Table of Contents

Solar power for agriculture is a set of loads, not a crop. A pump that fills a tank while the sun is up, a cold room that must run after dark, and a greenhouse fan that runs for an hour are three different systems. They share modules. They do not share a design. The useful question is which load has to run, for how many hours, and whether the utility is already at the meter.

Where the load is water, the sizing method already exists and should not be reinvented here. USDA Natural Resources Conservation Service Technical Note 28, October 2010, walks through daily volume, peak sun hours, total dynamic head, and then a pump curve. That note is the place for the hydraulic steps. This article is about which farm loads solar can carry, and which ones still need storage or a grid.

Solar power for agricultural water

A solar water pump is the cleanest agricultural fit when the tank, not the tap, is the storage. The array runs the pump during sun hours. The tank holds the day’s water. Friction after the tank is usually gravity and is not part of the pump head. Drawdown in the well is part of the lift and comes from the well log. The array wants to sit close to the pump so the wires stay short. Those are the note’s rules, and the full sequence is in how solar water pumps are sized.

Livestock numbers in that note are regional examples, including a milking cow at about 20 to 25 gallons a day in the Oregon tables. They are not a national stocking rate. Use the herd you have and the well you have. A pump sized on someone else’s gallons will either overflow a tank or leave animals short. Mounts outside the note’s criteria need an engineer. Solar does not waive that.

Solar power for agricultural buildings and cold storage

A packing shed, a dairy, or a cold store is usually a building with a roof and a utility service. That is distributed solar on a commercial roof, and the structure, the access, and the inverter landing are already covered in distributed solar on commercial buildings. What changes on a farm is the load shape. A cold room runs when the crop comes in, including at night. Midday solar does not cool a room at 2 a.m. unless the cold is stored as ice, as a lower thermostat setpoint while the sun is up, or as a battery. The Department of Energy’s description of storage is the plain one: keep energy and use it later. Later is a design, not a side effect of the modules.

A day-shift workshop can line up better. Lights, tools, and a welder that run while the sun is up are the same logic as any daytime commercial load. A large motor still has a start current the inverter must be rated for. A grid-tied inverter will not carry that motor through a utility outage. IEEE 1547-2018 requires it to stop energizing an island within 2 seconds. A farm that needs irrigation during a storm has to say so before the inverter is chosen. Otherwise the design is a bill reducer, which is a fair goal, and it should be sold as that.

Soiling on a farm is not the suburban dust PNNL uses as a mild example. The laboratory calls soiling the largest operations issue and says it is often hard to see. Near a dirt road or a harvest, modules collect a film that rain may not clear if the tilt is low. A low-tilt array in a dry season may need washing. A steep array in a wet season may not. Do not copy a monthly schedule from a desert paper onto a rainy barn roof. The method, without walking on the glass, is in how to clean solar panels.

What solar power for agriculture should not be asked to do

It should not be asked to be the only supply for a load that cannot stop, unless the storage and the backup were sized for the worst week you will accept. A well that must run every day of a drought, including cloudy days, is a larger battery or a generator problem. Cloudy-day output is diffuse light, not a fixed fraction of the nameplate. There is no honest single percentage. The distinction is in solar panels on a cloudy day.

It should not be asked to ignore the land. A ground mount in a field takes the field. Agrivoltaic layouts that leave crop or grazing height under the rows are a spacing and a structure decision, not a slogan. If the mount is ordinary ground racking, PNNL’s point stands: access is easy, and vegetation will grow into the array if nobody cuts it. Erosion at the piers is an inspection item. A roof that was going to exist anyway does not take the paddock, and it may not be strong enough. Both can be right. Neither is automatic.

It should not be asked to share one undersized charge controller across a pump and a house bank that were never designed together. A DC pump with its own controller is a different product from an AC well on a grid-tied inverter. Mixing the manuals is how the tank stays empty and the house battery boils. Read the pump’s voltage and the controller’s maximum PV voltage, especially the cold open-circuit voltage, before the modules are ordered.

Frequently asked questions

Is solar power for agriculture the same as a solar water pump?

A pump into a tank is one agricultural load, and it is the one with a published federal design note. Cold storage, a dairy, and a workshop are electrical loads with different hours. Size each one. Do not buy a pump kit for a cold room.

Can farm solar run at night?

The modules cannot. Storage can, if it was sized for those night hours. A grid-tied system without storage buys the night from the utility and stops exporting when the utility is down. Say which of those you are buying.

Do crops under the panels count as the design?

Only if the row height, the shade, and the machine access were designed for that crop. A standard ground mount blocks the land it covers. Calling it agrivoltaic does not add clearance that the steel does not have.

Sources and references

Pump method, tank storage, and regional livestock examples: USDA NRCS Technical Note 28. Soiling, vegetation, and roof access: Pacific Northwest National Laboratory. Cease-to-energize within 2 seconds: NREL and Sandia IEEE 1547-2018 primer. Storage as energy held for later: US Department of Energy.