Solar quote cost per kWp: calculate it, then check scope.

What cost per kWp tells you

Cost per kilowatt peak divides quoted installed price by proposed solar-array capacity. It gives two differently sized arrays one common price unit. If one quote contains 4.2 kWp and another contains 5.4 kWp, comparing only total price makes larger system look more expensive even when its quoted price per unit of peak capacity is lower.

kWp is rated peak output under standard test conditions, not annual generation and not power your home will receive at every moment. Cost per kWp normalises array size. It does not prove design quality, roof suitability, annual output, usable battery capacity, installer competence, or future savings.

Use complete comparable totals

Start with price homeowner would pay for complete quoted scope, including VAT where applicable and mandatory work shown in quote. Then check whether both totals contain same categories: installation, scaffolding, roof work, electrical enabling work, DNO work, monitoring, bird proofing, warranties, and handover. Cost per kWp calculated from mismatched scope can be precise and still misleading.

If one quote includes a battery and another does not, do not divide both headline totals by solar kWp and call result like-for-like. Ask for itemised solar-only and battery amounts, or compare complete packages as different propositions. Never invent a battery deduction when installer has not itemised one.

Apply formula to each written quote

Use quoted total that matches scope you want to compare and divide by array capacity in kWp. Keep original total, kWp, and calculation beside result so you can trace it back to written quote.

Example: Quote A is £8,400 for 4.2 kWp. Its cost per kWp is £2,000. Quote B is £9,600 for 5.4 kWp. Its cost per kWp is about £1,777.78. Quote B has lower quoted cost per kWp, but that does not make it better until equipment, layout, enabling work, warranties, battery scope, and performance assumptions are aligned.

Formula: Quoted installed total ÷ solar array size in kWp = quoted cost per kWp

Check quoted generation per kWp separately

Annual generation is measured in kWh, while array size is kWp. Dividing each installer-provided annual generation estimate by array kWp can expose different yield assumptions. A 4.2 kWp quote claiming 3,800 kWh gives about 905 kWh per kWp. A 5.4 kWp quote claiming 5,300 kWh gives about 981 kWh per kWp.

Difference may reflect roof orientation, shading, layout, model, or methodology. It may also reveal incompatible assumptions. It is a question to take back to installers, not a forecast from SolarQuote Check. MCS MIS 3002 requires performance estimate and supporting technical information to be communicated in writing at or before contract award.

Formula: Installer-provided annual generation in kWh ÷ array kWp = quoted kWh per kWp

Source: MCS MIS 3002 Issue 6.0 ↗

Inspect written technical information

Current MCS MIS 3002 Issue 6.0 lists minimum written technical information, including performance estimate, manufacturer datasheets for proposed modules and inverter, battery information when applicable, proposed module-layout drawing, and shading information under stated conditions. Those fields help explain why two quotes with similar kWp can differ.

Energy Saving Trust recommends getting multiple quotes and asking installers to explain electricity-price, self-consumption, export, shading, roof-orientation, and warranty assumptions. Compare exact written answers. A verbal promise should not silently fill a blank in one quote while other quote carries cost and scope in writing.

Source: MCS MIS 3002 Issue 6.0 ↗ · Energy Saving Trust installation guide ↗

Use official cost data as context, not verdict

Department for Energy Security and Net Zero publishes official solar PV cost data from MCS Installation Database, including installed cost per kW. That dataset can provide market context, but it does not describe your roof, electrical work, scaffolding, battery, equipment, installer margin, or contractual protection.

Do not use national average to declare individual quote fair or unfair. Use it to frame questions: which included work explains difference, whether capacity basis matches, and whether current quote contains components absent from dataset comparison. Decision still depends on written scope and household-specific design.

Source: DESNZ solar PV cost data ↗

Separate price metric from savings claims

Lower cost per kWp does not guarantee lower payback period. Quote-provided savings depend on annual generation, household self-consumption, import price, export tariff, battery behaviour, degradation, maintenance, and other assumptions. Put those assumptions side by side instead of treating each installer headline as measured outcome.

CMA consumer guidance explains consumer protections when buying green products and highlights need for clear information before purchase. SolarQuote Check records quote-provided savings and simple-payback figures as installer assumptions. It does not replace them with its own forecast or guarantee any saving.

Source: CMA green-products consumer guide ↗

Turn calculation into like-for-like decision record

Before choosing installer, keep both totals, capacities, cost per kWp, equipment, battery scope, enabling work, warranties, performance estimates, self-consumption assumptions, export assumptions, and unclear items together. Ask each installer to amend written quote where material field is missing.

SolarQuote Check UK compares two manually entered residential solar PV quotes in browser. £29 tool calculates totals and cost per kWp, exposes included or unclear work and mismatched assumptions, and creates downloadable local record. It does not upload quote documents, rank installers, or decide technical suitability.