Guide · Switzerland
Why your postcode matters when assessing a PV system
Only about 15 kilometres as the crow flies separate 3800 Interlaken and 3818 Grindelwald. Yet WattBilanz calculates a 2,239 kWh, or 17.7%, annual difference for the same 10 kWp system.
Short answerShort answer
In short: the postcode is not a formality
- A Swiss average hides regional differences in irradiance and horizon.
- In the WattBilanz example, the same 10 kWp system produces 12,667 kWh in Interlaken and 10,428 kWh in Grindelwald each year.
- The postcode allows the calculation to account for local sunlight and shading from mountains. A qualified installer must check shading from trees, neighbouring buildings and roof structures on site.
Why a Swiss average says little about one particular home
When you are thinking about solar panels, you want to know what your own roof can produce. A Swiss average gives you a rough starting point, but it cannot tell you how much sunlight reaches your home or how long the surrounding mountains hide the sun.
Interlaken and Grindelwald make this easy to see. Both are in the Bernese Oberland, only about 15 kilometres apart as the crow flies. Yet our calculation gives noticeably different generation figures for exactly the same system.
A fair comparison: only the location changes
Both calculations use 10 kWp, south orientation, a 30° roof pitch, 4,500 kWh household demand, no battery, a 30 ct/kWh import price and 6 ct/kWh export payment. Pronovo is included, with no additional local grant. PVGIS 5.3/SARAH-3 uses 2014–2023 weather years, 14% system loss and the terrain horizon.
3800 · 3818
The WattBilanz result
The place centres are about 15 kilometres apart as the crow flies. Every other input is identical.
| Metric | Interlaken | Grindelwald | Difference |
|---|---|---|---|
| Annual generation | 12,667 kWh | 10,428 kWh | 2,239 kWh |
| Generation per kWp | 1,267 kWh | 1,043 kWh | 224 kWh |
| Self-sufficiency | 36.7% | 34.3% | 2.4 points |
| Annual financial benefit | CHF 1,157 | CHF 996 | CHF 161 |
| Simple payback | 17.0 years | 19.8 years | 2.8 years |
| Result after 20 years | +CHF 3,437 | +CHF 225 | CHF 3,212 |
In this comparison, Grindelwald produces 17.7% less solar electricity than Interlaken. The difference comes from the location-specific solar profile, not from a different system size, orientation or tariff assumption.
Interlaken
Grindelwald
What your postcode accounts for
The postcode prevents a national average from being applied unchecked to every home. It therefore affects yield, self-consumption, payback and the 20-year result.
It is not a survey of the individual roof. PVGIS represents the wider location and terrain horizon, but not every tree, chimney, roof structure or recently built neighbouring property.
Always check local shading on site
Before an order is placed, the installer should check the sun path and shading on the actual roof. Trees, neighbouring buildings, chimneys and dormers are particularly relevant. A documented shading analysis should accompany the quotation where the situation is critical.
Data and further checks
- European Commission: PVGIS 5.3 and SARAH-3
- SFOE: Solar roof – suitability of the specific building roof
- SFOE/SwissEnergy: photovoltaics for your own electricity – account for shading
- ElCom: Swiss electricity tariffs 2026
- Open the Interlaken example ·
WB-7E3A176ACAB6C1EC - Open the Grindelwald example ·
WB-ACB3A3E3B85B298C
Calculator results and links checked on 22 September 2026.
Reproduce both calculations
The links open the Swiss WattBilanz calculator with identical assumptions and the relevant postcode. The calculation is rerun using the current data version.