SOLAR ENERGY COLLECTION SYSTEM

SYSTEME COLLECTEUR D'ENERGIE SOLAIRE

English Abstract

ABSTRACT OF THE DISCLOSURE
A solar energy collection system utilizes a series
of modular solar collectors. Each modular solar collector
comprises a plurality of parallel elongate envelopes
through which passes a single fluid flow pipe in alternate
directions in adjacent envelopes. An ideal or nearly ideal
reflector surface is provided in each envelope to reflect
and focus incident light on the fluid flow pipe.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A modular solar collector, comprising
a plurality of parallel elongate envelopes phys-
ically joined together in fixed immovable relationship to
each other in a module, each said envelope having an upper
transparent surface to admit light rays to the envelope,
a tube extending in each envelope from one end to
the other for conveying fluid to be heated into each en-
velope and for removing heated fluid from the envelope,
a selectively absorbing surface on said tube for
selectively absorbing energy having predetermined wave-
lengths and rejecting other wavelengths, and
an elongate reflector surface located internally
of each said envelope and arranged to reflect light received
through the transparent surface onto said tube,
said upper transparent surface and said tube
being dimensioned to provide a concentration ratio in each
envelope which is the ratio of the transverse width of the
upper transparent surface to the outer circumference of the
tube and has a value greater than about 0.5,
the locus of each said reflector surface being the
shape required to ensure that no less than about 75% of the
maximum efficiency of each collector is realized,
said maximum efficiency being provided by the shape
required to ensure that all incident rays received into
each envelope through the upper transparent surface thereof
with the acceptance angle determined by the equation:
<IMG>
where C is the concentration ratio and .theta. is the acceptance
angle, are concentrated on said tube while rays outside the
acceptance angle are reflected.
-10-

2. The collector of claim 1 wherein said reflector
locus is the shape required to ensure that no less than
about 90% of the maximum efficiency of the collector is
realized.
3. The collector of claim 1 wherein said concentration
ratio has a value of about 1.0 to about 3Ø
4. The collector of claim 3 wherein said concentration
ratio has a value of about 1.5 to about 2Ø
5. The collector of claim 1 wherein said plurality of
parallel elongate envelopes is provided by an integrally-
formed lower body member and an integrally-formed trans-
parent cover member which is joined in vacuum sealing
relationship with said body member.
6. The collector of claim 5 wherein said body member
is formed of vitreous ceramic material and said cover
member is formed of glass.
7. The collector of claim 6 wherein said reflector
surface in each said envelope is formed on the internal
surface thereof.
8. The collector of claim 5 wherein said tube passes
in continuous manner from one end of said module to the
other in alternate direction in each adjacent envelope and
said tube is supported in minimal heat conducting relation-
ship with said body member.
9. The collector of claim 8 wherein a groove is
provided at the bottom of each envelope and springs
surrounding the tube and seated in said groove provide
said tube support.
- 11 -

10. The collector of claim 1 wherein said tube has
light-energy actuable electricity generating material
layers provided thereon and electrical connectors extending
from said layers externally of the envelope.
12

Description

73~3
The present invention relates to a solar energy
collection system.
In our prior Canadian patent application Serial
No. 275~382, there is described a solar energy collector
comprising an outer evacuated envelope having an upper
transparent surface to admit light rays to the envelope
and a two-way tube extending in the envelope from one end
thereof towards the other and having a selectively absorbing
surface for selectively absorbing energy having predetermined
wavelengths and rejecting other wavelengths.
An elongate reflector surface is located internally
of the envelope and is arranged to reflect light received
through the upper transparent surface onto the two-way tube.
The locus of the reflector surface is designed to ~chieve
maximum efficiency and is the shape required to ensure that
all incident rays received into the envelope through the
upper transparent surface within the acceptance angle
determined by the equation:
C = 1
sin~
where C is the concentration ratio (i.e., the ratio of the
transverse width of the upper transparent surface to the
outer circumference of the tube) and ~ is the acceptance
.
angle,~are concentrated on the two-way tube while rays
outside the acceptance angle are reflected.
The system provided in accordance with our prior
invention iq highly efficient but suffers from the drawbacks
that it possesses a high evacuated volume per unit area of
collector and each individual collector requires its own
connection with a manifold conveying fluid to be heated
and heated fluid.
- 2 -
.

