How many solar panels do I need?

To generate as much electricity in a year as a typical home uses (2,500 kWh, Ofgem's figure for medium use), you need about 6 or 7 panels of 450 W, or 2.7 to 3.15 kWp, on a south-facing roof in most of Great Britain: 6 in London or Birmingham, 7 in Manchester or Glasgow. A home using more needs proportionally more, and an east- or west-facing roof needs about a quarter more. Whether to fit more than that depends on your roof, when you use electricity and what your exports earn, which this guide works through.

Panels needed to match your yearly use

The table shows how many 450 W panels it takes to generate your yearly electricity use, for Ofgem's three typical usage levels for homes on a single-rate meter.

Figures are yearly averages from PVGIS, the European Commission's solar model, for panels facing south at a 35° pitch with 14% system losses. Generation varies from year to year. Panel counts are rounded up. Ofgem's usage levels are for Great Britain; we use them for Belfast as a guide.

To work out your own number:

panels = yearly use in kWh ÷ (panel watts ÷ 1,000 × kWh per kWp where you live), rounded up

For a Birmingham home using 2,500 kWh: 0.45 kWp × 968 kWh per kWp = 436 kWh per panel, and 2,500 ÷ 436 = 5.7, so 6 panels, or 2.7 kWp.

Your yearly use is on your electricity bills or your supplier's app: add up the last 12 months, electricity only. If you can't find it, Ofgem's typical values are 1,600, 2,500 and 3,800 kWh a year. MCS-certified installers use 3,500 kWh when a household's use is unknown, so give your installer your real figure.

Try it for your own roof

Our solar panel calculator, for homes in England, Scotland and Wales, uses your address, roof direction and pitch instead of a city average, and shows how much of the output you would use at home.

Adjust for your roof direction and pitch

A south-facing roof at about 35° gets close to the most from each panel. Other roofs make less per panel, so you need more to reach the same yearly total. PVGIS figures for Birmingham, per kWp of panels:

On an east- or west-facing roof, divide by about 0.8: a household needing 6 panels on a south roof needs about 7 or 8 (6 ÷ 0.8 = 7.5). Panels split between east and west spread their output across the morning and evening, which can suit a home that uses more at those times. Trees, chimneys and neighbouring buildings cut output further; our guide to solar panel shading explains how installers allow for it.

Why matching your yearly use isn't the whole answer

Solar panels generate most around midday and in summer. In London, a panel makes less than a third as much in December as in June (36 kWh per kWp against 123). You can only use the power as it's made, or store it; the rest is exported.

Take a London home using 2,500 kWh a year, empty for half the day on weekdays, with no battery. These figures come from our calculator's model:

Six panels generate about a year's worth of electricity, but the home still buys around three-quarters of what it uses, mostly in the evening, at night and in winter. Going from 6 to 12 panels doubles generation but raises the share of the home's use covered only from 25% to 30%; nearly all the extra goes to the grid. So once you are past a household's daytime use, the number of panels is really a decision about exports.

Your daytime routine

MCS installers must estimate how much of your solar power you'll use following the MCS self-consumption guide, whose tables sort homes into three daytime patterns:

• Home all day: someone is usually in between 9am and 5pm on weekdays.
• In half the day: the home is usually empty for half the day, such as all morning or all afternoon.
• Out all day: the home is usually empty on weekdays.

For a London home using 2,500 kWh with 4 kWp of panels, our calculator gives 21%, 17% and 12% of the generation used at home for the three patterns. A battery raises the share: in a Manchester home using 3,600 kWh with 5 kWp, a 5 kWh battery (3 kW) takes it from 21% to 57%. Our battery storage guide explains when that pays.

Is it worth fitting more panels?

Compare what the extra panels earn with what they add to the quote. For the London home above, going from 8 to 10 panels adds this much in the first year:

"Value" is the electricity you no longer buy plus export payments, before the cost of the system. It assumes Ofgem's price cap average of 26.32p/kWh for October to December 2026 (no VAT on electricity in Great Britain until 31 March 2027), today's prices held flat and export rates checked on 24 September 2026. Export rates are set by suppliers and can change. We hold prices flat here: if electricity prices rose 2% a year, the extra panels' value would barely change, because nearly all their output is exported at a flat rate. Northern Ireland has no Smart Export Guarantee; what you're paid for exports there is up to your supplier.

