One of the most common questions from Swiss homeowners exploring solar is: "how many kilowatt-peaks do I actually need?" The honest answer is that it depends — but in a precise, calculable way. Understanding the variables lets you pressure-test any installer quote and make a confident decision.
Swiss Irradiation: Why Location Matters
Switzerland has more solar resource variation than its small area might suggest. The Swiss Federal Office of Energy (SFOE/BFE) and Meteotest publish canton-level irradiation data that forms the basis of any professional yield estimate.
| City | Annual Irradiation (kWh/m²) | Specific Yield (kWh/kWp) |
|---|---|---|
| Zürich | ~1,100 | ~950–1,050 |
| Bern | ~1,150 | ~980–1,080 |
| Geneva | ~1,300 | ~1,100–1,200 |
| Lugano | ~1,450 | ~1,200–1,350 |
| Davos (alpine) | ~1,350 | ~1,150–1,300 |
Geneva and Lugano benefit from more sunny days and a lower frequency of fog (Hochnebel), which regularly suppresses output in the Mittelland through autumn and winter.
The Core Sizing Formula
The starting point for any sizing exercise is your annual electricity consumption. Swiss households average around 3,500 to 5,500 kWh per year, though EV ownership can push this to 7,000–10,000 kWh.
Step 1 — Calculate your target coverage ratio. Most Swiss households aim for 60–80% solar self-sufficiency. Higher ratios require either significant battery storage or acceptance of large seasonal surpluses fed into the grid.
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Step 2 — Estimate required kWp:
Required kWp = (Annual consumption kWh × Coverage ratio) ÷ Specific yield kWh/kWp
Example — Zürich household, 5,000 kWh/year, 70% target:
(5,000 × 0.70) ÷ 1,000 = 3.5 kWp minimum
In practice, most installers recommend 5–8 kWp for a typical Zürich family home to account for seasonal variation and EV charging headroom.
Key Sizing Variables
Roof Orientation and Tilt
A south-facing roof at 30° tilt is the Swiss reference case. Deviations reduce output:
- South-east or south-west: approximately 5–10% reduction
- East or west: approximately 20–30% reduction
- Flat roof (with tilt frames): approximately 10–15% below optimum, but allows ideal orientation
Shading
Even partial shading from chimneys, dormers, or neighbouring buildings can cut output significantly. Modern string inverters with power optimisers (SolarEdge) or microinverter systems (Enphase) mitigate this, but cannot fully compensate for heavy shading. A professional shading analysis using PVsyst or PVGIS is worth requesting from your installer.
EV Charging
A typical EV driving 15,000 km per year in Switzerland needs roughly 2,500–3,500 kWh of additional electricity annually (at 17–23 kWh/100 km). If you plan to charge primarily from solar, add this to your consumption baseline before sizing.
Battery Storage
Adding a 10 kWh battery (e.g. BYD HVM or Fronius Symo GEN24 + BYD) typically lifts self-consumption from around 30% to 60–70% without changing the PV array size. This is often more cost-effective than oversizing panels.
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Practical Sizing Recommendations by Household Type
- 2-person household, no EV, Bern: 4–6 kWp
- 4-person household, no EV, Zürich: 6–9 kWp
- 4-person household + 1 EV, Zürich: 9–12 kWp
- 4-person household + 2 EVs, Geneva: 12–16 kWp
- Rural household with heat pump, any region: 12–20 kWp
Alpine Bonus: Cold Temperatures Boost Output
Solar panels are semiconductors — they are more efficient in cold conditions. Standard test conditions (STC) assume 25°C cell temperature. At the 10–15°C average temperatures typical of Swiss spring and autumn, most modern panels produce 3–5% more than their rated output. This alpine cold-weather bonus is a genuine yield advantage over solar systems in warmer European climates.