SEASONAL SOLAR TRACKING CONCENTRATING COLLECTOR

INSOLATEUR DE CONCENTRATION DES RAYONS SOLAIRES PAR POURSUITE SAISONNIERE

English Abstract

The present invention is a concentrating solar radiation collector that
consists of a
concentrator, ancillary reflectors, and an array of segmented absorbers. The
invention contains
reflectors and absorber arrays that are easily scaled to fit a wide range of
window sizes. The
assembly is designed to make use of inexpensive components in manufacturing.
The system is
designed for efficient assembly, disassembly and storage. The reflectors and
absorbers can be
removed during periods when an alternate use of the window is desired. The
present invention
extends the use of environmentally controlled spaces, such as architectural
glazed curtain walls,
three-season solariums and glazed patios, to the full year.

Claims

Claims
The embodiment of the invention in which an exclusive property of privilege is
claimed
are defined as follows:
1) A truss structure comprising:
at least two scissor-pairs, each scissors-pair comprising:
two essentially identical rigid struts, each comprising a central and a pair
of terminal pivot
points, with the central pivot point essentially equidistant from the terminal
pivot points
and lines joining the terminal pivot points to the central pivot point
intersect at the central
pivot point with a deviation angle between the two lines, and each strut being
pivotally
joined to the other of its pair by their central pivot points to form a
scissors-pair;
each scissors-pair being pivotally joined by two terminal pivot points to two
terminal
pivot point on an adjacent scissors-pair with both scissors-pairs essentially
in the same
plane;
a truss is thus formed of scissors-pairs that can be folded and unfolded, and
the distances
between the central pivot points and terminal pivot points are essentially
identical on all
struts within the truss, and the deviation angles for the scissors-pairs are
varied such that
the central pivot points lie at essentially equally spaced locations along a
desired curve,
a curve, defined by points on the truss at the same position relative to the
central pivot
point on all scissors-pairs, that is reasonably scalable with the height of
the curve, such
that all points deviate from the points of a perfectly scaled curve by less
than 5% of the
total curve length, over a range of extensions that includes the partially
extended truss to
the fully extended truss where the partially extended truss length is less
than half the fully
extended length.
2) A truss assembly according to claim of 1 where individual struts contain
multiple pairs
of terminal pivot points with different deviation angles.
3) A scalable asymmetric-parabola trough reflector comprising:


a pair of essentially identical trusses according to claim 1 or 2 unfolded to
essentially the
same length and displaced laterally from each other in essentially parallel
planes;
a multiplicity of guides fixed to all scissors-pairs on each truss, such that
the guides lie
along curves that are reasonably scalable with the truss length over a range
of folding and
unfolding positions of the truss, with the guides laying along essentially
identical curves
for both trusses; and
the reflector formed from a sheet of flexible reflective material with the
linear sides of the
reflector secured between the trusses near the ends of the trusses, and with
the reflector in
contact with the guides such that the reflector has a shape that essentially
follows the
curves defined by the guides.
4) A scalable asymmetric-parabola trough reflector, comprising:
a pair of essentially identical trusses according to claim 1 or 2 unfolded to
essentially the
same length and displaced laterally from each other in essentially parallel
planes;
a multiplicity of guides fixed to all scissors-pairs on each truss, such that
the guides lie
along curves that are reasonably scalable with the truss length over a range
of folding and
unfolding positions of the truss, with the guides laying along essentially
identical curves
for both trusses; and
a pair of rails of flexible material, each rail of dimensions similar to the
length of the curve
defined by the guides on each truss and width that is less than 5% of the
separation of the
trusses, each rail fixed to the guides on a truss such that the rail
essentially follows the
curve defined by the guides; and
the reflector formed from a sheet of flexible reflective material with the
linear sides of the
reflector secured between the trusses near the ends of the trusses, and with
the reflector in
contact with the rails such that the reflector has a shape that essentially
follows the curves
defined by the rails.
5) A scalable asymmetric-parabola trough reflector, comprising:
11




a pair of essentially identical trusses according to claim 1 or 2 unfolded to
essentially the
same length and displaced laterally from each other in essentially parallel
planes;

a pair of rails of flexible material, each rail of dimensions similar to the
length of the curve
defined by the terminal points on the concave side of the trusses and width
that is less than
5% of the separation of the trusses, fixed to the trusses near the terminal
points such that
the rails essentially follows the curves defined by the terminal points; and

the reflector formed from a sheet of flexible reflective material with the
linear sides of the
reflector secured between the trusses near the end of the trusses, and with
the reflector in
contact with the rails such that the reflector has a shape that essentially
follows the curves
defined by the rails.

