Photovoltaic Leaf Area Meter Development and Testing

Abstract

Photovoltaic (PV) panel was used to develop a simple and practical leaf area meter. Components of the developed PV leaf area meter include a PV panel as sensor, a wooden cabinet as enclosure, a flashlight as light source, and a commercial digital multimeter for voltage measurement. The principle of projected area measurement is the voltage generated by the PV panel varies directly with sample area, when corresponding panel surface is exposed to incident radiation. The PV leaf area meter performance was evaluated using cardboard cutouts of various geometrical shapes of known areas and the voltage generated had good correlation (r = 0.9911) with sample areas. Linear fits adequately modeled the areas from non-dimensional voltages (R2 > 0.98). Leaf samples from mango, sapodilla, guava, custard apple, and cotton covering a wide array of natural shapes were tested and compared among the existing graphical, scanner-based electronic leaf area meter, and digital planimeter methods. Digital planimeter produced better performance (R2 = 0.9996) than scanner-based electronic leaf area meter (R2 = 0.9979), followed by the PV leaf area meter linear regression calibration equations based on direct leaf samples (R2 = 0.9953) and leaf samples with glass cover (R2 = 0.9834). However, on testing with additional leaf samples, the glass cover method gave better predictions than direct leaf method. As leaf was flattened by the glass cover and represented the true projected leaf area, this method was recommended. PV leaf area meter costs only 3.9% of scanner-based electronic leaf area meter and 14.7% of digital planimeter. The developed PV leaf area meter had a mode of operation similar to a commercial electronic leaf area meter, yielded quick and reliable results, and was highly cost effective.