Agrivoltaics: dual-purpose panels both protect and payResearch & Extension
This article originally appeared in the Spring 2021 edition of AFG, available online here.
Damaging afternoon sun is being diverted away from orchards and used to generate power in a novel agrivoltaics project underway at Agriculture Victoria’s Tatura SmartFarm in Victoria’s Goulburn Valley.
In the three-year project funded under the state’s Agriculture Energy Investment Plan (AEIP) two different configurations of solar panels have been placed over the experimental pear orchard allowing researchers to investigate their potential to improve fruit quality and yield by protecting the trees and fruit from extreme heat and sun damage.
At the same time the panels are generating energy to power the experimental pear orchard’s irrigation pump and fertigation injectors with any surplus not stored in batteries sold into the grid.
Researchers hope if panels prove effective at strategically shading orchards they may offer growers another tool to adapt to change climate while also tackling one of growers’ largest input costs.
“What we are trying to show is the potential dual benefit of solar panels above an orchard,” Research Leader Crop Physiology, Dr Ian Goodwin said.
“The primary focus is protecting the fruit from excessive sun damage in the afternoon, but at the same time being able to generate some electricity to offset energy costs.”
It’s early days, but Ian said fruit surface temperatures were noticeably less under the panels when they were first installed in January this year.
“It was in the order of 5–10 degrees lower when the panels were shading the trees,” he said.
“That is quite substantial and definitely enough to prevent fruit damage and bleaching of the colour.”
Sunlight and fruit quality
Considerable research has already been undertaken at Tatura into the relationships between sunlight and fruit colour and quality, and into designing canopies to intercept as much light as possible for colour and sugar development but not so much that it damages the fruit.
“We’ve done quite a bit of work on an individual fruit scale and the effectiveness of the sun at different times of day,” Ian said. “We know if the sun’s hitting fruit in the morning, you get really good
colour development. It’ll do the same in the afternoon, apart from when it gets too hot. If the temperature goes up, combined with that radiation, it actually causes damage to the fruit.”
Sun damage of fruit surface is known to occur when the fruit temperature is above 47°C, significantly impacting crop value.
During summer months at the Tatura SmartFarm, fruit surface temperature frequently rises above 45°C and can reach 55°C.
“On a clear sky day the fruit surface temperature can be up to about 15 degrees higher than the air temperature,” Ian said.
Existing measures employed to protect fruit from sun damage include netting, overhead cooling and sprayable protectants.
Ian said damage was related to both the fruit surface temperature and the exposure time, so even short-term shading by panels could potentially reduce the risk of damage.
“For sunburn damage the fruit surface temperature needs to be at those high levels for about an hour,” he said. “So, if you can drop the temperature for a period of time, even if sun hits the
fruit again later on in the afternoon, it’s probably not enough time for damage to occur.”
Australia leads the world on per capita solar PV capacity and there are already a number of large-scale solar farms in combination with agricultural (predominantly grazing) operations – termed ‘agrivoltaics’ – at sites including Gannawarra and Numurkah, in Victoria, and Coleambally, Finley and Darlington Point in NSW.
Although combining solar farming with horticulture is already occurring overseas, Ian says the trial at Tatura is the first example of agrivoltaics in Australian horticulture he is aware of.
At Tatura the 160 Longi LR6-72HPH 435W panels (total capacity 52,000 Watts) have been set up on retrofitted supports directly above the trees.
The replicated experiment has six blocks in the north-south running rows of the blush pear orchard in three treatments:
- a no-panels control
- west-facing panels at 45°
- near horizontal (5°) panels.
“The west-facing configuration is intended to protect the trees, by casting a shadow in the mid-afternoon around 3 to 6 o’clock. We’re aiming to prevent that excessive radiation in the mid-afternoon,” Ian said.
“We can’t have all the configurations we would like, so the flat one is a mid-way between nothing and what we think is maximum protection. It is probably the most simplistic to construct but will
only shade between around 12.30–2.30pm.”
Ian said the expectation was that the ones facing west would provide the most protection, preventing sunburn damage and colour bleaching.
“They’ll also enable good colour development, because there’s plenty of sun getting through in the morning.”
The system is expected to generate an estimated 58,000 kWh per year which is stored in two batteries in the pump shed and used to power the irrigation pump and fertigation system, with an
excess feeding into the grid.
Ian said the ‘pretty serious’ structures required to support the panels were expensive and retro fitting them to a commercial scale orchard would be prohibitive.
“This is an experiment,” he said. “In the orchard you’d use the tree canopy trellising system to support solar panels as well.”
A project economist would be crunching numbers on the value of fruit quality gains and energy savings versus installation costs.
As well as assessing the impact of shadowing on fruit quality, the project will also be assessing how the panels will impact on a wide range of other factors including accumulation of chill necessary for flowering initiation, transpiration, flower timing, microclimate and photosynthesis.
Soil moisture probes, dendrometers and fruit thermocouples are just some of the sensors researchers which will be used to investigate the full range of impacts.
Newly appointed scientist Rajandeep Singh joined the project in August and will be helping to measure energy production and consumption, the impact of solar panels on microclimate, tree growth, fruit temperature, yield and fruit colour, fruit and leaf damage, tree transpiration and photosynthesis, and water use efficiency.
In addition, University of Melbourne master’s student Alex Newton is currently studying the effects of the solar panels on winter chill accumulation and flower timing.
“We will be looking at what the solar panels are doing with respect to firstly, how much chill is accumulated,” Ian said.
“The other question is does casting a shadow on the trees this time of year delay flowering.
“We plan to go up and down the rows with [Green Atlas] Cartographer every couple of days to count the number of open flowers and see if the solar panels are impacting on the timing of full
bloom,” he said.
“We would also like to know are we impacting on photosynthesis by shading those trees at certain times of the day.”
Italian researcher Professor Luca Corelli Grappadelli, who spent some months at Tatura in 2017 argued too much sun might cause photoinhibition and loss of production as energy
was diverted to repair chlorophyll cells in leaves damaged by excess sunlight.
“It may be that panels benefit photosynthesis by shading in the afternoon.”