This calculator estimates the annual electricity generated by a rooftop solar array from its rated DC capacity, local peak sun hours, system losses, and operating days. It also converts annual output into an average monthly figure.
Use it for early feasibility checks, bill-offset estimates, and comparisons between proposed system sizes. The result is an energy estimate rather than a production guarantee; actual output varies with weather, orientation, shading, equipment performance, and downtime.
1. Enter array capacity
Use the total rated DC capacity of all rooftop panels in kilowatts.
2. Enter solar resource
Use average daily peak sun hours for the site, not total daylight hours.
3. Account for losses
Include inverter, temperature, wiring, soiling, shading, and availability losses as one percentage.
4. Review annual and monthly energy
The main result shows net annual production, with gross, daily, and monthly estimates in the breakdown.
Annual output (kWh) = Array capacity (kW) × Peak sun hours per day × Operating days × (1 − System loss %)
Peak sun hours express daily solar energy as equivalent hours at 1,000 W/m². The formula assumes the entered annual average already reflects seasonal solar variation.
The result is the estimated net AC-equivalent electricity produced over the entered operating year.
Detailed design software may produce a different estimate by modeling hourly weather, panel orientation, shading, clipping, and equipment specifications.
Given: 8 kW array, 4.5 peak sun hours per day, 14% losses, and 365 days.
Calculation: Gross output = 8 × 4.5 × 365 = 13,140 kWh. Net output = 13,140 × 0.86 = 11,300.4 kWh.
Result: Approximately 11,300 kWh per year, averaging about 942 kWh per month.
No. Peak sun hours convert varying sunlight intensity into equivalent full-power hours and are usually much lower than total daylight time.
This calculator uses one combined loss percentage. Include inverter loss together with temperature, wiring, shading, soiling, and downtime.
No under this model, and realistic rooftop systems operate far below that theoretical maximum because sunlight is intermittent.
Use an annual-average peak sun hour value for this estimate. Monthly production requires month-specific solar data.
Not directly. Bill savings depend on when energy is used, export compensation, tariffs, and fixed utility charges.