3~3
: In accordance with the present invention, these
prior art difficulties are overcome by providing a modular
solar collector comprising a plurality of parallel collector
envelopes through which passes a single flow pipe in alter-
nate directions in adjacent envelopes.
The invention is described further, by way of
illustration, with re~erence to the accompanying drawings,
in which:
Figure 1 is a perspective view with parts broken
away for clarity of a solar energy collection system
comprising a single central manifold and a plurality of
collector modules provided on opposite sides of the central
manifold;
Figure 2 is a section taken on line 2-2 of Figure
l; . .
Figure 3 is a sectional view similar to Figure 2
of a modified form of collector;
Figure 4 is a perspective view of a detail o~ the
collector;
Figure 5 is a close up detail of another portion of :~
the collector; and
Figures 6 and 7 are perspective views of two
alternate fluid flow arrangements through the modular
collectors.
Referring to the drawings, a solar energy collection ~ ~:
system 10 comprises a plurality of collector modules 12 :
connected to a central elongate manifold 14.
The collector modules 12 and the elongate manifold
14 may be supported on a suitable support structure, such -
as, a building roo~, as illustrated in our copending
application descrlbed above. The number of modules 12
: - 3 - `

3~3
associated with each manifcld 14 may vary widely, as may
the number of manifolds 14 provided in a particular heating
system.
Each module 1~ comprises a plurality of individual
collectors 16. The individual collectors 16 have an
internal reflector surface 18 formed on a lower body portion
20. The reflectorsurface 18 may be provided by a thin
film o silver or other convenient highly reflective ma-terial.
The shape of the reflector surface 18 is described in detail
below. An upper transparent cover 22 and end caps 24
enclose an evacuated space 25 in each individual collector
16.
The individual collectors 16 are integrally joined
: :
together in each module 12 and are comprised of an integrally-
formed lower body member made up of body portions 20 and
an integrally-formed cover member made up of covers 22.
The cover member is sealingly joined to the lower body
member. The transverse width of the body portions 20 at
their upper extremity is maintained at a low value to
minimize the non-light receiving area of the module 12.
The evacuated spaces 25 may be individually evacuated,
or more preferably, fluid flow connection is provided
between the individual evacuated spaces throughout the
module, so that the whole internal volume of the module
may be evacuated in a single operation.
- The lower body portion 20 preferably is constructed
of vitreous ceramic material formed rom clay and vario~s
fluxes while the cover 22 preferably is constructed of
glass~ Vitreous ceramic materials are inexpensiv~ and
readily available, and can be formed into shaped objects
by molding or extr~sion, making them ideal for formation
~ _ 4 _

of integral molded or extruded lower boay portion.
Through the plurality of collectors 16 passes a
single 1uid flow pipe 26 by which fluid ~o be heated in
the module 12 passes successively through the plurality of
collectors from an inlet-outlet pipe 28 consisting of paral~ .
lel concentric tubes which connects the module 12 to the
manifol~ 14. As a result ~f this arrangement, fluid flows
successively in opposite directions in adjaoent collectors 16.
~ he tube 26 is supported at the appropriate location
in each of the collectors.16 by sprung wires 28 wound round
the tube 26 and having their eIlds 30 located in elongate
grooves 32 fonmed in the base of the body portion 20.
The use of the sprung wires 28`to support the tube 26 also ~ -
serves to minimize conducti~e heat losses between the tube
26 and ~he body portion 20 in each collector 16.
The outer surface of the tube 26 has a coating
layer thereon of a material, such as, chrome black, which
selectively absorbs energy of a certain wavelength
generally about 3 x 10-7tO about 3 x 10 6 meters, while
~0 not absorbing other wavelengths. The use of a selectively
absorbant material.coating in this way minimizes heat
lo~ses from the tube 26 through radiation.
Alternatively, at least the outer wall of the tube
26 may be ~ormed of a material which will act as a selective
: absorber, such.as, a black ceramic material.
By utili2ing the modular approach illustrated in
the dra~ingsi the individual collectors 16 may be diminished
in aimension with respect to t~ose described in our earlier
application, so that or the same temperature rise of fluid,
the evacuated space per unit ar~a can be considexably
decreased. Modules 12 may be formed of any desired number
- 5 -
- : ; .

