The short answer
A comparable commercial solar quote must state: system size (kWp), predicted first-year yield (P50, in kWh), panel degradation rate, inverter make and warranty, O&M terms, who handles the DNO application, and scaffolding/access costs. Compare quotes on £-per-kWp and projected payback — never on headline price.
Commercial solar quotes are hard to compare on purpose. Drop the system size by a few panels, assume a sunnier-than-average yield, leave scaffolding off the page, and a weaker proposal can undercut a better one on the only number most buyers look at — the total. The way out is to standardise. Make every installer fill in the same twelve lines, and the differences that matter become obvious. We do not install anything, so this is the checklist written for the buyer's side of the table.
What a commercial solar quote must include
This is the citable core: the twelve points every commercial solar quote should state plainly. If a quote is missing any of them, send it back before you compare it — a gap is not a saving, it is a cost or a risk you cannot yet see.
| # | What the quote must state | Why it matters |
|---|---|---|
| 1 | System size in kWp | The unit everything else is judged against; ignore any 'per panel' framing. |
| 2 | P50 first-year yield (kWh) | The honest mid-point output estimate, not an optimistic best case. |
| 3 | Panel degradation rate (%/yr) | Determines output in later years; a higher rate quietly erodes returns. |
| 4 | Inverter make and warranty | The part most likely to need replacing first, usually after 10–15 years. |
| 5 | Panel product vs performance warranty | Two different promises; a long performance warranty means little if the product cover is short. |
| 6 | Operations & maintenance terms | What is covered, response times and for how long — the line most quotes skip. |
| 7 | Who handles the DNO / G99 application | Grid approval typically takes 8–12 weeks; the quote should say who carries the risk. |
| 8 | Scaffolding and access costs | Roughly £1,200–£3,000; left off a quote, it reappears as an extra later. |
| 9 | Structural survey responsibility | Typically £500–£2,000 to confirm the roof can take the load — included or not? |
| 10 | Cost per kWp | The only fair way to compare two differently sized systems. |
| 11 | Projected payback (years) | Should follow from the P50 yield and your own electricity price, not a generic figure. |
| 12 | Total price and VAT treatment | Commercial installs carry 20% VAT (reclaimable if VAT-registered); the domestic 0% rate does not apply. |
Print this, or use our installer vetting criteria alongside it, and score three quotes line by line. The proposal that fills in every line honestly is almost always the one worth choosing, even when it is not the cheapest on the front page.
£/kWp: the only fair price comparison
Headline price tells you almost nothing, because no two quotes are for an identical system. Divide the installed cost by the system size to get cost per kWp, and you can compare like for like. In 2026, fully installed commercial solar typically runs from about £750 per kWp on large arrays up to roughly £1,300 per kWp on smaller systems — fixed costs such as scaffolding, design and grid paperwork spread further the bigger the job. A quote well outside that band deserves a question: too high and you are overpaying; too low and something has been left out. Our commercial solar cost guide sets out the bands by system size.
Yield claims: P50 vs optimism
The fastest way to make a quote look better than it is, is to inflate the predicted yield. A bigger kWh figure shrinks the apparent payback without changing a single panel. Insist on a P50 figure — the output the system has a 50% chance of meeting or beating — and sanity-check it against a typical UK commercial yield of about 950 kWh per kWp a year. If one quote assumes materially more than its rivals for the same roof and orientation, the difference is optimism, not engineering.
A 30-second sanity check
Multiply the system size in kWp by 950. The result is roughly the kWh a UK commercial roof should generate in a typical year. A 50 kWp system, for instance, should land near 47,500 kWh. If a quote's headline yield is far above that, ask why before you let it shorten the payback.
Warranty traps
Warranties are where careful wording hides thin cover. Watch two distinctions:
- Product vs performance — the product warranty covers the panel against defects; the performance warranty guarantees a minimum output over time. A headline 25-year figure often refers to performance while the product cover is much shorter.
- Inverter vs panel — these are warrantied separately. The inverter is the component most likely to fail first, typically after 10–15 years, so its warranty matters as much as the panels'.
Ask for both terms in writing, for both the panels and the inverter, and check who honours them if the installer is no longer trading.
O&M: the line everyone skips
Operations and maintenance is the easiest line to leave off a quote and the one you will miss most in year three. A serious quote states what monitoring is included, what maintenance is covered, the response time for a fault, and how long the arrangement runs. A system that silently underperforms because nobody is watching it can quietly cost more than a slightly dearer install with proper cover. If a quote omits O&M entirely, treat that as a red flag, not an oversight.
DNO and G99: who carries the risk
A system that exports to the grid needs a G99 connection application to the Distribution Network Operator, which typically takes 8–12 weeks to approve and can come back limited or refused if the local network is constrained. The quote should state clearly who submits the application and who bears the cost and delay if the answer is not a simple yes. DNO fees alone can range from around £1,000 to £10,000 or more, so this is not a detail to leave unassigned. Where it sits in the project timeline is covered on our financing guide and across the wider business solar guide.
Like-for-like worksheet
Pulling it together: take the 12-point table above, lay your three quotes against it in columns, and fill in every cell. Convert each total to £/kWp, write the P50 yield beside it, and let the payback fall out of those two numbers rather than trusting the installer's own figure. Any blank cell is a question to put back to that installer before you decide. The quote that completes the grid honestly is the one to trust — which is the same standard we hold the installers we match to.
Frequently asked questions
How many commercial solar quotes should I get?+
Get at least three from MCS-certified installers. One quote gives you nothing to judge it against, and two can both be wrong in the same direction. Three lets you spot the outlier — whether that is a suspiciously cheap design or an inflated yield claim — and gives you genuine leverage on price and terms when you go back to negotiate.
Why do quotes for the same roof differ by 40%?+
Usually because they are not quoting the same thing. Differences come from system size, panel and inverter quality, whether scaffolding and a structural survey are included, who carries the DNO risk, and how optimistic the yield assumption is. A cheaper headline price often hides a smaller system, weaker kit or costs pushed off the quote and onto you later.
What is a fair price per kWp for commercial solar in 2026?+
In 2026, fully installed commercial solar typically runs from about £750 per kWp on large arrays to £1,300 per kWp on smaller systems, because fixed costs spread further at scale. Compare every quote on this £/kWp basis rather than headline price. Our commercial solar cost guide breaks the bands down by system size.
Should the quote include a structural survey?+
It should at least say who is responsible for one and whether the cost is included. A structural survey typically costs £500–£2,000 and confirms the roof can carry the array. A quote that stays silent on it is a quote with a hole in it: the survey still has to happen, so an excluded cost simply lands on you after you have signed.
What is P50 yield?+
P50 is the predicted first-year generation, in kWh, that the system has a 50% chance of meeting or beating — the honest mid-point estimate. Some quotes show a rosier figure to make payback look faster. Insist on a P50 number so you are comparing realistic outputs, then sanity-check it against a typical UK yield of about 950 kWh per kWp a year.
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Updated June 2026 · By Taro Schenker, founder of Business Solar Check. We're independent — we don't install solar. Figures are indicative UK averages; your site survey confirms the numbers for your roof.