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1349-017 Lisboa Portugal

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The use of solar energy in the conservation of foods by dehydration

Man has always used dehydration to conserve his food.


In developed countries nowadays, we continue to dehydrate the most varied products: herbal and medicinal herbs, fruit, vegetables, mushrooms or goji, algae and all nuts. Dehydration is the basis of multiple processes in the pharmaceutical, food or cosmetic industry. [In developing countries, due to the non-existent or reduced cooling network, drying is still the primary method of preserving food, especially fish and cereals, sparing them of post-harvest losses due to deterioration or contamination.]


The quality of the drying requires a balance between the heat supplied and the relative humidity of the air inside the drying chamber. This is the only way to preserve the organoleptic and nutritional characteristics of plant material: stabilizing microbiological activity and chemical and enzymatic reactions. Conventional intensive drying (industrial) has the principle of heating the air that causes evaporation and entrainment of the water – that is, the dehydration of the products. This process is fueled by huge amounts of non-renewable fossil or electric energy.


When we think of solar energy as an alternative to conventional sources, we soon think of its intermittency and low density – the nights and the cloudy days. These factors would make it difficult to obtain a reliable drying system that is capable of operation at reasonably constant temperatures. This system allows at these times to minimize these drawbacks, using an auxiliary energy which ensures the continuity of the drying in a controlled environment.


During the day and whenever atmospheric conditions are favorable, the drying is carried out by convection of the air heated by the Sun and stored in the collectors; during the night and on rainy days, auxiliary equipment is automatically activated using the electric power – the dehumidifier and the heater. These auxiliaries promote dehydration in two ways – mechanical and air exchange with thermal differential, which together with the circulation of hot air are the three forms of drying of this system.


To automate the choice between these forms of drying and thus to take advantage of it, at any moment, in the most efficient way (more economic and faster) an algorithm and a controller that applies it have been developed. It is this controller that is the brain of the system and allows uninterrupted operation of the dehydrator.


It is also this controller that registers the drying parameters for further analysis and statistical treatment, traces drying curves and thus leaves the user to determine the drying, according to its needs or specificity of the final product to be obtained. As an IoT (Internet of Things) equipment, it enables the monitoring and control of drying, anywhere in the world and at any time.

In recent years, we have witnessed the entry into the market of innovative dehydration systems which, with the introduction of new technologies as well as the improvement of existing techniques, are able to overcome the very high energy costs and environmental damage inherent to intensive systems, without compromising the quality of the final product.




One of this systems is BLACKBLOCK ®, a dehydration solution, entirely Portuguese and award winning innovation. This drying system uses the Sun as the main source of thermal energy, which in itself is not new – there were already other natural or forced drying systems that did it. What BLACKBLOCK ® brings back is reliability and accessibility over the internet. This system consists of an isothermal drying chamber covered by thermal panels. Is in this “box” formed by these two elements that the air is heated, by capturing the radiant energy of the Sun and its transformation into thermal energy. Stored in this space, hot air is available to enter the drying chamber with the help of fans.


Built initially for Mediterranean climates like ours, it was designed to operate overseas, but has been adapted to operate inside buildings, particularly in colder climates in northern Europe. It is therefore possible to place it inside installations by moving the panels outwards and conducting the hot air with the help of pipes inwards. It is also possible to choose a mixed use, the equipment is moved to the outside during the day and collected at night. It is this bold solution that is under development for Iceland as part of a Horizon 2020 project, thus launching the Portuguese BLACKBLOCK ® for new challenges!


Gonçalo Costa Martins

Executive Director of BBKW




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