Performance Characterization of a Thin-Film Photovoltaic System Powered Evaporative Charcoal Cooler for Preservation of Avocado (Persea americana Mill.)

Abstract

Avocados are high moisture content agricultural produce with high vitamin C levels. However, they are highly perishable, and suffer from high postharvest losses ifappropriate and adequate storage facilities are not provided. The losses noted with the use of conventional storage techniques, such as under shade, result from physical, chemical and physiological changes that result from loss in moisture content. This study aimed on characterizing the performance of a thin-film photovoltaic (PV) system powered evaporative charcoal cooler for preservation of avocado. Specifically, the study focused on characterizing the performance of the PV technology under varying ambient conditions as an off-grid backup energy system, evaluating the performance of an improved evaporative charcoal cooler utilizing the PV technology for preservation of avocado, and assessing the cost-benefit of using the improved evaporative charcoal cooler utilizing the PV technology for preservation of avocado. The evaporative cooler consisted of a double wire mesh that held charcoal in place and was fitted with a drip for wetting the charcoal-laden walls, axial fans and data logger with digital humidity-temperature sensors. The study was conducted in Kimicha (Kirinyaga County, Kenya) with an evaporative charcoal cooler to investigate the optimal tilt angle for thin-film PV, and also at Juja (Kiambu County, Kenya) for comparison purposes. The results revealed that the optimum tilt angle is 5o (347.9±231.9 W) in Kimicha and 15o (517.7±131.3 W) in Juja for average maximum solar radiation of 973.5±219.9 and 1086.4±211.41 W/m2 in Kimicha and Juja, respectively. No load tests using the cooler showed that a 0.5 m/s air velocity had the greatest drop in temperature, which was 6.4°C, and the highest cooling efficiency of 84.7%. The average temperature of the cooler decreased significantly (P < 0.05) for both Hass and indigenous avocado, while the relative humidity increased significantly (P < 0.05). These conditions gave mean cooling efficiencies of 83.0% for the Hass variety and 87.2% for the indigenous variety, and an energy efficiency ratio of 14.21 for the cooler. The study found that the Hass avocados experienced a 3.9 and 7.5% weight reduction in the cooler and outdoors, respectively, while indigenous avocados had a 5.03 and 12.90% weight reduction in the cooler and outdoors, respectively. No significant change in vitamin C content, total soluble solids and firmness of Hass and indigenous avocados was noticed. The benefit-cost ratio and return on investment for the cooler were 2.88 and 188%, respectively. These results suggest that investing in an evaporative charcoal cooler is a viable option for small-scale farmers.