Figure
1. Energy Production Diagram.
SOLAR RADIATION COLLECTION.
Solar
thermal plants use two systems for concentrating the direct solar
radiation, because the diffuse radiation can not be used as in
photovoltaic’s. These systems are:
- Concentration onto a point.
consist of positioning all the mirrors onto a same point. It produces
high to very high temperature. Within this system there are two methods:
1) Stirling Dish:
consists of a mirror with a parabolic curved surface to concentrate
direct light to the focal point. The dish geometry is familiar being
used for antennas.
Figure
2. Stirling dish solar collection.
2) Tower: is based on overlapping
images from a field of mirrors and redirecting the sun’s rays towards a
receiver atop a tower.
Figure
3. Tower with mirrors field solar collection.
- Concentration onto a line is
based on concentrating all the solar radiation onto a linear receiver
located on top of the mirror as shown in the figure 4 and 5. As a rule,
concentrating energy onto a line produces lower temperatures than the
one onto a point. It happens because this system has a lower degree of
freedom for solar tracking.
1) The parabolic trough
currently is the most common system used. It is based on reflecting the
incident direct radiation from the trough to the focal line the length
of the trough. On top of them are located the heat carrier fluid
tubes.Mirrors function is to concentrate the maximum possible energy on
the tubes.
Figure
4. Parabolic-trough mirrors solar collection.
2)
Fresnel lenses are fabricated in linear form with the same cross
section as the circular lens but now producing a focal line instead of
a focal point. They are placed horizontally, and they will rotate
throughout the day to reflect the maximum possible energy on the fluid
heat carrier tubes.
Figure
5.Fresnel system solar collection.
