Abstract:
A solar heating apparatus, which includes a panel having one or more layers or a group of such layers, wherein one or more layers among such a group of layers constitutes a transparent medium. The panel includes at least two other layers among the group of layers, which constitute a reflective medium. The panel additionally includes one or more spaces formed between the layers and at least one other space formed between the other layers. A heat transfer fluid can be located within the space between the layers. The heat transfer fluid contains heat-absorbing particles, which are suspended in the heat transfer fluid and subject to a flow-force through the panel in a direction against a force of gravity. The heat-absorbing particles are held in light in the panel via a balance of a flow-force and the force of gravity. The heat-absorbing particles drift to the bottom of the panel when the flow-force stops.

Description:
CROSS-REFERENCE TO PROVISIONAL PATENT APPLICATION 
       [0001]    This patent application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/224,780 entitled, “Solar Heating Utilizing Dynamic Particle Flow Balancing,” which was filed on Jul. 10, 2009 and is incorporated herein by reference in its entirety. This patent application further claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/293,688 entitled, “Solar Heating Utilizing Dynamic Particle Flow Balancing,” which was filed on Jan. 10, 2010 and is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments relate to solar energy and solar heating applications. Embodiments also relate to solar thermal heating panels and associated devices and components. 
       BACKGROUND 
       [0003]    Solar energy is an attractive source of energy for heating, for example, a home or office building. Solar thermal devices are currently employed in some homes and other buildings to heat water. Such thermal solar devices are not usually utilized to heat the house. A major problem with using solar thermal water heating to heat a house is that many panels are required during the winter to produce the heat needed. During the summer, spring and fail, the solar intensities can be much higher, while at the same time there may be not be a need for heat. Another significant problem is that the cost of solar thermal panels for a home heat application is high, since a large number is required. 
         [0004]    Such systems present the significant problem of dissipating the waste heat generated by the solar collectors. One solution is to divert the hot water to a radiator and thus dissipate the heat into the atmosphere. This is, however, an expensive solution. Another solution is to physically cover the collectors. This is not ideal and even dangerous, as it leaves open the possibility that one could forget to cover the collectors or may simply be unable to perform for the task. Another solution involves the use of a motor to automatically turn the panels over. This is also an expensive solution and is prone to breakage due to motor failure or wind drag, which causes wear on the gear assembly. 
         [0005]    Another possible solution is to utilize a black liquid as the solar absorber and pump this black liquid through an insulated clear panel. However, there remains the problem of finding a stable black heat transfer fluid that will not damage the pump and the problems and potential huge mess of a leak. Since this fluid would have to be drained, the safety of the overall heating system is contingent on the pumps or valves not malfunctioning. After many uses, it is quite possible that the black liquid will stain the inside of the panel, leading to original problems of overheating during non-use. In addition, the panels may require a large pump, as a closed-loop circulation is not possible. 
         [0006]    A number of prior art solar thermal heating panels and related systems have been proposed. For example, U.S. Pat. No. 5,657,745 entitled “Solar Heat Collecting Panel,” which issued on Aug. 19, 1007 to Rudolf K. Damminger, utilizes a metallic heat absorption plate rather than a black liquid. U.S. Pat. No. 5,657,745, which is incorporated herein by reference, involves heating the black liquid to a high temperature. This approach, however, results in a number of problems. Any sufficiently insulated collector will attain high temperatures. The problem results in shutting it off when it is desired to stop heating. In this case, there is no method to prevent high stagnation temperatures, which could lead to the circulation fluid boiling, the panels melting, wood catching on fire, etc. 
         [0007]    An example of a prior art solar energy device is disclosed in U.S. Patent Application No. 20070210287, entitled “Transparent Plastic Articles Having Controlled Solar Energy Transmittance Properties and Methods of Making,” by inventor Carlos Guerra, which published on Sep. 13, 2007. U.S. Patent Application No. 20070210287 is also incorporated herein by reference and involves embedding plastic with special properties to prevent the transfer of light at wavelengths not in the visible spectrum so as to reduce the heat transfer. Although the material and article of U.S. Patent Application No. 20070210287 could be used in, for example, airplane windows, but is not suitable for use in solar thermal heating applications. 
