Typical costs by system size
A 3.5 kWp system — suited to a household with average energy consumption — costs between £5,500 and £8,000 installed. This covers 8–10 panels, a string inverter, cabling, and scaffolding. It generates roughly 3,000–3,500 kWh annually in the UK, covering about 60–70% of a typical household's electricity use.
A 6 kWp system, which suits larger homes or households with high consumption (an EV charger, heat pump, or large family), costs between £8,000 and £12,000. At around 16 panels, this is close to the practical maximum for most semi-detached or detached roofs.
Adding a battery (typically 5–10 kWh) adds £2,000–£5,000 to either system. Batteries allow you to store surplus daytime generation for evening use, increasing self-consumption from around 30% without a battery to 60–80% with one.
What drives costs up
Roof complexity is the biggest variable in labour cost. A straightforward south-facing pitched roof costs significantly less to scaffold and work on than a multi-plane, valley, or east-west split roof. Installers price in difficulty; a complex roof can add £500–£1,500 to the job.
Panel grade matters. Budget panels from lesser-known manufacturers cost less per unit but may underperform against their rated output and carry shorter manufacturer warranties. Premium panels from brands like SunPower, REC, Panasonic, or Q Cells cost more but have a 25-year performance warranty backed by a company with a long track record.
Inverter choice also affects price. Microinverters (one per panel) or DC optimisers cost more than a central string inverter but improve performance on shaded or complex roofs and allow panel-level monitoring. For a simple unshaded south-facing roof, a quality string inverter is cost-effective; for a partially shaded installation, the additional cost of optimisers is usually justified.
The Smart Export Guarantee offsets cost over time
Since 2020, all UK energy suppliers with 150,000 or more customers are required to offer a Smart Export Guarantee (SEG) tariff, which pays you for surplus electricity exported to the grid. Octopus Energy, E.ON, and EDF currently offer some of the most competitive SEG rates.
A typical 4 kWp system in the UK exports around 800–1,200 kWh annually. At a mid-range SEG rate of 15p per kWh, this generates £120–£180 per year in income. Combined with savings from self-consumed electricity (displacing grid imports at 24–30p/kWh), the payback period for a well-specified system is currently 8–12 years.
Your installation must be carried out by an MCS-certified installer to qualify for SEG. Always confirm MCS certification before signing a contract.
Ongoing maintenance costs
Once installed, the main ongoing costs are modest. A professional solar panel clean costs £4–£8 per panel, or typically £60–£150 for a standard domestic array. An electrical inspection every three to five years costs £100–£200. Inverter replacement — usually needed after 10–15 years — costs £500–£1,500 depending on type.
Keeping panels clean is one of the highest-return maintenance actions available: dirty panels lose 15–25% efficiency, and a single professional clean typically recovers that output for £80–£120. FindSolarCleaner.co.uk lists verified UK solar panel cleaners searchable by postcode.