Sizing & calculations
Module 4: Solar Energizer Sizing & Calculations
Sizing a solar fence energizer is a balance of three numbers: how much energy the energizer consumes per day, how many usable sun-hours the site gets, and how many days of backup autonomy (cloudy-day reserve) you want the battery to hold.
The working formula used in this module:
| Step | Calculation |
|---|---|
| 1. Daily energy need | Energizer joules × pulses/day (~86,400 for a 1 Hz unit) ÷ efficiency factor, or simply use the manufacturer's stated daily Wh draw |
| 2. Panel size | Daily Wh needed ÷ peak sun-hours for the site × 1.3 (safety margin for panel losses) |
| 3. Battery size | Daily Wh needed × desired autonomy days ÷ 12V ÷ 0.5 (avoid deep-discharging beyond 50%) |
Peak sun-hours (not daylight hours) is the figure that trips people up — it's the equivalent number of hours at 1,000W/m² a location receives, and it varies by latitude and season; most of the continental US ranges roughly 3–6 peak sun-hours/day, lowest in winter.
Always round up to the next commercially available panel and battery size, and re-check sizing seasonally — a system sized for summer sun-hours will under-charge through winter at most latitudes.
An 8Wh/day energizer at 4 peak sun-hours with 3 days autonomy needs roughly a 2.6W panel and a 4Ah battery on paper — in practice, round up to the smallest standard panel/battery combo the manufacturer sells for that energizer, since real-world losses are higher than the formula alone.