How to Compare Solar Quotes: What to Look for Before You Sign

Getting multiple solar quotes is the right first step — but comparing them meaningfully is where most homeowners get stuck. Quotes can look wildly different in price, detail, and assumptions, yet it is rarely obvious which one represents genuine value. This guide explains every element worth checking so you can make a confident, informed decision before you sign anything.

Start with MCS certification — it is non-negotiable

The single most important thing to verify is whether the installer holds current MCS (Microgeneration Certification Scheme) certification. MCS is the UK's quality mark for small-scale renewable installations and it carries real consequences: only systems installed by an MCS-certified contractor are eligible for Smart Export Guarantee (SEG) payments from your energy supplier. Ofgem mandates this as part of the SEG eligibility rules. You can check any installer's active certification status on the MCS Certified installer finder. If an installer cannot produce an MCS certificate number, do not proceed.

MCS certification also covers the products used: panels, inverters, and batteries must appear on the MCS Product Directory. A certified installer using off-directory products is a red flag — the resulting installation may not qualify for export payments or future grant schemes.

Check the panel specification in detail

A vague quote that simply says "10 solar panels" tells you almost nothing. A proper quote should name the panel manufacturer and model number, state the panel wattage (typically 380–430 W per panel for modern monocrystalline units), and give an efficiency percentage. The vast majority of modern monocrystalline panels achieve 20–23% cell efficiency. If a quote lists panels below 20% efficiency, ask why — older or lower-grade panels cost less upfront but produce less electricity over the system's lifetime.

Look at the product warranty (typically 12–25 years, covering manufacturing defects) and the performance guarantee (typically 25–30 years, guaranteeing minimum output — usually 80–87% of rated power after 25 years). Premium manufacturers such as Panasonic, LG, and SunPower offer 25-year product warranties; mainstream brands like JA Solar and Longi typically offer 12–15 years. For a deeper look at panel options, see our guide to the best solar panels in the UK.

Understand the inverter type and specification

The inverter converts DC electricity from your panels into AC power your home can use, and it is often where quotes diverge most significantly. There are three main configurations:

String inverter — one central unit; lower cost, but output from the entire string is limited by the weakest panel (affected by shading).
Microinverters — one per panel; maximises output under partial shade, easiest to expand, higher upfront cost.
Power optimisers + string inverter — a hybrid; each panel gets an optimiser while a single central inverter handles conversion.

The quote should name the inverter brand and model. Well-regarded brands include SolarEdge, Enphase, Fronius, SMA, and Solis. Inverter warranties are typically 5–12 years as standard; many manufacturers offer paid extensions to 20–25 years, which is worth considering given that replacing an inverter mid-system-life costs £500–£1,500. See our comparison of string inverters, microinverters, and power optimisers for full detail on which suits different roof configurations.

Scrutinise the estimated annual output and savings

Every reputable quote should include an estimated annual electricity generation figure in kWh per year. You can cross-check this independently using PVGIS — the European Commission's Joint Research Centre tool — which is free and requires only your postcode, system size, and roof orientation. A south-facing 4 kWp system in London typically produces around 3,500–3,800 kWh/year according to PVGIS; the same system in Scotland may produce 10–15% less. If a quote's output estimate is materially higher than PVGIS suggests, challenge it.

Equally important is the electricity unit price the installer has used to calculate your projected savings. If they have assumed a price that is significantly higher than your current tariff, the savings figure will look better than it should be. Ask for this assumption explicitly and apply your own rate if necessary. See our article on solar panel costs in the UK for typical payback period benchmarks.

Warranty terms — what good looks like

A well-structured quote or accompanying proposal document should cover four distinct warranties:

Panel product warranty — manufacturer covers defects; look for 15 years minimum, ideally 25.
Panel performance guarantee — manufacturer guarantees output retention; 25–30 years is standard.
Inverter warranty — manufacturer covers the inverter unit; 5–12 years standard, extensions available.
Workmanship (installation) warranty — installer covers the quality of the physical work; look for 2 years minimum, MCS sets minimum standards here, and some installers offer 5 years as standard.

Ask whether the workmanship warranty is backed by an Insurance-Backed Guarantee (IBG). An IBG protects you if the installer ceases trading before the warranty period ends — this is particularly important for long-term workmanship cover.

What the quote should include as standard

A complete, professional quote should explicitly state whether each of the following is included or is an additional cost:

Scaffolding — often the most commonly omitted cost. Erecting and dismantling scaffolding can add £500–£900 to the total.
DNO (Distribution Network Operator) application — legally required before connecting to the grid. Systems under 3.68 kW per phase are notified under G98 (within 28 days of install); larger systems need prior G99 approval, which can take 4–8 weeks. Your installer should handle this on your behalf.
Monitoring system — most modern inverters include an app or web portal; confirm this is set up as part of the installation.
Site survey — ideally conducted before the quote is finalised. A pre-sign survey ensures the system design is realistic for your roof.
Electrical works and consumer unit upgrades — some older properties require additional wiring or fuse board work; check whether this is in scope.

Insurance, payment schedule, and deposit terms

Confirm the installer carries public liability insurance of at least £2 million — this is an MCS requirement and protects you if accidental damage occurs during the installation. Ask for a copy of their certificate of insurance if it is not already included.

On payment terms, be cautious of installers requesting a deposit above 25–30% of the total before any work begins. If possible, structure payments in stages: deposit on contract signing, a second payment on installation day, and final payment on successful commissioning. Citizens Advice recommends paying by credit card where possible, as it provides Section 75 protection on purchases over £100.

Red flags to watch for

No MCS number or inability to confirm MCS certification status via the MCS installer finder.
Inverter or panel brand not named — or products not on the MCS Product Directory.
Annual output estimates significantly above PVGIS results for your location and roof orientation.
Savings calculations using an electricity price well above your current tariff.
Scaffolding quoted as a separate extra only after you have accepted the headline price.
High-pressure tactics, time-limited discounts, or reluctance to provide a written quote.
No mention of a pre-installation site survey.
Deposit requests above 30% before the survey or any work has started.

Putting it all together

The cheapest quote is rarely the best value. A system that underperforms its projections, loses its warranty when the installer ceases trading, or is installed by an uncertified contractor will cost more in the long run than a slightly higher quote from a reputable MCS installer using quality equipment. Request at least three quotes, compare them line by line against this checklist, and ask each installer to clarify anything that is not explicit in writing. For context on typical installed costs and what each system size delivers, see our guide to solar panel cost by system size. You should also understand how long the installation process takes in the UK so you can plan around survey, scaffolding, and DNO notification timelines.