Solar energy collecting structure

The structure disclosed includes an air supported transparent membrane which encloses a solar collector unit. The solar unit includes a solar collector element and two angled walls that support and position the element. The solar collector element receives and absorbs solar radiation and provides heat to a circulating fluid. The support walls extend forwardly and outwardly from the collector element and have reflecting facing surfaces to increase the amount of radiation falling on the element. The walls extend rearwardly of the element to define a chamber in which small rocks are stored to provide heat storage. The transparent membrane creates a greenhouse effect within the chamber defined by the membrane, increasing the operating temperature and thus the conversion efficiency of the solar collector element. Furthermore, the air supported membrane protects the solar collector unit from wind loading. Thus the unit can be lighter than otherwise might be the case and can be pivoted to have an optimum attitude as a function of the time of year. In addition, protection of the solar collector element from wind and rain means that a thin transparent plastic glazing can be and is used in the element.

BACKGROUND OF THE INVENTION 
This invention relates in general to solar collector devices and to solar 
heating and cooling systems employing such devices. 
Solar heating has long been considered a source of energy. But solar heat 
collectors have had poor efficiency. They have not converted enough of the 
incident radiation to heat to warrant the cost of installation. 
Accordingly there has been limited use of solar energy, particularly for 
heating and cooling. 
Solar radiation is converted into usable heat by flat plate solar collector 
elements. These collector elements include a metal plate, usually steel, 
aluminum or copper, which are painted black so as to absorb solar 
radiation. The metal plate is called an absorber plate. A first glass 
plate is spaced about two centimeters in front of this solar radiation 
absorbing surface thereby creating a dead air space which provides 
insulation from loss of heat off the front surface of the metal plate. A 
second glass plate is normally spaced another two centimeters from the 
first glass plate to create a second dead air space. In this fashion, 
convection currents at the front surface of the metal plate are minimized. 
These glass plate substantially increase the efficiency of operation of 
the solar collector element. They also reduce the amount of radiation 
incident on the metal plate. 
As used herein, reference to the "efficiency" of the solar collector 
element or unit or module refers to the percentage of solar radiation 
incident on the solar collector element that is converted to usable heat. 
In one type of solar heating system, the back surface of the metal absorber 
plate forms one surface of a chamber through which air is pumped. This air 
is heated by contact with the absorber plate. Since the air acts to cool 
the absorber plate this type of system is frequently called an air cooled 
collector type of solar heating system. The heated air is then used to 
heat any desired space such as the rooms of a building. In another type of 
solar heating system, called a water cooled collector type of system, 
water pipes are soldered to or otherwise permanently affixed to the back 
surface of the metal absorber plate. These so-called liquid cooled solar 
collectors heat the water which is then used to provide a hot water 
heating system. 
A major object of this invention is to increase the performance of a solar 
collector, meaning specifically to increase the amount of heat transmitted 
to the fluid that is used to carry off heat from the absorber plate. 
As used herein, the term "insolation" refers to the rate of solar radiation 
that falls on the surface of the collector element. Insolation is measured 
in calories/minute-cm.sup.2. An increase of insolation will improve the 
performance of the solar collector system. As indicated above, the term 
"efficiency" refers to a measure of the percentage of insolation which is 
converted to usable heat. Thus, an increase in insolation as well as an 
increase in efficiency will provide an improvement in the performance of a 
solar heating system. 
Accordingly, it is a purpose of this invention to improve both the 
insolation and the efficiency of a solar collector. 
A further purpose of this invention is to increase the performance of the 
solar collector to a point where the fluid being heated can readily be 
brought to a temperature (of at least 90.degree. C.) where the fluid can 
be used to power an absorption air conditioner, a Rankine cycle engine or 
the like. 
The overall performance of the system can also be improved if the solar 
collector structure permits changing the elevation of the solar collector 
unit a few times a year in order to optimize its orientation to incident 
solar radiation and thus increase its average insolation. Accordingly, it 
is a further object of this invention to provide a solar collector unit 
sufficiently light in weight so that its elevation can be changed when 
required. 
It is important that any increase in the performance of the solar collector 
occur in a solar collector design that does not greatly increase the cost 
of the collector or the cost of installation. Accordingly, it is a further 
purpose of this invention to provide an increase in the performance of a 
solar collector at a cost factor which reduces the unit cost of heat 
provided. 
