8kW Solar Panel System UK: The Full Electrification Size

An 8 kWp solar system sits between the popular 6 kWp bracket and the large-home 10 kWp territory. It is not oversized for the properties it suits, and it is not a compromise. For a detached house or large semi with an electric vehicle and a heat pump, 8 kWp is the size where the solar generation starts to meaningfully match the full-electrification electricity demand throughout the year.

This article covers what an 8 kWp system involves, what it costs, how much it generates, and the DNO connection rules that differ from smaller systems.

What does an 8kW system look like?

An 8 kWp solar system typically consists of:

• 18 panels at around 450W each (18 × 450W = 8,100W, sold as an 8 kWp system)
• Roof space: approximately 34–36 m² of usable, unshaded roof
• Inverter: an 8 kW hybrid or string inverter — a hybrid inverter is worth considering at this size if battery storage is part of the plan

Eighteen panels is a substantial array. On a single south-facing roof slope, this typically requires a 4-bed or larger detached property. On a semi-detached house, it is sometimes achievable by splitting panels across south and east/west slopes, though this reduces output compared to a single south-facing arrangement.

A common layout is two rows of 9 panels, or three rows of 6 — your installer will survey the roof and advise on orientation and shading before designing the array.

Which properties suit 8 kWp?

• 4-bed detached house with a large south-facing main roof: this is the typical fit for 8 kWp
• Large 4-bed semi-detached or end-of-terrace: achievable if panels can be spread across two slopes without significant shading
• Bungalow with a large roof footprint: the shallow pitch typical of bungalows still accommodates 18 panels on a larger plot
• Properties planning full electrification: homes where an EV and heat pump are already installed, or will be within the next 12–24 months

How much does an 8kW system cost?

The 0% VAT on supply-and-install applies until 31 March 2027. After that, VAT reverts to 5%.

The cost-per-kWp at 8 kWp is broadly similar to 6 kWp. The additional scaffold and labour costs are largely the same; the incremental cost comes mainly from the extra panels and the slightly larger inverter. If your roof can accommodate 18 panels without complexity, stepping from 6 kWp to 8 kWp typically adds £1,500–2,500 to the installed cost — a reasonable outlay given the proportional increase in generation.

How much electricity will an 8kW system generate?

Using the UK average yield of approximately 850 kWh per kWp per year:

• Annual output: approximately 6,800 kWh
• Summer peak (May): approximately 952 kWh
• Winter trough (December): approximately 232 kWh

By location:

• South of England: ~7,200–8,400 kWh/yr
• Midlands / Wales: ~6,400–7,200 kWh/yr
• North England: ~6,000–6,800 kWh/yr
• Scotland: ~5,600–6,400 kWh/yr

How much will I save?

Using April 2026 rate benchmarks (standard flat tariff: 24p/kWh):

These figures combine the value of electricity you avoid buying (at 24p/kWh) with a modest SEG export rate (3.3–5.2p/kWh) on the portion you do not use. The self-consumption rate has a large effect on total savings at this system size, because 6,800 kWh is more generation than a household without a battery or EV charger can readily absorb during daylight hours.

An EV charger that diverts surplus solar generation (such as the myenergi Zappi in ECO+ mode) and a battery both push self-consumption higher, significantly improving the return.

Is 8kW enough for my home?

"Covers X%" means annual generation divided by annual consumption. Seasonal mismatch still applies — winter imports will always be needed regardless of system size, and a large summer surplus is best captured with a battery or used for EV charging.

When 8 kWp makes sense

You have both an EV and a heat pump. This is the defining use case for 8 kWp. A heat pump adds roughly 3,000–5,000 kWh per year; an EV adds 2,000–4,000 kWh per year. Together, these push household electricity consumption to 7,000–9,000 kWh annually. An 8 kWp system generating 6,800 kWh covers a meaningful proportion of that demand, particularly in the spring and autumn shoulder seasons when heat pump use and solar generation overlap.

You are future-proofing. If an EV or heat pump is planned for the next few years, sizing at 8 kWp now avoids the cost and disruption of adding panels later. Expanding an existing installation typically requires a new inverter, additional scaffolding, and potentially a fresh DNO notification.

