Solar Panel System Size Calculator
Estimate the solar array size and panel count needed to offset a target amount of electricity use, or estimate production from an existing system size.
How to size a solar system
Start with electricity use, convert it to a daily average, then divide by usable solar energy per installed kilowatt.
With 400 W panels, that rounds up to 24 panels and a 9.6 kW array.
What are peak sun hours?
Peak sun hours are the equivalent number of hours per day when solar irradiance averages 1,000 watts per square metre. They are not the same as daylight hours. Use a local annual or seasonal solar-resource estimate when possible.
Solar calculator FAQ
What system-loss percentage should I use?
A rough planning assumption of 15–25% is common for combined real-world losses, but the correct value depends on system design and site conditions.
Does this include battery storage?
No. This calculator sizes the solar array. Battery sizing depends on backup duration, critical loads, depth of discharge, efficiency and reserve targets.
Can I use monthly electricity bills?
Yes. Use the kWh consumption shown on the bill, not the dollar amount. For a more reliable design, use a full year of consumption so seasonal changes are represented.