How to compare solar panel quotes, line by line

To compare solar panel quotes fairly, don't start with the total. First make sure each quote covers the same job: panel count and total kWp, the inverter's size, any battery's usable capacity, scaffolding and extras. Then work out the price per kWp, read each installer's MCS performance estimate and shade factor, and check who handles the grid paperwork. Finally, compare the deposit, payment stages and guarantees, because they decide who carries the risk if something goes wrong.

Put every quote on the same basis

Two quotes for "a 5 kW system" can describe very different jobs: 12 panels on two roof faces with a battery, or 10 panels on one face without. List what each quote includes and leaves out before you compare prices.

An MCS-certified installer must give you certain information in writing before you sign: the performance estimate, datasheets for the panels, inverter and any battery or optimisers, and a drawing of the panel layout. This applies to every MCS installer, under MIS 3002 Issue 6.0 on MCS's original scheme and under MCS 032:2025 on its redeveloped scheme. If a quote is missing any of them, ask before you compare it, whether it comes from a local installer or an energy supplier.

Work out the price per kWp

Divide the price of the panels and installation by the system size in kWp (kilowatt-peak, the panels' combined rated output). Leave any battery out, as government cost statistics do; if a quote gives one total, ask for the split.

For a benchmark, the Department for Energy Security and Net Zero (DESNZ) reports an average of £2,109 per kW of panel capacity for systems up to 4 kW and £1,651 per kW for systems of 4 to 10 kW, for panels fitted to existing homes in Great Britain between April 2025 and March 2026. Both include VAT and installation. They are averages, not quotes. Our solar panel cost guide has prices by system size, and solar battery cost covers batteries.

For a battery, divide its price by its usable capacity in kWh, not the larger "nominal" figure.

Check the VAT line too. Installing solar panels and batteries in a home currently carries 0% VAT, then 5% from 1 April 2027 unless extended. The zero rate needs the installer to supply and fit the equipment; kits sold without installation carry 20%.

Read the MCS performance estimate

The MCS estimate comes in a fixed table showing system size, orientation, pitch, postcode region, a kWh-per-kWp figure called Kk, the shade factor and the estimated output:

Annual output (kWh) = kWp × Kk × shade factor

Kk comes from MCS tables for your postcode zone, pitch and orientation, so two installers quoting for the same roof face should use the same Kk. If they don't, ask why.

It also shows how much of the solar your home should use itself (self-consumption), based on an occupancy pattern (home all day, in half the day or out all day) and your annual use, with a second section showing what any battery adds.

MCS's standard wording says the estimate "should not be considered as a guarantee of performance". If the roof was assessed remotely, the estimate must say actual performance "may be significantly lower or higher". On MCS's original scheme, any extra estimate from the installer's own software must not be more prominent than the MCS one.

The shade factor starts at 1.00 for an unshaded roof. The installer marks the horizon on a sun-path chart divided into segments worth 0.01 each: eleven affected segments give 0.89. Objects within 10 metres of the panels, such as a chimney, count more heavily; MCS's own near-object example gives 0.60 instead of 0.89. If the MCS method finds shading, the installer must give you the sun-path diagram. A 1.00 on a roof you know is shaded part of the day deserves a question; our solar panel shading guide explains the method.

Question the inverter size and the G98/G99 route

How your system connects to the network depends on the inverter's AC output, not on the panels' kWp. Up to 16 A per phase, which is 3.68 kW on a normal single-phase home supply, the installer can connect and then notify your distribution network operator (DNO) within 28 days, under the G98 procedure (in Great Britain; in Northern Ireland, NIE Networks uses G98/NI and G99/NI with the same 16 A threshold). Above that, the G99 procedure applies and the DNO must approve the connection before it goes ahead.

The limit counts every generator together, including a battery's own inverter. MCS gives the example of a 3 kW solar system and a 3 kW battery on the same single-phase supply: together they exceed 16 A, so G99 applies.

Some quotes pair a 5 to 6 kWp array with a 3.68 kW inverter. That keeps the system under G98, with no wait for approval, but the inverter caps output at 3.68 kW on the brightest days (known as clipping). That can be reasonable, for example on an east-west roof whose output is spread across the day. Ask why the installer chose that size, what clipping their design software estimates, and what G99 would add in time and cost.

If a quote needs G99, check who makes the application. If the design limits how much the system can export, MCS requires the installer to follow a separate standard, G100. Our guide to microinverters and string inverters covers the equipment choices.

Match the battery to your usage

A bigger battery is not always better value: on many days there isn't enough spare solar or evening use to fill and empty it. MCS's self-consumption tables show this for a home using 2,500 to 2,999 kWh a year, empty for half the day, with panels producing 3,600 to 3,899 kWh a year:

The first 5 kWh or so makes the big difference; after about 10 kWh the table barely moves.

Homes with a heat pump or electric car can also charge a battery from the grid on a cheaper overnight rate, so their size depends on the tariff too. On MCS's redeveloped scheme, the Customer Commitment says installers should make you aware that you shouldn't sign a contract based on specific energy prices, because tariffs vary and can change. Our solar battery storage guide explains sizing and tariffs.

