How to read a solar panel quote

A solar quote is a sales document. That is not an accusation, it is a description: it is written to be accepted. Reading one well means extracting the handful of facts that let you compare it with another, and asking about the things it has chosen not to say.

Here is the order that works, and the five questions that do most of the work.

What must be on it

Before anything else, check these are present:

• System size in kilowatts peak, and the panel count and wattage it comes from.
• Panel make and model.
• Inverter make, model and type, and whether it is battery ready.
• Estimated annual generation in kilowatt hours.
• Total price, with the VAT treatment shown. Domestic installations are zero rated until 31 March 2027, so a 20% VAT line against the qualifying work is a question to ask, not a cost to accept.
• What is excluded.
• Warranty terms, separately for panels, inverter and workmanship.

A quote missing the generation estimate or the exclusions is not ready to be compared with anything.

The five questions

One: what is the cost per kilowatt peak? Divide the total by the system size. A “£7,900 for 4.3kW” quote is £1,837 per kilowatt; a “£6,900 for 3.6kW” quote is £1,917. The cheaper looking quote is the dearer one, which is the entire point of the exercise. Then hold both against the government’s published medians, £1,780 per kilowatt for small systems and £1,697 for the 4 to 10kW band in 2025/26, so the comparison has an external anchor rather than two salespeople’s numbers.

Two: which tool produced the generation estimate, and what shading assumption did it use? The savings figure is downstream of this. An estimate that is ten per cent optimistic makes everything after it ten per cent wrong, and shading is where optimism hides. Certified installers are required to use the MCS standard estimation method, postcode irradiance, orientation, pitch and a shading assessment, so the real question is whether this quote did. An installer who surveyed properly answers immediately.

Three: what self consumption rate does the savings figure assume? This is the most influential number in the projection and the one least likely to be stated: moving it moves payback by years. If the answer is a round number with no reference to your household, the savings figure is generic.

Four: what is excluded, and what would it cost if needed? Scaffolding, consumer unit work, roof repairs, bird protection, long cable runs. Get it in writing; the full exclusions checklist covers which are legitimate and which are padding relocated below the headline.

Five: is the projection in today’s money, and does it include an inverter replacement? A twenty five year total built by compounding an assumed energy price rise, with no inverter replacement in it, is a marketing number.

Reading the savings projection

Most quotes include a long term savings table. Three things to check:

The escalation rate. If savings grow every year by an assumed percentage, find out what it is. An assumed 5% annual rise, compounded, roughly doubles the claimed annual saving by year fifteen, which is how a modest system acquires a spectacular twenty five year total. Ask to see the table at zero escalation; the system did not change, only the honesty of the total.

The degradation rate. Panels lose output slowly and steadily. A table where generation never falls is not modelling reality.

The replacement costs. Inverters do not last as long as panels. If a battery is included, it will need replacing sooner still, and its capacity declines along the way. Both belong in the table.

Warranties, read properly

Three separate things, often blurred together:

• Product warranty on the panels, covering manufacturing defects.
• Performance warranty on the panels, guaranteeing a remaining output percentage after a stated number of years.
• Workmanship warranty from the installer, covering the installation itself.

The third is the one that depends on the installer still trading. Ask what backs it if they are not: MCS requires membership of a consumer code such as RECC, and the code’s protections, deposit cover included, are the part of the reassurance you can actually verify.

Certification, checked independently

Verify registration on the MCS register rather than accepting a logo on a PDF. It takes a minute, and it is what the export side of your business case depends on: Smart Export Guarantee registration requires MCS or equivalent certification, so an uncertified installation forfeits export income for as long as you own it.

The finance page

If finance is offered, compare the total repayable against the cash price, not the monthly payment against your current bill. A monthly figure lower than your electricity bill is a sales framing, not a return: £7,100 borrowed over ten years at around 10% APR repays roughly £11,260, and the £4,000 gap belongs in the same table as the savings.

Then model the saving and the finance cost across the same period. If the interest consumes most of the saving, the installation may be sound and the deal poor.

Then judge it against your own model

The strongest position in any sales conversation is your own estimate, built from your consumption, your tariff and a conservative generation figure: the twenty minute version is enough to anchor you, and the calculator runs the full projection with the assumptions stated. Once you have it, the quote’s savings number stops being something to accept and becomes something to reconcile, line by line, with a document that was written to be checked.