How a 4kW Solar System Works: Output, Costs, and Payback in the UK
If you’re weighing up the benefits of going solar, a 4kW system is likely one of the first options you’ll come across, especially for an average UK home with 2 to 3 bedrooms. But how much electricity will it actually generate? Will it cover your needs? And just as importantly, what will it cost—and how long will it take to pay off?
Whether you’re trying to cut rising energy bills, reduce your reliance on the grid, or lower your carbon footprint, this guide gives you a clear picture of what to expect from a 4kW solar system. Read on and see if it’s the right move for your household.
How Much Electricity Does a 4kW Solar System Generate?
4kW solar panel systems in the UK can typically generate between 3,000 and 3,400 kWh of electricity per year, depending on location and roof conditions. In sunnier parts of the country—such as the South West or South East—well-optimised systems can even produce up to 4,000 kWh annually.
On average, you can expect around
3,400 kWh a year
280–300 kWh per month
9–10 kWh per day
To put that into context, Ofgem’s Typical Domestic Consumption Value for a medium-use household (typically 2–3 bedrooms) is 2,700 kWh per year. If this sounds like your household, a well-sited 4kW solar system could cover almost 100% of your daytime electricity needs in summer, and 30–50% of your annual usage overall.
Those figures can be even higher if you shift energy-intensive tasks like laundry, dishwasher cycles or EV charging into daylight hours—or if you add a battery to store surplus power for the evening.
Regional variation
Of course, solar output varies across the UK due to differences in sunlight (known as solar irradiance). The figures below are based on data from PVGIS (Photovoltaic Geographical Information System)—a European tool that uses climate and satellite data to estimate how much electricity solar panels will generate in a specific location.
Location | Solar Irradiance (kWh/kWp) | Estimated Annual Output (4kW system) |
Glasgow | 788 | ~3,150 kWh |
York | 901 | ~3,600 kWh |
Birmingham | 912 | ~3,650 kWh |
London | 960 | ~3,840 kWh |
Exeter | 1,000 | ~4,000 kWh |
What drives those numbers?
Beyond location, a few other key factors influence how much electricity your 4kW system will actually produce:
Roof orientation and tilt: A south-facing roof at a 30–40° angle delivers the best performance. East- or west-facing roofs typically produce 15–20% less.
Shading: Trees, chimneys or nearby buildings that block the sun—even just for part of the day—can reduce your total output by 5–10% or more.
Temperature: Solar panels work better in cooler conditions. Ironically, very hot summer days can slightly reduce efficiency.
System design: The quality of solar panels, the type of inverter, wiring losses, and whether your installer has optimised your system for your roof layout all affect the final numbers.
What Is the Cost of a 4kW Solar System?
To start off, a 4kW solar system usually includes:
8 to 10 solar panels, depending on their wattage (350W~450W); the setup will take up around 16–20 m2 of roof space.
An inverter to convert the electricity into usable power.
Mounting equipment, wiring, monitoring system, and full installation.
Optionally, a battery system—often in the 5–6 kWh range—to store surplus electricity for use at night or during low-sun periods.
Ball-park prices in 2025
Here’s what you can expect to pay for a 4kW solar installation in the current UK market:
Scenario | Typical Price (inc. VAT) |
Straightforward installation on a typical roof | £5,000 – £6,000 |
With premium panels or major national installer | £6,500 – £7,000 |
Complex roof or added planning requirements | £7,500 – £9,500 |
Battery storage (5–6 kWh) | + £2,000 – £3,500 |
*These prices typically include everything: consultation, system design, MCS-certified installation, equipment, and all electrical sign-offs.
Why your quote might be higher (or lower)
As you can see, there’s no single price tag for solar. Your final quote will depend on several property-specific factors:
Roof type & access: slate, high-pitch or multi-facet roofs add labour and mounting costs.
Panel efficiency & brand: monocrystalline modules cost £1,000–£1,500 per kW, while budget polycrystalline panels can be < £900 per kW.
Inverter and monitoring kit: optimisers and hybrid inverters add upfront cost but can claw back output lost to partial shading.
Battery or EV charger: bundling extras with the initial install often shaves a few hundred pounds off standalone prices.
Tax relief and incentives
One major benefit right now is that solar systems and home battery storage qualify for 0% VAT in the UK—at least until March 2027. This tax relief applies whether you’re buying a solar-only system or adding a battery, and it can shave hundreds of pounds off the total cost.
On top of that, there’s the Smart Export Guarantee (SEG). If your system generates more electricity than you use, you can export the surplus to the grid and get paid for it. SEG rates vary by supplier, but average around 9p per kWh, with some offering over 20p per kWh for certain tariff types. This means your solar panels don’t just reduce your bills—they can also generate a small income, helping you recoup your investment faster.
What Are the Savings and Payback Period?
As discussed, a typical 4kW solar system in the UK generates around 3,400 kWh per year. Without a battery, most households are able to use around 50% of that electricity directly, with the rest exported to the grid under the SEG.
Here’s how the savings typically break down:
1,700 kWh used on-site: At the April–June 2025 electricity price cap of 27.03p per kWh, this translates to ~£460 in annual bill savings.
1,700 kWh exported: SEG payments vary, but the average rate is between 9p and 12p per kWh. That’s worth an additional ~£150-£200 a year in export income.
Combined, that gives most homes a total yearly benefit of between £610 and £660. With installation costs for a 4kW solar system, currently around £5,000–£6,500 (including 0% VAT), payback time is about 7.6 to 10.7 years.
