Farming the sun and farming with the sun has significant potential for many New Zealand farmers. By Delwyn Dickey.

Looking at running large-scale solar arrays onfarm and selling power into the national grid could potentially be a new revenue stream for some farmers.

But installing big arrays is not cheap and most interested farmers will likely look at leasing their land to energy companies with deeper pockets and more expertise.

There are also limitations to where large-scale solar arrays can be installed.

One of the key constraints is proximity to the transmission line network that makes up Transpower New Zealand’s national power grid.

Large-scale solar farms are often found in clusters, around connections into grids.

But if you just want to provide for your own onfarm energy needs you can still sell off smaller amounts back to the grid through your own power connection.

Running a smaller scale array could be worth looking at particularly if you have high energy demands outside the milking operation – like powering irrigators.

A study done recently by government-run EECA (Energy Efficiency and Conservation Authority) looked at commercial-scale solar in NZ and analysed the financial performance of onsite solar for various business types and in different regions. This covered 144 different businesses around the country from big box retail to warehousing and corporate offices.

Included in the analysis was a single “quite large dairy farm” in Canterbury.

Internal returns on investment for a food and beverage production site and a corporate office in Auckland got returns of 7.2% and 7.6% respectively, and a wholesale food market in Christchurch 6.8%. But surprisingly, the dairy farm only notched up a 4.4% return.

Large Canterbury farms are likely to be drawing a lot of power through the dry summer months running irrigators, including some running 24 hours a day.

And many farms south of the Rakaia River also don’t get pressurised water to their property and have to pump even more.

But summer power consumption didn’t increase in the report data.

When EECA was queried over the dairy farm in their report, it turns out there was an irrigator onfarm but it had been on a different power meter, and not included in the report. The results were from power usage at the dairy shed, although this isn’t stated.

“As you’ll see from the report, the IRR for the cow shed wasn’t great in comparison to other business types that we looked at, but I’d expect solar powering an irrigator would be a reasonably good match,” Gareth Gretton, senior advisor at the authority says.

To see how an onfarm solar installation might perform we look across the Tasman.

SOLAR POWERED PIVOTSWhen Sandra Jefford and husband Wilco Droppert moved on to their 350-hectare dairy farm near Sale in Victoria, 11 years ago, they found themselves having to run centre pivot irrigators during warmer months.

“We came from a farm in a high rainfall area so when we came here, I thought the bills were just ridiculous – 70% of our energy cost was going into running the irrigators.”

There is a large dam on their farm, two bores and they also pump from the Avon River. Three pivot irrigators on the homeblock water their best pasture.

They took up a subsidy on energy audits for irrigation systems which saw them changing some aspects of their operation to make it more water efficient, then looked at solar arrays to power their system. Their business – Wilandra Farms is made up of several titles.

Regulations in Victoria make using renewable energy on larger farms, with multiple land titles, complicated.

Ideally a microgrid would be set up where power from renewable energy would be fed into the electricity grid and used wherever it was needed around the farm.

But power generated on one title can’t currently be taken across title boundaries.

This saw the couple installing solar at two sites on the farm and saw them replace a large diesel pump with two electric ones. The panels across the farm are all bi-facial, collecting the sun’s energy on both sides. The bigger 150-kilowatt (kW) array does much of the heavy lifting on the main farm title including for two electric pumps at the dam, a power line to another bore and two electric pivots (the last pivot – diesel operated – will also eventually change to an electric one). Here the panels are tilted and placed to collect early morning and later afternoon light, as well as the traditional north-facing for the rest of the day. Another 50kW array is used for another pump.

A smaller 29kW array is used for the dairy shed but isn’t as effective. The panels are only north facing, producing most power during the middle of the day when the dairy isn’t in use. Some additional east and west-facing panels too would be better here, Sandra says.

The management system, using AEI SmartBoxes, that coordinate the available power with the need to pump water, is a critical feature, Sandra says, with the mix of fixed and variable loads that are stopped and started as power changes, also important. Using solar power has seen them change their operation including doing most of the irrigation during the day, rather than at night when off-peak power prices are lower, so they get a much better sleep. Any pivot problems can now be sorted out during the day. Overall, the change has seen them save 15 hours of labour a week, in peak irrigation season.

Instead of pumping a lot of water directly from the bores to the pivots they now find it more cost effective to pump water into the dam using the free solar power generated, then pump it out when they’re ready, again using renewable energy. They might still use imported power during weekends during peak irrigation season.

Variable speed drives on the pumps mean they can run at very low levels of power.

“They may be 37kW pumps but once they’ve got 10kW of solar power – perhaps in the early morning, they can start automatically if we need water at the dam.”

Other changes included replacing a 150mm pipe with a 200mm diameter pipe to reduce the amount of energy needed to pump the water around.

The 299kW solar system cost A$348,000 (about NZ$376,000) – about A$1740/kW – but can only operate when it’s sunny. This should reduce power from the grid by 90% and see irrigation power costs during irrigation season drop from A$100,000 to under A$15,000. There are also plans to install two 15kW Britwind turbines, which Sandra reckons should produce a lot more kW power than solar panels.

The two turbines will have a 30kW output and cost A$279,000. This equates to A$9300 per kW.

“Because turbines can work during the night, you’ll get a lot more power out of five kilowatts of turbine in the long run. They may be more expensive per kilowatt to buy but the output is a lot higher,” Sandra says.

