In this article we will know about the what are main types of solar energy collectors . we also know about the types of solar energy collectors.
What are main types of Solar Energy Collectors
The first step in the solar energy utilization is the
collection of this energy. This is done through collectors whose surfaces are
designed for high absorptive and low emissivity.
these are following types of solar energy collectors. which is shown below. these are main types of solar energy collectors.
1. Flat Plate Collector.
A flat collector consists of the following basic element:. it is very efficient type solar energy collector.
1. A flat plate upon which the short wave solar radiation
falls and is absorbed and converted into heat energy.
2. An insulated container to eliminate or substantially
reduce thermal losses from the collection system.
3. One or more plates of glass or transparent plastic to reduce
the upward heat loss from the collection surface.
4. Tubes or channels to circulate the liquid required to remove the heat energy from the collector to the strong tank.
4. Tubes or channels to circulate the liquid required to remove the heat energy from the collector to the strong tank.
A flat plate collector is shown in Fig. Solar radiation
passes through the transparent cover and is absorbed by the collector plate. A
fluid flowing in a passage in contact with the collector is heated and the heat
from the fluid is extracted for use. The circulating pump keeps a continuous
circulation of the fluid through collector and strong tank. In the storage
tank, is working as heat ex changer, fluid heats water which is used for the
desire purpose. The efficiency of the collection and conversion process depends
on the heat loss to surroundings which in turn depends on the temperature at
which the collectors work. The cover plate is transparent to incoming radiation
but opaque to infra red radiation of the collector and thus reduces the heat
losses. Treating the collector surface with special coating reduces the heat
losses still further. These coating can be
(1) particles of copper oxide about 1 u m in diameter,
(2) semi- conductor like silica
(3) layered coatings of calcium oxide and magnesium oxide.
These coating have a high ratio of absorptive emissivity (about 10 to 15 or so) but are very expensive. Al though a variety may be used for the heat transfer in the collector flow channels. All practical system to date have used water or water ethylene glycerol solution, the letter additive being used primarily to avoid problem due to the freezing of liquid in the tube under subzero temperature conditions. it is very simple and less costly type solar energy collectors.
(1) particles of copper oxide about 1 u m in diameter,
(2) semi- conductor like silica
(3) layered coatings of calcium oxide and magnesium oxide.
These coating have a high ratio of absorptive emissivity (about 10 to 15 or so) but are very expensive. Al though a variety may be used for the heat transfer in the collector flow channels. All practical system to date have used water or water ethylene glycerol solution, the letter additive being used primarily to avoid problem due to the freezing of liquid in the tube under subzero temperature conditions. it is very simple and less costly type solar energy collectors.
Flat plate collector with honey comb structure.
There is a growing interest in the use of honey comb cellular structure of
various shapes. Some of which are shown in fig. 15.8.their excellent strength
to weight ratio they have many application in aircraft and aerospace
industries. Many materials like aluminum, glass, plastics etc. are used in the
manufacture
Of these structures. It has found that collectors with honey
comb cellular structures are more efficient and their use has been proposed in
solar heat collectors. The process of heat transfer is a multi mode phenomenon
and all the three modes, conduction, con- vection and radiation, should be
considered in assessing the overall performance of any structure. In term of
conduction affect the cellular surface. May be envisages as an extended surface
used to increase the heat transfer area. In terms of convection effects,
structure has been found to modify the convection transport from a heated body
and in terms of radiation effects, they have been proposed for the creation of
artificial black bodies and specials forms of terminal traps. An inclined flat
plate solar collector with honey comb structure is shown in diagram.
2. Concentrating Collectors
In spite of the
methods of reducing heat losses the maximum temperature at which a flat plate
collector works is quite low, around 100 C IN summer and around 40c in winter.
Concentrating collectors are more effective but very closely. Parabolic- at
around can be reflector used up to
30000 c However its direction has to be adjusted to follow the direction of sun
rays.
A hemostat (b) is often used to reflect the radiation
directly on the object to be heated. A combination of heliostat and
parabolic reflector may also be used. The heliostat reflects the sun’s rays
to the reflector. The heliostat can be adjusted to account for the change in
sun’s position. it is very useful type solar energy collector .
The reflective surface of a heliostat usually consist of
back silvered low iron glass or metalized plastic. These are fixed to light and
mechanically stiff back up structures. The reflective surface is generally made
up several small segments to allow better control of the flatness than a large
single surface. These segments are also easily replaced in case of damage. The
heliostats elements are mounted on that are fixed perpendicularly to a
horizontals elevation members. Azimuth ally are elevations movements are made by
separated drive mechanisms which typically consist of electric motor driven
gears connected to the axes.
Helios tats have been found to be very suitable as collectors
for solar power plants. Their cost is one of the key costs in the total cost of
the plant. It is expected that better manufacturing processes and mass
production will reduce their cost. hence it is main type of solar energy collector.
SOLAR PONDS.
Non-convective
solar ponds have been suggested for collecting solar energy on a large scale. A
solar pond is a shallow body of water, about 1 metre deep containing dissolved
salts to generate a stable density gradient (fresh water on top on denser salt
water at bottom). Some of the incident solar energy entering the pond surface
is absorbed throughout the depth and the remainder which penetrates the pond is
absorbed at the black bottom. If the pond had only fresh water (or water of the
same density) the lower layers would heat up, expand and rise to the surface.
Because of convective maxing and heat loss at the surface only a small
temperature rise in water would be realized. The convection can be eliminated
by initially creating a sufficiently strong salt concentration gradient. In
this case the thermal expansion in the bottom lower layers is insufficient to
destabilize the pond. With convection nearly eliminated the heat loss from the
lower layer is only by conduction. Because of its relatively low thermal
conductivity water acts as insulator and permits temperatures up to 90%c to be
developed in the bottom layers. solar pond is use full for solar energy collector to produce electricity,
One way to extract heat from solar ponds is to place pipes
in the lower layers and circulate water through these pipes. A simpler and more
efficient approach is to take advantage for stable density stratification and
use method of selective withdrawal, a technique often use for water quality
control in large reservoirs. A sink placed in stably stratified liquid
withdraws the liquid from a thin horizontal layer, just as one would draw a
single card from a deck. This flow is quite different from one that would occur
if the density of water were the same throughout. The phenomenon of selective
withdrawal provides means by which, firstly, the stable density gradient
required in the upper insulating layer can be corrected and maintained at
secondly the hot lower layer can be removed, passed through a heat ex changer and
returned at a lower temperature to the bottom of the bottom of the pond. It is
sometimes desirable to separate physically the bottom layer from the upper
layer by a thin zone transparent partition, generally made of plastic.
The use of solar ponds has been suggested for salt
production, space heating and power generation using organic fluid Rankin cycle
engines which can operate relatively low source temperatures.
Hence these are solar energy collector if you find any incorrect in above article you must comment below in comment box.