How to Vet a Commercial Solar Installer: 12 Checks Before You Sign
Updated 23 October 2026 · SEO Dons Editorial
What are the twelve checks, and where do you verify each?
Send the same list to every bidder, in the same words, then verify what comes back. Some rows rest on a legal duty, such as employers' liability insurance and the competence of anyone appointed under CDM 2015. The rest is buyer practice rather than law.
| Check | Ask for | Verify with |
|---|---|---|
| 1. MCS status and its limit | Certification number, and what the installer's MCS work covers at your size | MCS Find an Installer search |
| 2. Who certifies the electrical work | The named signatory, the scheme that assesses them and its scope | The scheme's register; GOV.UK's list of competent person schemes |
| 3. Standards the design follows | The code of practice, wiring standard and handover standard used | IET Code of Practice for grid-connected PV; BS 7671; IEC 62446-1 |
| 4. Insurance | Employers' liability, public liability and professional indemnity certificates, with insurer and limits | GOV.UK; the Financial Conduct Authority register |
| 5. Health and safety competence | A method statement and fragile-roof plan written for your roof, and a pre-qualification result | HSE's contractor guidance |
| 6. Management certificates | ISO 9001 and ISO 45001 certificates showing scope, body and expiry | The issuing certification body |
| 7. Subcontractors | A named list of who works on the roof and the electrics, with the same documents for each | The contract schedule |
| 8. Grid record at this size | Network operator offers and acceptances for comparable systems; who signs compliance forms | Energy Networks Association; the operator named on each offer |
| 9. Design and yield model | The model file or report, with shading, losses and orientation | PVGIS; the guide to reading a PVsyst report |
| 10. Company finances | Company number, filed documents, charges, officers | Companies House, via GOV.UK |
| 11. How warranties are backed | Each warranty in writing, the policy behind workmanship cover, and who holds it | The policy and insurer; see commercial solar warranties |
| 12. A comparable roof | A reference with a similar roof, size and age, plus its monitoring output | A visit or call with whoever runs the building |
Which badges stop short of a commercial roof?
MCS. MCS describes its certification as covering domestic and commercial installations up to a size it gives as 50 kW for electrical technologies. A 200 kW array, for example, is beyond that, so an installer's MCS listing says something about its smaller work and nothing about your system. Within the limit, MCS suggests checking status as you get a quote, before you sign and before work starts, to confirm certification has been maintained. The MCS and commercial solar guide covers the scheme at this scale.
RECC and TrustMark. RECC says it protects households and property owners buying or leasing small-scale generation for their homes, and describes itself as a TrustMark scheme operator, a quality scheme for the home improvement sector. A logo from either on a commercial proposal is not evidence about a commercial contract.
Electrical registration. GOV.UK lists competent person schemes by the work they self-certify. Its electrical categories cover fixed low or extra-low voltage installations in dwellings and, in other buildings, lighting or electrical heating systems, and a separate entry covers microgeneration and renewable technologies. Ask which category the registration sits under for rooftop generation on a business building.
Trade bodies and insurance-backed cover. A trade association logo shows membership of that body, so ask what, if anything, was assessed to join. MCS's page on insurance-backed cover sets the requirement for domestic installations, so a commercial buyer has to ask for the policy rather than assume one exists.
How do the CDM competence rules shape checks 5 to 7?
A business that commissions the work is normally the client under CDM 2015. HSE says commercial clients must appoint contractors and designers who have the skills, knowledge, experience and organisational capability for the job, and regulation 8(3) requires whoever appoints a contractor to take reasonable steps to satisfy themselves that it does.
HSE's contractor guidance lists ways to show it: training and continuing professional development records, professional body membership and references from earlier work for individuals, and for the organisation a pre-qualification result from an assessor in the Safety Schemes in Procurement forum or a self-assessment against Build UK's Common Assessment Standard. Rows 5 to 7 are the paper trail showing the business took reasonable steps. The CDM client duties guide covers the rest of the client's role.
BSI describes ISO 9001 as a quality management system standard and ISO 45001 as an occupational health and safety management system standard. Both speak to how a company runs its processes, not to the quality of one roof, so check that the scope names solar or electrical installation and that the issuing body confirms the certificate.
