How to pair a battery energizer and solar panel

When choosing a solar panel for your battery energizer; energizer draw (amps), available sunlight per day, and battery size all affect the output wattage needed.  

Determining the solar panel wattage needed to supply an energizer with power is relatively simple. To do so we use the Power Formula, P = EI. P is the wattage required, E is the battery's voltage, and I is the energizer's amperage draw.

Example, an energizer with a 100mA (.1 amp) per hour draw and a 12v battery would require 1.2 watts per hour, 28.8 watts or 2.4A throughout the day. The solar panel needs to supply the 2.4A to the battery in order for it to remain charged.

Now the fun part. It's not sunny 24 hrs a day. During the summer months, Premier receives about 5.5 hours of usable sunlight at our farm in SE Iowa (the panels are not tracking the sun). (Charts below indicate average hours of sunlight based on location and time of year.) This means the battery will be the sole power source for 18.5 hours "overnight". That's 1.85A. The panel will have to produce a days worth of energy in only 5.5 hours. That would be 2.4A/5.5 hours = 0.44A per hour. Recall that P=EI, so P = 12V x 0.44A = 5.3 Watts. A 5.3 W panel would provide enough current to run the energizer during the 5.5 hours or sunlight, plus enough current to replace what was used overnight.

Summer sunlight, hours available per average day. 

Winter sunlight, hours available per average day.

What about cloudy days where the panel is not supplying current? Assume Day one was sunny and the battery was topped off at sundown. Day two is cloudy. Sundown to sundown is 24 hrs, plus another 18.5 hours until Day 3 when the sun rises. That's 42.5 hours or 4.25A that needs to be recharged within 5.5 hours. Don't forget we also need to power the energizer until sundown on Day 3, so add .55A to that total, 4.8A. What's the wattage required? 4.8A / 5.5 Hours = 0.87A per hour. P = EI, 12V x .87A = 10.44 W.

The battery size determines the the number of days the energizer will run without sun light. The solar panel determines how many days it will take the battery to recover to full charge after a cloudy day(s).

For those wondering, what size energizer uses 100mA per hour? Most units in the 1 joule output range consume that much power.
If an out-of-box solar energizer kit does not fit your needs, a set-up to fit your situation can be easily designed using the formula above. Happy fencing!

Introducing PRS-I and PRS-B energizers

This Spring Premier added several new units to its PRS Energizer line-up. These units offer some of the same features of the original PRS line-up but with added enhancements.

Details…

• Output 0.5 or 0.25 joule. 
• Same UV treated, high-impact plastic outer case but the energizer inside varies in joules of output and energy use/hr.
• Include a backup battery charger.
• Have an easy-access on/off button.
• On/off button shows up very well at night (flashes green or red depending on battery charge level).
• Have an overcharge regulator to protect the battery.
• Can be placed on the ground or on the top of steel T posts.
• Include wires and clips to connect to the fence and the ground rod. 
• Larger batteries (in amp-hr) than competing units of similar output.

PRS-I vs PRS-B?

A “PRS-B” (for “Basic“) unit removes a steady 50 milliamperes per hour from the battery—which in turn must be recharged by the solar panel.

“PRS-I” units (for “Intelligent”) are able to reduce their energy demand when the fence’s voltage is high—due to few weeds touching the fence. 

This occurs in fall and winter for most fences and occurs all year for some horse, cattle and deer fences.

So an “I” unit’s battery is more likely to remain charged through the low sunlight days of autumn and winter.

0.25 vs 0.5 Joule?

0.25 joules will work for a roll of sheep netting or a strand of “weed-free” rope. It’s also enough for most cattle and horse temporary fences. Will work with a roll of PoultryNet or VersaNet but grass must be mowed or sprayed as needed to maintain adequate voltage. 

For multiple rolls of net we advise 0.5 joule units or larger.

Below is a video of setting up a new PRS for in-field use. If you have any questions give us a call at 1-800-282-6631 or visit our website at www.premier1supplies.com.