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Solar dryers are devices that use
Direct solar dryers expose the substance to be dehydrated to direct
solar energy
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essen ...
to dry substances, especially food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
. Solar dryers use the heat from sun to remove the moisture content of food substances. There are two general types of solar dryers: Direct and indirect.
Direct
Direct solar dryers expose the substance to be dehydrated to direct sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...
. Historically, food and clothing was dried in the sun by using lines, or laying the items on rocks or on top of tents. In Mongolia cheese and meat are still traditionally dried using the top of the ger (tent) as a solar dryer. In these systems the solar drying is assisted by the movement of the air (wind) that removes the more saturated air away from the items being dried. More recently, complex drying racks and solar tents were constructed as solar dryers.
One modern type of solar dryer has a black
Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...
absorbing surface which collects the light and converts it to heat; the substance to be dried is placed directly on this surface. These driers may have enclosures, glass covers and/or vents in order to increase efficiency
Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...
.
Indirect
In indirect solar dryers, the black surface heats incoming air rather than directly heating the substance to be dried. This heated air is then passed over the substance to be dried and exits upwards often through achimney
A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typ ...
, taking moisture
Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...
released from the substance with it. They can be very simple, just a tilted cold frame with black cloth to an insulated brick building with active ventilation
Ventilation may refer to:
* Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation
** Mechanical ventilation, in medicine, using artificial methods to assist breathing
*** Ventilator, a m ...
and a back-up heating system. One of the advantages of the indirect system is that it is easier to protect the food, or other substance, from contamination whether wind-blown or by birds, insects, or animals. Also, direct sun can chemically alter some foods making them less appetizing.
Solar drying is mostly carried out between 50-70 degree Celsius. Solar dryers such as Vyom and many other models now use polycarbonate sheets or UV preventive glass so that UV rays of the sun do not penetrate the food which leads to degradation of dried food. Solar dryers not only make the drying faster, it also prevents dust, pathogens, bird droppings, and interference of external agents that affect the quality of the food. Food items such as fruits, vegetables, spices and other items once dried in solar can be stored for longer period of time.
See also
*Solar cooker
A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize drink and other food materials. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful or as ...
References
External links
* {{Clear Dryers Solar energy