Leaf Area Meter Development using Photovoltaic Panel and Testing

Abstract

A simple and practical leaf area meter based on a photovoltaic (PV) panel was developed,and tested. Components of the developed PV leaf area meter are PV panel as sensor, wooden cabinet as enclosure, flashlight as light source, and commercial digital multimeter for voltagemeasurement. Variation in the voltage generated from the PV panel due to obstruction of incidentradiation by sample is the principle of the projected area measurement. Voltage generation from thePV panel varies inversely with the extent of obstruction. Conversely, voltage generated variesdirectly with sample area when corresponding panel surface is exposed to incident radiation.Variations due to reduction in light source intensity were accounted by non-dimensionalizing thevoltage readings based on the beginning and the end of experiments. The PV leaf area meterperformance was evaluated using cardboard cutouts of various geometrical shapes of known areasand the voltage generated had good correlation (r = 0.9911) with actual sample areas. Linear fitsadequately modeled (R2 > 0.98) the areas from non-dimensional voltages. Measurements with leafsamples from mango, sapodilla, guava, custard apple, and cotton were compared among theexisting graphical (considered as reference), scanner based electronic leaf area meter, and digitalplanimeter methods. Digital planimeter produced better performance (R2 = 0.9996) than scannerbased electronic leaf area meter (R2 = 0.9979). Linear regression calibration equation based ondirect leaf samples on the PV panel (R2 = 0.9953) gave slightly better performance than leaf sampleswith glass cover (R2 = 0.9834); however, the latter gave better predictions than the former in testingwith additional leaf samples. As leaves were flattened by the glass cover, projected area reductioneffect of leaf surface curvature was minimized and the true leaf area was measured. Hence, themeasurement procedure with glass cover on samples was recommended. PV leaf area meter costsonly 3.8% of the scanner- based electronic leaf area meter and 14.3% of the digital planimeter prices(2001 price information). The developed PV leaf area meter had a mode of operation similar to acommercial electronic leaf area meter, yielded quick and reliable results, and was highly costeffective.