Solar Fence Charger Calculator
Size a solar-powered electric fence energizer. Enter fence miles, vegetation, and animal type — get joule output, charger size, and solar panel recommendation.
How to Use This Calculator
Measure your fence length
Enter the total wire length in miles — not just the perimeter. A 1-mile perimeter fence with 3 wires = 3 miles of total wire. More wire = more capacitance = more energy drain. Longer fences need more powerful energizers to maintain adequate voltage at the far end.
Assess vegetation contact
The vegetation level is the single biggest variable in fence energizer sizing. Weeds and grass in contact with wire drain energy directly to ground. Heavy weed pressure can drain an undersized energizer to ineffective levels. If in doubt, select "moderate" and size up — an oversized energizer is far better than one that can't hold adequate voltage.
Select your animal type
Different animals require different shock intensity. Poultry have feathers that reduce conductivity — they need less energy. Cattle have thick hides and are less sensitive — they need 3+ joules of output. Predator control requires the highest energy to reliably deter bears, wolves, and large predators.
The Formula
Electric fence energizers pulse at about 1 millisecond per second — extremely low duty cycle. The continuous power draw is very low (0.3-3W), but you need a battery large enough for 3+ days of cloudy weather and a solar panel sized to recharge it daily. Output joules (stored energy per pulse) determine effectiveness; input watts determine battery drain.
Example: 3-Mile Cattle Fence
Beef cattle operation with moderate vegetation
A rancher has a 3-mile perimeter fence for cattle with moderate weed pressure and wants a solar energizer system that works reliably year-round in Kansas (5 peak sun hours).
Result
A Gallagher S400 or Parmak DF-SP-LI would be appropriate choices. The 20W panel and 12Ah battery provide reliable operation even through 3 consecutive cloudy days.