Only quote from installers who have done a site survey
A quote provided without a site survey — in person or, at minimum, via satellite imagery with roof measurement tools — cannot accurately assess your roof's usable area, shading from chimneys or neighbouring buildings, structural suitability, or the correct system size for your household. Do not accept a quote from a company that provides a price based on postcode and a phone conversation alone.
A site survey should identify: roof orientation and pitch; presence and extent of shading from any source; roof structure and fixing points; condition of roof covering (a re-roof before panel installation may be recommended if the roof is near end-of-life); distance from roof to consumer unit (affects cable run costs); and any listed building or conservation area constraints.
What a detailed quote should include
The quote document itself should specify: panel brand, model number, and rated wattage (not just "high efficiency panels"); inverter brand, model, and warranty term; number of panels and total system kWp; estimated annual generation in kWh (and the assumptions behind it — irradiance data source, shading losses applied, performance ratio used); projected energy bill saving and SEG income based on stated assumptions; total installed cost including VAT, scaffolding, DNO notification, and any electrical upgrades required.
The generation estimate should reference PVGIS or SAP calculation methodology — both use site-specific irradiance data. Be wary of estimates significantly above what PVGIS would predict for your location and roof orientation, as these inflate the apparent payback period.
Ask each installer to provide the payback calculation with explicit assumptions visible, so you can compare three quotes on the same basis rather than comparing three different sets of assumptions.
Red flags in solar quotes
Pressure tactics — "this price is only available today" or "we have a last installation slot this month" — are a common tool in high-pressure solar sales. Walk away from any company that uses time pressure to close a quote.
Quotes that guarantee a specific annual income or saving without detailed assumptions behind the figure are unrealistic. Generation varies with weather; grid import prices change; SEG rates are not guaranteed. A responsible installer will provide a range and state their assumptions clearly.
Unbranded or generic panel specifications ("Tier 1 panels", "premium efficiency") without model numbers should be questioned. Panel quality and warranty terms vary significantly; you need to know exactly what you are buying. Ask for the spec sheet.
MCS certification — the non-negotiable check
Any installer you receive a quote from should be MCS-certified. Check at mcscertified.com — enter the company name or certificate number and confirm the certification is current and covers solar PV.
MCS certification is required to issue the MCS installation certificate, which is required to register for the Smart Export Guarantee and to demonstrate warranty validity. An installation by a non-MCS installer is essentially uninsurable from a warranty and SEG perspective.
Once you have three comparable quotes from MCS-certified installers who have conducted site surveys and provided full specifications, you are in a strong position to make a considered decision. The cheapest quote is not always the best — inverter warranty length, panel brand track record, and the installer's post-installation support matter for a 25-year asset.