Power Plant Engineering

70 POWER PLANT ENGINEERING

point. Water/steam working fluid can also be used. The tubes have evacuated glass enclosure to reduce
the losses. The concentration ratio is between 40 and 100. The maximum oil temperature is limited to
400°C as oil degrades above this temperature. Alternately steam at 550°C can be directly generated in
the absorber tube.
These are commercially under operation. Fig. 2.14. shows a flow diagram of parabolic trough
solar power plant. The working fluid is heated in collectors and collected in hot storage tank (2). The
hot thermo-oil is used in boiler (5) to raise steam for the steam power plant. The boiler also is provided
with a back-up unit (6) fired with natural gas. The cooled oil is stored in tank (3) and pumped (4) back
to collector (1). Solar thermal power plants with a generating capacity of 80 MW are functioning in the
USA.
Solar Chimney Power Plant. The air stream is heated by solar radiation absorbed by the ground
and covered by a transparent cover. The hot air flow through or chimney which gives the air a certain
velocity due to pressure drop caused by the chimney effect. The hot air flows through an air turbine to
generate power.

Warm Air

Chimney

Air Turbine

Sola

r

Rad

iatio

ns

Cold Air

Generator

Cover

Fig. 2.15 Chimney Solar Power Plant.

2.16.3 Solar Energy Storage

It is well known that human beings have been using solar energy for different uses, from ancient

days. Find examples of these uses and add to the list given below.

1. To get salt from sea water.


2. To dry wet clothes


3. To dry firewood


4. To dry cereals


5. To dry fish


6. To dry leather
   We now use several appliances which work using solar energy. Appliances like solar cooker and
   solar heater absorb solar radiations and convert it into heat.
   Then what about a solar cell? Solar energy is converted into electrical energy and it is directly
   used or stored in a battery.