Agricultural products such as coffee, tobacco, tea, fruit, cocoa beans, rice, nuts, and timber generally require drying through a consistent application of relatively low heat. Traditionally, crop drying has been accomplished by burning wood and fossil fuels in ovens or open air drying under screened sunlight. These methods, however, have their shortcomings. The former is expensive and damages the environment and the latter is susceptible to the variety and unpredictability of the weather. Solar crop drying is a happy medium between these two methods and it dries crops with more efficiency, uniformity, and less expense. A solar crop drying system does not solely depend on solar energy to function; it combines fuel burning with the energy of the sun, thus reducing fossil fuel consumption. In this paper, the status of solar drying technologies in developing countries is presented. The various designs of solar dryers, its types and performance analysis are reviewed. Special attention is given to the solar drying technologies that facilitate drying of crops in off-sunshine hours. The solar dryers specifically designed or tested using specific crops like the vegetable dryer, fruit dryer, grain dryer, grape dryer, and so on are also reviewed with details about the specifications and the results. In short, the state of art technologies and development of solar dryers are presented in this paper.

A review of solar drying technologies

A wind¿diesel system with hydrogen storage: Joint optimisation of design and dispatch

Sun, oven (50 and 70 °C) and microwave oven (210 and 700 W) drying of onion slices were carried out to monitor the drying kinetics and quality degradation of the product. Page, “Modified Page” and “Midilli and Kucuk” models exhibited high coefficient of determination (R2) values, ranging between 0.994 and 0.999. The calculated effective diffusivity (Deff) values (m2/s) of onion slices for the sun, oven 50 °C and oven 70 °C, microwave 210 W and microwave 700 W drying process were 8.339 × 10−10, 7.468 × 10−10, 1.554 × 10−9, 4.009 × 10−8 and 4.869 × 10−8, respectively. Fresh and dried onion slices had high amounts of K (696.82–16357.55 mg/kg), Ca (69.64–340.03 mg/kg), Na (37.72–1895.43 mg/kg), Mg (3.31–964.77 mg/kg) and P (46.47–3384.07 mg/kg) minerals. The highest mineral values were determined in oven dried samples. Sun (L∗ 58.00 ± 4.83, a∗ 0.27 ± 0.10, b∗ 14.36 ± 2.40) and microwave oven drying (210 W) (L∗ 54.78 ± 7.54, a∗ −0.71 ± 0.09, b∗ 13.17 ± 1.05) revealed better colour values in the dried products. The phenolic contents of microwave oven dried samples (1664.39 ± 134.12 and 1623.59 ± 140.02 for 210 W and 700 W, respectively) were higher than those of the other dried onion slices.

Study the effect of sun, oven and microwave drying on quality of onion slices

Grape drying by using hybrid photovoltaic-thermal (PV/T) greenhouse dryer: An experimental study

O. Headley

Papers

Evaluation of solar dried thyme (Thymus vulgaris Linne) herbs

Renewable energy technologies in the Caribbean

High pressure liquid chromatographic analysis of the main pungent principles of solar dried West Indian ginger (Zingiber officinale Roscoe)

Solar drying of West Indian ginger (Zingiber officinale Roscoe) rhizome using a wire basket dryer

Extraction and evaluation of the main pungent principles of solar dried West Indian ginger (Zingiber officinale ROSCOE) rhizome