all about focusing type solar collectors

1. PRESENTATION
ON
FOCUSING TYPE SOLAR COLLECTORS
Session:2018-2019
Presented by:
Maga Ram Patel
DEPARTMENT OF RENEWABLE ENERGY ENGINEERING
College of Technology and Engineering
Maharana Pratap University of Agriculture and Technology
Udaipur - 313001

2. INTRODUCTION:
 Focusing collector is a device to collect solar energy
with high intensity of solar radiation on the energy
absorbing surface.
 A focusing collector is a special form of flat collector
modified by introducing a reflecting ( or refracting)
surface (concentrator) between the solar radiations and
the absorber.
 Focusing collectors can have radiation increases from
low value of 1.5 to 2, high values of the order of 10,000.
 Reach temperature up to 450-500 ⁰C.
 Receivers can be convex, flat, cylindrical or concave
and can be covered with glazing or uncovered.

3. SCHEMATIC OF CONCENTRATING/FOCUSING
COLLECTOR:

4. SOLAR CONCENTRATORS AND RECEIVER GEOMETRIES:
There is wide variety of means for increasing the flux of radiation on
receivers.
They can be classified on basis of:
 lenses or reflectors
 By the types of mounting and orienting systems
 By the concentration of the radiation they are able to
accomplish
 By materials used of construction, or by orientation
 Concentrator is a component used to increase the intensity of
energy flux on a receiver.
Concentration ratio (CR): it is the ratio of the area of the
concentrator aperture to the energy absorbing area of the
receiver.
CR = Aa/Ar
 It is determines the effectiveness of a concentrator.

5. SOME POSSIBLE FOCUSING SYSTEM CONFIGURATION:
1.Plane Reflector and Plane Receiver
Type: that both reflector and receiver
are plane. The concentration ratios are
relatively low, with maximum value of
four or less than four.
2.Conical Reflector and Cylindrical
Receiver Type: this system in which
reflector is conical and receiver is
cylindrical. Concentration ratio is little
higher than that of first case, it may be
of the order of 10.

6. 3. Fresnel Reflector: This consists of a parabolic shape
reflector made up of small segments.
The advantage of linear Fresnel lenses is that the
convenient mass production technique of extrusion of
thermoplastic materials can be applied to their fabrication.
A concentration ratio of about 10 is obtainable using them.

8. 4) Parabolic system: In a system consisting of a paraboloid
or a parabolic mirror and having receiver at its focal point.
The concentration ratios are very high and therefore can
be used where high temperatures are required. In
cylindrical system , the concentration ratio is lower than
paraboloid counterparts.
In both the cases the receiver is placed at the focus, i.e.
along the focal line in cylindrical parabolic system and at
the focus point in paraboloidal system.

9. TYPES OF CONCENTRATING OR FOCUSING COLLECTORS:
There are two methods by which the sun motion can be
readily tracked.
1. The first is the altazimuth method which requires the
tracking device to turn in both altitude and azimuth.
Paraboloidal solar collectors generally use this system.
2. The second one is the one-axis tracking in which the
collector tracks the sun in only one direction either from
east to west or from north to south.
Parabolic trough collectors (PTC) generally use this system.
These systems require continuous and adjustment to
compensate for the changes in the sun orientation.

10. LINE FOCUS COLLECTORS:
 These collectors, sometimes known
as parabolic troughs, use highly
reflective materials to collect and
concentrate the heat energy from
solar radiation.
 These collectors are composed of
parabolically shaped reflective
sections connected into a long
trough.
 A pipe that carries water is placed in
the center of this trough so that
sunlight collected by the reflective
material is focused onto the pipe,
heating the contents.
 These are very high powered
collectors and are thus generally
used to generate steam for Solar
thermal power plants.

11. POINT FOCUS COLLECTORS:
 These collectors are large
parabolic dishes composed of
some reflective material that
focus the Sun's energy onto a
single point.
 The heat from these collectors
is generally used for
driving Stirling engines.
 Although very effective at
collecting sunlight, they must
actively track the Sun across
the sky to be of any value.
These dishes can work alone
or be combined into an array
to gather even more energy
from the Sun.

