A 4kW solar panel system costs between £5,000 and £7,000 installed in 2026, generates roughly 3,400 to 3,800kWh per year depending on where you live, and can cut your electricity bill by £800 to £1,100 annually.
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Roughly 10 panels on your roof, generating between 3,400 and 3,800kWh of electricity per year. That's enough to cover 75% to 90% of a typical three-bed household's annual electricity use, though the exact figure depends on your roof orientation, pitch, shading, and how far north you live.
A house in Plymouth will outperform an identical setup in Newcastle by about 15%. South-facing roofs at a 30 to 35 degree pitch hit the sweet spot. See our guide on how solar panels work for more detail. East or west-facing? You'll lose around 15% to 20% of potential output, but it's still worth doing for most homes.
4kW sits in a particular niche. It's big enough to make a real dent in your bills but small enough to fit on most semi-detached and terraced roofs without needing planning permission. The system typically needs around 16 to 20 square metres of unshaded roof space, which works out to roughly half the south-facing side of a standard semi.
One thing worth knowing: "4kW" refers to peak output under ideal lab conditions. Your panels will rarely hit that number in real life. British weather being what it is, you'll generate most of your electricity between April and September, with a steep drop-off from November through January. On a grey December day, a 4kW system might produce less than 3kWh. On a sunny June afternoon, it could hit 25kWh.
So your actual savings depend heavily on when you use electricity, not just how much the panels produce. We'll get to that.
£5,000 to £7,000 fully installed, with most quotes landing around £5,800 to £6,200 for a standard setup. That price includes panels, inverter, mounting hardware, scaffolding, electrical work, and MCS certification.
Here's what shifts the price up or down:
| Factor | Lower end | Higher end |
|---|---|---|
| Panel brand | Budget tier (Trina, JA Solar) | Premium (SunPower, Maxeon) |
| Inverter type | String inverter | Microinverters (Enphase) |
| Roof complexity | Simple south-facing | Multiple planes, dormers, flat roof |
| Scaffolding | Standard two-storey | Three-storey or difficult access |
| Location | Midlands, North | London, South East |
Microinverters add £500 to £800 to the total but let each panel work independently, which matters if you have partial shading. For an unshaded south-facing roof, a string inverter does the job perfectly well.
Adding a battery storage system pushes the total to £8,500 to £12,000 depending on capacity. Most people start without one and add it later once they understand their generation and usage patterns.
And here's something the industry doesn't shout about: installation costs have actually crept up slightly since 2024, even though panel prices have dropped. Labour and scaffolding costs are the culprits. The panels themselves are cheaper than ever, but fitting them to a British roof still takes a full day of skilled work. See our guide on solar installation process and costs for more detail.
0% VAT applies to all domestic solar installations in the UK until at least 31 March 2027. That saves you roughly £1,000 to £1,400 on a 4kW system. If your installer is charging you 20% VAT on a residential solar job, challenge it.
For a two to four-person household using 2,900 to 4,100kWh of electricity per year, yes. That covers the majority of UK homes.
But "right size" depends on what you're optimising for. If you want to maximise self-consumption (using the electricity as it's generated rather than exporting it), 4kW is often the sweet spot for a household that's home during the day or runs appliances on timers. If nobody's home until 6pm and you don't have a battery, you'll export most of what you generate and only benefit through the Smart Export Guarantee, which pays considerably less than you'd save by using the electricity yourself.
Here's a rough guide:
| Household size | Annual usage | Best system size |
|---|---|---|
| 1 to 2 people | 1,800 to 2,900kWh | 3kW |
| 2 to 4 people | 2,900 to 4,100kWh | 4kW |
| 4+ people | 4,100kWh+ | 5kW to 6kW |
If you're planning to add an electric vehicle or a heat pump in the next few years, go bigger now. Retrofitting extra panels is possible but adds cost for scaffolding and a second installation visit. Our guide on how many panels you need walks through the maths in more detail.
One thing we see regularly: people undersize their system to save money upfront, then regret it two years later when they switch to an EV. The marginal cost of going from 4kW to 5kW at the point of installation is only £800 to £1,200. Adding that 1kW later costs nearly double.
