Solar calculators
Size an array from your electricity use, or find what a given array produces, using published sun hour data rather than a salesperson's estimate.
Solar panel output calculator
How much an array produces, or how many panels cover your bill, using NREL sun hours and PVWatts losses.
Solar panel tilt angle calculator
The best tilt for your latitude, and what your roof's pitch and direction are actually costing you.
Battery runtime & bank size calculator
How long a battery bank really lasts under load, and what size bank you need, with Peukert losses included.
What decides how much an array makes
- Array size in kilowatts. Panel wattage times the number of panels. A 400 W panel is the common residential size today, with 400 to 460 W the usual range.
- Peak sun hours. Not daylight hours. One peak sun hour is an hour of sunlight at 1,000 watts per square metre, so a location with 5 peak sun hours gets the equivalent of five hours at full strength spread over the whole day.
- System losses. Soiling, shading, wiring, mismatch, inverter conversion and the rest. These are not small: the standard assumption is that about a fifth of the DC nameplate never reaches the meter.
Orientation and tilt matter too. The figures here assume a reasonably sited array; a north-facing or heavily shaded roof will do worse than any calculator predicts.