Solar and heat pump payback explained

Payback is the upfront cost divided by what you save each year. For solar, savings come from electricity you no longer buy plus what you are paid for exporting the rest (the Smart Export Guarantee). For a heat pump, it's the difference between your gas bill and the extra electricity the heat pump uses.

What moves the number

• Sunshine: yields range from roughly 800 kWh/kWp in Scotland to over 1,000 in the south-west.
• Self-use: electricity you use yourself is worth about twice what you get for exporting it. Batteries raise self-use.
• Tariffs: time-of-use and heat pump tariffs can cut payback sharply.
• Insulation: a draughty home needs a bigger, costlier heat pump.

Every area page shows its assumptions so you can swap in your own figures with our solar and heat pump calculators.