£800 to £1,100 per year on a typical electricity bill, assuming you self-consume around 50% of what you generate. That figure uses Ofgem's current price cap rate of roughly 24.5p per kWh for electricity.
The maths works like this. A 4kW system in the Midlands generates about 3,600kWh per year. If you use 50% directly (1,800kWh), that's 1,800 × 24.5p = £441 saved on your bill. The other 50% gets exported. Under the Smart Export Guarantee, Octopus Energy currently pays around 15p per kWh, British Gas pays about 12p, and some smaller suppliers offer as little as 3p. At 15p, your export earnings add another £270 per year.
Total: roughly £710 in year one at 50% self-consumption. Push self-consumption to 70% (achievable with a battery, timer-controlled appliances, or working from home) and you're looking at closer to £900 to £1,100.
Payback period? At £6,000 installed cost, you're looking at 6 to 8 years. After that, it's essentially free electricity for the remaining 17 to 19 years of the panel warranty. Most panels are warranted for 25 years and will still produce 80% of their rated output at that point.
Honestly, the biggest variable isn't the panels. It's your behaviour. A household that runs the washing machine, dishwasher, and immersion heater during peak solar hours will save dramatically more than one that does everything after dark. Smart plugs and timer switches cost £15 to £30 each and can shift your self-consumption from 30% to 60% without changing your routine much.
Want to see whether solar panels are worth it for your specific situation? That guide breaks down the numbers by region and household type.
Two routes can cut your costs right now, and one of them could wipe the bill out entirely.
ECO4 is the big one. If your household receives qualifying benefits (Universal Credit, Pension Credit, Child Tax Credit, and several others) and your home has an EPC rating of D or below, ECO4 can fund solar panel installation at no cost to you. The scheme runs until December 2026. We've covered the full eligibility criteria and application process separately, but the key point for solar specifically is that your local authority and energy supplier both play a role in determining what measures get funded, and solar isn't always the first thing they'll offer. Insulation typically comes first.
The Smart Export Guarantee isn't technically a grant, but it puts money back in your pocket from day one. Every supplier with more than 150,000 customers must offer you a tariff for exported electricity. Rates vary wildly. Octopus Energy's Agile Export tariff can pay over 20p per kWh at peak times, while some suppliers offer a flat 3p. Shopping around here is genuinely worth an hour of your time.
And there's a quirky aside worth mentioning. The Boiler Upgrade Scheme gives you £7,500 towards a heat pump, and some homeowners are pairing that with a solar installation. The BUS grant doesn't cover solar directly, but if you're already getting scaffolding up for a heat pump, adding panels at the same time cuts installation costs. It's not a solar grant, but the combination works well financially.
The Great British Insulation Scheme, which closed in March 2026, previously covered some solar-adjacent measures but never funded panels directly.
MCS certification is non-negotiable. Without it, your installation won't qualify for the Smart Export Guarantee, you can't claim the 0% VAT rate, and you won't be eligible for any grant scheme.
Beyond that, here's what actually matters:
Get three quotes minimum. We see price differences of 30% or more for identical systems on the same street. The cheapest quote isn't always the best, but paying £7,500 for a system that three other installers quoted at £5,800 means someone's taking the mick.
Ask about the inverter warranty separately. Panels are typically warranted for 25 years, but inverters often only carry a 5 to 10-year warranty. Since inverter replacement costs £800 to £1,200, a longer warranty matters. Enphase microinverters come with 25 years as standard. SolarEdge optimisers offer 12 to 25 depending on the model.
Check their workmanship guarantee. MCS requires a minimum standard, but good installers offer their own guarantee on top, typically 5 to 10 years covering the physical installation, roof penetrations, and electrical work.
Look at their reviews on Trustpilot and Google, but also ask for addresses of recent local installations. A confident installer will happily point you to a house two streets away. Our guide to finding a trusted solar installer covers the vetting process in more detail.
So here's our honest take: the panel brand matters less than most people think. The difference between a mid-range Trina panel and a premium SunPower panel is maybe 3% to 5% more output per square metre. The difference between a good installer and a sloppy one is whether your roof leaks in five years. Spend your energy choosing the installer, not agonising over panel specs.
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