Most solar quotes are hard to compare because they are written to be persuasive rather than legible. Here is how to read one properly: the lines that should be on it, the ones that quietly go missing, and the two numbers that decide whether two quotes are the same purchase at all.
The national anchor, so you know where you stand
The Energy Saving Trust, whose solar advice was updated on 27 August 2026, describes a typical home system as 4.5 kWp — around twelve panels covering 20 to 30m² of roof — costing about £7,600 installed. On its own payback table, with export payments counted and fuel prices as of July 2026, a London home breaks even in about nine years. Installations are zero-rated for VAT until 31 March 2027, reverting to 5% from 1 April 2027.
That is the benchmark. It is not a price for your roof, and nobody’s quote should match it exactly.
The lines that should be there
A quote you can actually compare has all of this on it:
- Panels — count, manufacturer, model and wattage per panel. “4.5 kWp” is a total, not a specification.
- Inverter — make, model and rated output, and whether it is a hybrid (battery-ready) unit.
- Mounting system — the rails and fixings, and whether the roof is tile, slate or something that needs a different approach.
- DC and AC protection and isolation — the parts nobody asks about and every safe install needs.
- Scaffolding and safe access — a fixed cost that does not shrink with a smaller array.
- The MCS-certified installation — this is what keeps an export tariff available to you.
- The grid step — a G98 notification to the network operator after commissioning for systems up to 16 A per phase (3.68 kW single-phase), or a G99 application approved before installation above it. The second one has a timescale attached, which is why it belongs on the paperwork rather than in a conversation.
- Commissioning and handover — the certificates, the MCS registration and the documents you will need if you ever sell the house.
- Warranties — the manufacturer’s on the panels and inverter, and the installer’s workmanship warranty. Two different promises from two different companies.
If a battery is included, add its usable capacity (not just nominal), whether it is AC-coupled or hybrid, and whether a backup gateway is in the price.
The two numbers that decide comparability
Everything above matters, but two numbers do most of the work:
- Panel count × wattage. Twelve 440 W panels is 5.28 kWp; twelve 405 W panels is 4.86 kWp. Same “twelve panels”, 8% different system.
- Usable battery capacity, where storage is included. As Which? puts it, usable capacity is usually less than stated capacity, because batteries lose energy charging and discharging and most are not designed to be emptied completely.
Line those two up before you compare totals. If they differ, you are comparing two different systems and the cheaper one may simply be smaller.
What quietly goes missing
In the quotes people bring us for a second opinion, the usual absences are scaffolding, DC isolation, the G99 application where the design exceeds the G98 limit, and any statement of who handles the network paperwork at all. None of those are optional; they just move the cost somewhere less visible.
One more thing worth asking about: what happens if the survey finds something the quote assumed away — a roof in worse condition than it looked from the ground, a consumer unit that needs replacing, or a cable run twice as long as expected. A quote that cannot answer that is a price list, not a plan.
Ask for the honest no
The most useful line in a quote is sometimes the one that says a system will not pay. A north-facing main roof, heavy shading from a mature tree, or a household that is out all day and on a flat tariff can all make the arithmetic weak. Any installer can model that before the scaffolding goes up — and you should be told.
Our solar panels page sets out what an HCE installation includes and what the national cost figures are, the savings calculator lets you test your own bill against a generation estimate, and if storage is part of the plan, the solar battery storage cost page breaks that side down the same way.
Sources: Energy Saving Trust, Solar panels: costs, savings and benefits explained (updated 27 August 2026); HMRC VAT Notice 708/6; GOV.UK, Smart Export Guarantee; Energy Networks Association, EREC G98 and G99; Which?, Solar panel battery storage (15 May 2026). All read 25 September 2026.