Power an Electric Fence with Solar

article image
Photo by Adobe Stock/Trombax.
This inquisitive Scottish Highland steer is moments away from a shocking experience as he inspects the wire of an electric fence.

Electric fencing can be installed with basic hand tools and no prior fencing experience. And by adding a solar-powered fence energizer, you’ll make installation even simpler by eliminating the need for any grid connection. Not only that, but using a fence energizer powered by a solar-charged battery will also offer greater flexibility in placement on your property, allowing you to put the unit where needed without any consideration for a grid connection. You won’t have to worry about wayward animals if the utility grid goes down. You can even easily add it to, and use it in conjunction with, existing wood or metal fencing. All in all, solar-powered fencing may provide an attractive solution when compared with trying to install a fence energizer that runs on 120-volt alternating current (AC), especially for remote or very large fencing systems that suffer from a lack of utility outlets near the fence line.

The Basics

Before getting too much into the advantages of solar over conventional grid electricity, let’s review some electric fencing basics. The fencing type you choose, its height, strength, materials, and wire spacing will all depend entirely on what you’re trying to keep in or out.

A properly installed electric fence won’t cause serious harm to animals (or people!) that happen to come in contact with the energized wires. While most electric fencing consists of only a few bare wires strung between some lightweight insulators, it’s an animal’s learned fear of the fence — not the strength of the wire — that keeps the animal contained. Most animals that make initial contact with an electric fence will immediately back up. However, if the energized wires are spaced too far apart, an animal may be able to extend its head through to the other side before touching an energized wire. Feeling the sting further back on its neck, the startled animal may bolt straight through instead of backing up, no doubt dragging your new fence behind it! For this reason, you must use the correct wire spacing and fence design for the animals you’re trying to contain.

Some electric fencing systems use wires that are woven into a brightly colored flat tape or rope. This type of electric fencing material makes it easier for animals to recognize what happens when they get too near and thus remember to steer clear. Larger animals, such as horses and cattle, may be more manageable when using wider electric fencing tape because it’s easier for them to see than bare wire.

One of the newest forms of electric fencing is electrified netting. Woven into this non-metallic netting are tiny electrically interconnected metal strands. This fencing material works to contain smaller animals — goats, chickens, turkeys, rabbits, and even cats and dogs — better than wider-spaced electric fence wire.

Solar Fence Energizers

Electric fencing requires an energizer to deliver pulsed charges to the conductor, usually at or less than one high-voltage pulse per second. Comparing energizers can be confusing because few rating standards are used in their marketing. Some units list their output in volts, while others use joules (the international unit of energy measurement). Some brands advertise how many acres of fencing their unit can energize, while others publicize their power output in miles of fencing.

The best measurement of an electric fence energizer is how many joules of energy it delivers per pulse. A joule equals 1 watt-second of power output, or, more precisely, the amount of work required to generate 1 watt of power for 1 second. The largest off-the-shelf fence energizer I found locally had a rating of 6 joules and was advertised to energize up to 100 miles of fence wire. If this unit failed, all 100 miles of fence wire would instantly become useless. However, if you use multiple smaller energizers, any single failure would mean only one of the fenced areas would become non-energized. Remember that these ratings apply to the total length of wire used, not necessarily the length of the fence. So a 6-joule energizer that can energize 100 miles of fence wire would provide enough power for a 5-wire fence that’s 20 miles long (or a 4-wire fence that’s 25 miles long, and so on). A solar-powered energizer with an output of 0.5 to 1 joule should easily meet the needs of most small-scale homesteaders, providing enough power to energize miles of fence wire or enclose up to 50 acres of pasture.

Most self-contained solar energizers consist of a weatherproof enclosure containing a maintenance-free battery, with a small solar panel attached to the top on an adjustable mounting. Solar energizers with a larger capacity may require a bigger solar panel and battery, mounted separately from the energizer. The flexibility of the separate battery and solar panel will be especially useful if you need to reposition the solar panel away from the shade of nearby trees or would like to mount the panel on a raised pole.

Fence energizers powered by an external 12-volt battery typically cost half the price of energizers with a smaller built-in battery and solar panel. This price savings can help offset the added cost of buying a separate external battery, solar charge controller, and solar panel. Not only does this approach allow the use of a wider selection of solar panels, but the larger battery provides weeks of stand-alone operation during extended periods of low sunlight.

More expensive solar energizers may offer optional features, such as a digital display or meter, selective output levels, system trouble alarms, increased lightning protection, and a lower output at night to save battery charge. Large solar energizers are designed to be mounted on a wooden post, and only require connecting a jumper wire to the fence and a ground rod. Smaller, self-contained solar energizers intended for temporary electric fencing applications are designed to be placed directly on the ground and don’t require a fixed mounting.

