Note: Descriptions are shown in the official language in which they were submitted.
CA 02704650 2010-05-19
ASYMMETRIC SOLAR COLLECTOR SYSTEM
TECHNICAL FIELD
[0001] The present invention relates to a device and method for collecting
solar energy. In
particular, the present invention relates to an asymmetric solar collector
system with a zero
footprint, comprising a means to minimize water-based interference.
BACKGROUND
[0002] The total amount of energy available through solar thermal collection
is limited by the
size of the available area and the efficiency of the collectors. With moveable
mirrors to track the
position of the sun, parabolic trough solar collectors maximize the energy
collected by using
wide mirror apertures, while minimizing the heat loss with small area
absorbers. Increasing the
amount of energy collected requires increasing the area of the collector
installation. Thus, the
size of the area available for the collectors limits the total amount of
energy collectable for a
given location and installation. Maximizing the available area available for
solar collectors is
therefore paramount to increased energy collection.
[0003] Traditional concentrator designs typically employ symmetric or
"horizontally biased"
asymmetric mirrors where much of the sunlight is reflected up to an absorber.
These systems are
often used in horizontal arrays, where the collectors are arranged spatially
on a horizontal or
near-horizontal surface. In such arrays, the vertical profile of the
collectors is low, or the space
between collectors large, to minimize the amount of light blocked by adjacent
collectors when
the sun is low in the sky. The opposite is true for a vertically mounted array
of solar collector
where the collector's horizontal profile is minimized to reduce the amount of
light blocked by
vertically adjacent collectors when the sun is high in the sky.
[0004] Additionally, symmetrical or horizontally-biased designs deployed in
arrays cover
significant horizontal surface area. An example of a trough-like reflector
covering a large
horizontal surface area is disclosed in W02007109900A1 (Gerwing et al.).
Similarly,
W09857102A1 (Karlsson et al.) disclose an asymmetric parabolic reflector which
is
1
CA 02704650 2010-05-19
horizontally-biased, and thus, requires a large horizontal surface area. These
systems have a large
"footprint". The horizontal surface areas are not commonly available in urban
settings. Tall
buildings, such as apartment blocks, have significantly greater ratios of
vertical surface area to
horizontal area, and thus are limited in their solar energy collection
capability by the symmetrical
or horizontally biased market options. Such locations are optimal for
vertically-biased
collectors.
[00051 One factor related to efficient solar energy collection is the method
of absorption of solar
rays reflected from a parabolic trough. The principle energy gathering
components of parabolic
trough concentrating solar collectors are a parabolic trough mirror
(concentrator mirror) that
reflects sunlight into a narrow line at the mirror focus, and an absorber
placed along the focal
line of the mirror to intercept and absorb the reflected sunlight. The narrow
absorber is required
to span relatively large distances between supports and must have minimal
deflection (sag) due
to gravity in order to stay within the focal region of the concentrator
mirror. Absorber sag in
concentrating solar collectors pulls the absorber away from the focal line to
where it fails to
intercept all of the concentrated sunlight.
[00061 In traditional designs, it is common for absorbers to be constructed of
a single tube or a
multiplicity of tubes (as those found in flat plate solar collectors), with
thermally conductive fins,
or additional structures to cover the focal region of the collector, the
configuration of which is
uniquely determined by each design. The absorber must intercept the maximum
amount of
reflected sunlight at, or near, the focus of the reflector. Often these
absorbers are found to have
either a back plate or structural members that are employed to provide
support. Unfortunately, in
many cases, extra plates and additional structure lead to higher thermal loss
factors due to
increased absorber area, and the necessary temperature gradients to transfer
energy from the tips
of fins to the heat transfer fluid regions. It is recognised that some of
these structural elements
also mitigate losses by inclusion of insulation or geometric features to
reduce the heat loss.
Ultimately, these added complexities and necessary design features result in
additional costs.