A scalable asymmetric-parabola trough reflector, comprising:

a pair of essentially identical trusses according to claim 1 or 2 unfolded to
essentially the
same length and displaced laterally from each other in essentially parallel
planes;

a multiplicity of guides fixed to all scissors-pairs on each truss, such that
the guides lie
along curves that are reasonably scalable with the truss length over a range
of folding and
unfolding positions of the truss, with the guides laying along essentially
identical curves
for both trusses; and

a pair of rails of flexible material, each rail of dimensions similar to the
length of the curve
defined by the guides on each truss and width that is less than 5% of the
separation of the
trusses, each rail fixed to the guides on a truss such that the rail
essentially follows the
curve defined by the guides; and

the reflector is formed with a set of linear segments of reflective material
that lie in strips
spanning the space between the rails, with each strip connected to adjacent
strips and the
rails, and such that the strips follow the curvature of the rails in a piece-
wise manner when
extended and the strips stack to a compact stowed position when retracted; and

a means for extending and retracting the mirror segments.

12




7) A series of scalable asymmetric-parabola trough reflectors, comprising:
a multiplicity of reflectors in claims 3, 4, 5, and 6 wherein adjacent
reflectors share a
single truss at their common edge; and

the shared truss has means for supporting the reflectors on both sides of the
truss.

8) A trough-like curved reflector with essentially asymmetric-parabola cross-
section,
comprising:

a pair of shafts, wherein the shafts are fixed at both ends and flexed to form
essentially
identical and essentially asymmetric-parabola sections that are displaced
laterally from
each other in essentially parallel planes; and

the reflector is formed from a sheet of flexible reflective material guided by
to the shafts,
with a shape that essentially follows the curvature of the shafts, spanning
the space
between the shafts with linear sides of the reflector perpendicular to the
flexed curvature
of the shafts, and secured along the lengths of the shafts.

9) A trough-like curved reflector with an essentially asymmetric-parabolic
cross-section;
comprising:

a pair of shafts, wherein the shafts are fixed at both ends and flexed to form
essentially
identical and essentially asymmetric-parabola sections that are displaced
laterally from
each other in essentially parallel planes; and

the reflector is formed with a set of linear segments of reflective material
that lie in strips
spanning the space between the shafts, with each strip connected to adjacent
strips and the
shafts, and such that the strips follow the curvature of the shafts in a piece-
wise manner
when extended and the strips stack to a compact stowed position when
retracted, and

a means for extending and retracting the reflector segments.

10) A reflector according to claim 3, 4, 5, 7 or 8 where the reflective sheet
contains battens
that span the distance between the two trusses or shafts to support to the
reflector


13




11) A reflector in claim 10 where the battens perform the additional function
of connecting
the reflector to the means of support.

12) An fixed concentrating solar radiation collector system of the reflecting
type,
comprising:

an asymmetric-parabola trough primary reflector according to claim 3, 4, 5, 6,
7, 8, 9, 10
or 11 which can be reasonably scaled in the plane of the curve, forming a
curved reflector
where the leading edge of the reflector is abutted to and parallel with one
edge of the
frame of the aperture, where the reflector extends away from the first edge of
the aperture
and terminates at a depth behind the aperture, the reflector and depth to
which it extends
concentrates light entering the aperture to a linear focal band that is
projected onto the
plane that lies between and parallel to the terminal end of the reflector and
the second edge
of the aperture opposite the first edge, where the position of the focal band
between the
second edge of the aperture and the terminating end of the reflector moves
with the
incident sun angle;

a multiplicity of thermally separate absorber segments that extend out from
the terminal
edge of the primary reflector and extending generally towards the second edge
of the
aperture or towards the knee wall just below the second edge of the aperture,
with each
absorber segment running essentially parallel to the linear edge of the
primary reflector
such that the focal band of direct sunlight concentrated by the primary
reflector
illuminates a subset of the absorber segments;

each absorber segment having means for converting sunlight to heat and
conveying heat
to a heat transfer fluid that flows through a conduit within said absorber;

control means to selectively route heat transfer fluid to absorber segments
that meet
temperature requirements; and

a means for insulating the non-illuminated side of the absorber segments,

13) A concentrating solar radiation collector system according to claim 12
wherein:

14




a secondary reflector is placed along the edge of absorbers nearest the
aperture with the
reflective surface of the secondary reflector essentially facing the portion
of the larger
primary reflector near the absorber sections or facing the absorber sections
near to the
primary reflector.