         [0008]    An example of a solar heating panel is disclosed in U.S. Patent Application Publication No. 20080236572, entitled “Solar Heating Panel Fabricated From Multi-Wall Plastic Sheets,” by Guenter Schaefer, which published on Oct. 2, 2009. The device disclosed in U.S. Patent Application Publication No. 20080236572, which is incorporated herein by reference, utilizes a multi-wall plastic sheet and a dark material below a central absorber. The problem, again, with such a device is how does one actually turn the panel off? Because the absorber is built into the panel, there is not a practical and safe method or apparatus for turning the panel off when one does not desire to collect heat. This is of tremendous concern when the panel is constructed of plastic, which will melt and deform at high temperatures. 
         [0009]    The cost of heating a home or building is the majority of energy use for the average household. Although solar thermal energy provides an abundant source of energy for heating, unfortunately most households utilize fossil fuels to provide heat. This is unnecessary; as a properly designed house can incorporate solar windows to completely eliminate or dramatically reduce heating costs. Unfortunately our society has been shortsighted in this respect and we have the problem of heating millions of incredibly inefficient homes. The use of plastic as a source of a solar panel for heat generation is attractive because it is an abundant and inexpensive material and is both flexible and lightweight. Glass and metal, the dominate materials in the thermal solar panel market, do not share these attributes. 
         [0010]    A significant problem with plastic, however, is that exposure to high temperatures may degrade or deform the material, rendering the panels useless. To achieve an efficient temperature gain during cold ambient temperatures, the panels must be insulated from thermal loss. However, the insulation can lead to extremely high temperatures within the collector if the heat is not removed. If a pump fails, the electricity goes out, or a blockage forms in the circulation path, the circulation will stop and the temperature will rise in the panels. This is called the stagnation temperature, which can exceed boiling for highly insulated panels. This is a significant problem currently inhibiting the use of plastic as a source of solar heat generation. 
       BRIEF SUMMARY 
       [0011]    The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
         [0012]    It is, therefore, one aspect of the embodiments to provide for an improved solar heat source. 
         [0013]    It is still another aspect of the embodiments to provide for a heating system utilizing dynamic particle flow balancing. 
         [0014]    It is a further aspect of the embodiments to provide for an inexpensive and effective solar thermal panel that can be “turned off” when not in use. 
         [0015]    It is a further aspect of the embodiments to provide for the effective use of low-cost plastics as a medium for solar heat collection. 
         [0016]    The above and other aspects can be achieved as will now be described. A solar heating apparatus is disclosed, which includes a panel having a group of layers, wherein one or more layers among the group of layers constitute a transparent medium. The panel includes at least one other layer among the group of layers, which constitute a reflective medium. The panel additionally includes one or more spaces formed between the layers and at least one other space formed between the other layers. A heat transfer fluid can be located within the space between the layers. The heat transfer fluid contains heat-absorbing particles, which are suspended in the heat transfer fluid and subject to a flow-force through the panel in a direction against a force of gravity. The heat-absorbing particles are held in light in the panel via a balance of a flow-force and the force of gravity. The heat-absorbing particles drift to the bottom of the panel when the flow-force stops. The panel is preferably composed of plastic, although glass and/or other media may be utilized as well for high temperature operations that exceed the working temperature of plastic. Additionally, such an apparatus can include the use of a heat mass, wherein the heat transfer fluid is subject to circulation through the heat mass. The utilized fluid preferably possesses a low freezing point. Additionally, a vacuum or a gas may be located within the space formed between the two layers. 
         [0017]    A solar thermal panel is thus disclosed, which is based on liquid-particle dynamics, and which can reduce the cost of solar thermal panels by 75% or more. When fluid is pumped through the panels they become black and highly absorbent. When fluid is not circulating the panels become highly reflective. The overheating-prevention mechanism allows for the construction of an all-plastic solar thermal panel. A prototype panel has been constructed from commonly available materials to validate the principle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention. 
