Recent Advances of Solar Greenhouse Dryer: A Comprehensive Review

ABSTRACT Solar greenhouse dryers have emerged as an alternative renewable energy‐based drying technology to address the inefficiencies, long drying times, and post‐harvest losses associated with traditional open sun drying. This holistic review looks at recent technology developments in solar greenhouse dryers, looking at their set‐ups, their performance, and their applications in various climates and products. Significant outcomes indicate that solar greenhouse dryers have tremendous reduction in drying time, such as in the sinusoidal design which experiences temperatures of 49.11°C and dries products 32%–67% faster compared to the open sun systems, and energy efficiency (thermal efficiencies vary between 17.96% and 80.66%). The performance of hybrid systems that combine solar collectors, biomass, or a heat pump are even better and are already at specific moisture extraction rates: 3.725 kg/kWh and payback periods of as low as 0.41 years. Machine learning and CFDs allow optimising the design of dryers so that flow and temperature are evenly distributed. Also, solar greenhouse dryers reduce CO₂ emissions (up to 726.92 tonnes during their working life) and maintain quality of products as observed by color and increased content of essential oil in dried herbs. It is concluded that solar greenhouse dryers, especially those using hybrid and forced‐convection designs, are available as scalable, cost‐effective, clean drying alternatives with current materials, geometry and control technology innovations leading to an increased uptake of this technology in terms of global sustainable agriculture.