14) A concentrating solar radiation collector system according to claims 12 or
13 wherein a
mounting location for the reflector support is incorporated into the absorber
assembly.

15) A concentrating solar radiation collector system according to claims 12,
13, or 14 in
which the system is sized to fit an existing aperture.

16) A concentrating solar radiation collector system according to claims 12,
13, 14, or 15 in
which each segmented absorber is enclosed in an radiation transmitting cover.

17) A concentrating solar radiation collector system according to claims 12,
13, 14, 15, or
16 in which the reflector and absorber assembly are modular in that they can
be installed
independently of the other components.

15

Description

CA 02466343 2005-04-05
Disclosure
Background and Introduction
The performance of simple fixed flat panel solar collectors can be
significantly reduced
in the winter months due to excess parasitic losses to the surrounding
environment and the low
sun angles. Use of tracking trough and paraboliodal concentrators with
moveable mirrors have
lower losses but tend to be more complicated and have to deal with wind
loading. The present
invention employs a simple, fixed concentrating reflector with an array of
thermally separate
absorber segments. During operation, a heat transfer fluid is only routed to
the absorber
segments receiving sufficient energy to increase the tern perature of the heat
transfer fluid. This
can reduce the active absorber area to less than 20% of the area of a flat
panel and is
accompanied by a significant reduction in parasitic losses. The use of a fixed
mirror and
absorbers significantly reduces the structural complexity and costs associated
with the tracking
mirror systems.
The present invention falls into the class collectors of fixed mirror with
tracking
segmented absorbers but employs a mirror assembly that can be adjusted to fit
a wide range of
aperture sizes. These systems can produce significant energy conversion
improvements over
flat panel or non-tracking compound parabolic collector (CPC) solar
collectors. The present
invention is designed for, though not limited to, installation within existing
structures to take
advantage of vertical windows to collect solar energy primarily during winter
months. The
present design is also modular in nature such that a system or part of a
system can be removed
or relocated as the requirements for a given space char~;e. Possible
applications that make use
of all of these properties are glazed patios and three-season solariums where
the system can be
erected during the fall and winter months to collect he;it when the room is
not used for other
applications.
The present invention covers an immobile concentrating solar collector that
can easily
scale to fit existing aperture sizes. The invention includes designs for
mirror assemblies that
can easily adjust to fit existing apertures. One such design is a collapsible
truss assembly
wherein the shape of the curve created by the truss scales with the length of
the curve.
Extendible truss structwes have been produced elsewhere; however, this current
invention is
unique in that the curve followed by selected points on the truss is
reasonably scalable over a
range of folding configurations. Another scalable design has a flexible mirror
supported by a
pair of shafts that are flexed to provide the near parabolic shape of the
minor. In both cases,
minor material such as a highly reflective aluminum sheet or aluminized film
along with the
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CA 02466343 2005-04-05
shafts or rails that shape the mirror can be cut to fit a .riven aperture size
on site or at a retail
location. Other options include segmented minors where the number of segments
can be
matched to the length of the mirror curve.
All of the mirror assemblies noted in the previous paragraph can be easily
stored either
for shipping or on site where the collectors are used sea>onally. The truss
structures collapse to
a small fraction of their unfolded size. Flexed shaft supports relax to a
straight shaft with
minimal cross-section. Film mirrors can be rolled for compact storage.
Segmented mirrors
stack upon each other. Sheet minors can be placed against a wall. Some care
must be taken to
protect the reflective surfaces in the mirror elements but this adds little to
the stored volume.
All of the noted mirror assemblies can be reduced to occupy volumes much less
the volumes
they occupy in their erected states.
The noted mirror assemblies can deviate from perfect parabolic trough shapes;
however,
the coarse descretization of the focal region by the segmented absorbers in
the present invention
is more tolerant to minor imperfections than some of the more traditional
trough solar
concentrators with tracking minors. The combination of the noted mirror
systems using
segmented absorber solar collectors provide an inexpensive match for the
efficient capture of
solar radiation.
The present invention also makes allowances to reduce convective heat losses
from the
absorbers. A concentrating solar collector, with segmented absorbers installed
behind a vertical
window, can generate convective currents within the collector cavity. The
present invention
allows for individually glazed absorber segments to reduce heat loss from the