           [0019]      FIG. 1  illustrates a heating system, in accordance with an embodiment; 
           [0020]      FIG. 2  illustrates a side sectional view of the solar panel depicted in  FIG. 1 , in accordance with an embodiment; 
           [0021]      FIG. 3  illustrates a front view and a side view of the panel depicted in  FIGS. 1-2 , in accordance with an embodiment; 
           [0022]      FIG. 4  illustrates a front view of the panel, in accordance with an embodiment; 
           [0023]      FIG. 5  illustrates a front view of the panel with the circulation pump, in accordance with an embodiment; 
           [0024]      FIG. 6  illustrates a system, which may be employed with the system and components depicted in  FIG. 1-5 , in accordance with an embodiment; 
           [0025]      FIG. 7  illustrates a front view of the disclosed panel, in accordance with an embodiment; 
           [0026]      FIG. 8  illustrates a front view of the disclosed panel, in accordance with an embodiment; 
           [0027]      FIG. 9  illustrates an example of particle panel at various stages of activity, in accordance with an embodiment; 
           [0028]      FIG. 10  illustrates turbulent flow the front side of a particle panel during operation, in accordance with the disclosed embodiments; 
           [0029]      FIG. 11  illustrates laminar flow on the back side of a particle panel during operation, in accordance with the disclosed embodiments; 
           [0030]      FIG. 12  illustrates a schematic diagram of convection cells, in accordance with the disclosed embodiments; 
           [0031]      FIG. 13  illustrates a graph depicting the onset of convection currents, which cause increased heat dissipation in a cell, in accordance with the disclosed embodiments; 
           [0032]      FIG. 14  illustrates an alternative panel design allowing for horizontal placement, in accordance with the disclosed embodiments; and 
           [0033]      FIG. 15  illustrates the design of  FIG. 14  during four times after the panel circulation is turned off, showing how the panel transitions from an absorbing to non-absorbing, in accordance with the disclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate an embodiment of the present invention and are not intended to limit the scope of the invention. Note that in  FIGS. 1-6 , identical or similar parts or elements are generally indicated by identical reference numerals. 
         [0035]      FIG. 1  illustrates a heating system  100 , in accordance with an embodiment. In the configuration of system  100 , a building  109  generally includes a roof  111  upon which a thermal solar panel  101  is located. Light (as indicated by arrows  110 ) impinges on the panel  101 , where it is absorbed as heat by particles  219  suspended in a liquid that flows through the panel  101  in a direction against the force of gravity. Note that the particles  219  can be, for example, but not limited to silicon carbonate particles. 
         [0036]    The liquid is circulated through a heat mass  104 , through a controller  105 , and finally through a circulation pump  106 . A circulation pipe  102  is connected to the panel  101 . Note that an inset  113  is illustrated in  FIG. 1 , which depicts a detailed pictorial view of the circulation pipe  102 . The inset  113  indicates that the circulation pipe  102  includes the use of a secondary pipe  103  as a double walled circulation pipe for heat insulation purposes. It can be appreciated that although a pitched roof  111  is shown in  FIG. 1  with respect to the building  109 , it can be appreciated that the panel  101  may be located on a flat roof. Furthermore it can be appreciated that the panels  101  may be located on a surface other than a building roof, for example, the ground or a dedicated structure. 
         [0037]    The controller  105  can communicate with one or more sensors  142 ,  143  and  144  which are described in greater detail herein. In general, the heat mass  104  can be configured as an environment or object that absorbs and dissipates heat from another object utilizing thermal contact (e.g., either direct or radiant). As heat is collected by the panels, the heat moves into the heat mass  104 , which radiates the heat (as indicated by arrows  108 ) into the building  109 . The controller  105  may be optionally connected to a computer network (e.g., the Internet) via a network connection  107 . 
         [0038]    The controller  105  can be configured as a device that monitors and affects the operational conditions of system  100 . Such operational conditions can include output variables of the system  100 , which may be affected by adjusting particular input variables. For example, controller  105  may be a thermostat for detecting air temperature (e.g., an output variable) and directing the activities of system  100 . The air temperature reading within (and or external) to the building  109  may constitute feedback utilizing by controller  105 , and the air within the house with respect to a desired temperature may be considered a set point value. 
