The kit that cuts bills and carbon
Six technologies do most of the work in a low-carbon home. Here is what each one does, where it makes sense and where it does not, with a calculator for the numbers.
Generate your own electricity
Rooftop panels turn daylight into electricity you use first and export for credit when you make more than you need. A 4 kWp system on a UK roof makes roughly 3,600 to 4,000 kWh a year. Best on a south-ish, unshaded roof, and it pairs well with daytime use, a battery or an EV.
The value is not in the headline kWp but in how much you use yourself: a unit you generate and use is one you do not buy at around 26p, while export earns far less, so pairing panels with daytime use, a battery or an EV is what shortens the payback. Panels keep working for 25 years or more, fading only about 0.5% a year, so most of their life sits beyond payback.
Good to know
- 0% VAT until 31 March 2027
- Payback typically 7 to 14 years
- Panels degrade about 0.5% a year and last 25+ years
- Get paid to export via the Smart Export Guarantee
Store cheap or free energy for later
A battery holds daytime solar for the evening, or charges on a cheap overnight rate to power your home at peak. It does not make energy; it shifts when you use it. The case is strongest with solar, a wide off-peak gap or an EV. On export rates this high, payback can run long.
Sizing is the art: match a battery to your evening and overnight use, not to your roof or your total demand. Too small and it empties before the peak ends; too large and you pay for capacity you never cycle. The roughly 10% round-trip loss means the wider the gap between your cheap and peak rates, the better it pays, which is why a battery rarely makes sense without solar or a time-of-use tariff behind it.
Good to know
- Round-trip efficiency is about 90%
- Warranties run around 10 years or a cycle count
- Sized in usable kWh; 5 to 10 kWh suits most homes
- 0% VAT applies, even added on its own
Heating that runs on electricity
An air-source heat pump moves heat from outside into your home, delivering about three units of heat per unit of electricity. Against a gas boiler on a standard tariff it lands close to level on cost; a heat-pump tariff tips it cheaper, and it cuts carbon sharply. The grant (£7,500, or £9,000 for off-gas oil and LPG homes) covers most of the gap to a new boiler.
Success hinges on design, not the badge. A heat pump sized to a proper room-by-room heat-loss survey and run at a low flow temperature into large enough radiators (or underfloor) is cheap and comfortable; the same unit forced to run hot like a boiler is neither. Insulate first so it can be sized smaller, and choose an installer who commissions and tunes it rather than leaving factory defaults.
Good to know
- £7,500 or £9,000 Boiler Upgrade Scheme grant in England & Wales, depending on current heating fuel
- SCOP of 3.2 to 3.6 on radiators, higher on underfloor
- Insulate first so it can be sized smaller
- Works at low flow temperatures; design matters
Charge at home for about 2p a mile
A 7 kW home charger fills the car overnight. On an off-peak EV tariff near 7p per kWh, home charging works out around 2p a mile against roughly 14p on petrol. Public rapid charging is far dearer, so the saving depends on how much you charge at home.
The saving lives in the timing, not the speed: that 7 kW limit comes from the car's onboard charger, but it is plenty to refill overnight, and charging in a cheap window is what makes a mile cost pennies. A smart charger schedules it for you, can soak up spare solar, and with bidirectional hardware the car's large battery can even power your home at the evening peak.
Good to know
- Charger install is roughly £800 to £1,100
- Renters and flat owners may claim a £350 grant
- Pairs well with solar and a home battery
- Most EVs do 3.0 to 4.0 miles per kWh
Pay less by using power at the right time
Time-of-use tariffs charge less when the grid is quiet and more at the early-evening peak. Shift charging, heating or the dishwasher to cheap hours and the bill falls. They reward a smart meter and a bit of automation, and they make batteries and EVs work harder.
They reward flexibility, not everyone equally. A household that can move its EV charging, dishwasher or a battery into the cheap hours wins; one that uses most of its power at the evening peak with nothing to shift can pay more. A working smart meter sending half-hourly reads is the entry ticket, and automation captures the cheap hours without you watching the clock.
Good to know
- Off-peak EV rates reach as low as 7p per kWh
- Agile-style tariffs follow wholesale half-hourly
- Needs a smart meter sending half-hourly reads
- Best for households that can shift load
The cheapest unit of energy is the one you do not use
Loft and wall insulation and draught-proofing cut the heat your home loses, so everything you fit afterwards runs cheaper and smaller. Loft top-ups are often the fastest payback in the house, and several measures are grant-funded. Do the fabric first, then electrify.
Doing the fabric first shrinks the heat pump, the solar array and the bill all at once, because a leaky home needs a bigger, costlier heating system whatever the fuel. One technical caveat: mind the moisture balance. Seal uncontrolled draughts but keep deliberate ventilation, or warm damp air can condense somewhere you cannot see and cause damp, which is why solid-wall work in particular needs careful detailing.
Good to know
- Loft insulation often pays back in a few years
- Cavity walls are cheap to fill; solid walls cost more
- Grant help via ECO4 and the Great British Insulation Scheme
- Lowers the heat-pump size you need
Not sure what to do first?
The home energy audit builds a step-by-step plan for your home and budget, in the order that pays.