absorber.
List of Figures
The present invention will be further described according to the following
figures,
wherein:
Figure 1 shows a basic strut used in supporting an3 shaping the minor
elements:
Figure 2 shows a universal strut that contains pairs of terminal pivot points
for seven
different scissors-pairs;
Figure 3 shows a scissors-pair made using a pair universal struts;
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CA 02466343 2005-04-05
Figure 4 shows a set of three scissors-pairs of struts in a curved truss
assembly with
details for connecting the scissors-pairs and for defining the scalability of
curves defined by
points on the truss;
Figure 5 shows a truss consisting of seven scissors-pairs in an almost fully
extended
configuration;
Figure 6 shows a truss consisting of seven scissors-pairs in a partially
folded configuration
to illustrate the scalability of the curves;
Figure 7 shows an example of a guide that supports a reflective sheet or a
flexed rail that
supports the mirror along its curved shape;
Figure 8 shows a mirror assembly comprised of a pair of curved trusses, a
reflective sheet
and ancillary parts;
Figure 9 shows a two section mirror with three cLxved trusses with one truss
common to
both minors;
Figure 10 shows a mirror assembly comprised of a pair of flexed shafts and a
reflective
film mirror with battens for structural support
Figure 11 shows a segmented mirror element;
Figure 12 shows a solar collector with fixed concentrating curved truss mirror
and
selectable segmented absorbers installed adjacent to an existing window;
Figure 13 shows an inverted version of the solar <;ollector with a curved
truss supported
primary curved mirror and a secondary mirror extending from the aperture
towards the
absorbers;
Figure 14 shows an array of absorber segments that are individually glazed;
Figure 15 shows calculated solar concentration levels for a range of sun
angles and
absorber locations;
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CA 02466343 2005-04-05
Detailed Description
This section contains more detailed descriptions of the solar collectors and
mirror
structures than the introduction using the items shown and detailed in the
figures.
Figure 1 shows a basic strut used in supporting and shaping the mirror
elements. The
basic strut 100 contains a central pivot point 101 and a pair of terminal
pivot points 102 and 103
located equidistant from the central pivot point 101. Tl~e basic strut may
also include ancillary
points 104 that play no role in the shape of the truss. The central and
terminal pivot points
typically do not lay along a single line. The angle between lines defined by
the central pivot
points and each of the terminal pivot points meet at a deviation angle 8.
The truss formed by the struts is typically made up of a number of struts with
different
deviation angles. Figure 2 shows a universal strut 110 with an number of pairs
of terminal
points 112a and 113x, 112b and 113b, 112c and 113c, 112d and 113d, 112e and
113e, 112f and
I 13f, and 112g and 113g and a single central pivot point 111. All of the
terminal pivot points
are located the same distance from the central pivot points but the deviation
angles are unique
to each pair of terminal points. Some of the individual terminal pivot points
are part of more
~~ one pair of terminal pivot points.
Figure 3 shows a scissors-pair 115 made using universal struts 110 and I 10'.
The primed
number denotes the back strut in the assembly. The uni~~ersal struts are
connected at the central
pivot points 111 and I 11' and are allowed to rotate rela~:ive to each other.
The universal struts
can be oriented with all terminal pivot points on strut 110 in line with their
counterparts on strut
110' at the same time.
Figure 4 shows a set of three scissors-pairs 115a, 115b and 115c in a curved
truss
assembly 116. Each scissor-pair is connected to the adja~;ent scissors-pair
through the same pair
of terminal pivot points. Terminal pivot points 113a and 113a' in scissors-
pair 115a connected
to terminal pivot points 112b' and I 12b respectively in scissors-pair I I Sb.
Terminal pivot points
113b and 113b' in scissors-pair IlSb connected to terminal pivot points 112c'
and 112c
respectively in scissors-pair IlSc. The deviation anglers measured in the same
sense for all
struts, have the same sign when making a strut where there is no change in
curve direction.
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CA 02466343 2005-04-05
The truss resulting from the assembly in Figure ~l is a pair of rhombuses rA
and rB that
are essentially identical and tilted relative to each other by the deviation
angle 0b for the struts
in the scissors-pair 115b common to the two rhombuses. The deviation angles
are fixed and the
use of identical rhombuses along the entire truss ensures that the distances
between central pivot
points in adjacent scissors-pairs are identical. This ensLres that the curve
defined by the central
pivot points scales to the length of the curve. This is true for any set of
points that are translated
by the same distance in the same direction from the central pivot points.
Figures 5 and 6 show a pair of identical seven scissors-pairs trusses in
different folding
configurations. In these figures, curves c5 and c6 follow the terminal pivot
points on the
