3.1 Classification of Solar Collectors
Solar radiation is converted into thermal energy in the focus of solar thermal concentrating systems.
These systems are classified by their focus geometry as either point-focus concentrators (central receiver
systems and parabolic dishes) or line-focus concentrators (parabolic-trough collectors (PTC) and linear
Fresnel collectors). Most popular types of solar collectors are parabolic Dish, Parabolic Trough and
Power Tower system. Firstly, the parabolic dish system Fig (b) uses a computer to track the sun and
concentrate the sun's rays onto a receiver located at the focal point in front of the dish. Parabolic dish
systems can reach 1000 °C at the receiver, and achieve the highest efficiencies for converting solar
energy to electricity in the small-power capacity range. Secondly, the parabolic troughs concentrate
sunlight onto a receiver tube that is positioned along the focal line of the trough Fig (c). Occasionally a
transparent glass tube envelops the receiver tube to reduce heat loss. Parabolic troughs often use singleaxis
or dual-axis tracking system which permits temperatures at the receiver can reach 400 °C and produce steam for generating electricity. Thirdly, the heliostat uses a field of dual axis sun trackers that
direct solar energy to a large absorber located on a tower Fig (d). A solar power tower has a field of large
mirrors that follow the sun's path across the sky. The mirrors concentrate sunlight onto a receiver on top
of a high tower and computer tracks the mirrors aligned consequently the reflected rays of the sun are
always aimed at the receiver, where temperatures reach above 1000°C and produce high pressure steam
for generating electricity. Finally, this categories of collectors were used which reduces heat losses and
increases efficiency at high temperatures and thermal detoxification.