         [0039]      FIG. 2  illustrates a side sectional view of the solar panel  101  depicted in  FIG. 1 , in accordance with an embodiment. The panel(s)  101  can be constructed of, for example, four layers  220 ,  221 ,  222 , and  223 . Layers  222  and  223  are transparent and can be configured from materials, such as, for example, plastic, glass or any another transparent medium. Layer  221  can be configured as a reflective medium composed from a material, such as, for example, a thin polyester film. One example of such a film is Biaxially-oriented polyethylene terephthalate (boPET) polyester film, which can be employed for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation. Biaxially-oriented polyethylene terephthalate (boPET) is known by its trade names Mylar and Melinex. It can be appreciated, of course, that other types of materials may also be utilized in association with or in lieu of biaxially-oriented polyethylene terephthalate (boPET). 
         [0040]    Alternatively or in association with such material, layer  221  may be simply painted white. Layer  220  may be configured from any suitable material that possesses good heat retention properties. The space between layers  222  and  223  can be filled with a gas or a vacuum. The space between  220  and  221  can also be filled with a gas or a vacuum or any insulated material, for example fiberglass or Styrofoam. The space between  221  and  222  may be filled with a clear liquid heat transfer fluid having small heat-absorbing particles  219 . Such a liquid heat transfer fluid preferably possesses a low freezing point. A small lower portion  210  of panel  223  can be painted to provide shade from solar rays. 
         [0041]    Photons  211 ,  212 ,  213  and  214  demonstrate the basic operation of the system  100  and the panel  101 . Photons  211  that hit surface  210  are reflected and provide shade. Photons pass through transparent layers  223  and  222  may either be absorbed by a particle in the fluid  213 , reflected from layer  221  and then absorbed  214 , or else reflected out of the panel  101  and lost  212 . It is desired that the panels minimize the lost photons during operation. Gratings  224 ,  218  act as filters to prevent the particles from circulating through the entire system. Plugs  229 ,  230 ,  227  and  228  prevent liquid from entering the spaces between layers  222 ,  223  and  220 ,  221 . 
         [0042]      FIG. 3  illustrates a front view  301  and a side view  303  of the panel  101  depicted in  FIGS. 1-2 , in accordance with an embodiment. The circulation pipe  102  depicted in  FIG. 1  can be connected to the input port  226  and output port  216  illustrated in  FIG. 2 . Liquid heat transfer fluid flows into the panel  101  as indicated by arrow  209  and out of the panel  101  as indicated by arrow  215 . The flow of fluid can be distributed into multiple vertical channels  333  via an input flow distributor  225 . Liquid is directed from the channels to an output port  216  via an output flow distributor  217 . Particles  219  in the channels are subject to two primary forces: advection or flow as indicated by arrow  331 , and gravity as indicated by arrow  332 . Note that alternatively, the particles  219  may float rather than sink, or in combination therewith. In such an arrangement, the flow pushes the particles down and the buoyancy pushes them back up. Such a configuration allows for the construction of lighter panels and also panels that may become hotter due to increasing time in the collector by providing a snaking path up and down, where the “up” paths utilizes particles that sink and the “down” path utilize particles that float. 
         [0043]      FIG. 4  illustrates a front view of the panel  101 , in accordance with an embodiment. The flow force pushes the particles upward, while gravity pushes the particles downward. As the particles  219  are pushed upward they eventually are blocked by the grating  318 . As particles  219  are accumulated on the grating  438  within a channel  439 , the resistance to flow in the channel  439  increases, which causes a reduction in the flow of fluid through the channel  436 ,  434  and an increase in flow  437 ,  435  in another channel  440 . This results in the particles being pulled down by gravity in channel  439  and upward by flow in channel  440 . The end effect is a distribution of the particles throughout the channels. 