[00071 An absorber, heated by concentrated light, loses energy to its
surroundings through black
body radiation, forced and natural convection, and conduction. All of these
terms scale with the
area of the absorber. To maximize efficiency through the absorber area, the
ratio of the absorber
surface area to the light gathering aperture area of the concentrator is kept
to a minimum.
Designing to minimize absorber area is difficult, and reducing the size of the
absorber usually
reduces the structural rigidity of the absorber along its length. Single tube
absorbers made from
2
CA 02704650 2010-05-19
common metals (like steel, copper and aluminium), when supported at distant
endpoints, sag
significantly, with the absorber falling below the lower edge of the focal
line over the absorber
length, especially when heated. This draws the absorber out of the focal
region of the
concentrator mirror. The ratio of absorber length to diameter, for single tube
absorbers, with
most concentrators makes it impossible for the absorber to span large
distances between supports
without significant sag.
100081 While, for example, US 4,156,419; CN20131814; DE19925531; W0199964795;
and
W02008090461A2 all disclose absorbers comprising multiple tubes, none address
the problem
of sagging in a satisfactory manner.
[00091 Another disadvantage of symmetrical or horizontally-biased collector
designs is their
susceptibility to the accumulation of water phases (e.g. solid and/or liquid,
depending on the
ambient temperature) and particulate matter. In particular, mirror surfaces
with near-horizontal
slopes less than 45 degrees from horizontal accumulate different phases of
water and debris,
which impair the specular reflectivity of the mirror(s), and reduce the light
gathering efficiency.
[000101 In some designs, the mirrors employed in parabolic trough and trough-
like
concentrators are unprotected and subject to outdoor environmental conditions.
High reflectivity
mirrors, used in concentrating solar radiation collectors, have surface
temperatures that do not
increase significantly above ambient temperatures. On mirror surfaces having
an upward facing
component to their slope, water can accumulate as either solid or liquid and
may remain on the
surface of the mirror for sustained periods. The presence of water reduces the
specular reflection
of the mirror, lowering the performance of the solar collector. Typical
mirrored collector designs
employ mirrors that reflect 95% of the incident sunlight radiation, leaving
just 5% as heat
absorbed by the mirror surface. The low absorptivity that makes the mirror a
good reflector,
combined with conductive and convective losses, leaves very little residual
energy in the mirror
to the raise the mirror temperature significantly above the ambient
temperature.
[000111 Depending on the season and daily time-dependent location of the sun,
the mirror
may have a primarily upward facing surface for at least part of its curved
surface. Such upwards
facing surfaces may then be subject to accumulation of water. This is
especially problematic in
the winter when the water is often in the solid forms of ice or snow. Once on
the surface, the
area of the mirror that is covered by water is reflectively impaired and no
longer performs as
3
CA 02704650 2010-05-19
designed, with reduced specular reflectivity. Although US 4,015,585 discloses
a solar heating
device for melting snow, it is rather complex and expensive, as it requires
the use of a plurality
of pipes underlying a reflector, and circulating fluid there through.
[00012] There is thus a need for a device and method of solar collection with
minimal
vertical footprint, employing high-efficiency absorbers and means for
minimizing water-phase
accumulation.
SUMMARY
[00013] The present invention addresses the aforementioned issues through the
use of a
vertically-biased solar collector which provides for: zero-footprint; a
shallow collector depth; the
ability to stack collectors; minimization of component of horizontal mirror
surface area; and
proximity to a sold vertical surface area to reduce wind-loading leading to
mechanical simplicity.
[00014] The invention in its general form will first be described, and then
its
implementation in terms of preferred embodiments will be detailed hereafter.
These
embodiments are intended to demonstrate the principle of the invention, and
the manner of its
implementation. The invention in its broadest and more specific forms will
then be further
described, and defined, in each of the individual claims which conclude this
Specification.
[00015] In one aspect of the present invention, there is provided a novel,
vertically-biased
design of a solar collector. The cross-section of the mirror is an asymmetric
section of a
parabola. This asymmetry tilts the aperture vertically relative to designs
using a symmetric
mirror aperture which is perpendicular to the sun's rays. The mirror is
referred to as "vertically-
biased" for these reasons.
