Thermal solar energy collector

This invention contemplates a solar to thermal energy converter comprising spaced apart light polarizing materials defining a conduit therebetween for the passage of a fluid to be heated, the polarizing materials being positioned with respect to each other, whereby the amount of solar energy transmitted through the collector and hence absorbed by the fluid is controlled. Optionally and preferably, at least one of the light polarizing materials is moveable so that the axis of absorption of the polarizing materials can be adjusted with respect to each other and in reference to collector temperature so that a predetermined amount of light will be transmitted through the device, thereby controlling the temperature within the collector.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to solar thermal energy converters. 
2. Description of the Prior Art 
Numerous devices have been proposed for utilizing solar energy as a source 
of heat, particularly for home heating needs. Commercialization of such 
devices, however, has been inhibited because of the typically high initial 
capital costs of the solar heating systems presently available. 
One approach to reducing costs of solar heating systems involves increasing 
collector efficiency so as to reduce the total number of solar collectors 
required. High efficiency collectors, however, require special energy 
absorbing coatings on the absorber plate and/or plastic heat traps, for 
example, which minimize convection heat losses. One such selective 
absorber coating, for example, is disclosed in U.S. Pat. No. 3,958,554. A 
particularly useful device for preventing loss by thermal convection is 
disclosed in U.S. Pat. No. 4,019,496. These features, on the one hand, 
increase the thermal efficiency of solar collectors employing them but on 
the other hand necessitate that such solar thermal collectors be 
constructed of expensive materials which will sustain not only the high 
operating temperatures but also the significantly high temperatures that 
result as the heat load requirements of the collector system decreases. In 
other words, collectors, and particularly high efficiency collectors, must 
be designed to withstand temperatures and pressures under no flow or 
stagnant conditions, and such a design requires expensive materials of 
construction, and/or means for modulating the temperature within the 
collector. Another approach to reducing the costs of solar thermal systems 
is to fabricate solar collectors from relatively inexpensive materials 
such as plastics. In these instances, protecting the collector against 
thermal damage is also of vital importance. 
One technique proposed for protecting solar collectors from damage that may 
result from excessively high temperatures existing within the collector 
for lengthy periods of time requires the venting of the collector using 
ambient air and thermally actuated valves. U.S. Pat. No. 4,043,317 and 
U.S. Pat. No. 4,046,134 are exemplary of such type of air venting systems. 
Another technique used for protecting solar collectors from thermal damage 
is disclosed in U.S. Pat. No. 4,102,325. This patented system provides the 
heat exchange loop for rejecting excess heat to the atmosphere. 
Yet another technique for protecting the solar collector from the hazards 
of excessively high overtemperatures involves shading or otherwise 
blocking the incident solar radiation from falling on the absorber within 
the collector at predetermined temperature conditions. U.S. Pat. No. 
4,112,918 is illustrative of this technique. Indeed, in this regard, it is 
worth noting that polarizing windows can be employed to reduce, i.e. to 
block, the amount of light transmitted through a window and hence incident 
on the interior of a structure having such a window. An example of such 
polarizing window is disclosed in U.S. Pat. No. 4,123,141. 
Notwithstanding the foregoing technologies, there remains a need for a 
solar heat collector which is not only simple in construction but lower in 
cost, thereby overcoming some of the drawbacks of solar to thermal energy 
converters of the prior art. 
SUMMARY OF THE INVENTION 
Briefly stated, this invention contemplates a solar to thermal energy 
converter comprising spaced apart light polarizing materials defining a 
conduit therebetween for the passage of a fluid to be heated, the 
polarizing materials being positioned with respect to each other, whereby 
the amount of solar energy transmitted through the collector and hence 
absorbed by the fluid is controlled. 
Thus, in one embodiment of the present invention, a solar energy absorber 
is provided comprising spaced apart light polarizing materials between 
which a fluid is passed for heating by absorbed radiation. The axis of 
absorption or plane of polarization of each of the light polarizing 
materials are positioned so that a minimum amount of light is transmitted 
through the structure, thereby assuring for the maximum amount of 
absorption of radiant energy by the fluid to be heated thereby. 