Your roof is large enough to fit 18 panels well. A slightly under-used roof on a detached property is often better served by 8 kWp than 6 kWp, provided there is no significant shading.

You want a meaningful battery reserve. An 8 kWp system regularly fills a 10 kWh battery by mid-afternoon on a summer day, leaving the evening covered without grid imports. Smaller systems are less likely to fill a large battery reliably outside of peak summer.

DNO notification: G98 or G99?

This is one of the most important practical points about 8 kWp systems on a standard UK electricity supply.

The G98/G99 threshold

Most UK homes have a single-phase electricity supply (a single live conductor from the grid). On single-phase, the DNO threshold between simplified notification and full pre-approval is 3.68 kW of inverter output per phase.

• G98 (Fit and Inform): For systems up to 3.68 kW on single-phase. Your installer registers the installation with your DNO after the work is done. No pre-approval required.
• G99 (pre-approval): For systems above 3.68 kW on single-phase. Your installer must submit an application to your DNO and receive written approval before installation begins.

An 8 kWp system uses an inverter rated at or near 8 kW output. On a single-phase supply, this is more than twice the G98 threshold. An 8 kWp installation on single-phase supply requires G99 pre-approval.

What G99 means in practice

G99 is not a barrier — the vast majority of domestic applications are approved. It is an assessment of whether the local grid section can safely accommodate the additional generation capacity. Your installer submits the application; you do not need to contact the DNO directly.

The main practical effect is timing. G99 approval typically takes 4–10 weeks, depending on your DNO and the complexity of the local grid. Some DNOs offer a fast-track process for smaller domestic systems in the 4–16 kWp range, but this is not universal.

Three-phase supply: different rules

Some larger or older detached properties have a three-phase electricity supply (three separate live conductors, each capable of 3.68 kW). On three-phase, the combined G98 threshold is 11.04 kW (3.68 kW × 3 phases). An 8 kWp system stays within this limit, so only a G98 notification is required — not G99 pre-approval.

To check whether your property has single-phase or three-phase supply, look at your consumer unit (fuse board). Three-phase installations typically have three separate main fuses or MCBs at the top of the board. If you are unsure, your installer can confirm from the meter and supply tails.

Can I add a battery?

Yes. A 10–13 kWh battery is a well-matched pairing for 8 kWp. The reasoning:

• On a decent summer day, an 8 kWp system generates roughly 40–56 kWh. After daytime household use, a surplus of 15–30 kWh is common. A 10–13 kWh battery captures a useful portion of this for evening use.
• On spring and autumn days (the peak-season overlap with heat pump use), generation is lower but a 10 kWh battery still fills reliably most days.
• On winter days, generation drops significantly and a large battery provides diminishing returns — but it still captures short midday bursts.

Common pairings at 8 kWp:

• 10 kWh battery: a good default choice — captures the majority of useful surplus across the year without paying for capacity that rarely fills in winter
• 13 kWh battery: worth exploring if you have high evening demand, an EV that charges at home in the evenings, or if you want to extend battery-only operation through longer autumn nights

A hybrid inverter (installed as part of the system from the outset) makes battery integration straightforward and avoids the additional equipment cost of retro-fitting a separate battery inverter later.

Can I add more panels later?

Most 8 kW inverters accept up to 9.6–12 kWp of solar input — some degree of DC oversizing is standard practice and allows the inverter to operate closer to its rated output during shoulder months. This means adding 2–4 more panels to an 8 kWp system may be possible without replacing the inverter, depending on the specific model.

However, any expansion that takes the system above the existing G99 approval threshold will require a fresh DNO notification or amendment to the existing G99 approval. Factor this in if expansion is likely.

See the guide to adding panels to an existing system for the full process.

Next steps

• How to size your solar system — the full sizing methodology
• How much do solar panels cost in the UK? — UK-wide cost guide
• How many solar panels do I need? — practical sizing tool
• 6kW solar system UK — one step down if 8kW feels like too much
• 10kW solar system UK — one step up for larger properties and business use
• Adding panels to an existing solar system — if you want to expand later

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