A cheaper quote may cover less work. Compare scope, assumptions and responsibility before comparing totals.
Make the scope visible
Create a table with panel capacity, inverter model, installation work, scaffolding, connection, monitoring and aftercare. Mark anything excluded. If one quote includes a battery and the other does not, ask for separate prices before making a comparison.
Challenge the savings assumptions
Ask both companies to use the same household consumption, electricity price and export price. A savings estimate built around an optimistic self-use rate is not comparable with a cautious one. Keep financing costs and any assumed support payments visible rather than burying them in one payback figure.
Ask who solves a problem
Distinguish a product warranty from installation workmanship and performance estimates. Ask who handles a fault, labour, access equipment and replacement delivery. Request a written handover list and a clear payment schedule. Keep verbal promises in the written specification.