Calculate the solar array size and panel count needed to offset your daily energy use, from your own peak sun hours, system losses, and panel wattage.
Your numbers
Not the same as daylight hours — see the guidance below.
Aggregate losses from wiring, inverter, temperature, mismatch, and other real-world effects — you supply the total; there is no default.
Enter the rated wattage of the panel you plan to use — there is no default.
100% sizes the array to your full entered daily energy use.
Result
Your daily energy use, divided by how much sun your location actually gets and how much of that is lost to real-world system inefficiencies, gives the array size needed to offset it. Panels only come in fixed wattages, so the calculator rounds the requirement up to a whole number of panels — the actual installed array is always at least as large as the calculated requirement, never smaller.
required array W = (daily energy Wh × offset target / 100) / (peak sun hours × (1 − system losses / 100))
panel count = ceil(required array W / panel W)
actual array W = panel count × panel W
estimated annual kWh = (actual array W × peak sun hours × (1 − system losses / 100) × 365) / 1000
A home using 10 kWh/day, with 5 peak sun hours (looked up for its own location at NREL PVWatts), 20% system losses, and 400 W panels:
Peak sun hours is a measure of solar irradiance intensity — the equivalent number of hours per day at a standardized level of sunlight intensity (1,000 W/m²) that would deliver the same total energy as the actual variable sunlight received that day.
No, and this is the most common mistake. Daylight hours (how long the sun is above the horizon) are typically 9-15 hours depending on season and location. Peak sun hours, which measure irradiance intensity, are almost always lower — commonly in the 3-7 range across the US. Using daylight hours in this calculator will significantly undersize your array.
Use NREL's free PVWatts calculator (pvwatts.nrel.gov), enter your address, and it will show your location's solar resource data. FigureDesk doesn't host this data itself — PVWatts is the authoritative public source.
This depends on your specific equipment and installation — inverter efficiency, wiring length, temperature conditions, soiling, and shading all contribute. FigureDesk doesn't provide a default because these vary too much to assume; tools like PVWatts can help you estimate a reasonable aggregate figure for your system.
Enter the rated wattage of the specific panel model you plan to use, from its own datasheet. Panel wattage varies widely across products (roughly 300-600 W is common today), so there is no default here.
That's exactly what this calculator answers, once you supply your daily energy use, your location's peak sun hours, your system's loss estimate, and your chosen panel's wattage — see the panel count in the result above.
No. It assumes an unshaded, appropriately oriented array. Shading analysis requires site-specific data (tree lines, nearby structures, roof geometry) this calculator does not model.
No — panel physical dimensions vary by manufacturer and this calculator doesn't maintain that data. Check your chosen panel's datasheet for its dimensions to estimate roof space yourself.
No. It produces a calculated estimate from the inputs you provide. Actual production depends on weather, equipment performance, shading, system degradation over time, and installation quality — none of which this calculator can know in advance.
Size the battery bank to store energy from this array.
Size the inverter that converts this array's DC output to usable AC power.
Check how long a battery charged by this array would run your loads.
Compare against a fuel-powered generator as a backup or alternative.
NREL PVWatts Calculator — pvwatts.nrel.gov — the authoritative free public source for location-specific peak sun hours, maintained by the U.S. National Renewable Energy Laboratory. FigureDesk does not reproduce or host this data; use PVWatts directly to find your own value.
FigureDesk results are advisory and do not replace a licensed electrician, a qualified engineer, or the applicable local electrical code. Verify any electrical work against your local code and with a qualified professional before relying on it.