[00016] In another aspect of the present invention, there is provided a solar
collector
comprising: a) a reflector assembly for receiving solar radiation; and b) an
absorber positioned
for receiving solar radiation reflected from the reflector assembly, wherein
the reflector assembly
comprises a reflector surface having a longitudinal cross-sectional shape of
an asymmetric
parabola with a vertical bias.
4
CA 02704650 2010-05-19
[00017] In a further aspect of the present invention there is provided a
device for solar
energy collection comprising a plurality of the solar collectors described
above mounted on a
plurality of rows adjacent to a vertical or near-vertical surface.
[00018] In yet another aspect of the present invention there is provided a
solar absorber
having a truss-like structure, comprising two or more tubes and a means of
joining the tubes,
wherein the absorber has a sag to length ratio of about 1/500 or less.
[00019] The present invention comprises a shallow asymmetric parabolic solar
collector.
By vertically biasing the collector mounted on a vertical surface, the depth
of the collector is
reduced. The depth is defined as the distance from the vertical surface, upon
which the collector
is mounted, to the point on the collector furthest from the vertical surface.
The vertical bias of
the present invention requires less space for mounting nearer the support wall
than similar sized
symmetrical or horizontally-biased collectors, while still permitting the
collector to track the sun
year round, preferably for latitudes greater than 23 degrees North or South.
[00020] The present invention provides for a "zero-footprint" design, with no
need for a
horizontal footing and taking only the wall space at a depth for a single row
of collectors when
installed as an array. A deployment of a plurality of rows to create an array
of collectors
requires no horizontal space beyond that of the first row.
[00021] The vertical bias of the collectors provides for a low horizontal
profile, and makes
the collectors ideal for use in vertical arrays. Collector arrays using the
zero-footprint design are
suited, for example, in densely populated areas where horizontal real estate
is at a premium and
vertical real estate is plentiful. The zero-footprint design benefits, for
example, apartment block
deployments due to the stack-ability, and minimal collector depth.
[00022] A vertically-biased mirror increases the fraction of the year when the
entire mirror
has little near horizontal slope, and therefore minimizes the build-up of
efficiency-impairing
water (solid or liquid) and debris on the mirror surface, thus improving
overall operational
efficiency. Mirror life is prolonged with reduced particle accumulation and
longer cycle times
between cleaning.
CA 02704650 2010-05-19
[00023] The solar collector of the present invention is designed to be mounted
on a solid
vertical or near vertical surface. This takes advantage of the proximity to
the solid surface for
buffeting from wind loads. The application to wall mounting means that there
is no need for
wind load protection beyond that inherent in the design. Thus, a design of the
present invention
is light-weight. Infrastructure supports this light-weight device with no
requirement for special
reinforcement. The relative low weight of the present invention, translates
into lower
infrastructure, installation, and material costs.
[00024] The solar collector of the present invention can be integrated into
structural or
architectural features. Examples of these would be but not limited to building
curtain walls,
overhangs, steep roofs, fences, and geographic features.
[00025] The truss absorber of the present invention is designed to be
positioned along the
focal line of the reflected sunlight for a parabolic trough solar collector,
the region where the line
width of the concentrated sunlight is a minimum. The absorber must be
optimized to cover the
focal line height at the concentrator focus while being as small as possible
to minimize heat loss
to the surroundings. Only the smallest amount of design area is apportioned to
the absorber
height to account for sag. With a simple two-tube absorber design built as a
truss, the absorber is
greater and more rigid than a single tube absorber. This reduces the absorber
sag to a tolerable
amount. A simple two-tube absorber can also be easily pre-stressed during
fabrication to counter
the sag and reducing sag effectively to zero when installed. Two tubes are
used in the preferred
embodiment of the present invention; however a similar truss structure of
alternate embodiments
can be made with more than two tubes, if necessary, rigidly joined together to
make a truss
absorber that therefore meets the design requirement and intercepts all of the
reflected sunlight.
