Solar energy collection and storage - Solar Energy Sciences and Engineering Applications - page 124

Figure 4.1.3 A PV/T solar energy collector.
A solar heat pump uses low-temperature, low-quality energy from the outside
air, transferring heat from the cold reservoir to a warmer reservoir (Morrison, 1984).
The working fluid is alternately evaporated and condensed. A heat pump involves
isentropic compression in the compressor, constant-pressure heat rejection in the con-
denser, throttling in an expansion device and constant-pressure heat absorption in
an evaporator (Charters et al., 1980). Solar heat pumps for small-scale heating and
cooling applications are referred to as Combi + systems (Troi et al., 2008).
4.2 INTEGRAL COLLECTOR STORAGE SYSTEMS
4.2.1 Integral passive solar water heaters
Integral storage solar collectors are a tank, glazed lying on top of insulation
(Bainbridge, 1981; Arthur and Norton, 1988; Smyth et al., 1998; 1999; 2001a; 2001b;
2003; 2004; 2005; 2006). The water inside the collectors is heated by absorbed inci-
dent insolation. The heated water may be pumped directly to a demand or a hot storage
tank for later use. At night or during periods of low insolation, the water in the col-
lectors may be drained back to tank, thereby conserving the heat collected (Dickinson
et al., 1976). A typical example is illustrated in Figure 4.2.1. Many techniques are
available to determine the optimal design of such systems for particular climates and
hot water loads (Bar-Cohen, 1976; Chauhan and Kadambi, 1976).
4.2.2 Salt gradient solar ponds
A salt-gradient solar pond employs a salt concentration gradient to suppress natu-
ral convection. The physical processes are illustrated in Figure 4.2.2. Heated water