Eyserth's investment should pay itself off in less than 10 years (without taking into account any possible power price rises), with 25-year performance guarantee.
There are advantages to ground-based solar if you have the space for an array that might be 20x3m for a 10kW system. You have the flexibility to place the array in the best spot and at the perfect angle, unrestricted by building location; and placing the rectifier next to the panels reduces DC voltage drop-off, adding to efficiency.
Farmers often have equipment to drive in the supporting posts, so can do that themselves before the panels are fitted. Maintenance can be easier too, as all the equipment is at ground level, although more work may be needed to keep the area clear of shade from plants and trees.
Long term, a ground-based PV system can be expanded with less issues than a rooftop system, and this becomes more cost-effective if you had the foresight to install cabling with enough extra capacity.
It isn't all plain sailing. While you can still use the paddock where the array is placed, not everything mixes well. Sheep are fine and have the added benefit of keeping the weeds down, but according to Wairarapa farmer and Federated Farmers' energy spokesman Anders Crofoot, cattle are a different matter.
"You have to run a hot wire up high to keep cattle excluded," he said. "They lick connections, nose and scratch on the panels; if cattle can get at it they will wreck it in fairly short order."
However one dairy farm on Matakana Island is successfully using a 40kW array to reduce the cost of powering refrigeration for chilling milk, heating water and operating pumps.
At the other end of the scale, Chris Wells found space for a 10kW system at his 1.4 hectare property off the Kaipara Coast Highway. "We're semi-sustainable with sheep, chickens and a greenhouse for our own veg."
The array of forty 250W panels is sited in a paddock above their house. "We don't even see it as it's behind some low bush. "We use a lot of power, for a pool and a heat pump, plus water pumps," he said. "Our bills were $350 - 400 per month in summer."
Installed in November last year for about $23,000 (Wells was able to reduce the installation costs by building all the framing himself), output can be 76kWh on a sunny day. "Our power bills over the summer have been pretty much zero - maybe $10. It'll pay for itself in five to six years."
Although Wells would like to go off-grid, he doesn't think current battery technology makes that cost-effective for him. It can be for some; a Bombay Hills lifestyle property facing a $100,000 bill to connect to the grid has chosen a $60,000 field-based PV and battery system instead. For large or small properties, ground-based PV is growing fast.
What electricity companies pay you
When you use your own generated electricity, you save buying at the retail price. Here's what companies can offer if you produce more than you use and export to the grid:
• Contact: 17.285c per kWh for a peak load of less than 10kW
• Genesis: 5.25c - 5.95c per kWh depending on location
• Mercury: One for one offset of export and import provided exports are less than import. 3.5c per kWh over that.*
• Meridian: 25c per kWh for the first 5kWh (per billing day), 10c per kWh after that.
• Nova Energy: Buyback offer under review.
• Trustpower: 7c per kWh.
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