Why Mistakes Happen in the Swiss Market
Switzerland's solar installation rate has grown rapidly since 2022, driven by high electricity prices and the federal push toward the Energiestrategie 2050 net-zero target. The installation workforce has expanded quickly — not always with adequate quality control. Cantons vary in how rigorously they inspect completed installations, and the Pronovo EIV application process does not include a physical site inspection.
The result: a meaningful proportion of Swiss rooftop systems have at least one installation deficiency. Most are minor; some are significant and affect safety or long-term yield.
Mistake 1: Shading Not Modelled Correctly
What happens: the installer uses a simple online tool to estimate yield without properly modelling nearby trees, dormers, chimneys, or neighbouring buildings. The system underperforms from day one.
How to avoid it: require a Polysun simulation or equivalent that includes a site-specific shading analysis. For systems where partial shading is unavoidable, insist on module-level optimisers (SolarEdge or Tigo) or a microinverter solution — they limit string-level losses from one shaded panel affecting the whole array.
Mistake 2: Undersized or Incorrectly Positioned DC Cables
What happens: DC cables between panels and inverter are undersized for the actual current, leading to resistive losses of 2–5% annually, and in worst cases localised overheating. Cables routed without UV protection degrade prematurely in alpine UV conditions.
How to avoid it: ask your installer to specify cable cross-section (typically 4 mm² or 6 mm² for residential runs) and confirm cables are rated for outdoor UV exposure. In attic spaces, check that cables are not bundled tightly without ventilation — heat build-up accelerates insulation degradation.
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Mistake 3: No DC Isolator or Improperly Installed Isolator
What happens: Swiss fire safety regulations and the VSE EEA-CH standard require an accessible DC isolator between panels and inverter. Missing or incorrectly rated isolators create both regulatory violations and genuine fire risk.
How to avoid it: confirm the commissioning protocol explicitly lists the DC main disconnection device, its location, and its voltage/current rating. This item is checked during some cantonal inspections but not universally.
Mistake 4: Wrong Inverter Feed-In Limitation Setting
What happens: many Swiss grid operators impose a maximum feed-in limit (e.g., 3.68 kW for a single-phase connection). If the inverter is not configured to respect this limit, the grid operator may demand costly remediation or terminate the feed-in agreement.
How to avoid it: before installation, confirm your local Verteilnetzbetreiber's (VNB) feed-in rules. After installation, ask your installer to show you the inverter's feed-in limitation setting in the commissioning documentation.
Mistake 5: Missing or Incomplete Pronovo Registration
What happens: the homeowner misses the three-month Pronovo registration window post-commissioning — or the installer registers the wrong commissioning date — and the EIV application is rejected.
How to avoid it: clarify in your installer contract who is responsible for Pronovo registration. Reputable installers manage this as part of their service. Note the commissioning date in writing and set a calendar reminder for the 10-week mark if the installer has not confirmed submission.
Mistake 6: Roof Penetrations Without Proper Sealing
What happens: mounting feet are attached through the roof covering without appropriate waterproofing, leading to leaks — often not immediately visible. In Switzerland's high rainfall and freeze-thaw alpine conditions, water ingress damage can be significant.
How to avoid it: ask for a post-installation roof inspection report, ideally from your roofing company. For newer Swiss roofs with membrane waterproofing, confirm the installer uses compatible mounting hardware and sealing compounds.
Mistake 7: Battery Installed Without Proper Ventilation
What happens: lithium-ion batteries (BYD HVM, Sonnen eco, Tesla Powerwall) are installed in spaces with inadequate ventilation. While modern LFP batteries are significantly safer than older chemistries, installation guidelines from all manufacturers specify minimum air circulation requirements.
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How to avoid it: verify the installation location against the battery manufacturer's technical guidelines before the installation day. Most Swiss battery installations work well in utility rooms or garages with natural ventilation.
Common Mistakes at a Glance
| Mistake | Typical cost | Prevention |
|---|---|---|
| Shading not modelled | CHF 300–800/year yield loss | Require Polysun report |
| Undersized DC cables | 2–5% annual yield loss | Specify cable cross-section |
| Missing DC isolator | Regulatory breach + remediation | Check commissioning protocol |
| Wrong feed-in limitation | Grid operator fine or disconnection | Confirm VNB rules pre-install |
| Late Pronovo registration | EIV rebate lost (CHF 5,000–15,000) | Assign responsibility in contract |
| Poor roof sealing | Water damage (CHF 2,000–10,000+) | Post-install roof inspection |
| Battery ventilation fault | Warranty void | Check manufacturer specs |