Ask your installer to price both sizes, then divide the difference by the extra value. If two more panels added £600 to the quote (an example figure, not a price we have checked), they would pay for themselves in about 5 years at 12p (Octopus Outgoing, which needs Octopus as your electricity supplier: £600 ÷ £115 = 5.2) or about 10 years at 6p, open whoever supplies you (£600 ÷ £63 = 9.5), ignoring the small fall in output each year. Larger systems cost less per kW on average: in the government's 2025/26 cost data for Great Britain (DESNZ, domestic retrofit mean, per kW of panel capacity), systems on existing homes averaged £2,109 per kW up to 4 kW and £1,651 per kW for 4 to 10 kW, including VAT and excluding batteries. Our solar panel cost guide explains what a full quote includes, and the best export tariffs compares export rates and their conditions.

Your inverter and the 3.68 kW limit

The inverter turns the panels' electricity into the kind your home uses. In Great Britain, on a normal single-phase supply, systems whose inverters add up to no more than 3.68 kW (16 amps) can be connected first and notified to the network operator within 28 days. Above that, including any battery inverter in the total, your installer must apply to the network operator and get approval before connecting. Northern Ireland has the same limits, with 30 days to notify.

The limit is on the inverters, not the panels, so a system can have more kWp of panels than its inverter rating: ten 450 W panels (4.5 kWp) with a 3.68 kW inverter, for example, if the inverter's datasheet allows it. When the panels produce more than the inverter can pass on, the excess is lost ("clipping"). Ask the installer how much output they expect to lose on your design, and whether a bigger system would need network approval.

Planning for an electric car or heat pump

Add the new load to your yearly use before sizing. For a car, divide the miles you drive a year by the miles per kWh your car shows: 7,000 miles at 3.5 miles per kWh is 2,000 kWh (an example; use your own figures). In Birmingham that is 2,000 ÷ 436 = 4.6, so about five more panels to generate it over a year.

Timing matters even more here. A car charged overnight or in the evening uses little solar power directly. In our calculator's model, a Birmingham home using 4,500 kWh including an electric car, with 6 kWp of panels, uses 19% of its generation as it's made; with a 10 kWh battery (5 kW), 62%. A heat pump uses most of its electricity in winter, when panels make least, so panels will cover only a small part of its winter use; size the system for your roof and summer use, not for winter heating.

Will they fit on your roof?

A house-size panel is about 1.76 m by 1.13 m, or 2 m², on the datasheets we checked, so ten panels cover about 20 m² before the gaps needed at the roof edges and between panels. Our guide to solar panel sizes shows how to lay panels out and why the usable roof is smaller than the roof. If your roof is small, higher-wattage panels fit more kWp into the same space; see the most efficient solar panels.

What to ask your installer

Before you sign, an MCS-certified installer must give you in writing:

• an estimate of the system's yearly generation and of how much of it you'll use, worked out with the MCS self-consumption guide;
• the manufacturer's datasheets for the panels and the inverter;
• a drawing of the proposed panel layout.

Also ask:

• which daytime pattern and yearly use they assumed, and to rerun the estimate with your real figures;
• the price with two panels fewer and two panels more;
• the inverter size, whether the design needs network approval, and how much output clipping will cost.

Frequently asked questions

Is 10 solar panels enough for a house?

For many homes, yes, in terms of yearly output: ten 450 W panels (4.5 kWp) generate about 4,585 kWh a year in London, well over the typical 2,500 kWh. You'll still buy electricity in the evening, overnight and in winter unless you add a battery.

Can 4 solar panels power a house?

Not on their own. Four 450 W panels make about 1,834 kWh a year in London, less than a typical home uses, and nothing at night. In our London example they cover about 22% of the home's electricity use.

How much electricity does one solar panel produce?

A 450 W panel facing south at 35° produces about 384 kWh a year in Glasgow, 436 kWh in Birmingham and 458 kWh in London, going by PVGIS averages. East or west roofs produce about a fifth less.

How many solar panels do I need for a 3-bedroom house?

Bedrooms don't set it; your electricity use does. A home using Ofgem's typical 2,500 kWh needs about 6 or 7 panels of 450 W to generate that over a year, depending on where it is and which way the roof faces.

Can I go off-grid with solar panels?

Not with panels alone. They make nothing at night and little in winter, so a grid-connected home still buys electricity then. A battery covers some evening and night-time use.