BRIEF DESCRIPTION 
In brief, one embodiment described herein includes an elongated solar 
collector unit having first and second sidewalls that extend, for example, 
20 meters in length and which in cross section form two sides of an 
equilateral triangle. These walls may be four meters wide from the apex 
where they are joined to their respective outer ends. The walls extend 
East and West so that the open aperture defined by the walls optimally 
faces the sun. A solar collector element extends between the two walls and 
runs the length of the walls. This element is oriented at an angle of 
60.degree. to each of the two walls and is positioned about two meters out 
from the apex so that a chamber is defined by the back of the element and 
the two walls. This chamber, in cross section, is an equilateral triangle 
two meters on a side. The facing surfaces of the walls extending forward 
of the collector element are reflective so as to increase the amount of 
solar radiation falling on the collector element. 
This solar unit comprising, the walls and element, is enclosed in an air 
supported transparent plastic membrane which by virtue of a greenhouse 
effect provides an increased temperature environment for the collector 
unit. The membrane also takes the wind loading and thus protects the solar 
unit from forces due to wind. As a consequence, the solar unit is lighter 
and simpler in structure than otherwise would be the case. 
The solar element includes the usual black metallic absorber plate but 
instead of glass panels in front of the absorber plate, the glazing is 
constituted by thin transparent plastic membranes. 
In use, the air to be heated is pumped through a passageway immediately 
behind the absorber plate and is directed into the building to be heated. 
When the building is at a desired temperature, the heated air is 
redirected through the chamber behind the solar element where small rocks 
absorb and store heat. When extra heat is needed, as during the nighttime, 
cooler air from outside or from the building is pumped through the rocks 
to pick up the stored heat for delivery to the building. 
As in any air supported structure, the air supported membrane is stabilized 
by an air pressure maintained within the chamber defined by the membrane 
that is slightly greater than ambient air pressure. The air employed to 
maintain this pressure is preferably exhaust air from the building being 
heated so that maximum benefits of the greenhouse effect are obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIGS. 1 through 4, all of which refer to the same 
embodiment, there is shown a solar collector structure 10 having first and 
second longitudinal walls 12 and 14. The wall 14 rests on a surface such 
as a roof of the building 15 and may be termed a basewall. The wall 12 
extends up from the basewall 14 at an angle of 60.degree. and may be 
called a backwall because the aperture defined by the forward edges 12a 
and 14a of the two walls is generally considered the front of the 
collector unit 10. In a typical embodiment each of these walls 12 and 14 
may be four meters wide from apex 16 to ends 12a or 14a respectively. The 
length of the walls 12 or 14 may be any desired length and they could well 
be twenty-five meters long. 
The solar collector element 18 is deployed at an angle of 60.degree. to 
each of the two walls 12 and 14 and extends the length of the collector 
unit 10. As shown in the very much larger scale drawing of FIG. 4, the 
element 18 is composed of a number of layers. A key operative layer is a 
metal plate 20 which extends the length of the collector unit 10. The 
plate 20 is made of aluminum or steel and is coated black. The forward 
surface 20F of this plate 20 faces the aperture of the collector unit 10. 
The plate 20 receives and absorbs solar radiation and converts it into 
heat. Thus the metal plate 20 is called a solar absorber plate. This plate 
20 is typically four millimeters thick and preferably has a rough surface 
on the back. Immediately behind the plate 20 is a five centimeter deep 
passageway 22 which extends the length of the collector and through which 
the air to be heated is passed. This air, through contact with the back 
surface 20b of the metal plate, picks up heat from the plate 20 and 
carries the heat away to the rooms or area to be heated. As is known, this 
back surface 20b should be somewhat roughened so that there is a degree of 
turbulent flow and maximum transfer of heat from absorber plate 20 to air 
in the passageway 22. Rearwardly of the passageway 22 is an approximately 
five centimeters thick layer of encased glass fibers 23 that provide 
inulation and prevent undue loss of heat from the heated air in the 
passageway 22. In front of the absorber plate 20 there is a first thin 
transparent plastic sheet 24 that extends the length of the collector 10. 
This sheet may be as thin as 0.15 millimeters and may be made of 
polytetrafluoroethylene (Teflon) or polyvinylfluoride (Tedlar). The sheet 
24 is spaced approximately two centimeters from the plate 20 thereby 
providing a dead air space 25 that minimizes loss of heat from the front 
surface of the plate 20. A second thin transparent plastic membrane 26 
spaced another two centimeters in front of the first membrane 24 creates a 
second dead air space 27 to provide further insulation and further 
minimization of air currents that would convect heat away from the front 
surface of the absorber plate 20. These components of the solar collector 
element 18, specifically the glass fiber insulation 23, absorber plate 20 
and membrane 24 and 26 are all mounted in a channel 28. The channel, in 
turn, is mounted on the walls 12 and 14. The base of this channel 28 
together with the inboard half of the walls 12 and 14 defines a chamber 30 
which, in cross section, is an equilateral triangle having a side of two 
meters. The chamber 30 is substantially filled with small rocks 32 
(between one to five centimeters average diameter) which serve as a heat 
storage medium. 
