Solar Panels Calculator

Solar panels have become a mainstream home upgrade in the UK. Installation prices have fallen over the past decade, while electricity prices remain far higher than they were a few years ago. But whether solar is worth it for you depends on your roof, how you use electricity and the price you pay.

This guide explains the costs, how much panels generate and how to work out your payback. For figures based on your own home, use the solar panels calculator.

How much do solar panels cost?

A typical home solar system is between 3.5kWp and 5kWp, which is around 8 to 12 modern panels. As a rough guide, systems cost around £1,600 per kWp installed, so a 4kWp system is often around £6,000 to £7,000. Prices vary with the panels, inverter, roof type, scaffolding and where you live.

Residential solar panel installations in Great Britain currently benefit from 0% VAT, which runs until 31 March 2027.

Adding a battery

A home battery stores solar electricity you don't use during the day so you can use it in the evening. Batteries typically add £2,500 to £5,000 or more, depending on capacity. They increase how much of your own solar power you use, but also lengthen the payback period, so it's worth running the numbers both ways.

How much electricity do solar panels generate?

In the UK, each kWp of panels typically generates around 800 to 1,000kWh a year, depending on where you live, which way the roof faces and how much shade there is. A south-facing roof in southern England sits at the top of that range, while a north-facing roof in Scotland sits lower. East and west-facing roofs still work well, producing slightly less in total but spreading generation across the morning and afternoon.

A 4kWp system at 900kWh per kWp would produce about 3,600kWh a year, which is more than many households use in total. But most of it is generated in the middle of the day and in summer, when you may not be using much.

How solar panels save you money

There are two ways solar panels make money:

1. Using the electricity yourself

Every unit of solar electricity you use is one you don't buy from your supplier. This is the most valuable part, because you save the full price you'd otherwise pay per kWh. Without a battery, most homes use roughly 30% to 50% of what they generate. With a battery, that can rise to 70% to 80%.

2. Selling surplus to the grid

Electricity you don't use is exported to the grid. Under the Smart Export Guarantee (SEG), larger energy suppliers must offer you a payment for exported electricity. Rates vary widely between suppliers and tariffs, from a few pence to 15p or more per kWh, so it pays to shop around. You'll need a smart meter and an MCS-certified installation to qualify.

A worked example

A household with a 4kWp system costing £6,400, generating 900kWh per kWp, using 50% of it themselves, paying 26p per kWh for electricity and exporting the rest at 12p:

• Generation: about 3,600kWh in the first year
• Used at home: 1,800kWh, saving about £468
• Exported: 1,800kWh, earning about £216
• Total first-year benefit: about £684

At these prices, the system would pay for itself in about 10 years, and over 25 years the total benefit would exceed the cost by around £9,700. This assumes energy prices stay flat; if they rise, payback is faster. You can test your own assumptions in the solar panels calculator.

What affects whether solar is worth it?

• Roof direction and pitch. South-facing roofs are best, but east and west are fine.
• Shading. Trees, chimneys and neighbouring buildings reduce output.
• Your usage pattern. If someone's at home during the day, or you can run appliances, an electric vehicle or hot water when the sun's out, you'll use more of your own power.
• Electricity price. The more you pay per kWh, the more each solar unit is worth.
• Export rate. A good SEG tariff improves returns, especially without a battery.
• How long you'll stay. Panels last 25 years or more, so the longer you stay, the more you benefit.

Ongoing costs

Solar panels need very little maintenance, but you should budget for:

• Inverter replacement. Inverters typically last 10 to 15 years and often cost £800 to £1,500 to replace.
• Occasional cleaning, if panels become very dirty or covered by bird droppings.
• Gradual degradation. Panels lose a small amount of output each year, often around 0.5%.

Do you need planning permission?

Most home solar panel installations in England are permitted development, so they don't need planning permission, provided panels don't protrude more than 20cm from the roof slope and don't go above the highest part of the roof. Different rules apply to listed buildings, flats and some homes in conservation areas or World Heritage Sites. Check with your council if you're unsure. The rules in Scotland, Wales and Northern Ireland are similar but not identical.

Choosing an installer

1. Use an MCS-certified installer. This is needed for the Smart Export Guarantee.
2. Check they're a member of a consumer code such as RECC or HIES.
3. Ask for a shading assessment and a performance estimate for your roof.
4. Compare panel, inverter and battery warranties.
5. Get at least three quotes and compare total system size and cost per kWp.