Design, Construction and Performance Evaluation of a Postharvest Heat Storage Solar
The present study designed, constructed and undertook the performance evaluation of a post harvest passive solar crop dryer for drying agricultural produce. The solar crop dryer consists of a solar collector with dimensions 110 x 61 x 10cm, a drying chamber measuring 102 x54cm, a movable heat storage unit with the dimensions 40 x 35 x 13cm and drying trays each having an area of 1806cm2. The performance evaluation was conducted using three crops- tomatoes, pepper and okra which are locally produced. The test performance was done in both rainy and dry seasons to conform to the two major seasons in Nigeria and to determine the functionality of the crop seasonally. Open sun drying of the above crops was undertaken simultaneously as a control measure. Results of the performance evaluation showed that the highest chamber and ambient temperatures without the heat storage system incorporated was 53.3 and 32.8 oC respectively during the rainy season while the chamber and ambient temperatures with heat storage unit incorporated were 65.6 and 36.6 oC respectively. This indicates that the incorporation of heat storage unit improved the quality of heat output of the dryer temperature which was able to increase the drying process hours after the sun ceased shining. During the dry season (December), there was a little rise in ambient temperature as compared with rainy season. The maximum ambient and chamber temperature obtained during the dry season was 68.2 and 33.2oC respectively. As a result of the relative rise in temperature during the dry season, the rate of moisture lose was faster than during the raining season. As part of the performance evaluation the physicochemical properties of the crops were evaluated before and after drying. Physicorchemical properties evaluated includes: moisture, protein, fat, fibre, ash, carbohydrate and vitamin C, contents. The fresh, open and solar dried samples were analysed for their proximate composition using the recommended method of Association of Official Analytic Chemists (AOAC). Also, statistical analysis of the data was conducted using analysis of variance (ANOVA) using Completely Randomize Design (CRD) and means were separated by Duncan’s New Multiple Range test (DNMRT). Proximate analysis showed that solar dried vegetables had significantly (P < 0.05) higher protein, fibre, ash, carbohydrate and vitamin C except for the fat content that was significantly (P < 0.05) higher for all the open sun dried samples than the solar dried and fresh products. The nutrient which is highly affected by sun drying is vitamin C. Result indicates that moisture loss in solar dried vegetables was faster than the open dried samples and as such makes the solar dried products of lesser tendency to mould and bacterial growth. The open sun dried samples had to be carried into the sheltered place each time it rains. The observation is that the solar dried produce is of high quality and hygienically good for human consumption. Further processing of the dried crops will involve packaging for commercial purposes. This will also help in making these agricultural produce available in a relatively cheap prices in off season and also avert micronutrient deficiencies in diet especially among the low income groups in Nigeria.