In yet another embodiment of the present invention a solar collector is 
provided having at least two sheets of light polarizing material spaced 
apart from each other. One of the light polarizing materials, however, is 
moveable so that the axis of absorption of the polarizing materials can be 
adjusted with respect to each other and in reference to collector 
temperature so that a predetermined amount of light will be transmitted 
through the device, thereby controlling the temperature within the 
collector.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings and the key feature of the solar collector of 
the present invention, there is provided a solar energy absorber 
comprising spaced apart light polarizing materials which define a conduit 
therebetween for the passage of a fluid to be heated by solar radiation. 
In FIGS. 1 to 4, the spaced apart light polarizing materials are shown as 
sheet materials 11 and 12. The axes of absorption of the polarized sheet 
materials are designated in FIGS. 1 and 2 as arrows 14 and 15, 
respectively. 
It is an important feature of the present invention that the axis of 
absorption of the light polarizing material in the collector of the 
present invention be oriented at a predetermined orientation with respect 
to each other so that a maximum and a minimum light transmission through 
the structure can be effected. Thus, in the embodiments shown in FIGS. 1 
and 2, the axes of absorption 14 and 15 of the light polarizing material 
11 and 12 are substantially stantially at right angles to each other, 
thereby minimizing the amount of light that will be transmitted through 
the panels, thereby maximizing the amount of energy that will be absorbed 
by the fluid in the space between the light polarizing materials. 
In the embodiment shown in FIG. 2, a flat plate solar to thermal energy 
converter includes a generally rectangular frame 16 having upwardly 
extending side walls 17 and end walls 18. Any material can be used in 
fabricating the rectangular frame; however, it is particularly preferred 
in the practice of the present invention that the rectangular frame be 
formed from a lightweight sheet material, such as sheet metal. However, 
other materials having the requisite structural strength can also be 
employed. 
The solar to thermal energy converter 10 includes a cover plate 19 which 
serves to reduce heat loss as well as provide protection for the light 
polarizing materials within the collector. The cover plate is made of any 
material which is generally transparent to solar radiation. Typically 
cover plate 19 is made of glass or clear plastic. As is shown in FIG. 2, 
at least the bottom surface of the collector 10 is provided with an 
insulating material such as polyurethane foam insulation 20. Optionally 
the side walls may also be insulated with appropriate insulating material. 
Within the solar to thermal energy converter 10 are included two spaced 
apart light polarizing materials defining a conduit therebetween for the 
passage of fluid. The light polarizing materials are commercially 
available, and they can be fabricated from glass and plastics, for 
example, by well-known techniques. Consequently, the fabrication of the 
light polarizing materials does not constitute a part of the present 
invention. It is important, however, that these light polarizing materials 
11 and 12 have their axes of absorption 14 and 15 arranged at a 
predetermined position with respect to each other so as to affect the 
amount of solar radiation that is transmitted through them. Thus, in the 
embodiment shown in FIG. 2, the light polarizing materials have their axes 
of absorption arranged so as to be substantially perpendicular with 
respect to each other, thereby minimizing the amount of light that is 
transmitted through these light polarizing materials and consequently 
maximizing the amount of energy that will be absorbed by a fluid passing 
in the space between the light polarizing materials 11 and 12. A fluid 
inlet 21 is provided in one end 18 of flat plate collector 10 so as to 
communicate with the space defined by the light polarizing materials 11 
and 12. At the opposite end of the solar to thermal converter 10 is an 
outlet 22 communicating with the conduit defined by the spaced apart light 
polarizing materials 11 and 12. 
Manifold means (not shown) mounted in communication with inlet 21 and 
outlet 22 can be provided to connect a plurality of solar to thermal 
converters 10 in parallel relationship. Alternatively, a manifold or other 
suitable device (not shown) can be provided to communicate with inlet 21 
and outlet 24 to permit the serial connection of a plurality of solar to 
thermal converters 10. 
Optionally and preferably, fan or pump means (not shown) are provided for 
circulating the heat transfer fluid through the inlet of the converter 10 
and outwardly to a source or point of use for such heated fluid. 
