Solar System Downtime & Lost Energy Calculator
Estimate the energy production lost during solar system outages, along with the associated financial impact, based on your system's capacity, local irradiance, and downtime duration.
Nameplate DC capacity of the solar array
Typical peak sun hours per day at your location (1–8 h/day)
Accounts for inverter losses, wiring, temperature, soiling (typical 75–85%)
Total hours the system was non-operational
Blended rate used for self-consumption savings or feed-in tariff
Formulas Used
Daily Energy Output (kWh/day):
Eday = CapacitykWp × PSH × PR
Average Hourly Generation Rate (kWh/h):
Rhourly = Eday ÷ 24
Lost Energy During Downtime (kWh):
Elost = Rhourly × Downtimehours
Financial Loss ($):
Loss = Elost × Tariff$/kWh
Equivalent Production Days Lost:
Dayslost = Elost ÷ Eday
Assumptions & References
- Generation is modelled as a uniform average rate over 24 hours, derived from daily energy output. Actual generation is concentrated in daylight hours; this approach is appropriate for downtime spanning multiple days or unknown time-of-day outages.
- Performance Ratio (PR) accounts for all real-world losses: inverter efficiency, DC/AC wiring losses, temperature derating, soiling, shading, and mismatch. Typical residential systems achieve 75–85% (IEC 61724-1).
- Peak Sun Hours (PSH) represent the equivalent hours of 1,000 W/m² irradiance that deliver the same daily insolation. Source: NASA POWER / NREL PVWatts databases.
- The tariff entered should reflect the applicable rate — either the retail electricity rate (for self-consumed energy) or the feed-in tariff (for exported energy), or a blended rate where applicable.
- Degradation over system lifetime is not included; capacity is treated as the current effective nameplate rating.
- References: IEC 61724-1 (Photovoltaic system performance monitoring), NREL PVWatts Calculator methodology, EU JRC PVGIS documentation.