[00026] The simple multi-tube truss design of the present invention is also a
fin-less
design. With fins, heat must be conducted along the fins to the channel
containing the heat
transfer fluid. The higher temperature at the edge of the fin raises the heat
loss of the absorber.
The fin-less design results in minimal temperature gradient as the heat is
conducted directly
through the wall of the tube (about a distance of 1mm). In addition, there are
no back plate, nor
extra-structural elements, and therefore no additional loss factors.
[00027] Whereby a standard copper tube has a sag to length ratio of about 1/65
(i.e. the
sag is about 1/65 of the length of the tube), the absorber truss of the
present invention has sag to
6
CA 02704650 2010-05-19
length ratio of about 1/500 or less. For example, a truss absorber of the
present invention spans a
collector's design distance of 2.45 m with minimal sag less than 5 mm peak.
[00028] In addition, the truss absorber can, if desired, be employed to
support a non-
structural features without appreciably increasing the sag. The truss absorber
is preferably
externally finished with a selective coating with high absorptivity at visible
(solar) wavelengths
and low emissivity at thermal infrared wavelengths.
[00029] The solar collector of the present invention further comprises a solar
energy-
absorbing area integrated onto, or adjacent to, the sun facing surface
(mirror) of the solar
collector appliance. During operation, light is passively absorbed as heat by
area(s) with high
absorptivity at solar wavelengths, and conducted to the mirror surface of the
collector. The solar
energy absorbing area provides sufficient heat energy to increase the
temperature of the
surrounding material to evaporate, sublimate, liquefy or otherwise facilitate
removal of water
from the mirror surface, clearing the mirror of optical impairments.
[00030] The solar energy absorbing areas, once integrated onto the mirror's
surface, covers
less than about 5% of the total mirror surface area. This is a considerable
improvement when
compared to the typical loss of energy transfer due to presence of water which
is of the order of
20 to 50% of total mirror surface area. Since water accumulation on vertical
surfaces is usually
minimal, the absorptive material need only be applied to the relatively small
fraction of the
vertically-biased mirror that has a low slope. The 5% coverage of the
absorbent material over
the mirror need only apply to the low slope regions of the mirror.
[00031] The solar energy absorbing areas operate when the solar collector is
in operation.
Raising surface temperature of the solar collector by a few degrees above
ambient temperature is
all that is required to begin the evaporation, sublimation, or liquefaction
process. While the solar
energy absorbing areas are used on vertically-biased mirrors, they are also
applicable to existing
mirrored systems used to collect solar energy. For example, the solar energy
absorbing areas may
be extended to glazed systems flat panels or evacuated glass tubes where
impairments due to
water impact performance of transmitted solar radiation.
[00032] The solar energy absorbing areas may be integrated directly onto a
mirror or
affixed as an appendage using a stable, thermally conductive product.
7
CA 02704650 2010-05-19
[00033] The foregoing summarizes the principal features of the invention and
some of its
optional aspects. The invention may be further understood by the description
of the preferred
embodiments which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[00034] Figures 1 illustrates a side view of a vertically-biased asymmetric
parabolic
trough concentrating solar collector.
[00035] Figure 2 illustrates a front view of a vertically-biased asymmetric
parabolic
trough concentrating solar collector, showing the offset of the absorber to
the lower region of the
collector.
[00036] Figure 3 illustrates a partial isometric view of water accumulation on
the lower
edge of a solar collector.
[00037] Figure 4 illustrates a side view of a stacked deployment of vertically-
biased
collectors.
[00038] Figure 5 illustrates a side view of a stacked deployment of vertically-
biased
collectors during a seasonally high sun angle.
[00039] Figure 6 illustrates an elevation of a truss absorber with periodic
joints between
adjacent tubes.
