How to read a solar quote and spot overpricing

A solar quote is a breakdown of every cost and assumption behind your proposed system. It shows the equipment, the installed price, and a payback claim. Most of it is fair. Some of it is padding, and the padding hides in the same places on almost every quote you will read.

Here is how to go through one line by line, in the order the numbers actually matter, so you can tell a fair price from a fat one before you sign anything.

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Start with the system size in kWp

The first number that means anything is the system size, written in kWp (kilowatts peak). This is the rated output of all the panels added together under standard test conditions. A quote for ten 440 W panels gives you 4.4 kWp. The installer should state this near the top. If they bury it or quote you only a panel count, ask.

kWp is the anchor for everything else. You judge the price against it, you judge the production estimate against it, and you compare two quotes by it. Two installers might both quote "12 panels" while one fits 440 W panels and the other fits 405 W, so the panel count alone tells you almost nothing. Convert to kWp and compare like for like.

Watch the gap between kWp and the annual production figure in kilowatt-hours (kWh). A 5 kWp roof in Manchester produces roughly 4,300 kWh a year (approximate PVGIS-derived estimate for a south-facing roof at 35 degrees). The same array in Seville produces closer to 8,500 kWh (approximate PVGIS-derived estimate; eu-solarcalculator.com puts a 5 kWp south-facing system in Seville at about 8,359 kWh/yr). If a quote claims a number far above what your location and roof angle support, the payback maths underneath it is already wrong. You can sanity-check the production figure yourself in under a minute using PVGIS, the EU's free public irradiance tool, which is also what our calculator uses.

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Read the panel and inverter brands, not the marketing

Quotes love adjectives. "Premium tier-one panels with cutting-edge cell technology" tells you nothing you can verify. The brand and model number tell you everything.

For panels, look for the manufacturer, the model, and three figures: rated wattage, efficiency, and the warranty terms. A panel from Aiko, REC, Longi, or Jinko at 20 to 23% efficiency is solid mainstream kit. The efficiency matters most when your roof is small and you need to fit more watts into limited space. On a large roof, a cheaper panel that takes one extra square metre costs you nothing extra.

For the inverter, the brand carries real weight because it fails sooner than the panels. Panels last 25 years and longer; a string inverter typically runs 10 to 15 years (pv magazine, 2025). Fronius, SMA, SolarEdge, GoodWe, and Sungrow are names you can check. An unbranded or white-label inverter is the single clearest sign of a quote built down to a price. When it dies in year 11, you want a manufacturer still in business and parts still made.

The inverter also tells you the system design. A string inverter is one box for the whole array. Microinverters or power optimisers sit under each panel and cost more, and they earn that cost only on roofs with shading or several orientations. If your roof is one clean south-facing plane and the quote pushes microinverters, ask what problem they solve here. We cover the trade-off in inverters explained.

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Benchmark the price per kWp

This is the number that exposes overpricing, and almost no quote shows it to you. Take the total installed price, subtract any battery, and divide by the kWp.

As a rough guide for a straightforward residential install in 2026:

Market	Typical range per kWp	Notes
United Kingdom	£1,300–£1,800	VAT-inclusive (0% VAT applies until Mar 2027)
Western Europe	€1,100–€1,800	Wide country spread; DE and NL at the lower end
Australia	AUD 1,200–1,500 (pre-STC rebate)	Street price after the STC discount is ~AUD 900–1,050/kWp

Sources: UK range from Heatable 2026 and GOV.UK PV cost data; Europe range from SurgePV 2026; Australia pre-STC gross from Solar Choice Price Index Jun 2026.

Smaller systems sit at the top of each range because the fixed costs (scaffolding, the crew's day, the inverter, the paperwork) spread over fewer panels. A 3 kWp system will cost more per kWp than a 6 kWp one, and that is normal. A 5 kWp quote landing at double the top of the local range with standard panels and no awkward roof is a different matter. That gap is margin, and it is yours to question or walk away from.

Get the price per kWp from two or three installers. The spread will tell you the local fair band faster than any national average.

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Find the padding

Padding rarely sits in the headline. It hides in the add-ons, where you have no benchmark and the installer knows it.