Adding a 5–6 kWh battery (which typically costs an extra £2,000–£3,500) increases the amount of solar energy you use in the home to around 80%, reducing what you export but increasing your bill savings:
2,700 kWh used on-site: Saves around £735 a year on your electricity bill.
Only 700 kWh exported: Worth a smaller SEG income of ~£60–£80 per year, depending on the tariff.
So, total yearly benefit with a battery is usually around £795–£815.
With the full 4kW solar system with battery price between £7,000 and £10,000, the estimated payback is about 8.6 to 12.6 years.
Savings & payback overview
4kW Solar Panel System | Without Battery | With Battery |
Cost (inc. 0% VAT) | £5,000–£6,500 | £7,000-£10,000 |
Annual bill savings | £460 | £735 |
SEG payments | £150-£200 | £60–£80 |
Total annual savings | £610-£660 | £795–£815 |
Estimated payback period | 7.6 ~ 10.7 years | 8.6 ~ 12.6 years |
ROI after 25 years | £8,750 ~ £11,500 | £9,875~£13,375 |
*Assumes SEG rate of 9~12p/kWh and energy price of 27.03p/kWh (April–June 2025 cap). No inflation or degradation included.
Why a battery makes sense
Adding a battery keeps more of your own solar power rather than selling it back cheaply to the grid. With the SEG hovering around 10 p/kWh for most households, it often makes more sense to store surplus energy and avoid paying the grid’s higher rate.
Even with a slightly longer pay-back, a battery protects you from price spikes, gives basic backup in outages, and unlocks smart tariffs that let you top-up cheaply overnight—advantages that rarely show up in straight-line ROI calculations.
If you do want a high-capacity, future-proof battery unit, take a look at the EcoFlow DELTA Pro 3 Portable Power Station. It packs a hefty 4,096 Wh of LiFePO4 storage with an impressive 4,000-cycle lifespan.
With a 4,000W inverter (8,000W surge), it can handle most household appliances and accepts up to 2,600W of solar input. It runs quietly at just 30 dB and can easily expand up to 12kWh—perfect if you plan to add an EV or heat pump down the line.
EcoFlow DELTA Pro 3 Portable Power Station
What Are the Pros and Cons of Investing in a 4kW Solar System?
Still not sure whether a 4kW solar system is for you? Here’s a balanced look at its pros and cons to help you decide:
Pros
Lower electricity bills from day one: most households save £600+ a year.
Extra income through SEG: get paid for excess electricity you send to the grid.
Protection against rising energy prices: every kWh you generate reduces reliance on suppliers.
0% VAT on installation: reduces upfront cost, available until March 2027.
Eco-friendly: cuts about 0.9 tonnes of CO₂ emissions per year.
Can boost home value: solar panels are seen as a selling point for energy-conscious buyers.
Cons
High upfront cost: £5,000–£6,500 without a battery, and up to £10,000 with one.
Not all roofs are suitable: shading, poor orientation or limited space can reduce performance.
Savings depend on when you use electricity: the more you use during daylight, the better the return.
SEG rates can change: export income isn’t locked in.
Conclusion
A 4kW solar system is one of the most practical and cost-effective ways to cut your electricity bills, reduce your carbon footprint, and gain more control over your energy use. For many UK homes, it strikes the right balance between output, affordability, and roof space. With 0% VAT, it costs around £5,000–£6,500 without battery, can save you £600+ per year, and pays back in just 8-10 years.
Before making any decisions, it’s worth comparing quotes from MCS-certified installers and thinking through how and when your household uses electricity. The better your setup matches your habits, the more value you’ll unlock—year after year.
FAQs
What can I run on a 4kW solar system?
A 4kW solar PV system can comfortably supply most everyday household appliances, from LED lighting, desktop computers, and TVs to refrigerators and washing machines—especially during the longer summer days.
On a typical sunny day, such a system generates around 9-10 kWh of electricity, which is enough fuel to run a washing machine for an hour and still have energy left for kettles, TVs, laptops and some lighting. It’s well suited for small to medium family homes, workshops, lodges, or even static caravans. In winter or for energy-intensive appliances, you’ll likely draw on grid backup.
How much power will a 4kW solar system produce?
In practice, a 4kW solar setup in the UK yields approximately 3,000–4,000 kWh per year, depending on roof orientation, shading, and local sunlight. That equates to about 8–10 kWh per day on average—rising to 15 kWh when the sun is at its strongest. This output typically covers the energy needs of a 2‑ to 3‑bedroom household and can substantially reduce annual electricity bills by up to £700.
Can I run AC on a 4kW solar system?
Yes! You can use a 4kW solar system to run an air conditioning unit (AC), provided your inverter is sized appropriately and you have enough sunlight and consumption surplus. In practice, a decent inverter (ideally one rated at or above 4 kW) is essential to handle both the solar input and the AC’s starting surge.
On sunny days, the system can also support other household appliances simultaneously. However, during overcast periods or when the sun is low, you may need grid power to meet the AC’s higher demand.
How many solar panels do I need for 4kWh?
If you mean a 4kW (4,000W) system, you’d usually need around 8–12 solar panels, depending on panel wattage (e.g., 350–450 W models). Typical installations use ten 400W panels to reach the 4kW capacity, fitting within roughly 16 m² of roof space.
If your question refers to delivering 4 kWh per day, a single 1kW of panel capacity generally delivers about 4kWh on a UK summer’s day—so a 4kW system naturally meets that daily output target in sunny conditions.