In use, the air to be heated is fed through duct 33 into the passageway 22. 
The air passing along the passageway 22 absorbs heat from the absorber 
plate 20 and is then pumped to the area to be heated. Where the area to be 
heated has been adequately heated, or where not all of the air coming 
through the passageway 22 is required, this heated air is diverted by a 
valving mechanism (not shown) through duct 34 into one end of the chamber 
30. This heated air then passes through the chamber 30 and in so doing 
transfers a substantial portion of its heat to the rocks 32. The rocks 32 
are an adequate inexpensive storage medium for heat that can be used at a 
later point. Then, at night, when the solar collector element 18 is no 
longer providing significant heat, air to be heated can be passed through 
the rock filled chamber 30 to pick up heat from the rocks and to deliver 
it to the space to be heated. 
The inwardly facing surfaces 12s and 14s of the walls 12 and 14 are 
silvered, or otherwise made reflecting, along their width forward of the 
solar collector element 18. Thus, as shown in FIG. 3, these walls surfaces 
12s and 14s serve to reflect additional solar radiation onto the collector 
element 18 during a substantial portion of the day when solor radiation is 
available. Accordingly, the amount of insolation on the collector element 
18 is increased and the performance of the solar collector unif 10 
improved. 
A transparent plastic membrane 36, which may be made of 
polytetrafluoroethylene (Teflon) or polyvinylfluoroide (Tedlar) is 
connected across the forward ends 12a and 14a of the two walls thereby 
enclosing a chamber 38 in the zone immediately in front of the solar 
collector element 18. This membrane 36 is at least one mm thick. This 
chamber 38 is relatively substantial in size, extending not only the 
length of the collector device 10 but having two meter wide walls 12s, 14s 
and approximately a four meter wall along the width of the collector 
element 18. This chamber 38 creates a greenhouse effect thereby 
substantially raising the ambient temperature under which the collector 
element 18 operates and increasing the efficiency of the collector 
element. 
When the outside temperature is low enough so that the exhaust air is 
warmer than can be created by the greenhouse effect, then exhaust air from 
the area being heated is pumped through duct 40 and through chamber 38 to 
provide warm air within the chamber 38 and thus optimize the efficiency of 
the element 18. When the outside temperature is in the range of 2.degree. 
C. or warmer, the greenhouse effect (which adds as much as 15.degree. C.) 
will usually provide a higher temperature in the chamber 38 than can the 
exhaust air. In that case, the outlet duct (not shown) from the chamber 38 
is closed by a valve. Then exhaust air is pumped in only in amounts 
necessary to maintain the air inflated structure. 
As shown, the main transparent membrane 36 has a width greater than the 
straight line distance between the ends 12a and 14a. The exhaust air 
pumped into the chamber 38 is pumped in at a very slight pressure above 
atmospheric (about 2.5 cm of water) so that the membrane 36 is bowed 
outwardly and is stabilized by the air pressure in the same fashion as in 
an air support structure. In this fashion, a very effective support is 
provided for the membrane 36. In addition, the curvature of the membrane 
36 aids in resisting wind loading and increases the stability of the 
structure. 
In part for this reason, a further membrane 42 is connected between the 
apex 16 and the end 12a on the back side of the backwall 12. This membrane 
42 is also sized so that it will bow where shown when the chamber 44 
between the membrane 42 and wall 12 is provided with air under slight 
pressure. This membrane 42, together with the membrane 36, provides 
substantial wind resistance and structural stability so that the walls 12 
and 14 can be extended forward, as shown, to provide the reflective 
surfaces 12s and 14s. This back membrane 42, however, is opaque and may be 
made of a triple membrane of the type used in conventional air support 
structures. The insulation provided by the back membrane 42 together with 
the insulation provided by the air chamber 44 aids in preventing heat loss 
through the backwall 12 thereby further enhancing the performance of the 
collector unit 10. 
FIG. 1 shows inlet ducts 33, 34 and 40 leading respectively into one end of 
the chambers 22, 30 and 38. Comparable outlet ducts are provided at the 
other end but are not shown in the FIGS. 
