How Many Solar Panels Do I Need? Panels and kWp for Your Home

How Many Solar Panels Does a Typical UK Home Need?

A home with Ofgem's typical medium use of 2,500 kWh a year needs about 6 solar panels of 475 W: our sum matches 2.58 kWp to that use, on a south roof at 35 degrees with no shade and no postcode, and rounds up to whole panels. Your yearly electricity use, roof direction and roof space move the panel count up or down.

The calculator above shows the panel count matched to your use on your roof, and with no figure it uses a medium home's 2,500 kWh a year. In the DESNZ data, systems of 4 to 10 kWp cost less per kWp than systems up to 4 kWp. Your own roof changes the result, so price your size in the main calculator to see the cost and payback for that system size.

How Many Solar Panels Does a 1, 2, 3, 4 or 5-Bedroom House Need?

A 1, 2, 3, 4 or 5-bedroom house needs the solar panels that match its own electricity use, so the calculator sizes from use, not from bedrooms. Ofgem groups homes by use, not by bedrooms, and the table below shows its three typical bands.

Type the yearly figure from your own bill into the calculator, and the result shows the panels and kWp for that use on your roof.

How Do You Work Out How Many Solar Panels You Need?

To work out how many solar panels you need, size the system first: divide your yearly use by what 1 kWp generates on your roof, then divide by one panel's wattage. The sum has four steps.

1. Find your yearly electricity use in kWh.
2. Find the specific yield for your roof: the kWh that 1 kWp of panels generates in a year at your roof's direction and pitch. We call it kWh per kWp from here on.
3. Divide the yearly use by the kWh per kWp. The answer is the system size in kWp.
4. Multiply the kWp by 1,000, divide by the watts of one panel and round up. The answer is the panel count.

With 2,500 kWh of yearly use, 968.01 kWh per kWp and 475 W panels (our default wattage), the first box of the result card above gives the count; the card rounds the kWh per kWp to a whole number. The calculator uses the yield for your postcode area, adjusted for roof direction and pitch. With no postcode, or one outside our table, it uses a stand-in figure, and the result card says so. A system size and a panel count are only the start: the roof can lower the number.

The 1 kW per 1,000 kWh Rule of Thumb

Sizing at 1 kWp of solar panels for every 1,000 kWh of electricity you use a year treats every kWp as if it generated 1,000 kWh a year on any roof, so it leaves out roof direction, pitch and shade. It undersizes the system on a roof that generates less than that and oversizes it on a roof that generates more. The calculator uses the kWh per kWp for your own roof instead.

How the Calculator Reads Your Yearly Electricity Use

The calculator takes your yearly electricity use in three forms.

• Yearly use in kWh: the calculator uses the figure as it is.
• Monthly use in kWh: the calculator multiplies the figure by twelve.
• Monthly bill in pounds: the calculator takes off the daily standing charge and divides the rest by the price cap unit rate of 26.32p per kWh. For a Northern Ireland postcode it uses the Power NI standard unit rate and takes off no standing charge.

An empty box means the calculator uses Ofgem's typical medium value, 2,500 kWh a year, and the result card names the figure it used. Typical figures for other homes are in our guide to how much electricity a UK home uses.

How Many Solar Panels Are in a 3, 4, 5, 6 or 10 kW System?

A 4 kWp system is 9 panels of 475 W or 9 panels of 455 W. 475 W is our default panel wattage (our rule), which you can change in the calculator, and 455 W is the lowest wattage in its list. The table below converts nine system sizes to a panel count at both wattages, with the actual kWp of that count in brackets.

A higher panel wattage means fewer panels for the same kWp. It does not mean more electricity from each kWp. When the total capacity of the installation is above 3.68 kW on a single-phase supply, the G99 process applies and the network operator needs to be consulted before fitting. Panel dimensions are a separate subject, covered under solar panel sizes and wattage.

How Many kW Is 8, 10, 12, 16 or 20 Solar Panels?

16 solar panels of 475 W make 7.6 kWp. The reverse table gives the kWp of seven panel counts, so you can check the size on a quote.

To convert any other count, multiply the panels by the watts of one panel and divide by 1,000. A size that matches a year of use still does not power the house in every hour.

How Many Solar Panels Does It Take to Run a House?

No number of solar panels runs a house on its own. A system can match the electricity your house uses in a year, but panels make nothing at night and little on winter days, so you still buy from the grid or use a battery.

"Matched to your use" means the panels generate as many kWh in a year as the house uses in a year. The two do not happen at the same time. The house uses part of the generation as it is made, which is self-consumption. The rest is exported in summer, and the house buys electricity back in winter.

More panels raise generation. A battery moves generation into the evening. Which of the two helps more depends on when you use electricity, and that choice is the subject of our guide to more solar panels or a battery. The calculator above prices a battery beside the panels, and a separate tool shows how much a solar battery costs.

What Changes the Number of Solar Panels You Need?

Besides your yearly use, postcode area, roof pitch and panel wattage, three things change the number of solar panels you need: roof direction, roof space and extra electric loads. Roof direction and extra loads can raise the count, and roof space can lower it. Shade lowers generation but not the count. The G98 connection limit changes what happens before fitting, not the count, and the calculator shows a note for it.

Roof Direction and Shade

In our PVGIS calculation at 35 degrees, an east roof gives about 79.5% and a west roof about 78.9% of a south-facing roof's output, and a north-facing roof about 54.2%. A roof that generates less needs more panels for the same kWh. The calculator returns Poor fit for a north-facing roof.

