How to Choose a Factory Solar Installer: The Complete UK Checklist

Any legitimate installer will answer this immediately with their certificate number. Verify independently at mcscertified.com. The certificate should be in the legal trading name of the company you are contracting with — not a parent company, sister company, or previous trading name. Ask specifically: "Has your MCS certification ever been suspended or revoked?"

Good response: Immediate certificate number provided and encouragement to verify independently.

This is the single most important differentiator between residential/small commercial installers and genuine industrial specialists. A minimum of 10 completed industrial installations over 100kWp is a reasonable threshold. Ask for a project portfolio with system sizes, industry sectors, and installation dates. Installers with only residential experience will typically be evasive or inflate smaller commercial projects to sound more experienced.

Red flag: "We have extensive commercial experience" with no specifics on industrial system sizes.

G99 applications (for systems over 16A per phase or over 50kW) require detailed protection relay specifications, anti-islanding settings, and technical schedules that must be submitted to and approved by your Distribution Network Operator (DNO). This process typically takes 6–20 weeks. G100 applies to systems over 1MW. If an installer outsources this to a third party, ask who bears responsibility for delays, rejections, or resubmissions — and who pays the DNO fees if the application is rejected and needs to be redone.

Best answer: In-house G99 specialist who handles all DNO correspondence directly.

The structural roof survey determines whether your roof can safely carry the panel weight and wind loads for 25+ years. Ask specifically: "Is the structural engineer who signs off our survey employed by your company, or engaged as a subcontractor?" If subcontracted, ask: "Are they included in your professional indemnity insurance, or do they carry their own?" You need a clear chain of professional accountability if structural problems arise later.

Best answer: In-house chartered structural engineer, with PI coverage confirmed in the contract.

Industrial solar monitoring goes beyond a simple app showing generation figures. You should expect: real-time generation data at string or inverter level, fault alerts by email/SMS, export and import metering, half-hourly data export capability, and a web portal you can share with your energy manager or accountant. Ask specifically: "What happens to monitoring access if I switch energy management providers?" You must retain independent access to your data.

Best answer: Named monitoring platform, with client-owned data access independent of installer relationship.

This question tests whether the after-sales support structure is defined and resourced. Ask for the specific contact name, role, and communication channel for warranty claims and performance disputes in years 2–5. Ask what the defined response time is for: (a) system fault notification, (b) engineer on-site attendance, and (c) fault resolution. These should be in the contract, not just verbal assurances during the sales process.

Red flag: "Just call our office" with no defined response SLAs in the contract.

The defect liability period (DLP) is the period after practical completion during which the installer is obligated to rectify defects at their own cost. In construction contracts, 12 months is standard. For solar specifically, a well-structured contract will distinguish between: workmanship warranty (minimum 2 years, typically 5), equipment warranty (manufacturer warranties passthrough), and performance warranty (specifying minimum annual generation). Ask what happens to warranty obligations if the installer company goes into administration.

Best answer: 5-year workmanship warranty, with manufacturer warranties formally assigned to the client.

References from genuinely similar installations — same size category, same industry sector if possible — are the most reliable validation of capability. Request names and direct contact numbers, not just company names. When you call, ask three specific questions: (1) Did the system achieve the projected generation figure in year one? (2) Has there been any post-installation defect, and if so how was it resolved? (3) Would you use this installer again?

Red flag: Only written testimonials offered, or references who don't answer calls or respond to emails.

Solar company failures are not uncommon — the UK market has seen several large-scale insolvencies, including domestic installers and commercial operators. Understand specifically: (a) Are manufacturer warranties assigned directly to you as the client, not to the installer? (b) Is there an insolvency protection scheme in place? (c) Can you access monitoring data directly without the installer? (d) What happens to the G99 registration if the installer ceases trading? These are critical questions for a 25-year asset.

Best answer: Manufacturer warranties assigned directly to client, with escrow or insurance provision for workmanship claims.

The most common source of cost overruns on factory solar projects is items excluded from the initial quote. Specifically check: DNO application fees (can be £3,000–£20,000+ for large systems), scaffolding and access equipment (often £15,000–£40,000 on large roofs), DNO meter upgrade (required for smart export, typically £1,000–£3,000), electrical protection equipment (G99 relays and isolators), and planning fees if permitted development rights don't apply. A comprehensive quote will itemise all of these explicitly.

Red flag: Any vague language about "subject to DNO requirements" without a maximum cost estimate.