University of Otago researchers looked at the electricity consumption of six large scale dairy farms and found 20% of costs occurred in the dairy shed during morning milking.
That figure was based on a time-of-use pricing model in which electricity companies offer variable charges based on time of day, day of the week and time of year.
Flattening demand would reduce electricity costs for milking by 3.3% as demand shifted to off-peak periods.
Curtailing or avoiding irrigation during peak demand periods would further reduce costs, but researchers found time-of-use changes for irrigation were more difficult to make due to the necessity of applying water when it was needed.
In 2016, dairy farming used 5% of national electricity usage reflecting growth in the sector, increased irrigation but also greater mechanisation.
As a comparison, residential accounts for 32% of electricity consumption.
The researchers found using currently available technology for remote control management of machinery, scheduling and automation can lead to more efficient and accurate running of equipment and therefore electricity savings.
Most equipment is run simultaneously, including irrigators, which creates two electricity peaks a day.
These peaks are compounded by multiple farms following the same routine while connected to the same low-voltage network, with the potential for network congestion, possible voltage drop or a failure of the cable.
“Despite these problematic characteristics for the electricity grid, dairy farms are a potential source of demand flexibility due to their unique combination of high volumes of electricity consumption and their geographic dispersion around the regions of New Zealand,” the researchers said.
The six farms in the study used a total of one million kWh and the three irrigation pump houses used 1.2 million kWh between August 1, 2016 and May 15, 2017.
From July 17, daily consumption in the sheds gradually built from around 500 kWh/day to 3000 kWh/day at the beginning of September, peaking at 4000 kWh/day.
Daily electricity was stable until March when milk production started to fall as cows were dried off.
Peak electricity pricing is from 7am to 9.30am, which overlaps with milking, pushing the average daily electricity cost on the study farms to $776.24.
Time-of-use charging means that the first half of the morning milking, from 4.30am to 7am would cost an average of $95 per day, while the second half from 7am to 9.30am would cost $159.
“This means 20% of daily electricity costs, excluding irrigation, would come from the morning peak period, despite most of the milking activities occurring before the morning peak,” they said.
Electricity charges can be lowered by shifting some activities associated with milking to outside the morning peak pricing period, and using technology and automation will save electricity charges, but the researchers acknowledge starting milking two hours earlier could be unpopular with staff.
The cost of pumping, water heating and refrigeration alone use 90% of the electricity, but steps such as pumping shed water and storing overnight to supply the water requirements of the following day could cut costs.
Bore sourced water is earth chilled and can provide initial milk cooling through a plate heat exchanger to reduce the milk temperature from around 38C to between 12-15C, reducing the need for compression chillers.
The use of effluent pumps could also be avoided during peak periods, instead run during shoulder periods, reducing demand by up to 30kW.
Another option is to move to once-a-day (OAD) milking or 3-in-2 milking.
Shifting demand to flatten demand throughout the milking season at the mean use of 146 kW/day, would lower by 3.3% ($750.36 a day) or savings of $7428 for a 287-day milking season.
By using precision irrigation systems, applying water outside the peak electricity periods reduced pumping costs from $160/hr to $114/hour.
Savings can be significant.
“Without any changes to the existing regime of constant use across the day, the average cost is $3188/day,” the researchers said.
“Over the 80 days that irrigation was used in the season, this total cost would be $255,040.”