What should a grid-connection record at your size show?
The Energy Networks Association says a generator above 3.68 kW per phase comes under EREC G99, and MCS says G99 Type A covers 0.8 kW up to but not including 1 MW. The most useful reference is a comparable system in the same network operator's area, with the offer and acceptance records.
ENA also says compliance is the customer's responsibility, and the customer is quite often, but not always, the owner of the generation. Ask for a written statement of who submits the application, who signs the compliance forms and what type-test evidence comes with the inverters. ENA's LCT Register lets manufacturers declare compliance, but its use is not mandatory above 3.68 kW per phase, so a missing entry is a question, not proof of a problem. The guide to network capacity heat maps explains how to check headroom first.
How do you test the yield model and the company behind it?
PVGIS, the European Commission's online tool, gives yearly, monthly or hourly output for a location, with system losses included. Enter the proposed capacity, slope and orientation and compare the annual figure with the installer's. A gap is a prompt to ask what shading, losses or module data explain it. The quote comparison checklist walks through the steps.
Companies House, through GOV.UK, shows a company's registered address and incorporation date, current and former officers, images of its filed documents, mortgage charge data, previous names and insolvency information. A young company is not a fault in itself, but one with nothing filed to read and no comparable references leaves you relying on a warranty with little behind it.
In what order should you run the checks?
- Send one written request covering all twelve rows to every bidder.
- Do the register checks yourself first: MCS listing, Companies House, and the insurer on the Financial Conduct Authority register. They take minutes and remove weak bidders early.
- Read the documents: certificates, method statement and a sample handover pack against the IEC 62446-1 list.
- Put the grid and yield questions to each bidder in writing.
- Visit or call a comparable site with its output data in front of you.
- Write the answers into the contract, including named subcontractors and warranty documents, then compare prices using the checklist.
When you are ready to put bidders on the same brief, you can send an enquiry through the quote form. The installation guide shows where each check falls in a project programme.
Sources
- MCS: Becoming certified; Solar panels; Notifying DNOs; Insurance Backed Guarantee Products, checked 22 October 2026.
- RECC: Home page; About us, checked 22 October 2026.
- GOV.UK: Competent person schemes; Employers' liability insurance; Get information about a company, checked 22 October 2026.
- Health and Safety Executive: Commercial clients; Are you a contractor?, checked 22 October 2026.
- legislation.gov.uk: CDM Regulations 2015, regulation 8, checked 22 October 2026.
- IET: Wiring Matters, May 2022: Code of Practice for Grid-connected Solar Photovoltaic Systems, 2nd Edition, checked 22 October 2026.
- IEC: IEC 62446-1:2016, checked 22 October 2026.
- BSI: ISO 9001; ISO 45001, checked 22 October 2026.
- Energy Networks Association: Connecting generation, checked 22 October 2026.
- European Commission Joint Research Centre: PVGIS user manual, checked 22 October 2026.
Common questions
Does a commercial installer have to be MCS certified?
MCS certification covers electrical systems up to 50 kW, so for a larger array there is no MCS certificate to ask for. Within that size, MCS suggests checking status when you get a quote, before you sign and before work starts. Where MCS does not reach, use the other rows as your evidence.
Is an electrician's registration enough to install rooftop solar?
A registration shows assessment against the scope of the scheme that issued it. GOV.UK lists electrical categories for dwellings and, in other buildings, for lighting or electrical heating, with microgeneration listed separately. Ask which one applies to rooftop generation on a business building and who signs the certificate.
What if the installer uses subcontractors for the roof or electrical work?
The same test applies to each appointment, because CDM 2015 asks whoever appoints a contractor to take reasonable steps to confirm competence. Ask for the same insurance, method statement and competence evidence for each subcontractor, and have the contract name them. MCS also says an installer should tell customers which subcontractors will be involved.
How many references are enough?
There is no rule. Two or three on comparable roofs and sizes are more use than ten on different ones. Ask for at least one system that has run through a full year, and read its output against the original forecast.