Ask where the battery will go. On MCS's redeveloped scheme, the installer must state its location, size, weight, usable capacity, maximum power and any ventilation or fire-safety precautions in writing before you sign. Ask how the spot meets PAS 63100:2024, the BSI fire-safety specification for home battery installations.

Price the extras before you sign

Ask for each of these to be priced as its own line, or confirmed as excluded:

• Scaffolding for every side of the house that needs it.
• Bird protection (mesh around the panel edges). If pigeons nest on your roof or nearby, include it now: fitting it later usually means scaffolding again.
• Electrical work, such as a consumer unit upgrade or a long cable run.
• Monitoring, and whether you keep your own login.
• Roof work. If the installation could invalidate a roof warranty, MCS requires the installer to tell you in writing and get your written agreement.

Worked example: two quotes for the same roof

An illustration, not real quotes. The home uses 2,700 kWh a year and is empty for half the day. Both installers assumed a Kk of 850 kWh/kWp and a shade factor of 1.00 for the same south-facing roof.

Price per kWp. A: £7,450 ÷ 5.4 = £1,380 per kW. B: £7,150 ÷ 4.4 = £1,625 per kW. Both are below the DESNZ average of £1,651 per kW for 4–10 kW systems on existing homes.

Battery price per usable kWh. A: £3,300 ÷ 5.0 = £660. B: £4,450 ÷ 9.5 = £468.

Estimated generation. A: 5.4 × 850 × 1.00 = 4,590 kWh a year (the MCS formula ignores clipping, so A's real output will be somewhat lower). B: 4.4 × 850 × 1.00 = 3,740 kWh.

Solar used at home (MCS self-consumption table for this home). A: 44% of 4,590 = 2,020 kWh. B: 59% of 3,740 = 2,207 kWh. Against no battery (A 16%, B 19%), A's battery adds about 1,285 kWh a year and B's about 1,496 kWh. With 5 kWh instead of 9.5, B would use 52%, so its extra 4.5 kWh adds only about 262 kWh.

Grid route. A stays within 3.68 kW, so it connects under G98. B's 5 kW inverter needs G99 approval before it can be switched on.

Neither quote wins on its total: A gives more solar for less money but clips; B stores more but gets less from each extra kWh of battery. Ask A for the clipping estimate and B for the G99 timescale, then weigh your evening use and any heat pump or electric car plans.

Compare deposits and payment stages

Put each quote's deposit, stage payments and final payment side by side, with what you receive before each one: the more you pay before the equipment arrives, the more you stand to lose if the company stops trading. Then check each against its installer's protection. Code rules apply only to members, and MCS's redeveloped scheme, which most installers are moving to during 2026, no longer requires membership:

• RECC member: the deposit should be a reasonable share, such as 15%, and never above 25%; deposit and further advance payments together can't exceed 60%, and must be insured.
• HIES member: HIES protects deposits and stage payments up to 25% of the contract value or £5,000, whichever is lower, for 120 days from signing.
• MCS's redeveloped scheme: the installer must tell you how your deposit is protected and provide MCS-approved financial protection.

Paying part of the cost by credit card can add a claim against the card provider under section 75, for items over £100 and up to £30,000. If a quote includes finance, compare its total amount payable, including interest, with the others' cash prices, and check the firm on the FCA Register.

Check that each quote's cancellation terms match the law: if you sign at home or at a distance, you can cancel from signing until 14 days after the last of the equipment is delivered. Our guide to choosing a solar installer sets out your cancellation, card and complaint rights in full.

Before you choose a quote

Tick each line for every quote you are comparing.

• Same job. Panel count, total kWp, roof faces and exclusions listed, with the MCS estimate, datasheets and layout drawing.
• Price per kWp. Solar price divided by kWp, with any battery priced separately.
• Estimate. Same Kk for the same roof face; sun-path diagram if the shade factor is below 1.00.
• Inverter. AC rating, G98 or G99, who applies, and any clipping estimate.
• Battery. Usable kWh, what it adds in the MCS estimate, location and fire-safety answer.
• Extras. Scaffolding, bird protection and electrical work priced or excluded.
• Money. VAT rate, deposit, stage payments and total payable with any finance.
• Protection. Code membership, HIES cover or MCS financial protection checked, and cancellation terms in writing.

Estimate your own system

The calculator estimates generation, self-consumption and savings for your address in Great Britain, with or without a battery, and shows the figures with and without switching supplier for export. Use it to see whether a quote's size and figures are in a sensible range. It is an estimate, not a quote.

Frequently asked questions

How many solar panel quotes should I get?

No rule sets a number. Two or three fully itemised quotes, each with a survey and an MCS estimate, tell you more than many headline prices.

Why does one installer estimate more electricity than another?

Compare system size, Kk and shade factor. The same roof face should give the same Kk, so a higher output should come from more panels, another roof face or a different shade assessment.

Why is my 6 kWp quote using a 3.68 kW inverter?

It keeps the system within the G98 limit, so it can connect without waiting for approval, but it caps output on the brightest days. Ask for the clipping estimate.