1. Separate living space and usable roof area
Living space is not the roof area available for modules. Record dimensions, roof planes, obstacles, shading, access and mounting constraints. Request selected module dimensions and a complete layout with required clearances. Do not infer capacity from room count or a universal roof-area-to-kWp ratio.
2. Describe each home’s consumption
For all three home sizes, gather annual bills and available hourly readings. Specify occupancy, heating, hot water and vehicles. A small home with a heat pump and charging may use more electricity than a large, lightly occupied property. These illustrate usage differences, not average profiles. Calculate current demand and demand after planned work.
3. Compare capacities on the same roof
For each option, request installed price, monthly generation, direct use, surplus and remaining purchases. If self-consumption changes, clarify whether the figure means the share of generation used or the share of demand covered. For a battery, compare usable capacity, power, losses and added cost. A larger system alone does not establish greater savings per franc invested.
4. Build a budget from the quotation
Method example using deliberately chosen amounts: a CHF 20’000 quote for 8 kWp equals CHF 2’500/kWp. A hypothetical CHF 3’000 grant would leave CHF 17’000 before other items. This is neither a market tariff nor a Pronovo entitlement. Replace every input with your quotation and confirmed grant; check roof work, VAT, connection, battery and exclusions.
5. Prepare approvals and handover
Specify building and grid procedures, grant timing and contractor responsibilities. Check electrical skills and permissions, project references and any professional label separately. Compare warranty contracts, maintenance and service contacts. At handover, keep plans, tests, settings, serial numbers and generation assumptions; home floor area guarantees neither performance nor payback.