[00040] Figure 7 illustrates a close-up view of a joint between two tubes.
[00041] Figure 8 illustrates an elevation of a truss absorber with a
continuous joint
between adjacent tubes.
[00042] Figure 9 illustrates a close-up view of a continuous joint between two
tubes.
8
CA 02704650 2010-05-19
[00043] Figure 10 illustrates an end-on cross-sectional view of truss absorber
tubes and
joint.
[00044] Figure 11 illustrates a close-up view along the length of truss
absorber tubes
which are each rolled flat at the mid section.
[00045] Figure 12 illustrates cross-section of rectangular area of the tubes
at the flattened
section.
[00046] Figure 13 illustrates the elevation of two lengths of tubes with mid
sections rolled
flat configured and joined at an angle offset 0 from one another.
[00047] Figure 14 illustrates a cross-section of rectangular area of the tube
at the flattened
section assembled and joined at an angle offset 0 to one another.
[00048] Figure 15 illustrates a cross-sectional view with concentrated
sunlight on one side
of the truss absorber shown figure 10.
[00049] Figure 16 illustrates a cross-sectional view of a truss absorber
supporting a back
plate and providing for insulation and exposed absorber area reduction to
reduce heat loss.
[00050] Figure 17 illustrates a cross-section of a truss absorber encapsulated
in a partially
transparent partial back plate apparatus.
[00051] Figure 18 illustrates a cross-sectional view of a truss absorber
encapsulated in an
apparatus comprised of a clear transparent film or glazing to minimize
convective losses.
[00052] Figure 19 illustrates a partial isometric view of water accumulation
on the lower
edge of a solar collector, with a solar energy absorption area affixed to the
mirror.
[00053] Figure 20 illustrates a plurality of passive solar energy absorption
areas integrated
onto the surface of a solar collector.
9
CA 02704650 2010-05-19
DETAILED DESCRIPTION
[00054] Wherever ranges of values are referenced within this specification,
sub-ranges
therein are intended to be included within the scope of the invention unless
otherwise indicated.
Where characteristics are attributed to one or another variant of the
invention, unless otherwise
indicated, such characteristics are intended to apply to all other variants of
the invention where
such characteristics are appropriate or compatible with such other variants.
[00055] The following is given by way of illustration only and is not to be
considered
limitative of this invention. Many apparent variations are possible without
departing from the
spirit and scope thereof.
[00056] A preferred embodiment of the solar collector of the present invention
is shown in
Figure 1. The solar collector (2000) is vertically-biased, has a zero-
footprint, and can be
vertically stacked.
[00057] The mirror 200 is constrained to follow a parabolic arc between the
upper end
block 300 and lower end block 301. The distance between the upper end block
300 and lower
end block 301 is precisely defined by the cords 400. The angles between the
edges of the mirror
200 and the cords 400 (edge angles) are set by the upper and lower end blocks
300 and 301. The
mirror 200 is fixed to the upper end block 300 and lower end block 301 via the
upper mirror
support 201 and lower mirror support 202. The parabolic shape of the mirror is
achieved by
matching the distance between the upper and lower end blocks 300 and 301, and
the edge angles
of the mirror 200 set by the upper and lower end blocks, with the arc length
of the mirror.
[00058] The asymmetric parabolic shape in the mirror 200 is achieved by making
the edge
angle of the mirror 200 at the upper end block 300 different from the edge
angle of the mirror
200 at the lower end block 301. In the vertically-biased mirror 200 shown in
Figures 1 and 2, the
edge angle of the mirror 200 set by the upper end block 300 is smaller than
the edge angle of the
mirror 200 set by the lower end block 301. This makes the arc length for the
portion of the
mirror 200 between the vertex of the parabola and the upper end block 300
longer than the arc
length for the portion of the mirror 200 between the vertex of the parabola
and the lower end
CA 02704650 2010-05-19
block 301. For noon fall and winter sun angles a below 45 degrees, this
configuration is
vertically-biased in that the cord 400 is closer to vertical than it would be
for a symmetrical
mirror.