         [0044]      FIG. 5  illustrates a front view of the panel  101  in the absence of circulation provided by the circulation pump  106 , in accordance with an embodiment. When the circulation pump  106  is turned off, the flow through the channels stops, which causes the particles to fall to the bottom of the channels below the shaded surface  210 . As the channels no longer contain particles, the panel no longer absorbs heat. Thus, in the event of a system failure such as a leak in the circulation pipe or panel, a problem with the circulation pump, or a deliberate shut down via the controller, the flow within the system will be shut off and the panels will go into an inactive state, characterized by particles settling below the shaded region  541  wherein heat is not accumulated but rather reflected by area  210 . 
         [0045]    The controller  105  can measure the flow of heat circulation fluid as well as fluid temperature. In addition, the controller  105  may be connected to one or more sensor(s)  142 ,  143 , and  144  that respectively measure the temperature, light radiance, humidity, wind speed, or any other environmental variable, the inside temperature, the temperature of the heat-mass  104 , and so forth. Via the network connection  107 , remote computational services may be accessed, such as, for example, weather prediction services and data. In addition, the controller  105  may output the measured values of the sensors to a remote data collection service (e.g., via the Internet). The controller  105  may modify the flow of the circulation pump  106  to transport heat from the solar panels to the heat mass  104 . 
         [0046]      FIG. 6  illustrates a system  600 , which may be employed with the system  100  and components thereof depicted in  FIG. 1-5 , in accordance with an embodiment. Note that some buildings may already possess a radiant heat system, where hot fluid is circulated through a concrete floor. Such buildings may utilize heat mass  104  as a means of heat delivery. However, many buildings do not posses built-in heat mass. In such a case, heat mass  104  may be constructed, which allows for a number of possibilities for enhancing the effectiveness of the overall system  100 . A drawback of storing heat in a large heat mass is that heat is radiated into the adjacent room and the rate of heat transfer into the room may not be controlled. As the heat mass become larger, this introduces problems due to the ability to accurately predict the weather. For example, if it is predicted that the night will be particularly cold, then the heat mass should be heated to a higher temperature. If this turns out not to be true, then the house  109  will be excessively hot. It is thus appropriate to control the rate of heat transfer into and out of the heat mass. 
         [0047]    This can be accomplished with a thermal mass  605  contained within an insulated enclosure  604 . Heat is transferred into the heat mass though a pipe  606 . A radiator imbedded within the thermal mass  608  is connected to an external radiator  602  through a highly heat-conductive medium. This medium could be passive, for example a solid metal, or active, for example a circulating fluid or heat pump. Heat is radiated into the house via an active heat transfer mechanism. As an example, a fan  601  connected to a motor  605  may blow air through a radiator  602 . The motor  605  may be connected to the controller  105  through an electronic interface  607 . 
         [0048]      FIG. 7  illustrates a front view of the panel  101 , in accordance with an embodiment. The flow force pushes the particles downward, while buoyancy of the particle pushes the particles upward. One can appreciate that this is simply an inversion of the case where the particles sink. As the particles are pushed downward they eventually are blocked by the grating. As particles  701  are accumulated on the grating within a channel  439 , the resistance to flow in the channel  439  increases, which causes a reduction in the flow of fluid through the channel  436 ,  434  and an increase in flow  437 ,  435  in another channel  440 . This results in the particles being pulled up by their buoyancy  702  and downward by flow  703 . The end effect is a distribution of the particles throughout the channels. 
         [0049]      FIG. 8  illustrates a front view of the panel  101 , in accordance with an embodiment. Channels comprising particles that sink  801  and particles that float  802  are arranged in a snaking path  803 . Liquid heat transfer fluid enters the system through input port  226  and exits through output port  216 . Alternating sections of non-buoyant and buoyant particles comprise a path whereby a heat transfer fluid flows. Shaded regions  210  are provided in the condition that the flow stops, thus shielding the particles from solar absorption. Such an embodiment may be used to raise the temperature of the heat transfer fluid to a higher temperature in a smaller panel. 
         [0050]    Note that in some high-temperature embodiments, the disclosed panel(s) can be employed to heat liquid, which is stored in a thermal tank. A home generator, for example, can utilize heat to run a steam engine, which creates electricity that is pumped back into the grid. Steam is condensed and purified water results. Waste water from showers and sinks can be utilized. Such a system can generate house heat, water heat, electricity and also recycle water. 
