Renewable Energy

Solar Drying Units

  • September 2020
  • Project Status: On-Going

Herbs are an essential part of our culture as well as in our day to day life with applications ranging from culinary purpose to that of therapeutic use. Almost all parts of a herb including its leaves, roots, flowers, seeds, root bark, inner bark, resin, and pericarp find one or the other application as food ingredients or as medicine. Over and above the medical and technological advances and discoveries in the form of synthetic drugs, the awareness and benefits of natural products continues to grow.


Traditional medicine relies on phytochemical components of herbs that explore both its aromatic and functional properties for curing diseases. This form of medicine is most practiced in semi-urban, rural and tribal areas. Ayurveda, Siddha and Unani, the traditional medicinal system in India are globally recognized and are strongly rooted in the traditional knowledge related to herbs. For employing these herbs for medical applications, the preliminary step involves drying. Thermal drying is the most cost-effective approach, which could be either open sun-dried or control oven-dried. The former approach is an unhygienic and inefficient process as it results in over drying whereas using the latter approach leads to loss of the aroma of the herbs and so the final product gets compromised.


The team led by Dr Kashinath is very passionate towards developing mini prototypes that could help farmers reduce their work hours and increase productivity. With this rationale, the team wanted to develop a device that could help in drying herbs in minimal time. On brainstorming, the researchers came up with a product design empowered by sunlight which couple both drying and grinding processes. This dual application system will help in meeting the demand for powdered herbal products in limited time. The device was built in two parts with one dedicated for generating hot air (collector) and the other, a single unit (executor) comprising both drying cabinets and grinding chamber.


The collector is a slightly elevated rectangular box with openings for both inlet and outlet of air. The upper layer of the collector is made of glass and the inside of the collector is colored black to allow maximum heat absorption. The area of collector exposed to sunshine helps in heating up of the air. The basal part of the collector comprises double layered baffle plates with intermittent glass wool to prevent heat transfer. Over the double-layered plate, another series of baffle plates are placed perpendicular in crisscross orientation to trap and slow down the movement of air.


The synergic effect of black coating, glass wool, criss cross arrangement heats up the atmosphere air that enters through the inlet of the collector. The outlet is connected to the executor system where products can be dried by the hot air that passes from the outlet. Different chambers/cabinets are provided within the drying unit with a maximum capacity to hold 5 kg of raw material. Provision for small sliding trays is provided to introduce the raw material so as to circumvent and/or limit heat loss. Attached to the basal body of the drying cabinet is the mixer which assists in producing the powdered form of the product.


This prototype has shown a thermal efficiency of 85.22% over normal sun drying and has successfully provided the powdered form of basil, neem and lemongrass. The device is able to dry and grind 2 kg of each of the herbs within 2 hours. The team has initiated collaborations with researchers of Department of Nutraceuticals, in order to assess the aroma and shelf life of the finished powered products.

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