[00059] The angle (3 between the sunlight 100 and the normal to the cord 800
is a measure
of the degree of vertical-bias in the mirror 200. (3 is 0 degrees in a
symmetrical parabolic mirror.
When measured in the counter clockwise direction from the normal to the cord
800, vertically-
biased mirrors have positive values of 0. The mirror 200 in Figure 1 has a (3
angle that is
approximately 30 degrees. In a preferred embodiment, the forward vertical-bias
angle (3 ranges
from 5 degrees to 45 degrees, preferably between 15 and 25 degrees; and more
preferably
between 18 and 22 degrees. The solar collector of the present invention tracks
the sun and
maintains the angle 0 during normal light collecting operations.
[00060] The mirror material is that which is typically found in the art. For
example, the
mirror material may be: highly polished anodized aluminium with a surface
protected by a
micro coating that prevents oxidation; or aluminium foil over a substrate; or
aluminized film
over a substrate; a mirrored flexible sheet material (for example, mirrored
polycarbonate,
mirrored acrylic or mirrored fibreglass ); or a mirrored surface or back side
reflectively coated
material (for example, the mirror may be silver, aluminum or even stainless
steel).
[00061] The collector 2000 rotates about the axis of rotation 600 in the
preferred
embodiment to track the incident sunlight. Axis of rotation 600 could be
located differently in
alternate embodiments. The absorber 500 is located at the focal line of the
parabola. The
absorber lies in the focal region and adjacent the axis of rotation in
manifestations of this design
where the absorber is fixed in place. The front/aperture plane of the
collector 2000 is defined by
the cord 400, upper mirror support leading edge 201 and the lower mirror
support leading edge
202.The solar collector is driven by actuator(s) (not shown) that both move
and hold the
apparatus in place. The actuators are controlled by a controller designed to
track the sun's
movement and adjust the collector accordingly.
[00062] Figure 2 illustrates the view looking at the front plane of the
collector 2000. The
absorber 500, in both Figures 1 and 2, is deployed along the focal region of
the mirror 200 to
11
CA 02704650 2010-05-19
intersect the reflected sunlight. The absorber 500 is shown situated in the
lower half of the
collector as shown due to the vertically-biased asymmetry of the collector
mirror 200.
[00063] Figure 3 illustrates a partial isometric view of the vertically-biased
asymmetric
parabolic trough concentrating solar collector mirror 200 and depicts the
accumulation of water
720 on the lower mirror surfaces near the lower mirror support 202 where,
although present, the
amount of water accumulation is minimized with the reduction of near
horizontal surfaces by the
vertical bias of the present invention.
[00064] The vertical stackability of collectors 2000 is shown in Figure 4 with
the present
invention connected via a support structure 2001 to a vertical structure 3000.
Here the deployed
angle of the collector is depicted in an operationally seasonal mode with a
lower sun angle.
[00065] Figure 5 illustrates the collectors 2000 deployed on vertical
structure 3000
depicting a higher sun angle 101 and also depicting minimal shadowing 102 by
the collector that
is physically higher than the row below, where most of the sunlight 103 passes
to the next
collectors in subsequently lower rows. Blockage can be reduced with increased
vertical spacing
between collector 2000 rows, however the high southern (low northern for
southern hemisphere)
component of the sun elevation occur only in the early morning or late
afternoon for latitudes
above 40 North (below 40 South) in the spring and summer. The scenario of
blockage in this
case is not considered a problem since the majority of energy is collected
within a few hours of
mid day when, in the summer season, the southern (northern) component of the
sun elevation is
at its lowest daily elevation for a South (North) facing collector, reducing
the light blockage
during the peak collection period of the day. The slight degradations in
efficiency, due to
blockage at the extreme early and late periods of the day, therefore, impact
only minimally the
total daily energy collection.