         [0051]    A further embodiment involves the arrangement of a large number of such panels to pre-heat a fluid like oil, which is then passed through a smaller number of panels made from glass, heating the oil past 100° C. Such a fluid like oil can be then utilized to turn water to steam to run a turbine and generate electricity. The fact that the disclosed panels are inexpensive to produce and relatively durable can result in the production of cheap solar electricity. Currently solar thermal electric plants utilize mirrors focused onto pipes or a central tower. Mirror (e.g., glazed glass) is much more expensive then the disclosed panels, which are constructed from polycarbonate and black particles (e.g., like sand). The key is that one may utilize, for example, 100× the plastic panels to preheat and only utilize glass (which is even less expensive then mirror) to super heat. Construction cost of a plant could be reduced enormously (e.g., perhaps 10× reduction), which would make solar electricity generated in this manner competitive with coal. 
         [0052]    It is interesting to observe that household heating is a problem of the northern and southern latitudes. In this case, during the winter the sun is low on the horizon, which requires that the panels be placed near vertically. Such a configuration is preferable with respect to the some of the disclosed embodiments, as gravity pulls the particles down against the upward flow. The disclosed embodiments solve a significant problem, which is retrofitting millions of inefficient homes to provide heat in an environmentally sound manner. 
         [0053]    Note that heating and cooling account for 63% of the average household energy consumption. Whereas considerable attention is focused on electricity generation, the majority of residential energy is consumed producing or removing heat. The sun produces on average 5 kWh per square meter per day in the U.S. A roof one-fourth covered with solar thermal panels could provide a substantial majority of the heating and cooling for a house. Why does every home not have solar thermal panels covering a significant portion of its roof? Solar thermal panels are surprisingly expensive, ranging from $300 to $1000 per square meter, not including shipping and installation, which are substantial because of the panel weight and size. It would cost from $15,000 to $50,000 to cover ¼ of the average roof with solar panels, not including installation. If the cost of a solar thermal panel could be reduced to $100/sq. meter, it would have significant economic ramifications. The entry barrier to green energy would be removed for most. $1,000 worth of panels could provide most or all energy for hot water, and $5,000 could provide both water and space heat, and potentially cooling in the summer. 
         [0054]    Thus, why are solar thermal panels expensive? Efficient capture of heat when the ambient temperature is low requires insulation. Insulation prevents heat from escaping back into the air once it is captured, but it also causes a problem. If the heat is not removed from the panel, the temperature will rise to very high levels. This is the primary reason modern solar thermal panels are expensive: the panels must be capable of withstanding high stagnation temperatures. If an insulated solar thermal panel could be constructed entirely of cheap thermoplastics, it would cost a tiny fraction of current systems. This is observed in solar heating applications where insulation is not required, for example pool heating. The problem, of course, is that thermoplastics melt if exposed to high temperature. 
         [0055]    Insulated solar thermal panels can be constructed of plastic. What is needed is a completely reliable mechanism to regulate the panel&#39;s temperature. A particle panel provides this function. A particle panel for heating applications is oriented mostly vertical so that it is perpendicular to the sun, which is low on the horizon in the winter for all latitudes that actually need the energy. Liquid flows up through the panel. Small black particles trapped inside the panel via two wire filters are pushed up by the liquid flow, but are also pulled down by gravity. When the liquid is flowing, the particles are pushed against the wire mesh, stabilizing the flow rate to the particles sink rate, thus distributing themselves over the panel and becoming an efficient light absorber. When the flow stops or the fluid is drained back, the particles sink to the bottom, occupying a substantially lower cross-sectional area. A reflective surface behind the panel then reflects the light away and the panel stays cool. The ability to turn off when not in use prevents the panels from exceeding the upper working temperature of thermoplastics, thus allowing the construction of an all-plastic insulated panel. 
