Questions to ask a solar installer

Why the same questions matter

Consistent questions make quotes much easier to compare. If each firm answers a different set of questions, you end up comparing sales styles, not designs.

So write your list before the first visit, and ask every installer the same things. Ask for the answers in writing. A good firm will be glad to explain its choices, because clear answers help it win the work.

Use this page alongside our guides on finding an installer and preparing for a survey. Listen to how each firm answers, while noting what it says. Vague or defensive replies tell you something.

Design questions

The design decides how much power you get. Start here, since a better price cannot rescue a poor design.

• Why this system size? What did you base it on?
• What limits the layout, such as roof shape, vents, chimneys or shade?
• How did you assess orientation, tilt and shading?
• Which method and inputs gave the yearly generation estimate?
• How much of that power will I use at home, and how much will I export?

Ask to see the working. For example, tools such as PVGIS, from the European Commission, apply a default 14% system loss for cables, inverters, dirt and ageing. A fair estimate should say what losses it assumed. Be wary of estimates that look too perfect.

Also ask who checked the roof structure. MIS 3002 says a suitably competent person must check it for the loads that panels add. In addition, since 18 June 2026, MCS installers must give structural and wind loading calculations for some mounting systems. Ask for those documents.

Scope questions

Scope is where cheap quotes often hide gaps, so ask the firm to list what the price includes and excludes.

• Which panels, inverter and mounting system are included? Please give make and model.
• Is a battery included? If so, which one, and what is its capacity?
• Is scaffolding in the price?
• Are any electrical upgrades included, such as a new consumer unit?
• Is monitoring included, and does it need an app or a subscription?
• Is bird protection included, if you want it?
• Who makes good after the work, such as roof tiles, plaster or paint?

Then compare scope line by line. However, price matters too. Our solar panel costs guide shows what official data says about typical prices. DESNZ reports a median of around £1,780 per kW of declared net capacity for small installs in 2025 to 2026.

Ask about VAT too. According to HMRC, solar panels and batteries are zero-rated for VAT until 31 March 2027. The rate reverts to 5% from 1 April 2027 under current law. Check that your quote states the VAT treatment clearly.

Grid and responsibility questions

Someone has to tell your network operator about the system, and the quote should name who. Ask who handles each of these steps.

• Grid notification or application.
• Permissions, including planning or landlord consent where they apply.
• Electrical certification and commissioning.
• Handover, including a walk-through and the paperwork.
• Faults after handover.

Under MIS 3002, the MCS installer must notify your network operator under the G98 or G99 procedure. G98 covers systems up to 16 amps per phase, and G99 covers anything above. The limit counts all generators together, so panels plus a battery can tip a home into G99. Our guide to G98 and G99 grid connection explains the difference in plain terms.

Ask which route applies to your design, and what happens if the network operator asks for changes. Also ask whether you need a smart meter. You need half-hourly export readings to claim Smart Export Guarantee payments, which usually means a smart meter.

Battery questions

If a battery is part of the quote, ask about it separately. A battery adds cost and complexity, so it may not suit every home.

MCS advises you to choose a battery by how much energy it stores and how much it can deliver at once. Ask for both figures. Ask too whether the installer follows the MCS battery standard, MIS 3012.

Whether a battery pays back depends on your habits and tariff. Our guide on whether solar batteries are worth it goes through the main factors. Ask the installer to show the numbers behind any payback claim, including what happens if prices change.

Warranty and insurance questions

Warranties are only as good as the company behind them. Ask for each one in writing, and note who pays if the installer closes.

• How long is the warranty on panels, the inverter, the mounting system and any battery?
• How long is the workmanship warranty, and who backs it?
• Is the workmanship warranty insured?
• Does the roof warranty stay valid after the install?
• What is the process for a claim, and who do I call first?

RECC members must insure deposits, stage payments and the workmanship warranties they issue. That cover matters if the firm stops trading. Even so, check the wording, and keep a copy of every certificate.

Payment questions

Money questions are easier before you commit. Ask for a payment schedule that shows each stage and amount.

• How much is the deposit, and what is it for?
• Is the deposit insured, and by whom?
• What are the stage payments, and what triggers each one?
• Who exactly do I pay, and into which account?
• What is the cancellation period, and what do I lose if I cancel?
• If I use finance, who is the lender and what is the total cost?

Be cautious with large deposits, because they raise your risk if the firm fails. Our list of solar sales red flags covers pressure tactics in more detail. A fair firm will let you take the paperwork away.

Aftercare questions

A system should run quietly for years, yet faults do happen. Ask what support you get once the scaffolding has gone.

• What will I receive at handover, including certificates and manuals?
• How do I read the monitoring, and who watches for faults?
• What does a service involve, and is it needed?
• Who do I call about a fault, and how fast do you respond?
• What happens when the inverter needs replacing?

Ask for realistic answers. Inverters often need replacing before panels do, so any long payback should allow for that cost. If a firm cannot say how it supports customers after the sale, treat that as a warning.

Put it all in writing

After your visits, send each installer the same short list and ask for a written reply. Compare the answers side by side. Differences in scope, warranty or grid handling often explain differences in price.

Keep every quote, email and certificate in one folder. If you want help finding firms to ask, you can request quotes through our enquiry form. Nobody is contacted automatically. Whoever you speak to, the questions above still apply.