Solar Array Size Calculator

Solar array sizing begins with energy demand. Daily consumption in kilowatt-hours determines how much energy the system must produce over an average day. Peak power matters for inverters and loads, but array sizing is primarily an energy balance problem.

If a site uses 20 kWh per day, the array must produce that energy after accounting for sunlight, orientation, shading, temperature, wiring, inverter losses, and battery losses if storage is included. Nameplate panel watts are only the starting point.

Peak sun hours translate local solar resource into equivalent full-power hours. Five peak sun hours means the day's sunlight is roughly equivalent to five hours at 1,000 W/m2 irradiance. This is not the same as daylight duration.

Season matters. A system sized on annual average sun may underperform in winter. Off-grid systems and critical loads often size against the worst useful season or include generator backup. Grid-tied systems may size around annual production, economics, and net-metering rules.

Panels rarely produce nameplate power continuously. Temperature reduces voltage and power output. Dust, mismatch, wiring resistance, inverter efficiency, clipping, snow, and shading all reduce delivered energy. Derate factors account for these real-world losses.

Shading is especially important because partial shade can reduce output disproportionately, depending on module wiring and bypass diodes. A good array design considers roof geometry, nearby trees, chimneys, equipment, and future shading growth.

The right array size depends on load profile, roof or land area, budget, utility rules, inverter capacity, battery capacity, and reliability goals. Oversizing can improve winter production and battery recovery but may cause clipping or excess energy in summer. Undersizing lowers cost but may miss energy targets.

Solar sizing is therefore not just panel count. It is a system design decision that balances energy, power electronics, storage, site constraints, and economics.