         [0056]      FIG. 9  illustrates an example of particle panel  101  at various stages of activity, in accordance with an embodiment. In the embodiment depicted in  FIG. 9 , a prototype particle panel has been constructed from double-wall polycarbonate and acrylic plastic to validate the concept. The panel  101  turns on in approximately 10 seconds at household pressure. The power output was measured on a sunny November day in Santa Fe, N. Mex. and ranged from 750-830 W/m 2 . 45 micron stainless-steel wire mesh was melted into the channels of the plastic sheet, preventing the particles from escaping. 65 micron silicon carbonate particles were used. These particles are manufactured for use in the abrasives industry and are available pre-sifted into a multitude of grain sizes for relatively low cost. 50 pounds of particles were purchased for $120, which is enough for approximately 150 m 2  of panel. Another less expensive source of particles is coal slag, a waste product of coal-fired electric plants. In addition to low cost, a particle panel is likely to be highly efficient. In a traditional solar panel, heat is absorbed onto a solid black plate, where it must travel upward of 10 cm before transferring into water flowing through a pipe. This bottle neck can result in heat build-up, which translates to lower efficiencies due to heat loss. The particle panel design could greatly reduce this thermal conduction bottleneck. Although silicon carbonate has a lower heat conductivity than copper by a factor of 100, for example, the distance that the heat must travel to reach the water is only the particle radius, which is a factor of, for example, 3000 smaller. Thermal conduction thus favors the particle panel by a factor of, for example, 30. Of course, a great deal of further optimization could be done by decreasing the particle size and increasing the particle thermal conductivity, not to mention creating particle mixtures. 
         [0057]      FIG. 10  illustrates a configuration  890  depicting turbulent flow the front side of the particle panel  101  during operation, in accordance with the disclosed embodiments.  FIG. 11  illustrates a configuration  891  depicting laminar flow on the back side of the particle panel  101  during operation, in accordance with the disclosed embodiments.  FIG. 12  illustrates a schematic diagram  893  of convection cells (e.g., Bénard Convection Cells), in accordance with the disclosed embodiments.  FIG. 13  illustrates a graph  895  depicting the onset of convection currents, which cause increased heat dissipation in a cell, in accordance with the disclosed embodiments. 
         [0058]    The prototype particle panel stabilizes at a working pressure. During its on-state, if the panel is tilted slightly convection currents form quickly, with turbulent flow moving the fluid (e.g., water) up the front side and laminar flow down the back side. The existence of turbulent flow on the front side of the panel and laminar flow on the back side could be consistent with an energy-transfer maximization principle. It is well known that turbulence increases the efficiency of heat exchangers. Under an entropy-maximizing assumption 2  the particle-liquid dynamics of the panel will configure for maximal energy transfer rates. Similar emergent phenomena can be observed in Bénard Convection Cells. Bénard convection cells spontaneously appear in a liquid layer when heat is applied from below. Initially all dissipation through the fluid occurs via conduction and molecule to molecule interaction. When the gradient reaches a critical level the transition to highly organized convection occurs. Accompanying this transition is increased heat dissipation. 
         [0059]    If the same self-organizing principles are at work in a particle panel it will have tremendous value. The efficiency of heat transfer requires that the panels keep as low a working temperature as possible. The liquid dynamics of the panel could keep the panels at a temperature that maximizes energy transfer. 
         [0060]    Note that absorption coolers use a heat source to power a cooling cycle rather than electricity. Both absorption air coolers and compression air coolers use a refrigerant with a very low (e.g., sub-zero Fahrenheit) boiling point. In both types, when this refrigerant evaporates or boils, it takes some heat away with it, providing the cooling effect. The main difference between the two types is the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes the gas back into a liquid using a different method that needs only heat, and has no moving parts. The minimum temperature needed to drive an absorption cooler is, for example, 88° C. Solar thermal cooling systems are already being produced. The upper working temperature of polycarbonate is, for example, 115° C., which means plastic particle panels could be used as an energy source for air conditioning. Cooling, both for refrigeration and house space, accounts for 20% of the average American&#39;s energy costs. Whereas the prototype particle panel utilized gravity for continuous operation, a modified design using convection currents could be constructed. This allows the panels to lay horizontal, thus maximizing energy absorption in the summer months. 