concave side of the truss. The terminal pivot points are translated by the
same distance from the
central pivot points but the translation directions are not identical. Curves
formed in this
manner are not perfectly scalable to the length of the curve but they can be
reasonably scalable
over a large range of lxuss lengths. For the present invention, scalability is
considered
reasonable when the deviation of any point from its position in a perfectly
scaled curved is less
than 5% of the curve length. The curve through the germinal pivot points for
the trusses in
Figures 5 and 6 is reasonably scalable for truss length: ranging from the
fully extended truss
length to half of the fully extended truss length.
Figure 7 shows an example of a guide 140 that connects to the scissors-pair
through hole
141. A series of guides support a reflective sheet or a flexed rail along its
curved shape. The
flexible rail is secured to the guide with holes 142, 143, 144 or 145.
Figure 8 shows a mirror assembly 150 comprised ~~f a pair of curved trusses
152 and 153,
a pair of rails 154 and a reflective sheet 151. The trusses lay in parallel
planes that are displaced
laterally from each other by an amount slightly larger than the width of the
reflective sheet. The
minor surface is on the concave side of the reflective sheet. The reflective
sheet is supported
along the curves defined by the trusses via the rails.
Figwe 9 shows a two section mirror 160 with three curved trusses 162, 163 and
164 with
one truss common to both mirror sections. The curve3 truss 163 shared by the
two mirrors
sections has flexible rails 165 on both sides of the truss to support the two
reflective sheets 161.
In similar assemblies, a series ofN mirrors can be supported by N+1 txuss
curves.
Figure 10 shows a reflector assembly 170 comprised of a pair of flexed shafts
172 and an
aluminized film reflector sheet 171 with battens 173 for structural support.
The shafts i 72 are
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CA 02466343 2005-04-05
flexed to near parabolic curves with bending moment:, applied by mounts, not
shown, at the
ends of the shafts. The battens 173 play a number of rolls in the assembly
including:
maintaining the curved reflector profile between flexed shafts and providing
lateral support to
the flexed shafts. The battens may also be configured to provide a means for
connecting the
reflector to the shafts. Reflectors of this configuration can be rolled up for
compact storage
when not required.
Figure 11 shows a segmented mirror element 180. These are used in reflector
configurations where the mirror is broken into a number of linear elements.
The mirror segment
consists of a reflective portion 181 and a portion for interfacing with the
mirror support structure
182. The interfacing portion has holes 184 for connecting ropes or cables used
in hoisting the
reflectors into place.
The volume occupied by the mirror made up of se;;mented mirror elements can be
greatly
reduced for storage or shipping purposes. Alternatively the mirror structure
can be permanent
and the mirror can be retracted when a different use of the aperture is
required. The segmented
reflector option may also have an economic benefit 'vhen the mirror is damaged
and only
damaged reflector segments need replacement.
Figure 12 shows a solar collector 190 with fixed concentrating mirror Z 91
supported by
curved trusses 192 and an array of selectable segmented absorbers 195
installed adjacent to an
existing window 194. The segmented absorbers 195 am insulated, not shown.
Direct sunlight
entering the window is concentrated to a focal band para:!lel to the absorber
segments. The focal
band moves as the sun moves in the sky. The collector employs a series of
actuators (not shown)
to route heat transfer fluid to only those absorbers receiving sufficient
amounts of sunlight.
The higher light intensities and reduced active absorber areas of the
concentrating
collector, shown in Figure 12, result in significant heat capture improvements
over those for a
flat panel of similar aperture area. This is especially true in winter months
where cold outdoor
ambient temperatures greatly increase the parasitic losses which are
proportional to the surface
area of the absorbers. Installing the collector adjacent to a vertical window
also takes advantage
of the low winter sun. The optical performance of the ;,ollector in Figure 12
is highest in the
late autumn and early winter when low sun angles result in concentration
ratios of at least 10x
when averaged over a single absorber. The actual concentration values depend
on the number
of absorber segments and sun angle. A lOx concentration is achieved with eight
absorber
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CA 02466343 2005-04-05
segments and a southerly sun elevation of 25° for a south facing window
in the northern
hemisphere.
The collector in Figure 12 is easily erected within an existing structure to
gather solar
energy during autumn and winter months. This system can extend the use of a
three-season
solarium or glazed patio to the full year. The system can be modular where the
mirror supports,
reflective sheet and absorber assembly can be separated. This modular nature
allows for fast
assembly in the autumn. In the spring, the space is returned to its spring and
