Energy · Problem-solving calculator
Solar Array Size Calculator
Estimate solar array DC capacity and panel count from annual energy use, peak sun hours, system losses, and panel wattage.
- Free to use
- Runs in your browser
- Level B · Industry formula
- Last reviewed 2026-08-16
Calculator guide
What this calculator helps you solve
Estimate solar array DC capacity and panel count from annual energy use, peak sun hours, system losses, and panel wattage.
Inputs explained
- Annual electricity use to offset (kWh) — enter the value that applies to your operation or scenario.
- Average peak sun hours per day — enter the value that applies to your operation or scenario.
- System losses (%) — enter the value that applies to your operation or scenario.
- Panel rating (watts) — enter the value that applies to your operation or scenario.
Formula and methodology
Worked example
To offset 12,000 kWh/year with 4.5 peak sun hours/day and 14% losses requires about 8.50 kW DC. With 400 W panels, that rounds to 22 panels or 8.8 kW DC.
How to interpret the result
Use the result for preliminary sizing. Site-specific production depends on location, roof orientation, shading, temperature, inverter sizing, utility rules, and detailed production modeling.
What to keep in mind
- Peak sun hours should represent the site and array orientation rather than generic daylight hours.
- A professional solar design should verify structural, electrical, permitting, utility, and production assumptions.
Review approach
This calculator uses deterministic arithmetic and performs the calculation locally in your browser. Its value comes from combining multiple operational inputs into a decision-oriented result rather than returning a one-line conversion.
Review standard: Level B · Industry formula. How calculator reviews work.
Frequently asked questions
What decision can this calculator support?
Use the result for preliminary sizing. Site-specific production depends on location, roof orientation, shading, temperature, inverter sizing, utility rules, and detailed production modeling.
How is the result calculated?
Array kW = Annual kWh ÷ [365 × Peak Sun Hours × (1 − System Loss %)]; Panels = ceil(Array kW × 1000 ÷ Panel Watts).
Are the assumptions universal?
No. Operational, regulatory, technical, and industry assumptions vary. Use values that apply to your situation and verify professional or regulatory requirements where relevant.
Does CalculateMeasure store the values I enter?
The calculation runs in your browser and does not require sending the entered calculator values to a server to produce the result.