Compare Solar Panels and Batteries

Stage 5 covered what to look for. This stage lets you compare specific products side-by-side using the same scoring framework — five weighted criteria per category, derived from published manufacturer specifications.

How the scoring works

Every product on this site is scored against five weighted criteria. Understanding the criteria helps you interpret the scores rather than just accepting them.

For solar panels, the five criteria are:

• Efficiency / output rating— module efficiency at STC (standard test conditions), expressed as a percentage. Higher efficiency means more generation from the same roof area. N-type TOPCon panels now routinely exceed 22%, while older Mono PERC panels sit at 20–21%. Efficiency is weighted most heavily for space-constrained installs.
• Warranty length and terms— both the product warranty (covers manufacturing defects) and the performance warranty (guarantees a minimum output percentage at end of term). The modern baseline is 12 years product and 25 years performance at ≥85% output. Longer, more generous terms signal manufacturer confidence in build quality.
• Degradation rate— the annual percentage by which output falls after the first year. Typical range is 0.40–0.55%/year. A 0.40% panel retains roughly 90% output after 25 years; a 0.55% panel retains around 86%. The difference is modest per year but compounds over a 25-year system life.
• Price per watt— installed cost per Wp is the most direct measure of value. Efficiency and warranty matter more than headline panel price, but at similar spec levels, £/Wp determines payback. Scores penalise panels priced significantly above peers with equivalent specs.
• Temperature coefficient— how much output drops per degree Celsius above 25°C. Expressed as %/°C; lower (e.g. −0.25%/°C) is better. Less critical in the UK than in hotter climates, but still a differentiator between panel tiers.

For home batteries, the five criteria are:

• Usable capacity— the actual kWh you can store and use, after accounting for the depth-of-discharge limit. LFP batteries can typically discharge to 100% without damage; NMC batteries are usually limited to 80%. Always compare usable capacity, not nameplate.
• Warranty length and cycle count— most batteries carry a 10-year or 6,000-cycle warranty, whichever comes first. Some also guarantee a minimum capacity retention (e.g. ≥70% at end of warranty). A cycle guarantee above 6,000 is a sign of premium LFP chemistry.
• Round-trip efficiency— the percentage of energy put into the battery that you get back out. Well-specified LFP batteries achieve 95%+ round-trip efficiency. Lower figures mean more grid energy wasted on charge/discharge losses.
• Price per usable kWh— installed cost divided by usable capacity. The most useful cross-battery cost comparison metric. Current mid-market range is £600–£900/usable kWh installed.
• Chemistry and safety— LFP (Lithium Iron Phosphate) is preferred for UK home installs: lower fire risk, longer cycle life, and better high-temperature behaviour than NMC. Scores favour LFP unless NMC is paired with exceptional specifications elsewhere.

Two ways to use this page:

1. Browse the full catalogue by category, sort by score, look at the top 3–5 candidates.
2. Compare two or three specific models you've seen on a quote or recommendation, side-by-side.