Network Electrical Servicing renewable energy consultant Tim Campbell, of Invercargill, spoke at a DairyNZ Field Day about the part he played installing a solar system on Birgit and Jon Pemberton’s dairy farm expansion in Brydone, near Mataura.
The system features 140 solar panels near a new milking shed, which could produce 73.71kW.
Power use in the shed includes cows being milked each morning and afternoon, refrigeration of milk, operation of an effluent system and heating a water cylinder.
The 585-watt panels were connected to a 50kW inverter charger and a 100kWh battery.
"That system makes about 75% of the electricity this dairy shed will use a season."
The solar system could produce a kilowatt-hour (kWh) for about six cents, including GST, about a quarter of the price the Pembertons currently paid their power company.
The battery cost about eight cents to produce a kilowatt-hour.
So the total cost per kilowatt-hour from the battery was about 14 cents.
The Pembertons paid their electricity supplier Meridian, about 16 cents a kilowatt for a night rate from 11pm.
Using the battery after 11pm would only save two cents a kilowatt hour so it was switched off to extend its life.
The battery was expected to complete about 6000 cycles, going from fully-charged to 10% or lower.
If the battery was discharged daily, it would last about 16 years, Mr Campbell said.
During a power cut, the solar system would allow for milking once-a-day.
"You’re still in business, you’re still getting water to the cows and still getting refrigeration, all the basics required in the system."
Ground-mounted panels were more cost effective than installing on a shed roof.
Panels were easier to clean on the ground rather than a roof.
The panels were on a 35 degree angle, facing north and both sides could harvest light.
He estimated the upfront cost for the solar system would pays for itself through power bill savings and grid export revenue in about 6.5 years.
"Cooler sheds make a difference," Mr Pemberton said.
If more farmers installed solar and export to the grid, it would put price pressure on energy companies generating electricity and selling it to consumers.
"They won’t have the kilowatts to sell."
Rewiring Aotearoa chief executive Mike Casey, of Cromwell, also spoke at the field day.
He heard the rate farmers were installing solar in New Zealand was making it harder for energy traders to predict demand.
"I’m really excited about that because it if we can bring down the cost of energy for our economy, we can drive new industry and lower the cost of energy for our people, which is really cool."
A farmer should celebrate every sale of an electric vehicle, rather than a fossil-fuelled one, as it would use energy created in New Zealand, rather than offshore, such as Saudi Arabia.
"That vehicle will be using the energy we create and not the energy the Saudis create."
