 3-bed semi, yes — insulation top-up + 4 kWp solar + 5 kWh battery + heat pump (after BUS grant) totals £13,500-£14,500. Larger homes or premium kit (e.g. 16 kWh battery, 8 kWp solar) push toward £25,000.

What's the order of priority by emissions impact?

Heat pump > insulation > solar > battery. Heat pumps cut roughly 1.4 tonnes CO2/year for an average 12,000 kWh gas home; solar PV (4 kWp) cuts ~0.9 tonnes; insulation cuts ~0.4 tonnes; batteries are essentially neutral on emissions (slight loss due to round-trip efficiency).

Tool: Renewable Energy Mix Planner. Last reviewed: . Figures based on Ofgem price cap, gov.uk grant guidance, and Energy Saving Trust advice. Verify scheme eligibility with your installer before commissioning work.