How to choose a commercial solar installer — the vetting that actually matters

Here's an uncomfortable truth: the solar panels themselves are largely a commodity. Most tier-one modules perform within a few percent of each other and carry similar warranties. What you're actually buying when you sign a commercial solar contract is the installer — their workmanship, their judgement on your roof and grid connection, the contract they offer, and crucially whether they'll still exist to honour a warranty in ten years.

Get the installer right and a mediocre panel choice is fine. Get the installer wrong and the best panels in the world won't save you. Here's how to vet one.

1. MCS accreditation — verify it, don't take it on faith

MCS certification is the baseline: it's the technical standard and your gateway to the Smart Export Guarantee. Ask for the installer's MCS registration number and check it on the MCS website yourself. "We're MCS accredited" on a homepage isn't proof. (We explain why MCS matters more than the consumer codes for a business in MCS vs RECC.)

2. A genuine commercial track record

Plenty of installers built their business on domestic rooftops and are moving up into commercial. Commercial is a different discipline — larger arrays, DNO connections, structural loading, three-phase electrics. Ask:

• How many commercial projects have you completed, and in what size band (kWp)?
• Can you show me one like mine — similar size, similar building type (warehouse, office, agricultural)?

You want an installer for whom your project is routine, not a step up.

3. References you can actually check

Ask for two or three commercial reference customers and call them. Questions worth asking the reference: Did the install finish on time and on budget? Were there surprise extras after the survey? Is the system performing as promised? How responsive has aftercare been? A confident installer will hand these over; reluctance is a signal.

4. Financial stability — you're relying on them for years

This is the check most buyers skip and later regret. Your warranties and aftercare are only as good as the company behind them. Look the installer up on Companies House: how long have they traded, are accounts filed and healthy, any signs of distress? A 25-year performance warranty from a company that may not last five is worth little. For a significant install, this five-minute check matters.

5. Who actually does the work

Does the installer use in-house teams or subcontractors? Subcontracting isn't disqualifying, but you want to know who's accountable and that the electrical work is signed off by a registered electrician (NICEIC or NAPIT). Ask who carries the workmanship warranty if subcontractors did the job.

6. The contract — where your real protection lives

Because consumer codes largely don't protect business buyers, your safeguards have to be in the contract:

• Staged payments tied to milestones, not a large upfront deposit.
• A performance guarantee (minimum annual generation, with a remedy).
• A workmanship warranty distinct from the product warranties.
• Clear provisions for what happens if the installer becomes insolvent.

Our reading a commercial solar quote guide covers these line by line.

7. Insurance and aftercare

Confirm they carry liability and professional indemnity insurance appropriate to commercial work. Ask what aftercare looks like: do they monitor the system, what's the response time if output drops, and who do you actually call?

Red flags that should end the conversation

• Pressure selling — "this price is only good today," urgency tactics, reluctance to let you take the quote away.
• Deposit-heavy terms — a large upfront payment with little securing it.
• Vagueness on extras — "we'll see after the survey" left hanging instead of a fixed, all-in price.
• No commercial references, or only domestic ones.
• Reluctance to model self-consumption against your half-hourly data — a sign they're selling on headline generation, not real value (see south-facing vs east-west).
• Won't share their MCS number or Companies House details.

How many quotes?

Get two or three, and compare them like-for-like: same system size assumptions, same self-consumption basis, same inclusions. A single quote gives you nothing to benchmark; ten wastes everyone's time and marks you as a tyre-kicker. Three is the sweet spot.

Sanity-check, in one line each

1. MCS number — verified?
2. Commercial projects like mine — shown?
3. References — called?
4. Companies House — healthy?
5. Contract — staged payments, performance guarantee, insolvency cover?
6. Quote — fixed and all-in after survey?

Six yeses and you've found a serious installer.

The bottom line

Buy the installer, not the panels. Verify MCS, confirm a real commercial track record, check the company's financial health, call references, and insist on a contract that protects you — because the consumer codes won't. The firm that welcomes that scrutiny is the one worth hiring.

To benchmark any quote against independent numbers, run the calculator. To dig into the contract, see reading a commercial solar quote. For monthly guidance, subscribe to the Brief.

General information, not legal or financial advice.