Environmental Engineering Reference
In-Depth Information
1.2
1
Sun Tracking
0.8
0.6
Fixed Plate
0.4
0.2
0
13579 1 3 5 7 9 1 3
Hours
fig. 13.7
Solar output as a fraction of peak as
a function of time of day.
Solar thermal electric systems have the potential to
store energy as well. The storage is as heat, not as
electricity. A heat reservoir like the tank used in the
solar hot water system, but with a
fluid that can stand
much higher temperatures, can be heated during the
day and the heat extracted later to run the generating
turbines. Since the time of peak electrical demand usu-
ally starts a few hours after sunrise and ends a few hours
after sunset, this is an important advantage for the
thermoelectric systems.
There are two disadvantages to thermoelectric systems.
On a lightly overcast day, PV systems can still produce
%
to
% of their normal output, whereas focusing systems
produce nearly nothing. Also, the added cost of the
steam generation and turbine systems makes the thermo-
electric system too expensive for smaller installations. Even