summer use. The
mirror can be disassembled for storage. The absorher section can be moved to a
more
convenient location to continue collecting energy in a f.at panel
configuration.
The collector in Figure 12 can tolerate a moderate amount of primary minor
imperfections. Concentration band broadening due to primary mirror curvature
imperfections
may result in illumination of additional absorber segments. Some concentration
band
broadening is inevitable, even with a perfect primary mirror. Sources include
the angular width
of the sun and the incident angle of direct sunlight relative to the optical
axis of the fixed primary
mirror. In cases where the extra broadening results in light covering extra
absorber segments,
the heat transfer fluid is routed to all illuminated absorber segments that
mgt a threshold
temperature. Some energy can be lost especially if there is so much broadening
that no absorber
segments are heated above threshold, but, provided that the concentration band
broadening due
to mirror imperfections is reasonable compared to that o~.'inevitable sources
and the width of the
absorber segments, the system is fairly tolerant to minor imperfections.
Figure 13 shows an inverted version of the solar collector 200 with curved
trusses 201
supporting a primary curved mirror 201 and a secondary minor 207 extending
from the edge of
the aperture towards the absorbers. The performance of the inverted system
typically peaks at
times of year that differ from the peak times for the system in Figure 12. At
a location of 45°
north latitude, the performance for the system in Figw-e 12 peaks in December
and January
while the performance for the inverted system with a 45' tilt in Figure 13
peaks in October and
March.
Under the configuration shown in Figure 13, a significant fraction of the
light with
incidence angles almost parallel to the optical axis of the primary minor 201
is redirected by the
secondary minor 207 to the absorber segments nearest the secondary mirror.
This extends the
range of incidence angles that are concentrated to the absorber segments
nearest the aperture.
The secondary mirror 197 can also be used in the vertica arrangement in F
figure 12.
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Figure 13 shows a series of actuators 210 for controlling the flow of heat
transfer fluid to
different segments in the array of absorber segments 2U5. In Figure 13, each
actuator controls
the flow ofthe heat transfer fluid to a single absorber segment. Temperature
sensors, not shown,
measure the absorber and heat transfer fluid temperatures. The temperature
values are
compared and actuators are opened to permit the flow of heat transfer fluid to
those absorber
segments above some threshold temperature determined by the temperature of the
stored heat
transfer fluid.
Figure 14 shows an array of absorber segments a20 where the individual
segments 222
are individually glazed 221. The individual glazing is used to reduce
convective losses of the
system. The added glazing reduces the thermal conta~~t between the absorbers
and the main
body of air in the cavity. Alternatively, the aperture c,~n be doubly glazed
to isolate the cold
external glazing from the collector cavity. The reduced ~ ;onvective losses
with the extra glazing
layer have to be weighed against the reduced light intensities that result
from the non-ideal
transmittance of the extra glazing layer.
Figure 15 shows the solar concentration levels fir a range of sun angles and
absorber
locations. The calculations were done for an eight sel;ment absorber with a
vertical aperture
as shown in Figures I2. The concentration is highest, from 8 to lOx insolance,
between sun
elevations of 20° and 30°. These angles correspond to noon sun
elevations between the end of
October and mid-February for a location at 45° north latitude. The
concentration drops to
around 4x at the autumn and spring equinox on September 21 and March 21
respectively when
the noon sun is 45° above the horizon. The concentration drops below lx
in the spring and
summer months due to shading by the top of the reflector and increased
reflectivity at the
glazing surfaces due to high incidence angles.
The collector in Figures 12 can be erected such that the aperture is tilted
from vertical.
This shifts the time of year when the system is at peak optical efficiency. A
tilt of 10° away
from vertical will shift the peak efficiency to sun angles between 30°
and 40° with optimal
performance in October and late February / early March The 10° tilted
system has marginally
poorer performance than the vertical system in Figures 1 ~! in December and
January but the peak
performance curve is generally broader than for the ~~ertical system. The
broadened peak
performance curve with tilted collectors can be useful in areas where typical
heating
requirements extend into March and April.
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CA 02466343 2005-04-05
Various changes and variation in the preferred e~r~bodiment of the present
invention have
been described. Other modifications and embodimena of the present invention
that are not
presented here and are obvious to those of ordinary skill in the art are
within the spirit and scope
of the present invention.
20
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Representative Drawing