• Scaffolding is a real cost on a two-storey house, typically £400 to £800 for a standard install (Checkatrade scaffolding cost guide, 2026). Doubled or vaguely "included in a premium package," it is a common place to inflate.
• Bird protection, optimisers, and monitoring get bundled as standard when you may not need them. Ask for each as a line you can decline.
• "System design and consultation" fees on top of the install price are margin wearing a job title.
• Batteries quoted as part of one blended total hide their own price and their own weak payback. Make the installer split the battery out so you can judge it on its own terms. In most markets a battery extends payback rather than shortening it, and you want to see that on paper before you agree.

A quote that breaks every cost onto its own line is showing you respect. One that gives you a single big number and a discount "if you sign today" is managing you.

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Check the warranties and the payback claim

Three warranties matter, and they are not the same length. The product warranty covers the panel itself (good ones run 25 years). The performance warranty guarantees the panel still produces a set percentage after 25 years: budget panels typically floor at 80%, while quality residential panels from mid-to-premium manufacturers typically guarantee 85 to 94% (EnergySage, 2026). Panels degrade by roughly 0.25 to 0.5% a year. Modern N-type panels such as TOPCon and HJT sit at the lower end of that range; NREL's 2025 analysis puts the median across all field-deployed modules at 0.5%/yr (see NREL Photovoltaic Lifetime Project). The workmanship warranty covers the installer's labour, and this is the one that varies widely. Two years is thin. Ten is reassuring.

Then the payback claim, the figure designed to make you sign. Check what tariff it assumes. A quote that runs the maths at a high electricity price and a generous export rate produces a flattering payback. Reality then undershoots it for the next decade. Ask which tariff, which export rate, and whether the figure accounts for the inverter replacement you will pay for around year 12.

You do not have to take their word for any of it. We run the real economics on free, resale-permitted government climate data (PVGIS, NASA, and NREL), and we show you honest payback, NPV, and IRR for your roof in your country before you hand over a single contact detail. Use it to walk into the conversation already knowing the fair number, then read the quote against it line by line.

For more on the payback maths itself, see how the solar payback period, NPV, and IRR work.

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Frequently asked questions

What is a good price per kWp for solar in the UK in 2026?

A straightforward residential install in the UK runs roughly £1,300 to £1,800 per kWp installed, VAT-inclusive, with 0% VAT applying until March 2027. Smaller systems (under 4 kWp) land at the top of the range because fixed costs spread over fewer panels. Above £1,800/kWp on a standard roof warrants a second quote.

How do I calculate the cost per kWp from a quote?

Take the total installed price, subtract any battery storage cost, then divide by the system size in kWp. For example, a £8,400 quote for a 5.5 kWp system (no battery) works out to £1,527/kWp. That single number lets you compare any two quotes on equal terms.

How long does a solar inverter last?

A residential string inverter typically lasts 10 to 15 years, according to industry data confirmed by pv magazine (2025). Budget for one replacement over a 25-year panel life. Microinverters and power optimisers last longer (often 20 to 25 years) but cost more upfront.

What degradation rate should a solar quote assume?

A fair quote uses 0.4 to 0.5% annual degradation for standard panels. Modern N-type panels (TOPCon, HJT) can degrade as little as 0.25%/yr. NREL's field data sets the median across all deployed modules at 0.5%/yr. Any quote projecting output with no degradation, or implying panels hold full output for 25 years, is overstating production.

What is the difference between the product warranty and the performance warranty?

The product warranty covers physical defects and failure (typically 10 to 25 years). The performance warranty guarantees a minimum output percentage at year 25, ranging from 80% for budget panels to 85 to 92% for mid-to-premium residential panels (EnergySage, 2026). Both matter: a panel can still function while producing far less than promised. Check both figures on the spec sheet, not just the headline "25-year warranty."

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The bottom line

A solar quote is not a fixed fact. It is a set of assumptions, and some of those assumptions are more favourable to the installer than to you. The price per kWp tells you whether the headline number is in range. The add-on lines tell you where the margin lives. The warranty terms and tariff assumptions tell you whether the payback figure is honest.

Know the fair price for your market before you read the first quote. Know what production your roof can support. Then read every line and ask about every assumption that does not match your independent numbers.

Estimate your roof →

Estimate only, not a quote. Figures use local climate data and average tariffs; your installer's quote will be exact.