Point 1 — The price in CHF/kWp installed
Standardize quotes in CHF/kWp (watt-peak) to compare installations of different sizes. In 2026, a quality residential installation costs CHF 2 200–2 800/gross kWp. Below CHF 1 900/kWp: carefully study the quality of the components. Above CHF 3 000/kWp: ask for justification (premium components, BIPV, complex configuration?).
Item 2 — The exact make and model of the panels
Ask for the brand, model and Wc/panel power. Check: is it N-Type (TOPCon or HJT) or P-Type (PERC)? The performance guarantee (25 years ≥ 87%? or 12 years ≥ 90% only?). The yield (≥ 21% for good TOPCon 2026). The temperature coefficient (better = less negative: −0.26 to −0.35%/°C).
Item 3 — The inverter model and warranty
The inverter is the component most likely to fail. Check: recognized brand (Huawei, Fronius, SMA, Goodwe — no unknown brand without after-sales service in Switzerland), standard warranty (5–10 years), warranty extension possible (10–15 years for CHF 200–500), local after-sales service available in French-speaking Switzerland.
Item 4 — Production simulation (PVsyst or equivalent)
A serious installer submits a PVsyst or SolarEdge Designer simulation with: estimated annual production (kWh/year), modeled shading losses, expected Performance Ratio, monthly production distribution. Without simulation: production promises are worthless. Compare simulated production between quotes — if one projects 15% more without explanation, ask why.
Item 5 — Are all procedures included?
Check that the quote includes: (1) Pronovo registration and monitoring, (2) municipal announcement, (3) GRD connection request, (4) installation and commissioning report, (5) monitoring training. These procedures can represent 3–5 hours of administrative work — some charge for them as an option (CHF 300–600).
6–10 points summarized
Item 6 — Site guarantee: Distinguish statutory rights for defects from additional contractual warranties. Specify deadlines, acceptance, notification of defects and the responsible company. Item 7 — Mounting structure: ask for the system, material, roof compatibility, mechanical design and warranty. Item 8 — DC cables: have cable size and routing designed for length, current, losses, protection and applicable rules; one cable size does not suit every project. Item 9 — Monitoring: check access, functions, service duration and any subscription, including what remains available without the cloud. Item 10 — Verifiable references: ask for 3 customer contacts in your area established for 2+ years. Call them.