Friosol developed a sun collector based on adsorption.
By using adsorption the efficiency of heating by low sun rate is high due to the heat pipe effect. The system is also a solar cooler in summer.
Adsorption is a physical process in which moisture is condensed and held on the surface of material without any change of the structure of the material. Heating can over and over again reactivate the adsorbent material.
The solar cooler works on the basis of Adsorption of water by zeolite. Zeolite has a structure with a very large internal surface. In nature there are mani different types of zeolite. Synthetic zeolite is used as a substitute for phosphate in laundry detergent. This use of large quantities of zeolite led to comprehensive examination of its environmental effects. It was thereby shown that zeolite in no way endangers the environment and has no toxic quality.
Basics of cooling technology with zeolite
Of basic importance for the application of zeolite is a very large inner surface of between 800 and 1200 m²/g. Strong electrostatic forces are active within this hollow space. Polar molecules such as water are thereby absorbed, and as a result of heat dissipation they are integrated into the crystal structure (adsorption). If the process takes place in airless containers, the absorption of steam takes place at such a dramatic rate that the remainder of the water cools off dramatically and freezes to ice as a result of the high latent heat. This process continues until the zeolite is saturated with water. Some zeolites can absorb up to 25 % of its own weight . To use it again, the zeolite must again be dried, whereby it regains its full functional capability. This regeneration takes place through heating. Water is thereby driven out of the zeolite as steam (desorption). The efficiency of the system is based on the non linearity of the zeolites adsorption isotherms as compared to pressure. Zeolites will adsorb water vapour at low partial pressure and desorb a majority of it at high partial pressure. This difference in partial pressure may be achieved through temperature change which is experienced in a FRIOSOL solar panel going from high day temperatures to low night temperatures.
Low energy density and time of availability have been key problems in the use of solar energy. FRIOSOL storage systems overcome these problems. When dry, zeolites can store latent heat energy indefinitely if maintained in a controlled environment. The storage time is independent of thermal isolation. The stored energy can be liberated as needed by addition of water vapour .