[00066] Figure 6 illustrates an elevation of a truss absorber with periodic
joints between
adjacent tubes supported near the end points symbolized by two triangles
(199). The truss
absorber 500 of figure 6 comprises two or more tubes 510 and a means to
rigidly join the tubes
520 (or 550 from figure 8) in such a fashion as to yield a rigid absorber in
the direction between
the tubes 520 when deployed in a horizontal fashion length-wise and stacked
one tube above
another tube in a vertical or nearly vertical arrangement as shown.
12
CA 02704650 2010-05-19
[000671 A gap 610, of a preferred embodiment of the present invention is shown
in Figs. 7
and 10, between tubes 510 or 560 creates separation at the absorber ends to
allow for adaptors to
be fitted to the tubes to establish mating interconnection with additional
absorbers or system
plumbing. This gap also permits fixing points to be established between
adjacent tubes along the
truss' length. These fixing points enable ease of attachment of sensors, back
plates, or full
encasement coverings. An alternate embodiment may not include the gap 610,
securing the
tubes to one another without a gap 610.
[000681 Detail 520 and 550 from figures 6 through 9 are any material capable
to be
employed as a rigid means of attaching tubes and maintain rigidity beyond
temperatures of a
minimum of 25 C. Non-limiting examples include solder (e.g. melting
tin/antimony between the
two tubes), brass (e.g. the process of brazing), or a suitable high
temperature epoxy. Details 520
and 550 are attached to the tubes by conventional means, for example (but not
limited to)
welding, soldering, epoxy, or a combination thereof. Details 520 and 550 are
not applied within
about 0.5% to about 10%, preferably about 1%, from the ends of the tubes 510
to avoid
interference with the means of connecting the tubes to other systems.
[000691 Another form of tubes used to form a truss as introduced in figure 6
are shown in
figures 11 through 14. Here the tubes 510 have been transformed to become
partially flattened
tubes 560 giving a tube an approximately elliptical or rectangular profile for
most of the tube's
functional length. The tubes are not so flattened as to restrict or stop the
flow of heat transfer
fluid within the tube. These tubes are also not flattened within about 0,5% -
10%, preferably
about 1 % from the ends of the tubes in order to facilitate means of
connecting to other systems.
In Figs. 11-14, use of partially-flattened tubes yields an even stronger truss
in the direction
between the two tubes (vertical).
[000701 Figure 12 shows a cross-sectional view of the truss absorber 410 with
the
flattened tubes where the elongated widths of both tubes 560 are aligned
vertically. This truss
410 configuration yields a stronger truss 410 in the vertical direction than
that of truss 500.
[000711 Figures 13 and 14 show an application of the tubes 560 forming truss
415 where
the wider width dimension of one tube is aligned vertically and the wider
width of the second
tube is not aligned vertically but rather at an offset angle 0 to the first
tube.
13
CA 02704650 2010-05-19
[00072] A truss configuration 415 of Figs. 13 and 14 employs two tubes (560)
vertically
adjacent to each other to provide the strength to resist sagging, while the
second more
horizontally-biased tube 560 at and offset angle 0 to the first tube meets the
design requirement
to occupy the focal region and absorb the concentrated sunlight. Conversely
for a similar
horizontally biased arrangement, application of truss absorber 500 or 410
would not benefit from
the strength of the truss 415 configuration. Employing truss absorbers 500 or
410 to a horizontal
configuration, as this in 415, would result in "sag".
[00073] Concentrated sunlight 570 (Fig. 15) is reflected to the `front' face
of the truss
absorber 500 where it is intercepted. Concentrated sunlight is incident upon
roughly 50% of the
absorber surface. Absorbed energy is efficiently conducted through the tubing
walls to the
working fluid. Direct sunlight 580 strikes roughly 50% of the absorber 500
area on the `back'
face of the truss. The truss absorber in this case can be any of the preferred
embodiments of 500,
410 or 415, absorber 500 embodiment is shown for illustration here.