  • The Wilandra Smart Power Project was part-funded by Victoria’s Agriculture Energy Investment Plan. Anyone keen on a trip across the ditch to see how it works can book in to a field day on February 2 – bookings at

Hybrid system cuts cost and emissions

Karin Stark (with daughter Noa): Batteries would solve their hybrid issues.

Sorting out a hybrid solar irrigation system can be tricky as Kiwi-born Karin Stark, director of Farm Renewables Consulting found out.

Four years ago cotton and wheat farmers Karin and partner Jon Elder were spending about A$350,000 each year on diesel to pump groundwater from bores for their summer crops at Narromine, New South Wales. Karin was working for the NSW government running courses in renewable energy at the time, including a few on solar irrigation after farmers had shown some interest to cut costs.

“We got 60 or 70 farmers in the room at Warren, which is a little town in the middle of nowhere, for example,” she says.

When a neighbour put in a 100kW solar/diesel pump – possibly one of the first commercially viable pumps in the country, Karin and Jon were keen to get something similar up and running on their place.

Their 500kW solar/diesel hybrid system sees an electric water pump run partially off the solar array with the diesel generator kicking in when solar input, on overcast days, reduces. At night the diesel generator works by itself to fill their reservoirs for irrigation. The array has 1550 solar panels and is installed on one hectare of land. With three-quarters of their water coming from bores, the system pumps 15 megalitres of water a day with solar contributing up to seven megalitres of that. In their first year it cut their diesel bill nearly in half, saving about A$180,000 along with eliminating 500 tonnes of carbon emissions per year.

As early adopters of a hybrid system Karin says their experience may help other farmers iron out issues. It was hoped the savings would pay off the new system in five years. But blending the diesel generator with the solar has proved problematic and set the payback period by a couple of years.

The problem lies with the big 500kVA Cat generator they have, Karin says, and why batteries would make a big difference.

“The Cat generators are made to work on their own.”

When it’s cloudy, the solar starts to drop its power to the pump, and the generator isn’t quick enough to replace that lost solar. The whole thing will switch off, she says.

“My partner Jon was going out there turning it on and off. Also, you don’t want that water to be going up and down the shaft because it stirs up the silt at the bottom.”

The other problem is calling on the massive diesel generator to just trickle in a light bulb’s worth of power at sunrise or sunset when the solar setup starts to reduce the power it’s providing. Because they are made to be working at 60% efficiency, not 10% it can cause glazing on the generator, Karin advises.

Battery storage would use the battery instead of the diesel generator for those little bits where you just need to blend a little bit to provide the power that’s required for the pump, she says.

Because they use a lot of energy they have been quoted between A$400,000 and A$600,000 for a battery big enough for the load. For her part, while seeing batteries work at household scale or really big storage scale that sees Tesla batteries used by Australian national power companies, Karin thinks it may take a few years yet of technology development before battery storage will work for that mid-scale high-irrigation agricultural scene they operate in. For some less power-hungry farms, solar arrays and batteries are already being used in rural Australia. In Western

Australia, energy provider Western Power has started removing power lines to some farms and replacing them with standalone power systems – solar arrays and batteries.

Their solar arrays of about 60 panels provide nearly 20kW of energy – about four-times the amount of a standard rooftop array. Supplying the systems is cheaper, they say, than the cost of maintaining some long-distance power lines with few residents connected, which are also vulnerable to things like falling trees or bush fires. Western Power has installed 100 solar systems so far but is looking at 4000 in the next 10 years and up to 6000 in the following 20 to 30 years.

Back in NZ principal technical advisor with Irrigation NZ, Stephen McNally can see advantages for farmers having more control over their power supply.

Some energy companies have been trialling power shedding in the southern Rakaia area, which could be an indicator of where things may head.

Voluntary shedding works like a lower-priced energy plan where hot water cylinders are turned off when the loading gets too high. In this instance it could mean the irrigator turns off for a time. Last year, Stephen recalls the Ministry of Business Innovation and Employment and ECCA were discussing bringing in a similar star rating for water pumps as is used for appliances to show how energy efficient they are.

“Pumping accounts for quite a lot of the connected load in New Zealand,” Stephen says. “Farmers have to pump their irrigation water – so anything that gives them a little bit of independence on energy production is likely to be a good thing.

“In the future people may well look at putting in more renewables like solar and small hydro schemes. If you’re storing or moving water for farming purposes you’ve got a stored energy source so you could be running it through a mini or micro turbine.

“With some areas getting drier in the summer – the east coast of the North Island from Wairarapa, Hawke’s Bay, Gisborne, right up through the Bay of Plenty could become more significant irrigated areas in the future.”

A regional response may be needed to tackle this increase in water and energy needs in the future, but it may also lead to a national collective water and energy balance being looked at.

“If you’re going to supply water storage for irrigated areas (as with the combined Northland councils’ Kaipara water scheme and its new reservoir to supply 7000 hectares of new horticultural land), then you have the opportunity for renewable energy options,” he says.

“We talk about New Zealanders being resilient. That doesn’t mean toughing it out, or sucking it up. It means having a quiet sit down and a think. We can solve these issues – sometimes we just need the time to think about things in a calm and considered way. And that’s resilience.”