How many watts of panel you need from your daily energy and your worst-month sun — with a real-world derate, not lab numbers.
The designer sizes the array against your loads and climate, matches the MPPT, battery and cabling, and draws the wiring.
Design my system — freeNo account needed to design. Same engine, same standards as this calculator.
Required watts = daily Wh ÷ (peak sun-hours × system derate). The derate (~0.72) accounts for real-world losses lab ratings ignore. Crucially, size for your worst month: winter sun can be a third of summer.
A factor (~0.72) for real-world losses — heat, wiring, MPPT and charge efficiency — that panel nameplate ratings ignore. Using it stops you under-sizing.
About a minute. No account, no email.