Harnessing Solar Heat by Brian Norton

Author:Brian Norton
Language: eng
Format: epub
Publisher: Springer Netherlands, Dordrecht

From the late 1950s to the late 1980s (with a break in the late 1960/early 1970s) experimental solar ponds have been operating in Israel (Tabor 1981; Tabor and Matz 1964). A salt-gradient solar pond of 2.5 m depth and 200 m2 effective collector area was constructed in August 1975, at the Ohio State University, USA, for space heating (Nielsen 1976). A solar pond constructed in 1978 has heated an outdoor swimming pool in summer and a recreation building during part of the winter, In Miamisburg, Ohio, USA (Bryant et al. 1979).

The application of solar ponds for electric-power production usually employs an organic vapour Rankine Cycle engine to convert solar-pond heat to mechanical work, and then into electricity. However, to obtain a low cost per generated Watt, solar ponds of several kilometers are required.

Many techniques have been considered in order to suppress natural convection in order to create a solar pond. The most common method used is salt-stratification. Salinity increases with depth in the NCZ until the LCZ is reached: the highest salt concentration occurs uniformly throughout this region. Here the solar radiation will heat the highly saline water, but because of its high relative density (due to its salt content), this hot salt-water will not rise into the lower salinity layers. Thus the heat is stored, yet inhibited from being transferred by convection. Chemically-stable salts, as well as any natural brine can be used to establish a salt-stratified solar pond. A selected salt must be safe to handle; non-toxic; cheap and readily available; not reduce significantly the insolation transmission characteristics of water; and solubility should be temperature dependent. The variation of solubility with temperature for candidate salts is shown in Fig. 7.12.

Fig. 7.12Solarbility of salts in water

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