Solar energy conversion with thermal cycles - Solar Energy Sciences and Engineering Applications - page 421

Figure 14.3.2 Schematic of two possible configurations of solar fields (the central line must be seen as
symmetric axis).
a “U shape'' pipe: the cold and hot headers can be on the same side leading to the so-
called “central-feed configuration''. This layout minimizes the piping and allows direct
access to each collector row without buried pipes. One drawback is that this configu-
ration is not balanced from a pressure drop point of view; therefore pressure balancing
valves are required at each row, adding significant pressure drops. An alternative layout
can be represented by the “direct return'' and “reverse-return'' configurations (Kreith
and Goswami, 2007), where the cold and hot headers are on different sides of the
rows. In particular, the inverse return configuration balances the pressure drop but
requires longer connecting pipes.
To summarize, the typical layout configuration is the central feed since it reduces
piping length and thermal losses, keeping a good access to the collectors.
The tracking orientation of the trough can be either in a N-S direction, an E-W
direction or anywhere in between; the direction which guarantees the highest collection
of solar energy is N-S. As an example, the electricity produced in a year from a parabolic
trough-based solar plant located in the United States at a latitude of 34 ◦ is shown in
Figure 14.3.3. The only difference between the two cases is in the axis orientation.