The power of LiDAR
How does light interception affect yield and fruit quality, particularly if trees are grown under solar panels? AgVic researchers are using light detection and ranging technology to find out.
Nowadays, light detection and ranging (LiDAR) is commonly used to detect the distance to an object. In horticulture, we can use a LiDAR scanner to create a digital twin of the orchard canopy with the exact location of every leaf and piece of fruit and then estimate the light distribution through the canopy from the position of the sun in the sky.
Light interception and its effects on yield and fruit quality is being measured as part of the PIPS 4 Profit Pear production systems for future climates (AP22002) project. Taking the opportunity to work with the Agriculture Victoria project team, visiting University of Pisa student, Lorenzo Bonzi, used LiDAR technology to scan the agrivoltaics experiment at the Tatura SmartFarm to estimate the effects of the experiment’s solar panels on light distribution through the tree canopy.
Agrivoltaic farming is the practice of growing crops underneath solar panels. In apple and pear orchards, agrivoltaics has the potential to improve fruit quality and marketable yield by protecting trees and fruit from damage while generating electricity. The agrivoltaics experiment at the Tatura SmartFarm is being undertaken in a 10-year-old block of the blush pear ANP-0118 (marketed as Lanya™). Trees are grafted on BP1 rootstock and trained to an open Tatura trellis with a tree and row spacing of 1m and 4.5m, respectively, and rows orientated north to south. Static solar panels are mounted on elevated structures spanning 10 trees. There are three replicates of three treatments: control (i.e. no solar panels), west-facing panel arrays angled at 45° from the horizontal plane (45W), and west-facing panel arrays angled at 5° from the horizontal plane (5W) (see Figure 1).
Figure 1: The agrivoltaics experiment at the Tatura SmartFarm. There are three treatments consisting of a control (i.e. no solar panels), west-facing panels angled at 45° from the horizontal plane, and west-facing panels angled at 5° from the horizontal plane.
One replicate of each of the three treatments was scanned using a stationary LiDAR (BLK360 G1, Leica Geosystems Ag, Heerbrugg, Switzerland, see Figure 2) mounted at 1.5m from the ground level on a tripod equipped with a horizontal level indicator. At this height, the scanner was approximately halfway up the tree to intercept the whole structure of the tree and the panels. To obtain the best image resolution, the LiDAR was operated in overcast sky conditions to avoid direct sunlight and excessive brightness. The scans were performed on the east and west sides of the row. Two scans per side were obtained for each treatment. The acquired scans were uploaded to a computer and processed by merging the images to create a ‘point cloud’ representation of the trees, the solar panels and the supporting infrastructure. The point cloud files were then uploaded to the open-source software CloudCompare (v. 2.13 alpha, Grenoble, France) to determine light distribution in the canopy throughout the growing season.
Fig 2: The LiDAR scanner used to capture ‘point cloud’ data of the pear trees in the agrivoltaics experiment.
Canopy light distribution for the control, 45W and 5W treatments are shown in Figure 3. Canopy illumination was greatest in the control, followed by the 45W treatment and then lowest in the 5W treatment. Average illumination in the upper section of the canopy in the control treatment was approximately 58 per cent of unobstructed sunlight compared to approximately 35 per cent and 22 per cent in the 45W and 5W treatments, respectively. In the lower section of the canopy, average illumination was much lower at approximately 8 per cent, 6 per cent and 1 per cent in the control, 45W and 5W treatments, respectively. This would likely impact on leaf photosynthesis as more leaves were below light saturation in the agrivoltaic treatments. Irrespective of agrivoltaic treatment, leaf illumination was greatest on the outside compared to the inside of the V, although the range was greater on the inside. This could have significant impacts on the consistency of fruit blush colour development and flower bud formation.
Fig 3: Canopy light distribution in the agrivoltaics experiment at the Tatura SmartFarm showing illumination in the control (left), the 45W treatment (centre) and the 5W treatment (right). The data in this figure was generated from a LiDAR scanner combined with a sun position model.
Additional measurements of fruit size and skin colour in different vertical zones were taken and will be compared to the estimates of the light environment. We anticipate that this will start to build a functional relationship between light and colour. In particular, the solar panels completely shade the fruit at certain times of the day, irrespective of the height of the fruit in the canopy. This will not only strongly influence the absolute sunlight available for fruit colour development, but also for leaf photosynthesis.
Detrimental effects of excessive shading caused by solar panels on fruit red pigmentation and return bloom can be turned to growers’ advantage if solar panels were installed above pear (or apple) cultivars with green peel market requirements. Alternatively, photo-selective solar panel technology that transmits wavelengths of sunlight that are critical for yield and fruit quality could be used, or even manoeuvrable panels that are positioned to expose or protect fruit depending on weather and phenology. Either way, point clouds obtained with LiDAR scanners enable the modelling of light responses of apple and pear cultivars under different agrivoltaic and orchard netting configurations and can deliver valuable and objective information on the utility of protected cropping to improve growers’ bottom lines.
Acknowledgement
This study is a component of the PIPS 4 Profit Program’s Pear production systems for future climates (AP22002) project, funded by Hort Innovation, using the Hort Innovation Apple and Pear research and development levies, contributions from the Australian Government and co-investment from Agriculture Victoria. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.
This article was first published in the Winter 2024 edition of AFG.
