Panel installation and wiring

How Many Solar Panels Do I Need for My UK Home?

The right number of panels is not a fixed answer: it follows from your electricity usage, your roof, and the size of inverter you choose. This guide walks through the sizing logic step by step, in plain terms, so you can check whether a quote is right before you sign anything.

Helpful video reference. EvoEnergy’s “Recommended Maximum Size for Domestic Solar Systems in the UK” covers the practical limits on domestic system sizing, including how the SEG export rate changes above 4 kWp. EvoEnergy is a UK solar, battery storage and EV charging provider.

1. Start with your annual electricity usage, not panel count

The question "how many panels" is the wrong starting point. The right starting point is your annual electricity usage in kWh, which you can find on a bill or in your smart meter app. The UK average for a typical household sits around 2,700 to 3,400 kWh a year, but yours will differ depending on household size, whether you heat with electricity, and whether you plan to add an EV charger.

If you already have a solar system and are adding to it, or if you have a heat pump or EV charger on the way, use your most recent 12-month usage figure rather than an estimate. Smart meter half-hourly data gives the most accurate picture of when you use electricity through the day, which also helps size a battery correctly if you are considering one.

2. Converting usage to system size in kWp

System size for solar is measured in kilowatt-peak (kWp), which is the rated output of all the panels combined under ideal test conditions. In the UK, a rough rule of thumb is to divide your annual usage by 850 to get the kWp system that would produce roughly enough electricity to cover your full annual demand.

For a 3,400 kWh household that gives 4 kWp. For a 2,500 kWh household, closer to 3 kWp. In practice, you will not self-consume everything you generate in real time, so you will export some electricity during the middle of the day, which lowers the effective benefit. The sizing calculation is a starting point, not a precise target.

3. Panel count follows from kWp and panel wattage

Modern UK domestic panels typically have a rated output of between 400 W and 450 W per panel. To find panel count, divide your target kWp by the wattage of the panel your installer is specifying. A 4 kWp system using 400 W panels needs 10 panels; using 430 W panels, 10 panels gives you 4.3 kWp.

Panel wattage has increased steadily over recent years. Panels sold as standard domestic units in 2020 were commonly 320 to 360 W. The same roof space in 2025 can now accommodate higher-wattage panels, which means you can generate more electricity without needing more roof area.

4. What limits you: roof space, shading, and orientation

Each panel takes up roughly 1.7 to 2 square metres of roof area. A 10-panel system at 1.8 m2 per panel needs around 18 m2 of clear, usable roof. Skylights, soil stacks, and chimney stacks all reduce usable area, and any shading from a neighbouring roof, chimney, or tree will reduce output significantly, especially if it falls on panels wired in series where one shaded panel affects the whole string.

A south-facing roof at 30 to 45 degrees gives the best annual yield in the UK. East and west-facing roofs still work well and typically produce around 80 to 85 percent of the equivalent south-facing system. North-facing roofs are generally not suitable: annual output is too low relative to installation cost to make the economics work for most households.

5. The 3.68 kW inverter threshold and G98 vs G99

In the UK, grid-tied inverters with an AC output up to 3.68 kW fall under the simpler G98 notification route, where the paperwork is submitted on installation day and the system can be energised immediately. Above that threshold, a G99 application is required, which must be submitted before installation and approved by the DNO before the system can go live. G99 approval times vary by area but can be eight to twelve weeks or longer in parts of South East England where UK Power Networks is dealing with high solar connection volumes.

This is why many installers in Kent and East Kent recommend keeping the inverter at or just below 3.68 kW AC, even if the panel array itself is rated slightly above that in kWp. The inverter clips the peak output, which has a minor effect on annual generation, but avoids the G99 timeline entirely. If your usage genuinely justifies a larger system and you are happy to wait for G99 approval, a bigger inverter is a sensible option.

Frequently Asked Questions

How many solar panels does a typical UK home need?

Most UK three-bedroom homes with average electricity usage end up with 8 to 12 panels, delivering around 3.5 to 4.5 kWp. Larger households or those planning an EV charger often want 12 to 16 panels. The right number depends on your actual annual usage, your roof space, and how much of your own electricity you want to cover.

Does my roof direction matter for sizing?

Yes. A south-facing roof at 35 to 40 degrees gives the best annual output in the UK. East or west-facing roofs typically produce around 80 to 85 percent of an equivalent south-facing system, which means you may need one or two extra panels to achieve the same annual yield. North-facing roofs are generally not suitable for solar in the UK.

Why do some installers recommend 3.68 kW inverters?

3.68 kW is the single-phase threshold for the simpler G98 notification process. Inverters rated above this need a G99 application from the DNO before the system can be switched on, adding weeks or months to the project. Keeping the inverter at or below 3.68 kW AC avoids that wait. The panels themselves can still be rated above 3.68 kWp, as the inverter clips the excess output on the very best days.

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