12. TYPES OF CONCENTRATING OR FOCUSING
COLLECTORS:
There are different types of concentrating or focusing
collector depending upon the concentrator and receiver
geometries.
 There are as Follows:
 Cylindrical parabolic collector.
 Central receiver collector.
 Compound parabolic collector

13. CYLINDRICAL PARABOLIC COLLECTOR:
 It is a system consisting of a parabolic reflector and having
receiver at its focal point.
 The concentration ratios are very high and therefore can be
used where high temperatures are required.
 In a cylindrical system, the concentration ratio is lower than
paraboloid counterparts.
 In both the cases the receiver is placed at the focus, i.e.
along the focal line in cylindrical parabolic system and at
the focus point in paraboloidal system.
 The parabolic geometry is given by the relation
Y2 = 4aX
where a = semi major axis.

14. A TYPICAL CYLINDRICAL PARABOLIC SYSTEM:

15. a) Basic geometry of a parabolic
cylinder mirror.
b) Basic geometry of a
paraboloid

16. CENTRAL RECEIVER COLLECTOR:
The concept of central receiver collector is simple.
 In order to avoid the cost and heat losses in transporting a
working fluid to a central location, use of sunlight itself as
the transfer medium is proposed.
 To implement the concept, one needs a field of mirrors
provided with the means of directing reflected sunlight to a
central location, or a location at one edge of the field of
mirrors.
 In the typical central receiver, the reflector is composed of
many smaller mirrors each with its own heliostat to follow
the sun.
 The heliostat are generally located in the horizontal plane,
but when the situation is favourable, can simply follow the
existing terrain.

17.  The basic difference between a
single mirror concentrator and
the heliostat system is that the
heliostat system has a dilute
mirror.
 This diluteness is generally
termed as the fill factor.
 A central receiver with a fill
factor of 40% means that 40%
of the land area is covered by
mirrors.
 Schematic arrangement of
central receiver- heliostat array.

18. COMPOUND PARABOLIC COLLECTOR (CPC) OR
WINSTON COLLECTOR:
 It is possible to concentrate solar radiation by a factor of
10 without diurnal tracking using this type of collector.
 A compound parabolic concentrating collector is show in
Fig. ( in next slide)
 It consists of two parabolic reflectors which funnel the
radiation from aperture to absorber.
 The right and left half belong to different parabolas
(hence the name compound parabolic concentrator).
 The axis of the right branch, for instance, makes an
angle Ѳc , with the collector mid plane, and its focus is at
A. At the end points C and D, the slope is parallel to the
collector mid-plane.

19.  The compound parabolic
collector developed by
Winston represents what may
be called as ideal
concentrator in the sense that
for a given field of view it
achieves the maximum
possible concentration ratio
given by:
CR = W/b = 1/SinѲc
Where,
W = entrance aperature
b = exit aperture, covered by
the absorber
Ѳc = field of view (half angle)

20. ADVANTAGE OF CONCENTRATING TYPE COLLECTORS:
 Surface required less material or provide high collection
of radiation.
 For a concentrator system the cost per unit area of solar
collecting surface is therefore potentially less than that of
the flat-plate collector.
 Heat loss rate is less than flat-plate collection low
maintenance.
 Can be used for power generation
 We can get high concentration or radiation.
 Litter or no antifreeze is required to protect the absorber
in concentrator systems.

21. DISADVANTAGE OF CONCENTRATING TYPE COLLECTORS:
 Only beam radiation collected because diffuse component
cannot be reflected and is thus lost.
 Additional requirement of maintenance particularly to retain
the quality of reflecting surface against dirt, weather,
oxidation etc.
 Non- uniform flux on the absorber whereas flux in flat-plate
collector is uniform.
 Additional optical losses such as reflectance loss and the
intercept loss, so they introduce additional factors in
energy balances.
 These disadvantage have restricted the utility of focusing
collectors and no long time practical applications of
focusing collectors other than for furnaces are being made.