Development and performance evaluation of greenhouse solar dryer for unthreshed Teff crops

Almost everyone in Ethiopia eats Teff (Eragrostis teff [Zucc.] Trotter), a leading cereal crop. However, the low adoption of contemporary harvest and postharvest technology in production leads to significant grain losses. The crop is typically left in the field long after physiological maturity and remains there after harvesting for further drying. These practices result in substantial grain losses due to shattering and harsh weather conditions. This research focuses on developing and assessing a cost-effective greenhouse solar dryer for harvested unthreshed Teff crops. The crops were harvested at different maturity stages. The natural and forced convection greenhouse solar dryers were tested using three Teff crop varieties, namely Abay (ACC-225931), Hibre (Dz-Cr-419), and Quncho (Dz-Cr-387(RIL-355)). The study examined how temperature, relative humidity, air velocity, and solar radiation affected the dryer's performance. The forced convection greenhouse solar dryer outperformed the natural convection and open sun drying modes. The Midilli et al. model was shown to have the best match by the thin-layer drying kinetics investigation; it had the lowest root mean square error (RMS = 0.012944), the minimum chi-square value (X2 = 0.000182), and the greatest coefficient of determination (R2 = 0.9972). The crop's activation energy fluctuated between 33.13 and 64.23 kJ/mol across the tests, while its effective moisture diffusivity ranged between 4.04148 x 10-9 and 8.6994 x 10-9 m2/s. According to the results, greenhouse solar dryers can potentially reduce postharvest losses and improve Teff grain quality.