The questions you ask a solar installer before signing matter more than almost any other decision in the buying process, because a good set of answers separates a properly designed, MCS-compliant system from one that underperforms or causes problems years down the line. Most installers are used to being asked these questions and won’t be put off by a thorough homeowner – if anything, hesitation or vague answers here are themselves a useful warning sign.
Certification and Accreditation Questions to Ask First
Before discussing panels, price or anything else, confirm the fundamentals that determine whether you’ll be eligible for grants, warranties and a mortgage-friendly installation later.
“Are you MCS certified, and can I see your certificate number?”
MCS (Microgeneration Certification Scheme) certification is the baseline standard for UK solar installers and is required for eligibility for schemes like the Smart Export Guarantee. A legitimate installer will give you a certificate number you can verify directly on the MCS website, not just a logo on their van or website.
“Which consumer protection code are you a member of?”
Membership of a scheme such as RECC (Renewable Energy Consumer Code) gives you access to independent dispute resolution if something goes wrong after installation. An installer with no consumer code membership leaves you with far less recourse if a dispute arises over workmanship or performance.
Design and Specification Questions
“What is my modelled annual output figure, and how was it calculated?”
A good installer can explain their choice in terms of your roof, budget and goals – not just “these are what we always fit.” If your property is coastal, ask specifically whether the panels and fixings are rated for salt corrosion resistance; if you’re planning an EV or heat pump, ask whether the inverter and any battery are sized with that future load in mind.
“Why have you specified these particular panels and this inverter?”
“Have you carried out a proper shading assessment, and what did it show?”
Shading from chimneys, trees or neighbouring buildings can disproportionately affect string output. Ask to see the shading analysis, not just be told “it should be fine” – a legitimate site survey will have modelled this rather than estimated it by eye.
Warranty and Aftercare Questions
| Question | What a good answer looks like | Red flag answer |
|---|---|---|
| Panel product warranty length | 10-15 years, in writing from the manufacturer | Vague or “lifetime” with no documentation |
| Panel performance warranty | 25-30 years, guaranteeing 85%+ output at year 25 | No performance guarantee offered |
| Inverter warranty | 5-12 years depending on brand, extendable | Under 5 years with no extension option |
| Workmanship warranty | Typically 2-10 years from the installer directly | No installer workmanship warranty at all |
| What happens if the installer goes out of business | Insurance-backed guarantee (e.g. via a scheme like HIES or similar) | No answer, or vague reassurance with nothing in writing |
Practical Installation and Access Questions
“Is scaffolding, and any roof repair work identified during survey, included in the quoted price?”
Scaffolding costs and any necessary roof repairs identified during a proper site survey should be itemised in your quote, not added as a surprise once work begins. If a quote seems unusually low compared with others, missing scaffolding or contingency costs are a common reason.
“How long will installation take, and what disruption should I expect?”
A typical domestic installation takes 1-3 days depending on system size and roof complexity. Ask specifically about power interruptions, whether you’ll need to be home, and how long any DNO (district network operator) grid connection approval is expected to take before the system can be switched on and exporting.
“Will you handle the DNO application, and is it a standard or non-standard connection?”
Most domestic systems qualify for a standard, faster DNO connection process, but larger systems or certain grid-constrained areas require a non-standard application that can take considerably longer. A good installer handles this application on your behalf and will tell you upfront which category your installation falls into.
Cost, Payment and Finance Questions
“Can you give me an itemised price breakdown rather than a single total figure?”
An itemised quote – panels, inverter, mounting, scaffolding, DNO fees, VAT treatment, and labour separately – makes it far easier to compare fairly against other quotes and spot where costs differ. A single bundled figure makes genuine comparison much harder.
“What deposit do you require, and when is the balance due?”
Be cautious of any installer asking for a large deposit (more than around 25-30%) well in advance of work starting, particularly without stage payments tied to milestones like scaffolding erection, panel delivery, and completion. RECC-code members are bound by specific rules around deposit levels and cancellation rights that are worth asking about directly.
Frequently Asked Questions About Choosing a Solar Installer
How many quotes should I get before choosing a solar installer?
Most independent guidance recommends at least three quotes from MCS-certified installers, comparing not just total price but panel specification, warranty terms, and modelled output figures side by side. Wildly different quotes for what’s presented as the same system size are usually a sign of differing component quality or missing scope, so dig into the specification before assuming the cheapest is the best value.
How can I check whether an installer is reputable before they visit?
Verify their MCS certificate number directly on the MCS website, check consumer code membership (such as RECC) through that scheme’s own member list, and look for independent reviews rather than testimonials curated on the installer’s own site. Companies House filings can also show how long a business has actually been trading under its current name.
Should I be suspicious of a solar installer who cold-calls or knocks on my door?
Not automatically, but it warrants extra scrutiny rather than less – pressure tactics, same-day discounts, or reluctance to leave a written quote for you to review are red flags regardless of how the enquiry started. Apply the same certification and consumer-code checks whether the installer found you or you found them.
What does it mean if an installer avoids answering one of these questions directly?
Treat it as a genuine warning sign rather than a minor gap. A properly accredited, experienced installer should be able to answer every question above clearly and in writing, because these aren’t obscure technical details – they’re the basic information any MCS-compliant installation process is required to generate anyway.
