Energy
Estimate daily and annual energy production from a solar system.
Enter your numbers to see the answer.
Solar generation calculator guide
A solar array’s rated size tells you what it can produce under laboratory conditions; how much electricity you actually get depends on the sun at your location and on losses in the real system. This calculator multiplies system size by peak sun hours per day, removes a system-loss percentage, and reports daily and annual kilowatt-hours. Peak sun hours is the number of hours of equivalent full sun (1,000 W/m²) a tilted panel sees on an average day: about 3.5 in northern Europe or the UK, 4 to 5 across most of the United States, Bangladesh, and northern India, and 5 to 6 in Rajasthan, Arizona, or inland Australia. System losses of 15 to 20 percent cover inverter conversion, wiring, soiling, module mismatch, temperature derating on hot roofs, and a little shading; NREL’s PVWatts uses 14 percent by default before temperature. Use the result to check an installer’s yield claim, to estimate savings for the payback calculator, or to see how many panels you need for a target daily load.
Daily generation (kWh) = system size (kW) × peak sun hours (h/day) × (1 − losses ÷ 100). Annual generation (kWh) = daily generation × 365.
Worked example with the defaults: a 5 kW system, 4.5 peak sun hours per day, and 20% losses. Daily generation = 5 × 4.5 × (1 − 0.20) = 22.5 × 0.8 = 18 kWh per day. Annual generation = 18 × 365 = 6,570 kWh per year, the figure the calculator displays. That equals 1,314 kWh per installed kW per year, a typical specific yield for a well-oriented roof in the mid-latitudes. At 3.5 sun hours the same array would give 14 kWh per day and 5,110 kWh per year.
System size is DC kilowatts — the sum of your panels’ rated watts divided by 1,000 (twelve 450 W panels are 5.4 kW). Peak sun hours are hours per day of equivalent full sun; NREL’s resource maps and the PVGIS tool give these as kWh/m²/day, which is the same number. Losses are a percentage of gross output. Results are in kWh per day and per year; multiply the annual figure by your tariff to see the money value, or divide your daily household kWh by the daily figure to see what fraction of your use the array covers.
This is a modelled estimate, not a meter reading. Real consumption moves with weather, occupancy, appliance age, standing charges, and tariff structure, and equipment rarely runs at its nameplate rating. Use the figure to compare options against each other, then confirm against your own bill and the manufacturer's specification before committing to a purchase. On this page the figure rests entirely on solar system size, peak sun hours, system losses, market / jurisdiction, effective date, data source, update owner and review date, so start there if the solar generation calculator returns something you did not expect.
Good to know: quoting peak sun hours as daylight hours is the largest error — a location with 12 hours of daylight typically has only 4 to 5 peak sun hours. Using the sunny-season figure for the whole year overstates yield, so use the annual average or run summer and winter separately. Ignoring temperature is the second trap: panels lose about 0.3 to 0.4 percent of output per degree above 25 °C, and roof-mounted modules in Dhaka or Chennai in May can run at 60 to 70 °C, which is 12 to 18 percent below rating before other losses. A north-facing roof in the northern hemisphere (or south-facing in the southern) can lose 30 percent or more.
Energy results depend on tariffs, equipment behavior, region, weather, and installation assumptions. Verify rates and electrical decisions with the utility, manufacturer, or qualified professional.
Sources
How it works
Estimate daily and annual energy production from a solar system. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Solar system size = 5 kW · Peak sun hours = 4.5 hours/day · System losses = 20 % → 6,570 kWh/year (estimated annual solar generation). Change an input above and this example updates with your numbers.
Common questions
About 18 kWh per day at 4.5 peak sun hours and 20 percent losses, or roughly 6,570 kWh per year. In a sunnier location with 5.5 sun hours the same system gives about 22 kWh per day; at 3.5 hours, about 14 kWh.
One kilowatt of panels produces about 3.6 units (kWh) per day at 4.5 peak sun hours with 20 percent losses, or 1,300 to 1,400 units per year. In Rajasthan or Gujarat with 5.5 sun hours expect closer to 4.4 units per day; in Bangladesh’s monsoon months, 2.5 to 3.
Peak sun hours are the equivalent hours per day of full sunshine at 1,000 W/m². A day with 12 hours of varying light might total 4.5 peak sun hours. NREL publishes maps of this value; most of the United States falls between 4 and 5.5, and much of South Asia between 4.5 and 5.5.
Between 14 and 20 percent for a residential rooftop. NREL’s PVWatts defaults to 14.08 percent for soiling, wiring, mismatch, connections, degradation, and availability, before inverter efficiency and temperature. Use 20 percent for a hot, dusty roof or a string with some shading.
Divide your daily kWh by the per-kW daily yield. A home using 20 kWh per day in a 4.5 sun-hour location needs about 20 ÷ 3.6 ≈ 5.6 kW, or thirteen 450 W panels. Use the solar panel count calculator to convert kW into panels.