Solar Panel Output Calculator
Solar panel output is the usable AC electricity a photovoltaic array actually delivers after real-world losses — not the nameplate DC rating stamped on the back of the panel. This calculator takes your panel wattage, panel count, location's average peak sun hours, and a system derate factor, then reports daily and annual AC energy output. The peak sun hours input comes straight from our Solar Irradiance Calculator, and once you know your annual production you can put it to work in our Solar Payback Calculator.
The nameplate wattage of a single panel under Standard Test Conditions (STC): 1,000 W/m2 irradiance, 25C cell temperature, AM1.5 spectrum. Found on the panel datasheet or IEC 61215 rating label.
Total panel count in the array. Multiply panel wattage by this count and divide by 1,000 to get DC system size in kW.
Peak sun hours vary by location — roughly 3-4 in cloudier northern regions, 5-6+ in the sunny Southwest. Use the Solar Irradiance Calculator to estimate your specific location's value.
Accounts for inverter losses, wiring, soiling, temperature effects, and mismatch. NREL's PVWatts tool uses a similar ~86% default; 80-85% is a commonly used range for planning estimates.
(panel wattage × number of panels) ÷ 1000
DC size × peak sun hours × derate
daily AC output × 365
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →An 8 kW system (twenty 400W panels) in a location with 5.0 average peak sun hours produces roughly 11,972 kWh a year after accounting for real-world system losses -- about 1,497 kWh per kW installed. That per-kW figure is a useful sanity check: it should typically land in the 1,200-1,600 kWh/kW/year range for most of the continental U.S., with sunnier regions like the Southwest reaching higher and cloudier northern regions landing lower.
How solar panel output is calculated
This calculator converts a solar array's nameplate hardware into the usable AC electricity it actually delivers, through three steps.
DC System Size (kW) = (Panel Wattage (W) × Number of Panels) ÷ 1000. Panel wattage is the STC (Standard Test Conditions) rating printed on the datasheet — measured at 1,000 W/m2 irradiance, a 25C cell temperature, and the AM1.5 spectrum — and multiplying by the panel count gives total array wattage, which divided by 1,000 becomes kilowatts of DC capacity. Twenty 400W panels yield (400 × 20) ÷ 1000 = 8 kW DC.
Daily AC Energy Output (kWh) = DC System Size (kW) × Average Daily Peak Sun Hours × (System Derate Factor (%) ÷ 100). Peak sun hours are not daylight hours — they represent the equivalent number of hours per day at maximum solar intensity (1,000 W/m2) needed to deliver the same total energy as the actual variable sunlight received throughout the day, so a location with 12 hours of daylight may still only have 5 peak sun hours of usable solar energy. The system derate factor accounts for the real-world losses that keep a fielded array from delivering its nameplate rating: inverter DC-to-AC conversion losses, wiring resistance, dust and dirt (soiling), panel operating temperature above the 25C test standard (output drops roughly 0.3-0.5% per C above 25), and slight mismatches between panels. NREL's PVWatts tool uses a similar ~86% default; 80-85% is a commonly used planning range. At 8 kW, 5.0 peak sun hours, and an 82% derate, daily output is 8 × 5.0 × 0.82 = 32.8 kWh.
Annual AC Energy Output (kWh) = Daily AC Energy Output (kWh) × 365, giving 32.8 × 365 = 11,972 kWh at the defaults. A useful sanity check is annual output per kW of installed DC capacity: 11,972 ÷ 8 = 1,497 kWh/kW/year, which should typically land in the 1,200-1,600 kWh/kW/year range for most of the continental U.S. — sunnier regions like the Southwest reach higher and cloudier northern regions land lower. Two notes on the model. First, peak sun hours are a long-term average; actual daily production swings with weather and seasons, so annual totals are far more reliable than any single day. Second, this simplified model does not separately model shading, array tilt/azimuth geometry, inverter clipping, or panel degradation over time — for production estimates used in project financing, validate against NREL's PVWatts tool or a full system simulation. Data sources: NREL PVWatts tool and National Solar Radiation Database (NSRDB) for peak sun hours and system derate factors; panel STC (Standard Test Conditions) ratings from IEC 61215 and manufacturer specifications; system loss factors from NREL solar performance modeling and utility-scale/residential solar project monitoring data; inverter efficiency and soiling loss data from manufacturer specifications and field performance studies. Verification: with defaults (400W × 20 panels, 5.0 peak sun hours, 82% derate), DC System Size = 8 kW, Daily AC Energy Output = 32.8 kWh, Annual AC Energy Output = 11,972 kWh.