How to choose a commercial solar installer in the UK
A commercial solar system is a 25-year decision — but the installer typically only stays around for 10. Here's the 12-point checklist to separate the specialists from the sales operations.
The 12-point checklist
- MCS certification for the exact system size band you're buying.
- RECC or equivalent consumer/commercial code membership.
- Public liability insurance to at least £5m and employer's liability to £10m.
- NICEIC or NAPIT electrical accreditation for the AC side.
- Working-at-heights and CSCS/CISRS scaffold competencies for the install team.
- Positive Companies House filings — 3+ years trading, no CCJs, growing turnover.
- Reference sites of similar scale (kWp) in the same sector — request three.
- Written workmanship warranty of 10 years minimum, on top of panel/inverter warranties.
- Named O&M plan with 24-hour response SLA and remote monitoring included.
- DNO application handled in-house, not subbed out.
- Independent commissioning report to G99 standards, not just installer sign-off.
- Clear, fixed-price quote — no 'subject to survey' variables above 5%.
Questions to ask on the site visit
- Who is the named project manager and what's their solar-specific experience?
- How many kWp have you installed in the last 12 months at this size?
- Is the DNO application handled in-house or sub-contracted?
- What happens in year 8 if the inverter fails and the OEM has folded?
- Show me a real O&M report from a similar client.
Related reading
FAQ
How do I know a commercial solar installer is legitimate?
Check MCS certification (mcscertified.com), RECC membership, Companies House trading history (3+ years, growing turnover), and ask for three reference sites at similar scale in the last 24 months. Legitimate installers list all of this openly.
What warranties should a commercial solar installer offer?
A minimum of: 25-year panel performance warranty, 10–12 year inverter warranty (or extendable), and a 10-year workmanship warranty on the installation itself. Anything shorter than 5 years on workmanship is a red flag.
Do commercial solar installers need MCS?
MCS is required for systems that will claim Smart Export Guarantee payments and is expected by insurers and lenders. Some very large (>1 MW) projects use equivalent international standards — that's fine, but for UK commercial rooftop MCS is the norm.
How many quotes should I get for commercial solar?
Three from qualified installers is the sweet spot. Fewer and you can't triangulate price; more and the process becomes unmanageable. Ask each to quote on the same specification so numbers are comparable.
What's a red flag when choosing a commercial solar installer?
Any of: no reference sites, no in-house electrical team, refusing to name the panel/inverter brand until you sign, upfront deposits above 10%, workmanship warranty under 5 years, or pressure to close within 48 hours.