Solar Panel Cost by System Size (2026)

The most common question after “how much do solar panels cost?” is “how much should I get?” The two questions are closely linked: bigger systems cost more upfront but generate more, and the right size depends on your roof, your electricity consumption, and whether you're adding a battery. This guide sets out costs and generation figures for the three most common residential system sizes in the UK, with a note on who each suits and what the per-kWp economics look like.

The per-kWp benchmark

Before looking at specific sizes, it helps to understand the pricing benchmark. Most UK installers charge £1,500–£2,200 per kilowatt-peak (kWp) for a standard residential installation, including labour, mounting hardware, inverter, and zero-rated VAT. Quotes below £1,400 per kWp warrant scrutiny; quotes above £2,500 per kWp need a clear explanation (difficult roof access, specialist mounting, premium panels). The full picture of what drives prices up or down is in the solar panel cost and savings guide.

4 kWp: the most popular choice

A 4 kWp system typically comprises 10–12 panels (each around 400W) covering roughly 18–22m² of roof space. It is by far the most commonly installed size in the UK.

Installed cost: £6,000–£8,000 including zero-rated VAT. At mid-range pricing of around £1,750 per kWp, a 4 kWp system comes in at approximately £7,000.

Annual generation: Around 3,400–3,800 kWh per year in central England on a south-facing roof with no significant shading. In Scotland this is typically 15–20% lower; in the south of England slightly more.

Who it suits: A 4 kWp system is a good match for a 3-bed home with annual electricity consumption around 3,000–4,000 kWh, no EV, and no heat pump. It will generate broadly in line with that household's annual consumption, though not necessarily when the household needs it. If you want to cover more of your consumption directly, daytime habits or a battery matter more than raw system size.

Limitations: If you plan to add an EV or heat pump within the next few years, a 4 kWp system will quickly become undersized relative to your total consumption. It's worth sizing up if the roof allows it. Understanding how many panels you actually need based on your specific consumption is the right starting point before accepting a standard quote.

6 kWp: the growing household choice

A 6 kWp system needs 15–16 panels and around 27–30m² of usable roof. It represents a significant step up in both cost and generation — and increasingly in value, as more UK households add EVs or heat pumps.

Installed cost: £8,000–£12,000 including zero-rated VAT. Per-kWp costs often drop slightly as size increases because labour and survey costs are partly fixed; a 6 kWp system at £1,700 per kWp comes in at around £10,200.

Annual generation: Around 5,100–5,700 kWh per year in central England. That's enough to cover the average 3-bed household's consumption (around 3,500 kWh) and an EV adding 2,000–3,000 kWh per year, with some surplus for export on good days.

Who it suits: A 6 kWp system suits a larger home, a household with an EV, or anyone with above-average electricity consumption. It also makes a strong case for battery storage: the additional generation gives more surplus to store, making the battery more productive. The case for 6 kWp strengthens further if you have a heat pump, which can add 3,000–5,000 kWh to your annual consumption.

8 kWp: high-consumption and larger properties

An 8 kWp system requires 19–20 panels and typically 36–40m² of usable roof. It is less common in standard residential installations but increasingly relevant for larger properties, households running both an EV and a heat pump, or those with unusually high consumption.

Installed cost: Around £10,000–£15,000 including zero-rated VAT. At this scale, installers may also need to notify the Distribution Network Operator (DNO) before installation, which can add a few weeks to the project timeline. Some properties may require a 3-phase electricity supply check — ask your installer to clarify this before specifying 8 kWp.

Annual generation: Around 6,800–7,600 kWh per year in central England. For a household consuming 6,000–8,000 kWh per year (a 3-bed home with an EV and a heat pump), this level of generation can cover a large proportion of annual demand, particularly in spring and summer.

Who it suits: Larger homes (4–5 bedrooms), households running multiple high-consumption devices, or anyone with a roof area that can accommodate it and a long-term view on energy use. The per-kWp economics at 8 kWp are similar to 6 kWp — the fixed costs are spread over more capacity. Whether the additional generation is financially justified depends on how much of it you'll actually consume rather than export at ~5p/kWh.

Per-kWp economics: bigger is not always better

The common assumption that bigger systems are better value per kWp is broadly true but not the whole story. Additional generation beyond what you can reasonably self-consume goes to the grid at around 5p/kWh rather than avoiding imports at 24–28p. If a 4 kWp system already generates more than you can use without a battery, a 6 kWp system adds cost faster than it adds value — unless you add storage or significantly increase consumption (EV, heat pump).

The right approach is to model expected self-consumption at each size before deciding. If your annual consumption is 3,500 kWh and you have no plans to change that, a 4–5 kWp system is likely the right scale. If you're planning an EV within two years, sizing up to 6 kWp from the start is almost always the more economical choice than retrofitting later.

The payback implications of each size, including worked examples, are set out in the payback period guide. For the broader verdict on whether any of these sizes stacks up financially for your situation, see are solar panels worth it in the UK?.

Comparing panels across brands and tiers

System size is partly determined by the panel wattage you specify. A 400W panel requires 10 panels for a 4 kWp system; a 430W panel achieves the same capacity in 10 panels with slightly less roof space. Higher-wattage panels can allow a larger system on a constrained roof. The trade-off is typically cost — higher-wattage panels from Tier 1 manufacturers cost more per panel but degrade more slowly over 25 years. Our solar panel product guide covers the main brands and tiers currently available in the UK.

Getting quotes for each size

When requesting quotes, specify the system size you want rather than asking the installer to recommend one — you'll get more comparable quotes and make it clearer you've done the research. Ask each installer to confirm the number of panels, their wattage, the inverter brand and model, and the expected annual generation in kWh (not just kWp capacity). When you're ready to compare, get quotes from vetted MCS-certified installers in your area.