Solar PV without the marketing fog

Solar marketing in the UK is, to put it politely, optimistic. Generation figures get extrapolated from European peak-summer days; payback periods are calculated against pre-2022 energy prices that no one currently pays; the 'free electricity' framing ignores the fact that your roof is generating most when you're not at home using it. The result is that quite a lot of households end up with a system that works, but doesn't deliver what they were sold.

I'm not anti-solar. We measure ours every day, and the numbers are genuinely good — but they are good in a specific way that the marketing rarely captures. This piece is what I'd want a friend to know before signing a quote: what a typical UK system actually generates, what an honest install costs in 2026, what the export-rate-versus-self-consumption split looks like in practice, and where the corner-cutting installers tend to put the kink in the deal.

The headline: PV is one of the better capital investments available to a UK homeowner in 2026, but only if you go in with realistic numbers and don't pay over the odds. The marketing fog hides simple arithmetic.

What a UK array actually generates

The single number worth memorising is around 850–950 kWh per kWp per year for a well-positioned south-facing UK roof at typical pitch, with the lower end for north-of-Manchester and the higher end for the south coast. East/west splits drop you to about 80–85% of that figure. Heavy shading takes a much bigger bite — sometimes 30–40%.

So a 4 kWp system on a south-facing roof in the Midlands generates roughly 3,400–3,800 kWh/year. A 6 kWp system gets you 5,100–5,700 kWh. That's the real-world figure. If a quote shows you 4,800 kWh from a 4 kWp array, the spreadsheet has been told you live in Spain.

Within that annual total, the seasonal distribution matters. Roughly 65–70% of UK generation falls between April and September. December and January between them produce around 5–7% of the annual total. This is why a system sized purely against your annual import figure underwhelms in winter — the curve is brutally seasonal.

Honest install costs in 2026

For a straightforward UK install with no major roof or electrical complications:

• 4 kWp system, panel-only (no battery): £4,800–£6,500 typical. Outliers either side, but the genuinely competitive market sits inside this band.
• 4 kWp + 5 kWh battery: £8,500–£11,500.
• 6 kWp + 10 kWh battery: £11,500–£15,500.
• 10 kWp + 15 kWh battery (typical for larger detached): £17,500–£23,500.

VAT on residential domestic solar is currently 0% under the zero-rated installation relief, which has held the headline numbers down. If a quote splits the supply and install lines and applies 20% to one of them, ask why — most installers package it correctly, but not all.

Cost variation between quotes for genuinely identical specifications is usually 20–35% on the same job. The cheapest is rarely the right answer; the most expensive rarely justifies the premium. Look at three quotes, ask for itemised inverter and panel model numbers, and check that the inverter warranty matches what's claimed in the headline number.

Self-consumption versus export: the actual economics

Here's where most marketing falls apart. Solar saves you money in two ways: self-consumption (you use what you generate, displacing imported electricity) and export (you sell what you don't use to the grid via SEG).

Self-consumption is worth roughly the price you pay for grid electricity, currently around 26–28p/kWh on a standard tariff. Export under SEG is currently paid at anywhere from 4p to 16p/kWh depending on your tariff, with most market rates sitting around 7–11p/kWh.

Consequence: every kWh you self-consume is worth around three times every kWh you export. The economic value of your system is overwhelmingly determined by your self-consumption ratio, which for a typical UK household with no battery and no behaviour shift sits between 25% and 40%. Add a 5kWh battery and that ratio rises to 55–70%. Add behaviour shift (running washing/dishwasher in the day) and you can push to 70–80%.

This is why the 'how much can I export?' question is the wrong question. The right question is 'how much can I self-consume?' — and the answer is overwhelmingly determined by whether you have a battery and what your day-time usage profile looks like.

The battery question

Should you add a battery? The honest answer in 2026 is: for most UK households, yes if the budget stretches; no if it doesn't and you'd cut corners elsewhere to fit one.

The economics of a battery are simple: you're trading capital for a self-consumption uplift of around 25–35 percentage points. For a typical 4 kWp household with 4,000 kWh/year generation, that uplift is worth around 1,200 kWh/year of grid displacement, which at 27p/kWh is roughly £325/year of additional saving. A 5 kWh battery costs £3,500–£4,500 fitted on top of an existing PV install. Simple payback: 11–14 years. That's not great.

But — and this matters — a battery on a time-of-use tariff is a different proposition entirely. Cheap-rate overnight charging plus solar-charging during the day plus discharge at peak rate can move the saving figure to £550–£800/year for the same household, taking payback to 6–9 years. The tariff turns the battery from a self-consumption tool into an arbitrage tool, and that's where the maths gets interesting.

