Reading a Solar Quote Line by Line

A quote for a 4.4 kWp array with a battery landed in my inbox last spring at £13,480. A second quote, same house, same roof, near-identical kit list, came in at £8,940. Neither installer was lying. Neither was doing anything unusual. The gap was almost entirely in four lines that most homeowners skim past because they look like boilerplate.

If you already track your consumption in a spreadsheet or watch your smart meter feed in Home Assistant, you have everything you need to take a quote apart properly. The trick is knowing which numbers are set by physics and wholesale markets, and which ones are set by how busy the installer’s diary is that month.

What actually arrives in the PDF

Here is the shape of a typical UK quote, lightly anonymised, for a 1930s semi in the Midlands with a south-west facing rear slope:

Nothing here is fraudulent. But notice what the document does: it bundles labour and margin invisibly into the hardware lines. Line 1 prices panels at £440 each. Nobody pays £440 for a 440W panel.

Rebuild it as a bill of materials

The first job is to separate what the installer paid from what they charged. Trade pricing is not secret. Midsummer Energy, Segen and Sunsynk’s distributor network all publish or semi-publish price lists, and retail suppliers who sell to the public (Bimble Solar, Fogstar Energy, Sunstore) give you a hard ceiling on component cost. Whatever a homeowner can buy at retail, a certified installer is buying for less.

Rebuilding the quote above from public retail prices:

COMPONENT                              UNIT      QTY     LINE
JA Solar 440W N-type (retail)          £82        10     £820
Fox ESS H1-3.7-E hybrid inverter       £860        1     £860
Fogstar Energy 15.5kWh LFP             £2,190      1   £2,190
K2 Systems on-roof rail + clamps       £52        10     £520
AC/DC isolators, 6mm DC, SWA, SPD      £310        1     £310
Henley block + CU modification         £140        1     £140
Scaffolding (2 lifts, rear elevation)  £850        1     £850
                                                      -------
MATERIALS AT RETAIL                                    £5,690

Note I substituted a larger battery, because 15.5 kWh of Fogstar costs less at retail than the 9.5 kWh unit on line 3 costs at quote. Hold that thought.

Against a £13,480 quote, materials at full retail account for 42%. The remaining £7,790 is labour, overheads, insurance, scheme membership, warranty provision, customer acquisition and profit. That is not automatically outrageous. Two electricians and a labourer for two days, at genuine loaded cost, is somewhere around £1,400 to £1,900. Add van, insurance, MCS scheme fees amortised across installs, and a realistic figure for a small firm is £2,500 to £3,500 of overhead and labour on a job this size.

Which leaves roughly £4,000 unaccounted for. Sometimes that is honest margin on a firm carrying real warranty risk for 10 years. Sometimes it is a sales commission of £1,500 paid to the person who sat in your living room with an iPad.

The lines that genuinely do not move

Scaffolding is the most rigid cost in the document. A two-lift tower on a single elevation runs £600 to £1,100 in most of England, more inside the M25, and you cannot argue a scaffolder down because the installer is not the one being paid. Ask for the scaffolder’s own quote. A good installer will forward it without complaint. If they refuse, you have learned something about how the rest of the document was priced.

DNO work is similarly fixed, and often mispriced upward. Under G98, a single-phase system exporting up to 16A (about 3.68 kW) is a notification, not an application: the installer tells the DNO within 28 days of commissioning and that is the end of it. Under G99, which is what you need above that threshold or for larger battery inverters, there is a formal application and your DNO has up to 45 working days to respond. The application itself is usually free. A £350 line for “G99 compliance” is paying for maybe ninety minutes of form-filling. It is negotiable, and it is one of the first things to query.

Panel and inverter costs move within a narrow band. Tier-one N-type panels have been £70 to £95 per unit at retail for a while now, and the spread between a Solis, a Fox ESS and a GivEnergy hybrid at the same power rating is a few hundred pounds, not a few thousand. VAT is currently zero-rated on domestic solar and battery storage in the UK until 31 March 2027, so if a quote shows VAT on the solar works, something is wrong with the quote or with your installation’s classification.

