Most homeowners receive multiple solar quotes that are effectively impossible to compare solar quotes side-by-side at face value: different panel brands, different inverters, different system sizes, and wildly different totals. This guide gives you a professional framework for normalising any set of UK or EU quotes in 2026 so you can make a confident, informed decision.
Step One: Normalise to Cost per Watt-Peak
The most important normalisation step is converting each quote to a £/Wp or €/Wp figure (cost per watt-peak of installed capacity). This immediately removes the effect of different system sizes.
Formula: Total installed price ÷ system capacity in watts = £/Wp or €/Wp.
In 2026, competitive UK installed prices for residential systems run approximately:
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- 3–4 kWp: £1.05–1.25/Wp
- 5–7 kWp: £0.90–1.10/Wp
- 8–10 kWp+: £0.80–1.00/Wp
EU equivalents vary by country but typically run €0.85–1.30/Wp for the same size range, with Northern Europe (Germany, Netherlands) at the higher end and Southern Europe (Spain, Portugal, Italy) somewhat lower.
A quote significantly above these ranges needs a justification — premium equipment, complex roof, specific inverter technology. A quote significantly below them should raise the question of what has been omitted or substituted.
Step Two: Evaluate the Equipment Tier
Not all panels and inverters are equal. Compare on these axes:
- Panel efficiency: Premium Tier 1 panels in 2026 run 21–23% module efficiency. Anything below 19% is below current market standard for new installations.
- Panel degradation warranty: Industry-leading warranties guarantee no more than 0.4–0.5% degradation per year, reaching 80–82% of rated output after 25–30 years. Check the specific year 25 output guarantee — some cheaper brands guarantee only 80% at year 25 with 0.7% annual degradation.
- Inverter brand and service network: Fronius, SMA, SolarEdge, Enphase, Sungrow, and Growatt all have EU/UK service infrastructure. Unknown brands without a local service operation are a support risk over a 25-year system life.
- Inverter warranty: Standard is 5–10 years with extension options. SolarEdge and Enphase offer 25-year inverter warranties on their premium lines — relevant when comparing microinverter vs string quotes.
When comparing quotes, add a notional cost for equipment that is not equivalent — for instance, if Quote A uses a panel with 25% weaker degradation warranty, account for the expected yield difference over 25 years.
Step Three: Check Scope Completeness
Price differences often reflect scope differences rather than efficiency. Check each quote for:
- DNO application and grid connection notification — required in the UK for all systems. Some quotes exclude this as an "additional cost."
- Scaffolding — should always be included in the quote price, not added later.
- Electrical consumer unit upgrade — sometimes necessary; find out if any quote assumes an upgrade and others do not.
- Monitoring system setup — confirm whether portal setup and app configuration are included.
- MCS certificate issuance — required for SEG tariff access in the UK; confirm it is included.
- VAT — residential solar in the UK is zero-rated for VAT. EU rates vary by member state (0–10% reduced rate in most). Confirm whether quoted prices are inclusive.
Step Four: Score on Five Axes
Once you have normalised quotes for scope and equipment, score each installer across five dimensions, 1–5:
- Price competitiveness — based on £/Wp or €/Wp versus market benchmarks
- Equipment quality — panel efficiency, degradation warranty, inverter brand
- Installer credibility — certifications, reviews, reference customers
- Scope completeness — all items included without hidden extras
- Post-installation support — warranty terms, response commitments, monitoring setup
The highest total score across five axes — not the lowest headline price — should determine your choice. A quote that saves £400 upfront but uses a lower-tier inverter with no UK service centre could cost significantly more over a decade of ownership.
Understanding Yield Estimates — and Verifying Them
Every quote should include a projected annual yield in kWh. Cross-check this against the free PVGIS tool (re.jrc.ec.europa.eu), entering your postcode and the proposed system size and orientation. Quotes more than 10% above the PVGIS estimate for equivalent conditions should be queried — inflated yield figures are used to shorten apparent payback periods and are a form of mis-selling.
Key Takeaways
- Convert every quote to £/Wp or €/Wp as the first normalisation step — this removes the effect of different system sizes.
- Check degradation warranty terms carefully: a 0.7%/year degradation rate compounds to a meaningfully lower year-25 output versus a 0.4%/year guarantee.
- Verify scope completeness — DNO application, scaffolding, monitoring setup, and MCS certificate are all frequently excluded from low headline quotes.
- Score on five axes (price, equipment, credibility, scope, support) rather than selecting on price alone.
- Cross-check yield estimates against PVGIS — estimates more than 10% above PVGIS for your location warrant a direct question to the installer.
Taking two hours to properly normalise your quotes is one of the highest-value activities you can do before committing to a solar installation. The framework above gives you everything you need to make that comparison confidently.