Referring now to FIG. 3, there is shown two spaced apart light polarizing 
materials 11 and 12 which are separated by a plurality of separating ribs 
23 which serve to define a serpentine path in the conduit between the 
light polarizing materials 11 and 12 through which the fluid must flow en 
route from the inlet to the outlet of the collector. As will be readily 
appreciated, the inlet 23 and outlet 24 of frame 16 will, of course, be 
sized and positioned to correspond with inlet 25 and outlet 26 of the 
conduit defined by the spaced apart light polarizing materials 11 and 12. 
Referring to FIG. 4, an alternate embodiment of the present invention is 
shown in which the light polarizing materials 11 and 12 are spaced apart 
by spacers 23, thereby defining a tortuous path for the flow of fluid in 
the conduit between the spaced apart light polarizing materials 11 and 12. 
In the construction of FIG. 4, as illustrated, the top protective layer 19 
is also connected to the polarizing material and spaced therefrom by 
connecting ribs 27. This unitary construction shown in FIG. 4 offers 
significant handling and manufacturing advantages. 
In the construction illustrated in FIG. 5, the light polarizing materials 
41 and 42 of the vacuum jacketed tubular collector 40 define a space 
therebetween which serves as a conduit for the flow of material to be 
heated shown generally by the dotted lines 43. As can be seen in FIG. 5, 
the axes of absorption 44 and 45, respectively, of the light polarizing 
materials 41 and 42 are arranged to be substantially perpendicular with 
respect to each other, thereby minimizing the amount of light that will be 
transmitted by the light polarizing material and thereby maximizing the 
amount of energy that will be absorbed by the fluid flowing through the 
conduit defined by the spaced apart light polarizing materials 41 and 42. 
As is shown in FIG. 5, such typical tubular solar to thermal energy 
converters also include an external glass tubular vacuum jacketed cover 
46. 
In the foregoing devices, the spaced apart light polarizing materials are 
arranged at a predetermined fixed angle of orientation with respect to 
each other; however, as indicated herein the present invention also 
contemplates moveable light polarizing materials whereby the axis of 
absorption of the polarizing materials can be adjusted with respect to 
each other so as to affect the amount of radiant energy that is adsorbed. 
In this manner the temperature within the collector can be modulated or 
controlled. For example, in FIG. 6 the spaced apart light polarizing 
materials are shown as circular sheet materials 51 and 52. The axes of 
absorption of the polarized sheet materials are designated by arrows 54 
and 55. Using a temperature sensing means (not shown) and means (not 
shown) for rotating at least one of the polarizing materials, the plane of 
polarization of the polarizing materials can be adjusted with respect to 
each other so that the amount of light that will be transmitted through 
the device can be varied continuously from a minimum to a maximum and vice 
versa. Rotation of the light polarizing materials, of course, will be 
performed in response to the temperature within the collector thereby 
serving to modulate the temperature in the collector. 
In the embodiment shown in FIG. 7, the spaced apart light polarizing 
materials 61 and 62 each comprise a plurality of strips 61a, 61b, 61c etc. 
and 62a, 62b, 62c, etc. in which the axis of absorption (designated by 
arrows 64, 65, 66 and 67) in each adjacent strip is different, and 
preferably at right angles to the axis of absorption in the preceeding 
strip. By lateral movement of at least one of the polarizing materials in 
the direction indicated by arrow 68 results in the positioning of the 
strips in each of the two spaced apart polarizing materials with respect 
to each other so that a predetermined amount of light will be transmitted 
through the solar collector having the polarizing materials thereby 
affecting the amount of energy that is absorbed by the fluid contained in 
the collector. 
In constructing a solar collector employing this embodiment of the present 
invention, it is preferred to secure one of the polarizing materials in a 
fixed position and to mount the second polarizing material spaced apart 
from the other in a slideably moveable position. A temperature responsive 
piston, spring or the like is preferrably used to move the second 
polarizing material relative to the first so that the amount of solar 
radiant energy that is capable of being absorbed will be at a maximum when 
a predetermined low temperature exists in the collector and at a minimum 
when a predetermined high temperature exists in the collector. 
Although the present invention has been described with a certain degree of 
particularity, it is understood that the present disclosure has been made 
by way of example, and that changes in details of structure may be made 
without departing from the spirit thereof.