Patent application title: SOLAR THERMAL HEATING UTILIZING DYNAMIC PARTICLE FLOW BALANCING
Alex Nugent (Santa Fe, NM, US)
IPC8 Class: AF24J248FI
Class name: Stoves and furnaces solar heat collector particular fluent medium including radiation absorbing material
Publication date: 2011-01-13
Patent application number: 20110005514
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.
1. A solar heating apparatus, comprising:a panel having a plurality of
layers, wherein at least two layers among said plurality of layers
comprise a transparent medium and at least two other layers among said
plurality of layers comprise a reflective medium;at least one space
formed between said at least two layers;at least one other space formed
between said at least two other layers; anda heat transfer fluid located
within said space between said at least two layers, said liquid heat
transfer fluid having heat-absorbing particles therein, said
heat-absorbing particles suspended in said heat transfer fluid and
subject to a flow-force through said panel in a direction against a force
of gravity, said heat-absorbing particles held in light in said panel via
a balance of a flow-force and said force of gravity, said heat-absorbing
particles subject to drifting to a bottom of said panel when said
2. The apparatus of claim 1 wherein said panel comprises plastic and wherein said heat-absorbing particles comprise silicon carbonate particles.
3. The apparatus of claim 1 further comprising a heat mass, said heat transfer fluid subject to a circulation through said heat mass.
4. The apparatus of claim 1 wherein said fluid comprises a low freezing point.
5. The apparatus of claim 1 further comprising a vacuum located within said space formed between said at least two layers.
6. The apparatus of claim 1 further comprising a gas located within said space formed between said at least two layers.
7. A solar heating apparatus, comprising:a solar panel, wherein a plurality of particles are maintained in light via a balance of a flow-force and gravity, such that said plurality of particles fall to a bottom of said shaded area wherein said flow-force terminates.
8. The apparatus of claim 7 wherein said solar panel comprises plastic.
9. The apparatus of claim 7 wherein said solar panel comprises glass.
10. The apparatus of claim 7 wherein said solar panel comprises a plurality of layers, wherein at least two layers among said plurality of layers comprise a transparent medium and at least two other layers among said plurality of layers comprise a reflective medium.
11. The apparatus of claim 10 wherein said solar panel further comprises at least one space formed between said at least two layers and at least one other space formed between said at least two other layers.
12. The apparatus of claim 11 further comprising:a heat transfer fluid located within said space between said at least two layers, said liquid heat transfer fluid having heat-absorbing particles therein, said heat-absorbing particles suspended in said heat transfer fluid and subject to a flow-force through said panel in a direction against a force of gravity, said heat-absorbing particles held in light in said panel via a balance of a flow-force and said force of gravity, said heat-absorbing particles subject to drifting to a bottom of said panel when said flow-force stops.
13. A solar thermal heating system, comprising:a building to be heated;a solar panel, wherein a plurality of particles are maintained in light via a balance of a flow-force and gravity, such that said plurality of particles fall to a bottom of said shaded area wherein said flow-force terminates in order to generate thermal heat for heating said building.
14. The system of claim 13 wherein said solar comprises a plurality of layers, wherein at least two layers among said plurality of layers comprise a transparent medium and at least two other layers among said plurality of layers comprise a reflective medium.
15. The system of claim 14 further comprising:at least one space formed between said at least two layers;at least one other space formed between said at least two other layers; anda heat transfer fluid located within said space between said at least two layers, said liquid heat transfer fluid having heat-absorbing particles therein, said heat-absorbing particles suspended in said heat transfer fluid and subject to a flow-force through said panel in a direction against a force of gravity, said heat-absorbing particles held in light in said panel via a balance of a flow-force and said force of gravity, said heat-absorbing particles subject to drifting to a bottom of said panel when said flow-force stops.
16. The system of claim 15 wherein said panel comprises plastic.
17. The system of claim 15 further comprising a heat mass, said heat transfer fluid subject to a circulation through said heat mass.
18. The system of claim 15 wherein said fluid comprises a low freezing point.
19. The system of claim 15 further comprising a vacuum located within said space formed between said at least two layers.
20. The system of claim 15 further comprising a gas located within said space formed between said at least two layers.
CROSS-REFERENCE TO PROVISIONAL PATENT APPLICATION
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.
Embodiments relate to solar energy and solar heating applications. Embodiments also relate to solar thermal heating panels and associated devices and components.
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.
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.
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.
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.
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.
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.
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.
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.
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.
It is, therefore, one aspect of the embodiments to provide for an improved solar heat source.
It is still another aspect of the embodiments to provide for a heating system utilizing dynamic particle flow balancing.
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.
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.
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.
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
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.
FIG. 1 illustrates a heating system, in accordance with an embodiment;
FIG. 2 illustrates a side sectional view of the solar panel depicted in FIG. 1, in accordance with an embodiment;
FIG. 3 illustrates a front view and a side view of the panel depicted in FIGS. 1-2, in accordance with an embodiment;
FIG. 4 illustrates a front view of the panel, in accordance with an embodiment;
FIG. 5 illustrates a front view of the panel with the circulation pump, in accordance with an embodiment;
FIG. 6 illustrates a system, which may be employed with the system and components depicted in FIG. 1-5, in accordance with an embodiment;
FIG. 7 illustrates a front view of the disclosed panel, in accordance with an embodiment;
FIG. 8 illustrates a front view of the disclosed panel, in accordance with an embodiment;
FIG. 9 illustrates an example of particle panel at various stages of activity, in accordance with an embodiment;
FIG. 10 illustrates turbulent flow the front side of a particle panel during operation, in accordance with the disclosed embodiments;
FIG. 11 illustrates laminar flow on the back side of a particle panel during operation, in accordance with the disclosed embodiments;
FIG. 12 illustrates a schematic diagram of convection cells, in accordance with the disclosed embodiments;
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;
FIG. 14 illustrates an alternative panel design allowing for horizontal placement, in accordance with the disclosed embodiments; and
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 1/4 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.
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.
Insulated solar thermal panels can be constructed of plastic. What is needed is a completely reliable mechanism to regulate the panel'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.
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/m2. 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 m2 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.
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., Benard 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.
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 assumption2 the particle-liquid dynamics of the panel will configure for maximal energy transfer rates. Similar emergent phenomena can be observed in Benard Convection Cells. Benard 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.
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.
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'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.
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 IN1 and optionally into port IN2 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.
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/m2 to $71.00/m2 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.
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.
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.
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 m2 of 70% efficient panels could fill the thermal tank.
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.
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.
Patent applications by Alex Nugent, Santa Fe, NM US
Patent applications in class Particular fluent medium including radiation absorbing material
Patent applications in all subclasses Particular fluent medium including radiation absorbing material