Solar for irrigation and sprinkler pumps

A pump motor’s nameplate horsepower converts to roughly 1–1.3 kW of electrical draw per horsepower while running, plus a startup surge of two to three times that for a second or two. A 1.5 hp lawn sprinkler pump on a well or ditch draws about 1.5–2 kW; a 5 hp acreage pump runs closer to 4–6 kW. What matters for solar is hours, not watts.

Run a 1.5 hp pump two hours a day for a six-month season and you use roughly 550–700 kWh a year. A 5 hp pump running six hours a day through the same season lands at 4,000–6,000 kWh. That second number is as much as a whole house uses, which is why acreage owners on irrigation notice the bill and lawn owners often don’t.

Pull your last twelve months of bills and look at the May–September jump over the winter baseline. That jump is the pump, the AC and not much else, and it is the number we size against.

On a property with utility service, the cleanest answer is an ordinary grid-tied array with net metering. The panels send summer surplus to the grid, the pump draws from the grid whenever the timer says, and the meter nets it out. You get no batteries, no DC pump, no controller to babysit, and the same array also offsets the house.

A well-placed kilowatt of solar in Colorado produces roughly 1,300–1,600 kWh a year (NREL PVWatts), so a 5 hp irrigation pump’s season is about 3–4 kW of array on its own. In practice we size for the whole meter, and the pump becomes one line in the load list.

The catch is whether the pump is on its own meter. Ditch and well pumps out by the property line often are. Some Colorado utilities allow net-metering credits from one meter to offset another on the same contiguous property; others don’t, and a separate meter may need its own small array. We check that with your utility before drawing anything.

When the pump sits a few hundred feet from the house, a ground mount near the pump house is often the better build: short wire runs, a clear south exposure, and no roof penetrations. Ground mounts cost somewhat more per watt than a roof array because of the racking and trenching, but they can be angled for best annual output and are easy to clear of snow.

In hail country, a ground mount lets us set a steeper tilt that sheds stones and snow better than a low-slope roof. It also keeps panels away from the roof line if the house is due for a re-roof soon, which is worth thinking about before you commit to a roof array.

Several Colorado rural electric co-ops bill irrigation pumping on its own rate class, sometimes with a seasonal demand charge or a fixed monthly fee that runs only during the watering season. Those tariffs can make the per-kWh price on the pump meter different from the house rate, and demand charges aren’t offset by energy credits.

Colorado’s net-metering statute for co-ops and municipal utilities (C.R.S. 40-9.5-118) guarantees net metering only up to 10 kW residential and 25 kW commercial; above that it is the utility’s call. A big pivot or multi-pump operation can bump against that ceiling, and the interconnection rules get more involved. Verify the tariff on your specific meter before assuming credits apply.

For a stock tank, a remote garden plot or a pond-fed drip line with no power nearby, a small DC solar pump running straight off a 100–600 W panel makes sense: it pumps when the sun shines, which is roughly when plants want water, and needs no battery if you let it fill a tank or cistern that gravity-feeds later. Kits from irrigation and ranch suppliers run very roughly a few hundred to a few thousand dollars depending on lift and flow; prices vary widely.

We don’t install those. We can, however, put a grid-tied array on the barn or shop that the whole property draws from, which is usually the better path once there is any meter on site. Farm-scale center pivots and multi-hundred-horsepower pumps are a commercial project; our agricultural solar page covers that.