How it was paid for
After the solar panels, the household has spent about £31,300 of its own money on the other retrofit measures (about £37,500 with the panels). Those measures now save roughly £2,500 a year in running costs against a typical home running one petrol car the same miles (an illustration), and the panels' Feed-in Tariff has paid roughly £15,000 since 2012. This page sets out what each measure cost, what it saves, and the tariff, each told once.
The short version
After the solar panels, the household has spent about £31,300 of its own money on the other measures in these stories, about £37,500 with the panels. In return the house, with its one electric car, costs roughly £2,500 a year less to run than a typical home that runs one petrol car the same miles (an illustration; see "What it saves"). Separately, the panels have earned a Feed-in Tariff, roughly £15,000 since 2012, which the homeowner has put back into the house.
2012: the panels
In February 2012 eight panels were quoted at £6,269.26 including VAT, with no grant recorded.
2023: the battery, the loft and the floor
In July 2023 the first 6 kWh of battery cost £6,150. In August the loft was insulated and boarded for £2,380, and in November the cavity under the ground floor was insulated for £2,745. There was no grant for any of them.
2024: the heat pump, the extension and the second battery
The heat pump was quoted at £8,200, radiators included. The government's Boiler Upgrade Scheme paid £7,500, so the household paid £700, plus £1,200 to disconnect the gas: £1,900 in cash, and Octopus later gave £350 of account credit and £350 of wood after a delayed installation. The rear bathroom extension was finished in September 2024 and cost about £12,000, with no VAT: £8,093 for the original bathroom and roof estimates, £1,650 for roofing, and about £2,400 more for the window, shower tray, shelving, plastering and render, and the walk-in shower, basin and toilet. In October a further 3 kWh of battery and the EV charger together cost £2,335.
2026: the front door, and the glazing to come
In February 2026 a composite front door cost £3,612, replacing a wooden one fitted in 2017 for £2,500. Double glazing is quoted at £3,563.23 including VAT but has not been fitted, so it is not counted anywhere on this page.
Adding it up
Counting only the household's own money, the measures after the panels came to about £31,300, and about £37,500 with the panels. The grant and the goodwill on the heat pump came on top. These are costs, not a record of what paid for what.
What it saves
The running costs tell the other half. The house's whole electricity bill in 2025 was about £440 once its export income is taken off (the Octopus app's £481.61 less about £40), and that one bill covers the heating, hot water, cooking and the car, because there is no gas. This house has one car, so the comparison is with a typical home that has one petrol car doing the same 6,800 miles: its gas and electricity (Ofgem's typical bill, about £1,750) plus the petrol (about £1,200) comes to about £2,950. A home with more cars, or more miles, would have a different bill. The difference is roughly £2,500 a year. That is an illustration of scale, not a bill and not a payback calculation: it is against a typical home with one petrol car, not this house before it changed, which was never measured, and it counts running costs only. "How this house compares" has the working.
The panels' Feed-in Tariff
Apart from all that, the panels have paid the household a Feed-in Tariff on every unit they generate since 2012: about 49p a unit at the start, about £1,100 a year now, by the homeowner's account, and roughly £15,000 so far, which is more than twice what the panels cost. That is about half of the £31,300 spent on the later measures and about two-fifths of the £37,500 with the panels, and the homeowner has reinvested much of it in them. Which measure it paid for, and how much, is not recorded, and this page does not guess.
How the Feed-in Tariff total is worked out
The homeowner gave two figures: a starting rate of about 49p a unit in 2012 and about £1,100 a year now. On the panels' roughly 1,750 kWh a year, 49p is about £860 a year. The total above assumes the yearly payment rose steadily from about £860 to about £1,100 over the 14 and a half years since the panels went up, which gives roughly £14,500 by now. If the payments had always been £1,100 the total would be about £16,000, so the total is quoted as roughly £15,000. In reality the rate rises in steps with inflation and the panels' output varies from year to year. These are estimates from two remembered figures, not statements.
Benefits
- The house, with its one electric car, costs roughly £2,500 a year less to run than a typical home's gas and electricity plus the petrol for one car doing the same miles: about £440 in 2025 against about £2,950 (an illustration; running costs only, not a payback).
- A government grant and Octopus's goodwill covered most of the heat pump: the household paid £700, plus £1,200 to disconnect the gas.
Limitations
- This is one household's outcome: the Feed-in Tariff closed to new applicants on 31 March 2019, and prices, grants and quotations differ between houses and years.
- The saving is an illustration: it is against Ofgem's typical bill and the same miles in a petrol car, not this house's old bills, which were never measured. The equipment's cost is not counted against it, and it is not a payback calculation.
- The Feed-in Tariff total is an estimate from two figures the homeowner remembers, between a steady rise and a flat £1,100; it is not taken from statements.
- The costs are the totals on quotations and estimates as the homeowner records them; the extension's is the sum of two estimates and extras, about £12,000, with no VAT. They are not a ledger, and the double glazing, quoted but not yet fitted, is not counted.