A solar fence energizer has a low power drain on the battery because the output power is pulsed on and off, rather than remaining continuously energized. This cycling allows time for the power circuits to increase the 12-volt battery voltage to more than 5,000 volts, which is then discharged in short pulses. In addition, this pulsing effect provides more shock value to an animal in the form of multiple “stings,” rather than a single continuous discharge.

The three disadvantages of using a solar-powered electric fence energizer include the need to locate the solar panel where it will receive lots of sun; the higher cost; and the occasional replacement of the battery. However, high-quality, sealed absorbed glass mat (AGM) batteries and gel-cell batteries will power an energizer for four or more years before replacement is necessary.

If you’re already using a grid-connected energizer, converting to solar power will be very easy. It will require replacing your 120-volt AC energizer with a self-contained solar energizer with its own battery and solar panel. Unlike your existing grid-connected energizer, your solar energizer can be located almost anywhere with ample sun.

Installation

After placing or mounting the solar energizer, position the solar panel for maximum performance — typically with the panel’s face oriented either due south or southwest. A tilt angle equal to the latitude of your location will provide the best overall year-round performance for most homesteads. This will be in the 30- to 40-degree range for the southern half of the United States, and the 40- to 50-degree range for the northern half.

The battery-charging output of any solar panel will be substantially reduced by the shadow cast by even a small branch onto a very small part of the panel. While the solar panel will most likely be in total shade during the very early morning and late afternoon hours (when the sun is lower on the horizon and shadows are long), you should try your best to avoid any shading between 9 a.m. and 4 p.m., when the sun is highest in the sky.

If you plan to assemble your own custom system, make sure your fence energizer is designed for the voltage of the external battery you want to use. A sealed recreational vehicle (RV) or marine battery will provide many more days of operation during long periods of cloudy weather than a model with a smaller internal battery. Maintenance-free deep-cycle batteries are designed for continuous charge and discharge cycling. Car batteries have much thinner plates to reduce weight and aren’t designed for this constant cycling.

I prefer using either a sealed AGM or gel-cell battery instead of a wet-cell battery. Because they’re totally sealed, they can be mounted in any position, and there’s no danger of an animal tipping them over and spilling liquid acid. A BCI Group No. 22NF sealed battery that has a 55-amp-hour capacity is more than adequate for energizing miles of electric fencing and can store extra power for locations that experience weeks of cloudy weather. This is a significantly longer operating period than is possible with the 6- to 10-amp-hour internal battery typically included with most packaged solar energizers.

When selecting a solar panel to keep your energizer battery charged, make sure it’s rated for 12-volt charging. Typically, the nameplate will list a 21-volt DC open-circuit voltage and a 17-volt charging voltage. A solar panel rated at 6 to 10 watts should be able to maintain the battery for an energizer rated at 0.3 to 0.5 joule, while a solar panel rated at 12 to 20 watts should be able to maintain the battery for an energizer rated at 1 to 2 joules. Which you choose will ultimately depend on the size of your fenced area, your climate conditions, and your latitude.

Grounding

Anytime an animal comes in contact with an energized fence wire, they’re completing an electrical circuit. Unfortunately, one of the most neglected areas of electric fence installation is properly grounding the system.

The ground rod is typically a copper-clad steel rod driven into the earth next to the energizer. Grounding is a major part of the electrical path from the animal back to the energizer, and must be installed correctly, otherwise this electrical circuit won’t be complete. Fenced areas that stay slightly damp year-round may only require one ground rod, while very dry climates may require multiple ground rods (typically spaced at least 10 feet apart) to achieve adequate ground contact. These ground rods are the same as those used for grounding a home’s electrical service and should be driven 6 to 8 feet into the earth.

Testing and Maintenance

After you’ve installed the fence, ground rods, and solar-powered fence energizer, and properly positioned the solar panel, it’s time to test. This task will be best performed using a high-voltage fence tester. These typically cost less than $10 — cheap insurance for keeping your valuable animals from heading to town. As you walk along the fence line, check the output of each wire and note any section of wire that’s not energized or that has a low voltage level.

If any objects, tree branches, or tall weeds come in contact with an electrified fence, they can drain off voltage and significantly lower the shock value, or even short all the voltage to ground. Walk your fence line regularly and keep all weeds and tall grass at least 5 feet away from either side of the fencing. You’ll also want to check around the solar panel to make sure that weeds or bushes haven’t grown tall enough to shade any part of it.

As with any electrically energized equipment, be sure to follow the manufacturer’s installation and safety instructions, and never rely totally on any electric fence to keep animals away from cliffs, highways, or deep bodies of water. You should still use traditional metal or wood fencing in conjunction with electric fencing for property boundaries, and use electric for internal division of pastures, gardens, and temporary grazing areas. You can even attach new solar-powered electric fencing to existing wood or metal fencing using the proper insulators. With a reasonable level of maintenance, your solar-powered fencing system should provide many years of trouble-free performance.