As used herein, the term "solar collector element" refers to the element 
18, which is shown in detail in FIG. 4, or any similar such element. As 
used herein the phrase "solar collector unit" refers to the solar 
collector element plus any support structure such as the walls 12 and 14 
which is associated with it. As used herein, the phrase "solar collector 
structure" refers to the entire solar collector related structure 
including the membranes that provide the greenhouse effect and resist wind 
loading. 
FIG. 5 represents a second embodiment of this invention which may be 
preferred under certain conditions particularly where wind loading is 
expected to be high. Most of the elements in the FIG. 5 embodiment are the 
same as in the FIG. 2 embodiment and thus the same reference numerals are 
used. In particular, the solar collector element 18 and the sidewalls 
12,14 are the same. However, instead of having two membranes attached 
across the ends of the sidewalls, a single transparent air supported 
membrane 50 encloses the solar collector unit 12, 14, 18. The membrane 50 
is spaced from the ends 12a, 14a of the sidewalls 12, 14 by an amount 
sufficient so that any movement or adjustment of the membrane under wind 
loading will not result in contact between the membrane 50 and the 
sidewalls 12 or 14 thereby minimizing the loading on these sidewalls and 
permitting the construction of a lighter and less expensive unit. 
FIG. 6 illustrates a further embodiment in which the solar unit 12, 14, 18 
is supported on a stand 52 so that it can pivot about an axis 54. In this 
fashion the elevation of the solar unit can be readily adjusted during the 
course of the year to provide an optimum attitude toward the sun. The FIG. 
6 arrangement is feasible because of the lightweight nature of the unit 
made possible by this invention. In the FIG. 6 arrangement the rock 
storage medium is not included because it would be unduly heavy and make 
the pivoting arrangement complex and costly. The pivoting in FIG. 6 may be 
achieved by journalling the stand 52 to a longitudinal support bar (not 
shown) attached to the back surface of the channel 28. 
The solar collector unit is normally and optimally alligned in an East West 
direction, facing South in the northern hemisphere. During the summer when 
the sun rises higher than during the winter, it would be optimum to have 
the solar facing aperture (that is, the distance between the points 12a 
and 14a) elevated more upwardly as is shown in FIG. 6. In the winter, the 
vertical attitude or elevation shown in FIG. 1 or 5 might be preferable. 
This adjustment can be made with the FIG. 6 construction because the 
membrane 50 does not have to be moved to make the adjustment. 
The employment of the membranes 36 and 42 or the overall membrane 50 makes 
it possible to provide a structure which is resistant to wind loading and 
to do so with a unit that is relatively light compared to what otherwise 
would have to be the case. The elimination of glass plates and 
minimization of the size of the framework all tend toward a lighter and 
less costly structure. The lighter solar collector unit makes possible a 
design in which the elevation of the unit to the sun during the course of 
the year can be adjusted at a reasonable cost in equipment and labor. 
The combined effect of the increased temperature of the air in the chamber 
38 and the increased insolation due to the reflective surfaces 12s and 14s 
improves the performance of the system significantly. The improvement is 
sufficient so that there is a wide range of ambient conditions in which 
this solar collector can be used to heat fluid to a temperature high 
enough, i.e. over 90.degree. C., so that the fluid can provide the 
temperature differential required in an absorption air conditioner or to 
run an engine employing the Rankine cycle. 
The membranes, such as the membrane 50, is referred to herein as 
transparent. This is because the present preferred membrane will have a 
light transmission characteristic close to the range of glass. However, it 
should be understood that the light transmission characteristic might well 
be substantially less than that of glass and that the term transparent as 
used in the specification and claims herein simply means that the membrane 
so characterized has a substantial light transmission characteristic. 
There is a trade-off between structural integrity of the membrane and its 
transparency characteristic. Under some circumstances, the improved 
performance of the structure of this invention may permit striking a 
balance in that trade-off which would employ a less transparent but more 
structurally sound membrane. Known membranes which may be usable in the 
device of this invention have a light transmission characteristic that 
ranges from as low as 40% to as high as 98%. Structural considerations 
will normally dictate that the other membrane 36 or 50 will have lower 
light transmissivity than will the glazing membranes 24, 26. 
Although three embodiments of the invention have been illustrated and 
described in detail, the invention can be adapted to a number of different 
arrangements. For example, an air cooled solar collector element 18 has 
been described but the invention can readily be adapted to a water cooled 
type of absorber plate and collector arrangement.