Shade from nearby buildings, trees or chimneys cuts output, and heavy shade also returns Poor fit. Optimisers stop one shaded panel from reducing what the other panels generate (Energy Saving Trust). The effect of each direction is the subject of our guide to which way solar panels should face, and morning output is covered under east-facing solar panels.

Roof Space Caps the Count

Roof space caps the panel count: the calculator never recommends more panels than the number you say fit. The calculator does not estimate roof space from a house type, so type the count from a quote or a roof plan. To count the panels for your own usable roof area, see how many solar panels fit on your roof.

An Electric Car, Heat Pump or Other Big Load

An electric car, a heat pump or another big load adds its own kWh a year to your use, and the system size scales with the total. Type the extra kWh a year in question 4 of the calculator. The result then shows three lines: the panels for your use today, the panels with the planned load and the difference between them.

Take the yearly figure from the estimate for your car or heat pump, from your meter, or from the appliance label for a hot tub or air conditioning. The calculator has no default figure for an electric car or a heat pump, because we hold no sourced value for either yet. The calculator does not model what time of day the extra load runs. The larger system still has to fit the roof and pass the G98 connection limit, so the roof cap and the export note apply to the larger count too.

The G98 Connection Limit: 3.68 kW per Phase

Installations up to 3.68 kW on a single-phase supply connect under G98. Above that, the G99 process applies and your distribution network operator (DNO) needs to be consulted before installation. The DNO is the company that runs the local electricity network. G98 and G99 are the Energy Networks Association's Engineering Recommendations for connecting small and larger generators.

The limit applies to the inverter and to export, not to the panel count, and the installer designs around it. The calculator adds a note when the recommended size is above the limit. It does not cap export. A roof may hold more panels than your use asks for, which raises the next question.

Should You Fit More Solar Panels Than You Need?

Sometimes. A bigger system costs less per kWp in the DESNZ data, and its extra output earns export income on a Smart Export Guarantee tariff. Whether the bigger size pays back sooner depends on your roof, your use and the price, and the calculator shows the payback for each size.

The cost data shows the first effect. The DESNZ mean for home retrofits is £2,109 per kWp of panels fitted for systems up to 4 kWp and £1,651 per kWp for systems of 4 to 10 kWp (DESNZ Solar PV cost data, April 2025 to March 2026). The export side depends on a tariff: a Smart Export Guarantee tariff pays for each exported kWh, and the calculator uses 13p per kWh, our calculation from Ofgem figures. The Smart Export Guarantee is not the Feed-in Tariff, which is closed to new applicants.

Compare the two sizes before you decide. Run the calculator with your own roof figure, then without it, and read the payback years on each result. One date affects the price: home solar carries 0% VAT until 31 March 2027 and 5% from 1 April 2027 (HMRC VAT Notice 708/6).

How We Work Out Your Panel Count

We work out your panel count from four inputs: your yearly use, the kWh per kWp for your roof, the panel wattage and the panels that fit. The list below also names the shade factor and the cost.

• Yearly use: your own figure, or Ofgem's typical medium value of 2,500 kWh a year.
• kWh per kWp: the figure for your postcode area, or a stand-in of 968.01 when no area is set, scaled for roof direction and pitch.
• Shade factor: lowers generation for some or heavy shade. It does not change the size rule.
• Panel wattage: 475 W by default, our rule (the median of the panel wattages four suppliers name for their own packages), unless you pick another; the result card states the wattage used.
• Roof space: the count you type. It caps the recommended size.
• Installed cost: the DESNZ Solar PV cost data mean per kWp for home retrofits in the size band, April 2025 to March 2026.

The size rule is kWp = yearly use / kWh per kWp, and the count is kWp x 1,000 / panel watts, rounded up. Generation is kWp x kWh per kWp x shade factor. The worked examples behind these sums are our own, not an official body's. The estimate leaves out a yield finer than your postcode area, a roof estimate from the house type, panel dimensions and an export cap for systems above the G98 limit. A survey turns the estimate into a measured design.

Get a Free Survey to Confirm the Size

An installer measures your roof and designs the panel layout at a survey, then gives you a quote. A survey is the next step after a Good fit or Borderline result, and it has four stages.

The survey request form on this site is not open yet.

You will get phone calls. That is how surveys are arranged. We are paid by Leads 2 Trade Limited when a homeowner we refer asks for a survey. You are never charged. It does not change our figures.

We do not refer tenants, people who are only researching, postcodes outside the installers' coverage, plug-in solar shoppers or households eligible only for funded schemes. A Poor fit result gets no survey offer. The request form is not open on this site yet. When it opens, this is where you get a free survey from MCS-registered installers.

What Size Battery Goes With Your Panels?

The calculator does not recommend a battery size: pick "Add one" in question 9 and it prices a battery of the size you choose beside the panels. Whether to add panels or a battery depends on when you use electricity, and the solar battery cost calculator prices the battery on its own. The price of panels and a battery fitted together is a separate page: solar and battery package costs.

Can You Add More Solar Panels to an Existing System?

Yes. You can add more solar panels to an existing system when the roof has space and the solar inverter, or a second inverter, can take them. The network operator must be told.

The sizing sums on this page work for an extension too. The reverse table above gives the kWp of the added panels, and the generation rule is the same: kWp x kWh per kWp x shade factor. An extension that takes the total capacity of the installation above 3.68 kW on a single-phase supply brings in the G99 process, and the DNO needs to be consulted before fitting. The calculator sizes a new system only. It does not price an extension, and it does not model the effect of added panels on Feed-in Tariff payments.

More Sizing Guides

The roof direction, pitch, shade and roof space questions in the calculator above cover the main sizing choices today. The yearly kWh from each panel or system is the subject of our guide to solar panel output in kWh per year.

Solar Panel Sizing Questions