Patent Application
20110005514
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.
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.
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
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
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.
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.
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.
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.
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 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.
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.
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 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.
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
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61224780 | Jul 2009 | US | |
| 61293688 | Jan 2010 | US |
