Solar Array Sizing Estimator
Engineers powering off-grid RTUs, gauges, and telemetry radios use this to get a first estimate of the solar array size a site needs. Enter the daily energy the load consumes, the peak sun hours from your own solar-resource data, and a derate factor, and it returns the array wattage.
An off-grid array has to generate a full day's load plus enough extra to cover conversion and weather losses, within the limited hours of usable sun a site gets. This estimator divides the daily energy by the product of peak sun hours and a derate factor to give the nameplate array wattage.
The Estimator
Result
Peak sun hours must come from your own solar-resource data for the site.
The Formula
The array must supply the daily energy within the day's usable sun hours, after losses:
Worked example. A 10 W load running continuously uses 10 × 24 = 240 Wh/day. At a site with 4 peak sun hours in the worst month and a 0.7 derate: array W = 240 / (4 × 0.7) = 240 / 2.8 = 85.7 W. You would round up to the next standard panel and confirm the battery reserve separately.
Assumptions and Limits
- Peak sun hours is a site- and season-specific input you must supply from a solar-resource dataset or map. Using an annual-average figure instead of the worst design month will undersize the array for winter.
- The default 0.7 derate is a common lumped allowance for charge-controller, wiring, temperature, and soiling losses. Replace it with a figure built from your actual components and site conditions where you can.
- This sizes generation only. It does not size the battery reserve; use the battery autonomy calculator to cover cloudy-day autonomy.
- Results are engineering estimates. Verify against panel datasheets, a proper loss analysis, and local irradiance data before purchasing.
FAQ
Where do I get peak sun hours?
From a solar-resource dataset or map for your latitude and array tilt, using the worst design month for a year-round site. It is not a value this tool can assume, because it varies widely by location and season, so you enter it directly.
Why derate by 0.7?
Real systems lose energy in the charge controller, wiring, hot panels, dust, and imperfect array orientation. A 0.7 factor is a common lumped allowance; a detailed design replaces it with the product of the individual loss factors.
Does a bigger array remove the need for a battery?
No. The array only makes power when the sun shines. The battery carries the site through nights and cloudy stretches, so size both: this estimator for generation and the battery autonomy calculator for reserve.
Automation services
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