1. Read kWp, kW and kWh
kWp describes rated module capacity under reference conditions. kW measures power at an instant; kWh measures energy over a period. Do not compare kWp capacity with annual consumption without a generation calculation. Chosen arithmetic example: twenty 400 Wp modules total 8 kWp; this does not yet establish your roof’s kWh output.
2. Request site-specific generation
Document orientation, tilt, weather data, shading, snow, availability and assumed losses. Request monthly results and their limitations. Cell efficiency, rated capacity and annual energy are not interchangeable. A technology or brand does not guarantee identical gains on every roof; compare exact models in the same calculation.
3. Compare generation and hourly demand
Record consumption, occupancy, hot water, heating and current or planned charging. Separate direct use, battery charging, surplus and grid purchases. Producing as many kWh as annual consumption does not necessarily cover every hour or winter. Use the same profiles for storage and no-storage options.
4. Read the complete-system price
Request equipment, mounting, access, roof work, electrical work, connection, testing and VAT. Separate options and excluded work. CHF/kWp is comparable only when capacity and included services are consistent. Ask for a schedule, payment terms and how construction changes are handled. The itemised quote remains the basis of the building’s budget.
5. Check grants and procedures separately
Identify the Pronovo programme, local conditions and documents required for the system. Specify responsibility, filing date, plant certification and follow-up. Clarify building notification or permission and grid technical approval for the site. Grants, building permissions and electrical authorisations follow different procedures; a voluntary label does not replace them.
6. Prepare handover and operation
Keep the layout, serial numbers, tests, documented settings and warranties. Specify data access, alerts, maintenance and fault contacts. Product, power and installation warranties have different terms. Compare model terms and uncovered charges; do not infer actual service life from a warranty expiry date alone.