The lines that vary threefold

Battery pricing is where the money hides. The £3,900 line for 9.5 kWh works out at £411 per kWh installed. Fogstar retail LFP is currently around £141 per kWh. GivEnergy’s All-in-One, a genuinely different product with its own inverter and a proper warranty, sits nearer £300 per kWh at trade. The spread between the cheapest credible battery and the most expensive one on an otherwise identical quote is routinely £3,000 on a domestic job.

“Installation” and “roof works” are the second soft spot. A quote that shows £980 for mounting when the rail and clamps cost £520 is charging £460 for the fitting. Fine. A quote showing £2,400 for the same thing is charging you for a sales funnel.

Then there is the bundled discount, which deserves special suspicion. When a quote says “£16,200, today’s price £13,480”, the £16,200 was never a price. It is an anchor. Model the £13,480 against your own BOM and ignore the strikethrough entirely.

Getting AI to do the decomposition

The useful workflow is not “paste the PDF into a chatbot and ask if it’s a good deal”. It is to build a reference BOM yourself, once, and then have the model do the arithmetic and the flagging against it. Put your retail component prices into a CSV, keep it in the same folder as the quotes, and run something like this against each new quote:

Here are three things:
1. bom_retail.csv — public retail prices for components, per unit
2. quote_installer_a.pdf — a UK solar quote
3. My roof: 32° pitch, 218° azimuth, no shading before 15:00

For the quote:
- Map each line item to rows in bom_retail.csv where possible
- Output a table: quote line, retail materials cost, implied
  labour+margin, implied margin as % of line
- Flag any line where implied margin exceeds 80% of materials
- Compute total £/kWp and £/kWh(battery) installed
- Do NOT estimate my annual yield; I'll do that in PVGIS

That last instruction matters. Language models are poor at solar yield and will happily invent a plausible-sounding kWh figure. Get generation from PVGIS v5.3 (the European Commission’s tool, free, no signup, accepts your exact tilt and azimuth) or from the MCS Solar Energy Calculator if you want the number your installer’s MCS paperwork will use. Then feed that figure back in as a fixed input.

For the self-consumption side, your own data beats any modelled assumption. If you are on Octopus, pull half-hourly consumption from the Octopus API or the Home Assistant Octopus Energy integration, export a year of it, and have the model simulate battery dispatch against your actual load shape rather than a generic profile. A 9.5 kWh battery and a 15.5 kWh battery produce very different payback numbers for a household that runs a heat pump versus one that is out all day. The deeper modelling methods sit in our cost models and AI quote analysis work, including how to handle Agile import pricing in the same simulation.

What three quotes for one roof looked like

Running the same decomposition across the three quotes I collected:

                     QUOTE A    QUOTE B    QUOTE C
Headline             £13,480     £9,850     £8,940
Panels (kWp)            4.40       4.40       4.84
Battery (kWh)            9.5        9.5       15.5
£ per kWp installed   £3,064     £2,239     £1,847
£ per kWh battery       £411       £289       £141
Implied non-material  £7,790     £4,610     £3,250
Scaffolding line      £1,100       £900       £850
DNO line                £350       £150         £0

Quote C was a two-person firm forty minutes away who did not send a salesperson, quoted from photographs and a Google Earth measurement, and asked me to confirm the consumer unit had space. They were MCS certified, which is the thing that matters for Smart Export Guarantee eligibility, and their scaffolding line was a forwarded PDF from the scaffolder.

Quote A came from a national installer with a call centre. The difference in hardware quality between A and C was negligible. The difference in price was £4,540.

When the next quote arrives, ask for exactly one thing before you discuss price: the manufacturer and model number of every component, including the mounting system and the battery cells. A firm that will not put “Fox ESS H1-3.7-E” on paper, and instead writes “3.6 kW hybrid inverter”, is protecting its ability to substitute. That single request changes what the rest of the negotiation feels like.