How Solar-Powered Gate Openers Work

The parts, and how the power flows

“Photovoltaic materials and devices convert sunlight into electrical energy,” in the US Department of Energy’s words, and the modules produce direct current (DC). A gate operator built for solar is a DC operator, so the panel’s output can charge its batteries directly through the maker’s harness. Using the LiftMaster CSW24UL swing gate operator’s manual as the worked example, the chain is:

• Solar panels. Not included with the operator; they’re accessories. The manual requires a minimum of two 10 W panels in series and allows a maximum of six, which matches its “solar power max” of 60 watts.
• Solar harness kit. The maker’s harness connects the panels and the larger batteries to the control board.
• Batteries. Two 12 V batteries wired in series make the 24 V system. The operator ships with two 7 Ah batteries; for solar, two 33 Ah batteries in an extra battery tray store more.
• Control board and motor. The board takes the battery power, runs the motor when the gate is told to move, and powers the accessories.
• Accessories. Remotes, a myQ device, an expansion board and loop detectors all draw a small current around the clock, whether the gate moves or not. On solar, that standby draw matters as much as the gate’s movement.

At night and on cloudy days nothing changes for the gate: it runs on the batteries, and the panel tops them up again when the sun is out. Everything else about an automatic gate stays the same, including the safety rules in UL 325 and ASTM F2200.

How many cycles a day? The standby draw decides

The manual’s solar table is the most useful thing a buyer can look at, because it shows what really limits a solar gate. It lists cycles per day for each panel size, battery size and sun zone, at different levels of standby current: the draw of the control board and accessories while the gate sits still.

The manual’s standby figures, at 24 V:

• Control board with no radios programmed: 2.7 mA
• One or more remote controls programmed: +1 mA
• A myQ device or wireless dual gate: +2.4 mA
• Expansion board: +11.1 mA
• Each loop detector (up to three, plugged into the expansion board): +3.8 mA

Those look tiny, but they run 24 hours a day, and the table shows the effect. In Zone 2 with 33 Ah batteries, a 40 W panel is rated about 92 cycles a day at 5 mA of standby draw, but 44 at 100 mA. A 20 W panel is rated 40 at 5 mA and 20 at 50 mA, and the table gives no rating at 100 mA. The manual also says the heaters sold for photo-eyes are not recommended on solar, and the operator’s own heater can’t be used at all.

The maker calls these numbers approximations that “vary based on gate construction, installation, and temperature.” A flat figure like “about 10 cycles a day” doesn’t match the maker’s table; what you get depends on the parts you choose. For more on sizing to your traffic, see solar gate cycle limits.

Where the panel goes

“The location of the panel(s) is critical to the success of the installation,” the manual says. Its rules:

• Face due south. The manual: “Solar panel(s) MUST be installed facing south. Use a compass to determine direction.”
• No shade. Keep the area around the panel clear of shadows for a 180° arc from east to west. “If the panel(s) is not casting a shadow, the battery is not being charged.”
• Think about winter. Trees or buildings that don’t shade the panel in summer can shade it in winter, when the sun sits lower. The manual suggests tilting the panel up to 15° steeper to favor winter.
• Mind the wire run. If the best sunny spot is away from the gate, the wire from panel to operator has a maximum length that depends on its gauge and the panel watts (table below).

On a lot with big live oaks, the gate post is often not the sunny spot. A separate post for the panel, with the wire run sized to the table, is the usual answer.

Connecting solar, or adding it to an opener you already have

People search for “how to connect a solar panel to a gate opener” as if it were a single wire. In the CSW24UL manual it is a set of parts from the operator’s maker:

• Replace the two 7 Ah batteries with two 33 Ah batteries, in the additional battery tray.
• Install the Solar Harness Kit, with its white jumper between the two batteries so they’re in series, and its red and black leads between the batteries and the board’s battery plug.
• Mount two to six panels in series, facing south, and run wire of the right gauge for the distance.
• Give up the operator heater: the manual says a heater can’t be used with solar, and two 33 Ah batteries won’t fit in the enclosure with one.

So adding solar is possible when the operator’s maker supports it and lists the parts. If your opener’s manual has no solar section, don’t improvise one. The wiring errors the manual lists include putting a 12 V battery on a 24 V system and the reverse. Ask for the maker’s solar parts, or an operator that has them. See gate automation and access control for the options.

When the batteries run low

A solar gate’s weak moment is a long cloudy stretch, when the batteries drain faster than the panel refills them. The CSW24UL manual lets you decide in advance what the gate does then:

• When there’s no AC power and the battery is critically low (under 23 V), the gate latches at a limit until the battery recovers.
• An option switch sets which limit: set to OPEN, the gate opens and stays open; set to CLOSE, it stays closed.
• Before that, the operator beeps three times with a command when the battery is low.

Which setting is right depends on the property. A gate that keeps livestock in usually needs to fail closed; an entrance that emergency vehicles must reach may need to fail open. The manual also notes that batteries degrade over time with temperature and use, so a solar gate that was fine for years can start to fall short. Batteries are a maintenance item. For an entrance with no power at all and simple needs, a bump gate is the no-battery alternative.

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