FIELD OF THE INVENTION
The present invention relates to a parabolic trough solar collector system in
general and a parabolic trough reflector having the receiver axis passing through
centre of gravity in particular. More particularly, the invention relates to a
parabolic trough solar collector system with reflector rotatable in an axis collinear
with the axis of the stationary receiver with minimum torque.
BACKGROUND OF THE INVENTION
Parabolic trough solar collector systems use a curved, mirrored trough which
reflects the direct solar radiation onto a tube (also called a receiver, absorber or
collector) containing a fluid running the length of the trough, positioned at the
focal point of the reflectors. The trough is parabolic along one axis and linear in
the orthogonal axis. The parabolic trough is generally aligned on a north-south
axis and is rotated in east west direction to track the sun each sky day so that
the direct radiation remains focused on the receiver. However, seasonal changes
in the angle of sunlight parallel to the trough does not require adjustment of the
mirrors, since the light is simply concentrated elsewhere on the receiver. Thus
the trough design does not require tracking on a second axis.

A fluid (also called heat transfer fluid) passes through the receiver and becomes
very hot. Common fluids are synthetic oil, molten salt and pressurized steam.
The fluid is then sent to heat exchangers to produce steam. The steam is then
used as utility or sent to a standard steam turbine generator to produce
electricity.
Generally, a receiver tube is connected to the parabolic trough collector system
and the receiver tube also moves along with parabolic trough to remain in the
focus line of the parabolic reflector. It makes the total system more complicated
to track along with the sun and also the receiver tube to incorporate flexible
and/or rotational joints to allow the tube to move as the system follows
throughout the day and remain connected with a fixed heat collection system.
These flexible / rotational joints limit the operating temperatures and pressures
of the receiver tube, and inter alia causes a source for loss of thermodynamic
efficiency, wear and possible leakage.
US 2010/0065045 describes a parabolic trough solar collector system having a
parabolic reflector used with an independently supported collector tube. This
assembly rotates along a single axis to maintain a focus line of the parabolic
reflector surface at the same location as the center of the circles.
US 2011/0100358 teaches a parabolic trough collector which does not require a
massive support and uses a sandwich structure. The particular shape minimizes
wind loads by centering the receiver in a parabola and the center of focus act as
the center of rotation.

US 8333186 B2 discloses a parabolic trough solar collector system having a
parabolic reflector used with an independently supported collector tube. This
assembly rests on a plurality of support and drives rollers supported by a roller
support arm and a roller support column. The parabolic reflector assembly
rotates against the roller along a single axis to maintain a focus line of the
parabolic reflective surface at the same location as the center of the circle.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a parabolic trough solar
collector system having center of gravity at focal line of a parabolic trough
assembly which allows a receiver to be independent of trough movement
avoiding flexible and/or rotational joints and also allows the tracking of trough
with minimum torque.
SUMMARY OF THE INVENTION
Accordingly, there is provided a parabolic trough solar collector system receiving
a sun ray all throughout the day time, the system comprising a parabolic trough
acting as a reflector having a receiver tube placed at the focal length of the
trough, the trough being supported by a metallic structure over bush bearing
assembly; the parabolic trough enabled to move along east-west direction
maintaining the receiver tube fixed and stationary, wherein the trough is

rotatable at a minimum torque along an axis collinear with the axis of the
stationary receiver tube, the rotational axis of the trough constantly coinciding
with the focal line allowing the receiver to be focused to incident of sun rays all
through the day time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows an end plate of parabolic trough solar collector showing
centre of gravity at the focal line according to the invention.
Figure 2 - shows a receiver fixed with end plate (only a part of end plate
were shown) parabolic trough collector according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The parabolic trough solar collector system of the invention comprises a
parabolic reflector with or without end plates [1] supported by a structure
which directs the sun light to a receiver tube [4] placed at the focal line of
the trough (reflector). The present invention teaches a parabolic trough solar
collector system having centre of gravity [2] at focal line of the trough by
balancing the torque of all the components with reference to the focal line of
the trough. The receiver tube [4] is placed at this focal line, which remains
stationary and fixed while the parabolic reflector moves along east - west
direction to track the sun. Since the axis of rotation and focal line are
coinciding with each other, the receiver tube always remains in focus.

An excel based program calculates the various dimensions of the parabolic
trough. The 'focal length' and 'linear dimension' of the parabola is calculated
using this program by the inputs 'aperture width', and 'depth' of the parabola.
The weight of the parabolic trough collector is also calculated using these
dimensions and density of individual materials used.
The above program was used to configure the parabolic trough collector with the
center of gravity [2] at focal point [2] as shown in figure 1.
The fixed receiver tube [4] is supported by the trough assembly using bearings
[3] or bushes, which shows the receiver tube [4] to remain stationary and
independent of trough movement as shown in figure 2. The parabolic trough
reflector having its centre of gravity [2] at focal line rotates along the same line.

WE CLAIM :
1. A parabolic trough solar collector system receiving a sun ray all
throughout the day time, the system comprising:
- a parabolic trough acting as a reflector having a receiver tube placed at
the focal length of the trough, the trough being supported by a metallic
structure over bush or bearing assembly;
- the parabolic trough enabled to move along east-west direction
maintaining the receiver tube fixed and stationary,
wherein the trough is rotatable at a minimum torque along an axis collinear
with the axis of the stationary receiver tube, the rotational axis of the trough
constantly coinciding with the focal line allowing the receiver to be focused to
incident of sun rays all through the day time.

2. The system as claimed in claim 1, wherein the parabolic trough in
particular the value of focal length and linear dimension of the parabola is
determined by using a programmed processor based on the input value of
aperture width and depth of the parabola, and wherein the weight of the
parabolic trough collector is calculated based on said two inputs and an
additional input for example, the density of individual materials used in
forming the trough.

ABSTRACT

The invention relates to a parabolic trough solar collector system receiving a sun
ray all throughout the day time, the system comprising a parabolic trough acting
as a reflector having a receiver tube placed at the focal length of the trough, the
trough being supported by a metallic structure over bush or bearing assembly;
the parabolic trough enabled to move along east-west direction maintaining the
receiver tube fixed and stationary wherein the trough is rotatable at a minimum
torque along an axis collinear with the axis of the stationary receiver tube, the
rotational axis of the trough constantly coinciding with the focal line allowing the
receiver to be focused to incident of sun rays all through the day time.