How to choose a solar installer

The equipment is mature and the physics is settled. What varies between installers is the quality of the survey, the honesty of the generation estimate and the standard of the roof work. None of those show up in the price, and all of them can be tested from your kitchen table with the six checks below.

One: did they actually survey?

Someone should have visited, got near the roof, looked in the loft and opened your consumer unit.

A quote produced from an aerial photograph and a phone call cannot know your rafter spacing, your roof covering’s condition, whether your board has a spare way, or what the chimney shades in December.

If nobody came, the quote is an estimate wearing a quote’s clothes, and every downstream number inherits the guesswork.

Two: where did the generation figure come from?

Every quote carries an annual generation estimate, and every savings figure is downstream of it. An estimate ten per cent high makes the payback look ten per cent better than it will be.

Ask which modelling tool produced it, whether shading was measured or assumed, and what degradation rate is applied. There is a right answer available: certified installers are required to produce the figure by the MCS estimation method, postcode irradiance, orientation, pitch and a shading assessment, so “the MCS standard method, here is the shading survey” is what competence sounds like. You can also cross-check any figure yourself in the European Commission’s PVGIS tool in five minutes.

An installer who surveyed properly answers immediately and specifically. One who cannot is quoting from a template.

Three: what self-consumption rate did they assume?

The most influential number in the projection and the one least likely to be stated.

Move it from a low figure to a high one and payback shifts by years with nothing physical changing. Ask what was assumed and why that figure describes your household.

If the answer is a round number with no reference to your occupancy or your consumption, the savings figure is generic.

Four: what is excluded?

Get it in writing:

“Please confirm everything excluded from this price, and the likely cost if it turns out to be needed.”

Scaffolding, consumer unit work, roof repairs, bird protection, long cable runs: the full checklist of what belongs inside a quote covers which exclusions are legitimate. An installer who has looked at your property can answer in a paragraph. One who has not will be vague, and the gaps arrive as extras on the day the scaffold is already up, when your negotiating position is at its weakest.

While you are asking, add one more: which grid connection route applies, G98 notification or a G99 application, and whether the timeline in the quote reflects it. An installer promising next week for a system that needs prior G99 approval has already told you about their paperwork.

Five: check the certification independently

Do not accept a logo on a PDF. Search the MCS register by company name or registration number.

Confirm the business is currently certified, and certified for the specific technology you are buying. Certification is per technology: solar photovoltaic registration does not cover battery storage or heat pumps, and a package quote needs cover for all of it.

This matters commercially as well as technically. Export payments under the Smart Export Guarantee require MCS or equivalent certification, so an uncertified installation removes a few hundred pounds a year of projected return for as long as you own it. Check the consumer code too: MCS installers must belong to one, RECC is the largest, and the code’s deposit protection is the part of “fully insured and accredited” you can actually verify.

Six: who does the roof work?

Ask whether the roof crew are employed or subcontracted, and how long they have worked together.

This is where installations go wrong. Water ingress at the mounting penetrations is the failure that ruins a roof, and it is a workmanship problem rather than an equipment one. Subcontracting is normal and not a red flag; not knowing who is coming is.

Also ask what happens if a slate breaks. The right answer is that they carry replacements and expect some breakage. The wrong answer is that it does not happen.

What not to weight heavily

Panel brand. Gets disproportionate sales attention and rarely decides whether an installation pays. The datasheet warranty terms are the checkable part; the adjectives are not.

Company size. A national firm carries a sales force and a marketing budget; a two-person local outfit carries neither. Larger may mean a stronger warranty covenant, or may mean you are funding advertising. Judge the six points above instead, and judge the price per kilowatt peak against the published medians rather than by the size of the brochure.

A discount for signing today. Solar pricing is not volatile week to week, and the government’s cost data shows a stable, gently falling market. An offer that expires when the salesperson leaves your kitchen is a sales technique, and it is the single most reliable signal on this page: competent, busy installers do not need it.

Then bring your own numbers

The strongest position in any of these conversations is your own estimate of what the system will save, built from your consumption, your tariff and a conservative generation figure: the twenty minute method produces it, and the calculator extends it across twenty five honest years.

With that in hand, the quote’s savings number stops being a claim you have to accept and becomes something you can reconcile against your own working, and the installer who welcomes that conversation is usually the one to hire.