The rule of thumb: if you're going to be on a time-of-use tariff, a battery is probably worth it. If you're staying on a flat-rate tariff, it probably isn't, unless you place high value on grid resilience for its own sake.

Where the marketing claims fall apart

Here are the recurring patterns that I'd flag in any quote you receive:

1. Generation figures based on European data. If a UK quote shows more than about 950 kWh/kWp/year, the spreadsheet is wrong. Ask for the source data.
2. Payback calculated against a peak energy price you no longer pay. A lot of quotes still calculate against the 2022/23 cap. Recalculate against your current actual tariff before believing the headline.
3. Self-consumption assumed at 60–70% with no battery. Wishful thinking unless you genuinely are home all day with high consumption. Most households without a battery come in at 25–40%.
4. 'Smart' panel claims that don't reduce to a per-panel optimiser. Optimisers can be useful in shaded or split-array installs; if your roof is uniform south-facing they add cost without adding much yield.
5. 20-year warranties that turn out to be split between three suppliers. Read the warranty terms. Panel-warranty, inverter-warranty, and workmanship-warranty are three different things; a 'lifetime' headline often hides a 5-year inverter warranty.
6. Battery 'usable' capacity vs nameplate. A 5 kWh battery typically has 4.0–4.5 kWh of usable depth-of-discharge. Quote the usable number, not the nameplate.

What a good quote looks like

A quote you can trust will have all of the following written down:

• Specific panel make, model, and wattage with datasheet linked or attached
• Specific inverter make, model, and warranty period (5/10/12 years)
• Annual generation estimate with the methodology spelled out (PVGIS or similar) and a postcode-level irradiance figure
• Estimated self-consumption with and without battery, with a stated assumption about household occupancy pattern
• Price split between supply and install, with VAT treatment explicit
• Workmanship warranty term separate from product warranty
• Scaffolding, electrical, and DNO notification costs included or itemised — not 'subject to survey'
• SEG export rate quoted, even if you're not using their preferred tariff
• An MCS certificate commitment, with the certifying body named

Anything missing from this list is a question, not necessarily a deal-breaker. But in our experience the installers who provide all of this without being asked are also the ones who do the install properly.

What I'd actually do in 2026

For a typical 3-bed semi in the UK in 2026 with an unshaded south-facing roof and a reasonable budget, my own recommendation runs roughly:

1. Size the array as large as the roof will reasonably take — usually 4–6 kWp. The marginal cost per kWp drops as you scale, and over-generation is no longer uneconomic at SEG rates.
2. Add a battery sized at 1.5–2x your average daily evening consumption — typically 5–10 kWh.
3. Move to a time-of-use tariff to make the battery work harder.
4. Ignore optimisers unless your roof is shaded.
5. Get three quotes, reject the cheapest, interrogate the middle one, and check that the most expensive is justified by something concrete (better inverter, longer workmanship warranty, real installer track record).

In our setup, the system has been on the roof long enough to give us a clean fifth-year reading, and the actual generation has come in within 3% of the original PVGIS-based estimate. That's the discipline I'd want from any installer's headline figure.

Long-term operation: what to expect after install

The first install conversation is the loud one. The next 25 years of operation are the quiet one, and worth thinking about up front. A well-installed UK PV array needs very little. We get the panels checked once every 3–4 years for soiling, fixings, and any visible micro-cracking — about £80–£150 for a maintenance visit. Inverter replacement is the one cost most owners forget: most string inverters have a 10–12 year practical life, and the replacement at year 12 is typically £900–£1,500 fitted. If your quote shows a 20-year payback that doesn't include this, the spreadsheet is missing a line.

Generation degradation is real but slow — typically 0.4–0.6% per year for modern panels, so a 4 kWp array delivering 3,800 kWh in year one is delivering around 3,400 kWh in year 25. Plan for the worst-year figure, not the headline. Insurance — most home contents policies cover roof-mounted PV by default, but check your specific policy and report the install to your insurer when it goes live. Some policies require notification.

The other long-term consideration is roof replacement. If your roof is older than about 30 years, factor in that you may need to come off the panels and re-fit them at some point in the 25-year horizon. The cost of removal-and-refit is roughly £1,500–£2,500 per kWp. If a roof replacement is plausible within 10 years, plan for it now rather than discovering it later.

Solar PV in 2026 is a genuinely good capital investment in the UK, with payback periods for properly priced systems landing in the 6–10 year range when you include realistic self-consumption ratios and current export tariffs. Add a battery and a time-of-use tariff and that figure tightens. Pay over the odds for a marketing-fog quote and it stretches to 12+ years.

The technology isn't the variable. The variable is whether you've cut through the marketing assumptions to your actual numbers — your roof, your usage, your tariff, your behaviour. Do that work first, and the install becomes the easy part.