Guide · Switzerland
Are east and west roof areas worth adding to a south-facing PV system?
The question is not whether a south-facing system produces more over the year. It is what additional east- and west-facing roof areas really contribute to the household.
Short answerQuick answer
Are east and west roof areas worth adding to a south-facing PV system?
In Bern, adding 2.5 kWp east and 2.5 kWp west raises modelled annual generation from about 12,232 to 17,120 kWh. The household directly uses only around 40 kWh more; at the assumed tariffs, the 20-year result improves by about CHF 530 before maintenance, degradation or replacement.
The practical question: should you use the east and west roof areas too?
We compare 10 kWp facing south with the same system plus 2.5 kWp east and 2.5 kWp west. Both options use a 30° pitch and 10 kWh battery; household demand, tariffs and grants stay the same.
This is not a claim that one orientation is always best. It quantifies the contribution of additional roof sections in this particular case. The output is a PVGIS model for postcode 3011; actual shading and usable roof area need to be checked on site.
South-facing PV plus east and west roof areas: what is the extra benefit?
In Bern (postcode 3011), we compare 10 kWp facing south with the same system plus 2.5 kWp east and 2.5 kWp west. Both options use a 30° roof pitch and a 10 kWh battery; household demand (4,050 kWh/year), tariffs and grants stay the same.
| Annual metric | 10 kWp south | South + 2.5 kWp east + 2.5 kWp west |
|---|---|---|
| PV generation | 12,232 kWh | 17,120 kWh |
| PV self-consumption share | 33.9% | 24.4% |
| Household demand covered | 3,886 kWh · 95.9% | 3,926 kWh · 96.9% |
| Grid imports | 164 kWh | 124 kWh |
| Grid exports | 8,088 kWh | 12,936 kWh |
| Net investment | CHF 26,700 | CHF 33,700 |
| Annual savings | CHF 1,850 | CHF 2,227 |
| Result after 20 years | + CHF 10,301 | + CHF 10,831 |
Monthly PV generation
| Month | 10 kWp south | South + east/west |
|---|---|---|
| January | 552 kWh | 703 kWh |
| February | 736 kWh | 968 kWh |
| March | 1,127 kWh | 1,544 kWh |
| April | 1,303 kWh | 1,849 kWh |
| May | 1,284 kWh | 1,878 kWh |
| June | 1,412 kWh | 2,080 kWh |
| July | 1,441 kWh | 2,112 kWh |
| August | 1,334 kWh | 1,914 kWh |
| September | 1,175 kWh | 1,630 kWh |
| October | 894 kWh | 1,194 kWh |
| November | 519 kWh | 674 kWh |
| December | 456 kWh | 575 kWh |
The extra roof areas add about 4,888 kWh/year, but the household directly uses only about 40 kWh more; exports rise by about 4,848 kWh. An additional CHF 7,000 investment brings roughly CHF 376 more annual savings and only CHF 530 more over 20 years. That small margin can disappear with maintenance, replacement or lower output. Actual shading and usable roof area must be checked on site.
Official and specialist sources
- SFOE: photovoltaic market – 2025 price study
- ElCom: electricity tariffs 2026
- Pronovo: one-off payment calculator
- SwissEnergy: home battery storage
- SwissEnergy: self-consumption
- European Commission: PVGIS
- WattBilanz: Pronovo, exports, guarantees of origin and tax
Sources and price assumptions last checked on 18 September 2026.
Continue with your own data
Add each usable roof section separately and compare both annual generation and how much of it you can use at home.