Solar can carry a large share of a dairy's electricity, but not simply by covering the shed roof with panels. Milking happens around dawn and again in the mid-to-late afternoon, when panels produce little or nothing, while the energy-hungry jobs that follow (cooling the vat, heating wash water, pumping) can often be moved into the middle of the day. The dairies that get the most from solar usually reshape their loads first, then size the array, and only then decide how much battery they need to cover what remains of the milking peaks.

Where the energy goes in a dairy

Every shed is different, but the same handful of loads turn up on most dairy energy bills. Knowing when each one runs is more useful than knowing its size.

On many farms, milk cooling and hot water together make up a large slice of the dairy's use. They are also the most flexible loads, which is why they are the first place to look.

Why the twice-daily peak is the hard part

A milking starts several motors close together: the vacuum pump, the milk pump, water pumps and, as warm milk reaches the vat, the refrigeration compressor. Most are three-phase motors, and their starting currents stack into a short, sharp demand peak. In winter, the morning milking often finishes before the sun is high enough to help at all.

For a grid-connected dairy, those peaks cost money in two ways. On a time-of-use tariff, the afternoon milking can fall into the most expensive window. On a demand tariff, one badly timed start-up can set the charge for the whole month. For a dairy on a hybrid or off-grid system, the same peaks decide how large the inverter must be, whatever the day's total energy use.

Cut the cooling load before you size anything

Every kilowatt-hour of cooling you avoid is one you never have to generate, store or pay for. Common measures include:

• Pre-cooling with a plate heat exchanger. Running bore or tank water through a plate cooler removes much of the heat before milk reaches the vat. The warmed water can go on to stock troughs, so little is wasted.
• Chilled water or ice bank storage. Some systems chill water in the middle of the day and use that stored cold at milking time. It works like a thermal battery, and is often cheaper per kilowatt-hour than an electrical one.
• Looking after the refrigeration unit. A shaded, well-ventilated condenser with clean coils works less hard. Ask a refrigeration technician to check the refrigerant charge and controls.
• Variable speed drives on vacuum pumps. Matching pump speed to actual demand can reduce both energy use and start-up current. Changes to the milking plant should be made with your milking machine technician.

Milk still has to be cooled within the time and temperature limits set by your processor and food safety requirements, so check any change to the cooling process against those rules first.

Hot water: the easiest load to move

Wash water is heated in storage, so it does not need to be heated at the moment it is used. Setting the element or heat pump to run from late morning to early afternoon lets it soak up solar that would otherwise be exported for a few cents per kilowatt-hour. A heat pump uses considerably less electricity than a resistive element for the same heat, although its output falls on frosty mornings. Make sure the stored volume and temperature still suit your cleaning chemicals and the plant manufacturer's wash program.

Where a battery earns its place

Once cooling and hot water have been pushed into daylight, what remains is mostly the milking itself plus the cooling tail after the afternoon milking. A battery can cover:

1. the morning milking, before the array starts producing;
2. the fall in solar output during the afternoon milking and early evening cooling;
3. demand peaks, by supplying power while several motors start together; and
4. backup for vat cooling during a grid outage, when a full vat is at risk.

To size it, log the kilowatt-hours used from the start of each milking until the vat reaches temperature, on both a summer and a winter day. That figure, not the farm's daily total, is the starting point. Because the loads are three-phase, the battery must sit behind a three-phase hybrid inverter with enough continuous and surge rating for the motors it has to run. A generator remains sensible insurance for long outages.

Siting the array and equipment

Dairy roofs are often large, but they may face the wrong way, carry old sheeting or sit in the path of wash-down spray and yard dust. A ground-mounted array in a nearby paddock can face north at a better tilt, at the cost of trenching. Keep inverters and batteries out of the dairy itself: humidity, ammonia from the yard and effluent area, and high-pressure hoses are hard on electronics. A dry, ventilated plant room or a separate enclosure a short distance away is usually a better home.

Before committing, gather twelve months of interval data from your retailer, along with nameplate details for the vacuum pump, refrigeration unit and water heater. That data shows exactly which half-hours set your peaks and how much midday surplus a given array would create.

Next steps

Start with the load and timing picture, then size generation and storage around it. The guides to solar for farms and battery backup for rural properties cover the wider design questions. When you are ready, request a free assessment from Blue Energy Solar so an accredited installer can look at your dairy, switchboard and data on site. Farm Solar (from $19,900 for a 15 kW system, installed) and Interval-Data Analysis (from $490 for 12 months of 15/30-minute data) are listed in the energy market; prices are indicative and confirmed after a site assessment.

Frequently asked questions

Can the milking plant keep running during a blackout?

Only if the system was designed for it. The battery needs a backup-capable three-phase inverter with enough surge rating for the vacuum pump and refrigeration compressor, and the dairy circuits must be wired to the backed-up side of the switchboard. Many farms back up vat cooling and lighting from the battery and run the full milking plant from a generator through a properly installed changeover switch.

Can effluent pumping run on solar?

Often, yes. Effluent pond or sump pumps and travelling irrigators rarely need to run at a fixed time of day, so they can usually be scheduled for the middle of the day when the array is producing strongly. Any change to timing still has to fit your effluent management plan and licence conditions, and pump controls should be modified only by a licensed electrician.

Should we replace an old refrigeration unit before adding solar?

It is worth checking first. An ageing compressor with worn components can use noticeably more electricity than a correctly sized modern unit, and that extra load would otherwise be built into your solar and battery design. Ask a refrigeration technician to assess the unit's condition and running hours, then size the energy system around the cooling load you will actually have.