         [0061]    An example of a panel design for cooling applications is shown in the configurations depicted in  FIG. 14  and  FIG. 15 .  FIG. 14  illustrates an alternative panel design for panel  101 , which allows for horizontal placement, in accordance with another embodiment. Top and side views of the alternative design of panel  101  are shown in  FIG. 14 .  FIG. 15  illustrates one possible design of panel  101  depicted in  FIG. 14  during four times (t=0, t=1, t=2, and t=3) after the panel circulation is turned off, demonstrating how the panel transitions from an absorbing to non-absorbing, in accordance with the disclosed embodiments. In general, heat transfer fluid is circulated into port IN 1  and optionally into port IN 2  associated with panel  101 . Horizontal, tilted and reflective slats run along the width of the panel  101  depicted in  FIGS. 14-15 . As the fluid is pumped into the panel  101 , a circulation current is created, which distributes particles  219  trapped within the panel  101  to the sun-facing side, thereby collecting thermal energy and transferring this energy into the circulating fluid. When the circulation is shut off, the particles  219  sink between the slats to the bottom of the panel  101 . The reflective slate then provides shade for the particles  219  while reflecting light out of the panel  101 . Such a design allows the panel(s)  101  (e.g., one or more panels) to be oriented with the surface directed vertically, thus maximizing solar adsorption during the summer months when the sun is near vertical and energy for air conditioning systems as needed. 
         [0062]    The cost of a solar system involves more than the cost of the panels. Currently available panels are extremely heavy, at 38 pounds per square meter, for example. This does not include a crating charge, which amounts to $33 per square meter. Shipping in the continental United States ranges, for example, from $0.30 to $1.00 per pound, depending on the distance. It therefore costs from $44.00/m 2  to $71.00/m 2  just to deliver a modern solar thermal panel. A plastic particle panel would be constructed of thin plastics and foam and weigh approximately 1 pound. Its size, weight and superior durability means it can fit in a standard cardboard box and shipped via standard mail. It is conceivable that under efficient manufacturing conditions, the cost to buy and ship a particle panel could be comparable the cost to just ship a traditional panel. 
         [0063]    Once a solar panel has arrived, it must be installed. Conventional solar panels suffer from high stagnation temperatures, which can potentially boil circulating fluid. The high maximal temperatures that can develop require substantially more expensive plumbing systems, including pressure relief values, pressure checks, and copper pipe. The low temperatures and pressures of particle panel could eliminate a significant cost of plumbing, as the panels could be hooked up with plastic tubing and operated at low working pressures. The weight of traditional panels is another big consideration during installation. 
         [0064]    Heating a house with solar energy requires that a system within the house distribute the heat. Many houses contain hydronic heating systems, where hot water is circulated through the floor. In these cases, the conversion is simple and inexpensive. In the absence of a hydronic system, inexpensive space heaters could be installed. The unit would consist of a volume of water (e.g., 50 to 100 gallons or more) stored in an insulated container. Liquid could be pumped from the container to a radiator, where a fan would blow the heat into the room. For a room kept at, for example, 25° C., 100 gallons of water at 50° C. could store 10.6 kWh of energy. This is equivalent to an average 1.0 kW electric space heater operating continuously all night long. Such a system could be constructed very affordable. The area on the roof above a typical room is sufficient to capture the energy needed for heating during the day and storing sufficient energy for the night. If a larger thermal mass is used, 100% solar heating and cooling becomes possible. 
         [0065]    Water has the highest volumetric heat capacity of all commonly used materials and can be added by the home owner for negligible cost. Thermal mass water tanks could be constructed, either in an insulated shed or buried. A cubic volume of 25° C. water 3 meters squared, for example, could store 780 kWh of heat energy. This is equivalent to $100 in electric energy at, for example, 13¢/kWh and is sufficient to ride out a 10-day winter storm. Twenty-two hours of direct sun exposure falling on 50 m 2  of 70% efficient panels could fill the thermal tank. 
         [0066]    The panels disclosed herein (e.g., panel  101 ) can eliminate the cost barrier to green energy for most home owners. The total system cost will be substantially lower than existing solar systems, and the panel efficiency could be much higher. Combined with thermal energy storage, most homes could be converted to 100% solar heating and cooling. 
         [0067]    It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.