[00074] A non-structural back plate 590 (figure 16) may be added to the design
to improve
efficiency. The truss absorber 500 in this case is fully capable of supporting
the back plate. To
help minimize losses, insulation 595 can be added to the design between the
truss absorber and
the back plate. The back plate 590, while itself continuous end-to-end
following the absorber, is
attached only periodically along the length of the truss to minimize
conduction of heat away
from the truss absorber to the back plate. The truss absorber in this case can
be any of the
preferred embodiments of 500, 410 or 415, absorber 500 embodiment is shown for
illustration
here.
[00075] An apparatus 620 of Fig. 15 encapsulates the truss for its entire
length and is fully
supported by the truss absorber 500. This apparatus 620 can be added to the
design to reduce
convective and radiation losses at both the front, where an optically
transparent covering 630
transmits concentrated sunlight to the absorber, and the back, where a plate
640 shields the
absorber from forced convection. The apparatus enshrouds the truss design and
is attached only
periodically along the length of the truss to minimize conduction of heat to
the apparatus, away
from the absorber. The apparatus 620 can also be insulated 595 on the back
side.
[00076] Figure 18 shows optically transparent apparatus 650 encapsulating the
truss along
the truss' length. This embodiment permits sunlight, both reflected from the
concentrator mirror
14
CA 02704650 2010-05-19
570 and directly from the sun 580, to strike the absorber while minimizing
convective heat
losses. The truss absorber in this case can be any of the preferred
embodiments of 500, 410 or
415, absorber 500 embodiment is shown for illustration here.
[00077] Figure 19 shows a partial isometric view of the lower edge of the
mirror of a
concentrating solar collector's mirror surface 200 with a significant
component of upward facing
surface area and having depicted herein the accumulation of water 720 on the
surface. Passive
solar energy absorption area 900 is adjacent to the mirror and affixed to the
mirror in a
thermally conductive fashion.
[00078] Figure 20 shows a partial isometric view of the concentrating solar
collector's
mirror surface 700 with a significant component of upward facing surface area
and having
depicted herein the accumulation of water 720 on the surface. A plurality of
passive solar energy
absorption areas 730 is integrated onto the surface to distribute the heat
over the primarily
horizontal region of mirror surface. Heat is conducted away from the
absorption areas via the
mirror material. The preferred embodiment of the thermally absorption areas
730 are not limited
to circular or oval shapes, but could be realized in any pattern, such as a
matrix of small dots,
linear areas running parallel to the straight edge of the mirror 740, or
vertical linear stripes
perpendicular to the straight edge of the mirror 740. The surface area of
mirror to be integrated
with the solar energy absorption area shall not exceed 5% of the total mirror
area on the portion
of the mirror that is susceptible to accumulation of water. For a vertically-
biased mirror this is
the lower portion of the mirror, for a symmetrical or horizontally biased
mirror this absorbent
area is applied to the entire mirror surface.
[00079] A matrix of thermally absorptive `dots' or islands or a strip may be
applied via a
spraying process directly to the surface requiring heating. Alternatively, a
strip of thermally
absorptive material may be placed adjacent to and bridged thermally to a
surface which will
benefit from the heating.
[00080] Examples of the thermally absorptive material include, but are not
limited to:
black paint; highly-absorptive, low-emissive coating material; anodizing of a
thermally
absorptive compound; film; etching, or a combination thereof. The thermally
absorptive material
raises the temperature a few degrees above ambient to start the process of
liquefaction,
sublimation or evaporation.
CA 02704650 2010-05-19
=
CONCLUSION
[000811 The foregoing has constituted a description of specific embodiments
showing how
the invention may be applied and put into use. These embodiments are only
exemplary. The
invention in its broadest, and more specific aspects, is further described and
defined in the claims
which now follow.
[000821 These claims, and the language used therein, are to be understood in
terms of the
variants of the invention which have been described. They are not to be
restricted to such
variants, but are to be read as covering the full scope of the invention as is
implicit within the
invention and the disclosure that has been provided herein.
16