of individual collectors 16 commensurate with the
temperature rise desired during passage of fluid therethrough.
Referring to the individual collectors 16, the
concentration ratio (C) refers to the relative dimensions
of the radiation-receiving portion and radiation-absorbing
portion of the collectorl5, while the acceptance angle (~)
refers to the angle within which all rays entering the
collector 16 through the radiation-receiving portion are
absorbed by the radiation-ab6orbing portion of the collector
while rays entering the collector through the radiation-
receiving portion outside that angle are reflected.
Referring to Figure 3, the concentration ratio
(C) o~ the collector 16 is determined by the ratio:
C = Entrance Aperture Width - A
Absorber Tube Circumference 2~ R
The acceptance angIe (~ is the angle to the axis (~) within
which all rays entering the collector 16 through the upper ,
surface 22 are absorbed by tube 26 while rays outside that
angle are re1ected back without being absorbed. The
~0 limiting condition or acceptance of rays for absorption is
a ray which is reflected by the reflecting surface 18 to
pass tangentially to the tube 26, as illustrated.
In a collector 16 of maximum efficiency~ the
acceptance angle (~) is determ,in~d by the concentration ratio
(C), in accordance with the equation:
C = 1
sin~ '
and the locus of the reflecting surface 18 of the collector
16 is the shape corresponding to ~hat equation.
It will be seen from the above equations that, as
the concentration ratio (C) increases, the acceptance angle
(B) decreases. The value of the acceptance angle will
-- 6 --

determine the length of time during a given day when
the collector 16 will absorb light rays, assuming that the
collector 16 is located in a fixed relationship with
respect to the sun movement. The value of the concentration
ratio will determine the temperature rise attainable in
the tube 26 during the time that rays are accepted within
the acceptance angle, with an increase in concentration ..
ratio leading to an increase in temperature under otherwise
fixed conditions.
The minimum concentration ratio is about 0~5 and
the upper limit of concentration ratio for a fixed location
system is about 10. If the collector module 12 is mounted
to track the sun.'s movement on a dail~ basis or if the ~;~
sun's rays aan be concentrated within the narrow acceptance
angle which exis~s at these high concentration ratios, then
the concentration ratio may exceed 10, although it will
rarely exceed 50.
Pre~erably, the concentration ratio is about 1.0
to about 3.0, most preferably about 1~5 to about 2.0, which
provides a good balance of acceptance angle and concentra-
tion ratio, 50 that the collector 16 has a sufficiently
wide acceptance angle to absorb rays over a long period of
daylight hours, while at the same time providing a good
heating effect on the fluid flowing through the collector
! .
: : 16.
If the physical height of the body porkion 20 is
: decreased withouk otherwise altering the shape of the
reflector, as shown in the modification of Figure 3 wherein
i the dotted outline represents the locus at maximum efficiency
and the solid outline with cover 22A represents the
decreased height body, the concentration ratio is decreased

i'3~3
and this leads to a less than maxim~m efficiency of
collector 16. Since, however, the upper portion of the
reflecting surface 18 adjacent the upper surface 22 is
almo.st parallel and has only a minor effect on the rays
which are absorbed by the tube 26, the loss of efficiency
need only be minor, while the material saving achieved
thereby may be considerable.
Generally, when the truncated form of body 20 is
adopted, ~he concentration ratio (C) is always maintained
gFeater than about ~.5~ The maximum loss of eficiency
from ideal conditions is about 25%, while preferably the
loss of efficiency tolerated on truncation is less than
about 10%.
The collectors 16 also each may achieve a photo-
\ voltaic function by producing an electrical output from
I collected solar energy. ~he tube 26 may be coated with
j light energy actuable electricity generating material
layers which communicate through suitable electrical
connection to exterior of each collector 16.
Figures 6 and 7 illustrate two alternative flow
patterns with respect to the plurality of modules 12. In
the embodiment of Figure 7, the manifold 14 has an inlet
pipe 34 ~or the passage o fluid to be heated, such as
air, water or other convenient fluid from one end of
the manlfold ~o the other, and an outlet pipe 36 for receipt
o~ heated ~luid. The inlet pipe 34 feeds each of the
m~dule~ 12 in parallel and the outlet pipP 36 receives heated :~
fluld from each ~f the modules 12 in parallel.
In the embodiment of Figure6, inlet and outlet
tubes 34 and 36 are again provided, but in this case a
- 8 - ;:
.. , ~ .
.~. ..,:

7'3~3
central pipe 38 also is utilized. Fl~id to be hea-ted passes
in parallel to groups of modules 12 and fluid passes in
series through each member of the group of modules, as
illustrated. Heated fluid passes in parallel from t~e
groups of modules.
The truncation of the body of the collector described
with respect to the illustrated embodiment is also applicable
to the form of collector which is described in our copending
application Serial No. 275,382, and as described above and
is included within the scope o~ the invention.
The present invention, therefore, provides an
improved form of solar collec~ion system. Modifications
are possible within the ~cope of this invention.
:1
O
`
.