Solar System Downtime & Lost Energy Calculator
ANA›Life Services Authority›National Calculator Authority›Solar System Downtime & Lost Energy Calculator
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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.
System Capacity (kWp)
Nameplate DC capacity of the solar array
Average Daily Peak Sun Hours (PSH)
Typical peak sun hours per day at your location (1–8 h/day)
System Performance Ratio (%)
Accounts for inverter losses, wiring, temperature, soiling (typical 75–85%)
Downtime Duration (hours)
Total hours the system was non-operational
Electricity Tariff / Feed-in Rate ($/kWh)
Blended rate used for self-consumption savings or feed-in tariff
Calculate Lost Energy
### Results
Average Hourly Generation Rate— Lost Energy— Lost Energy (MWh)— Financial Loss— Equivalent Days of Production Lost—
function solCalc() { var errEl = document.getElementById('sol-error'); var resEl = document.getElementById('sol-result'); errEl.style.display = 'none'; resEl.style.display = 'none';
// --- Read inputs --- var capacity = parseFloat(document.getElementById('sol-capacity').value); var psh = parseFloat(document.getElementById('sol-irradiance').value); var prPct = parseFloat(document.getElementById('sol-pr').value); var downtime = parseFloat(document.getElementById('sol-downtime').value); var tariff = parseFloat(document.getElementById('sol-tariff').value);
// --- Validation --- var errors = []; if (isNaN(capacity) || capacity 8) errors.push('Peak Sun Hours must be between 0.1 and 8.'); if (isNaN(prPct) || prPct 100) errors.push('Performance Ratio must be between 1 and 100.'); if (isNaN(downtime) || downtime 0) { errEl.innerHTML = errors.join(''); errEl.style.display = 'block'; return; }
// --- Core Formulas --- // Performance Ratio as decimal var PR = prPct / 100;
// Daily energy output (kWh/day): // E_day = Capacity_kWp × PSH × PR var E_day = capacity * psh * PR;
// Average hourly generation rate (kWh/h): // R_hourly = E_day / 24 // (averaged over 24 h; generation only occurs during daylight but // this gives the mean rate used for downtime spanning multiple days) var R_hourly = E_day / 24;
// Lost energy during downtime (kWh): // E_lost = R_hourly × downtime_hours var E_lost = R_hourly * downtime;
// Financial loss ($): // Loss_$ = E_lost × tariff var financialLoss = E_lost * tariff;
// Equivalent full production days lost: // Days_lost = E_lost / E_day var daysLost = (E_day > 0) ? (E_lost / E_day) : 0;
// --- Display --- document.getElementById('sol-hourly-rate').textContent = R_hourly.toFixed(4) + ' kWh/h'; document.getElementById('sol-lost-energy').textContent = E_lost.toFixed(3) + ' kWh'; document.getElementById('sol-lost-mwh').textContent = (E_lost / 1000).toFixed(6) + ' MWh'; document.getElementById('sol-financial').textContent = '$' + financialLoss.toFixed(2); document.getElementById('sol-days').textContent = daysLost.toFixed(3) + ' day(s)';
resEl.style.display = 'block'; }
#### Formulas Used
Daily Energy Output (kWh/day):
Eday = CapacitykWp × PSH × PR
Average Hourly Generation Rate (kWh/h):
Rhourly = Eday ÷ 24
Lost Energy During Downtime (kWh):
Elost = Rhourly × Downtimehours
Financial Loss ($):
Loss = Elost × Tariff$/kWh
Equivalent Production Days Lost:
Dayslost = Elost ÷ Eday
#### Assumptions & References
- 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.
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