Title:
SYSTEM AND PROCESS FOR USING SOLAR RADIATION TO PRODUCE ELECTRICITY
Kind Code:
A1


Abstract:
A system for capturing solar radiation at a variable rate and providing heat at a constant rate to an electrical generating station is described. The system uses a thermal storage component that includes two or more thermal storage zones to coordinate the rate and quantity of heat delivered to the generating station.



Inventors:
Addie, Andrew R. (Stow, OH, US)
Sherman, Daniel C. (Hudson, OH, US)
Warner, Dean A. (Kent, OH, US)
Application Number:
12/577222
Publication Date:
04/15/2010
Filing Date:
10/12/2009
Primary Class:
International Classes:
F24J2/34
View Patent Images:
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Primary Examiner:
SHEPPARD, JASON A
Attorney, Agent or Firm:
SAINT-GOBAIN NORPRO (3840 FISHCREEK ROAD, STOW, OH, 44224, US)
Claims:
What is claimed is:

1. A system for using solar radiation to produce electricity, comprising: (a) a solar collector that receives solar radiation at a variable rate, measured as joules per hour, and uses said radiation to heat a thermal transfer fluid; (b) a thermal storage component connected to said collector, said thermal storage component comprising at least a first thermal storage zone and a second thermal storage zone, said storage zones comprise ceramic packing elements, wherein said first zone's heat transfer coefficient per unit volume exceeds said second zone's heat transfer coefficient per unit volume by at least 10 percent; and to (c) an electrical generating station connected to said thermal storage component, wherein said thermal transfer fluid transfers heat at a constant rate, measured as joules per hour, and a constant temperature to said generating station.

2. The system of claim 1 wherein said first zone's specific heat capacity exceeds said second zone's specific heat capacity by at least 10 percent.

3. The system of claim 1 wherein the geometric surface area per unit volume of said first zone's packing elements exceeds said the geometric surface area per unit volume of second zone's packing elements by at least 10 percent.

4. The system of claim 1 wherein said first zone's mass per unit volume exceeds said second zone's mass per unit volume by at least 10 percent.

5. The system of claim 1 wherein said generating station houses an expandable fluid that reversibly converts from a liquid to a gas in response to increases and decreases in the temperature of the expandable fluid, and wherein said transfer of heat to said generating station expands the volume of the expandable fluid which drives said generator.

6. The system of claim 3 wherein said first storage zone's geometric surface area per unit volume exceeds said second zone's geometric surface area per unit volume by at least 15 percent.

7. The system of claim 1 wherein said zones comprise randomly oriented packing elements.

8. The system of claim 1 wherein said system further comprises a supplemental source of heat.

9. The system of claim 1 wherein said system further comprises a thermal equilibration tank.

10. A system for using solar radiation to produce electricity, comprising: (a) a solar collector that receives solar radiation at a variable rate, measured as joules per hour, and uses said radiation to heat a thermal transfer fluid; (b) a thermal storage component connected to said collector, said thermal storage component comprising at least a first thermal storage zone and a second thermal storage zone, said storage zones comprise ceramic packing elements wherein the individual thermal conductivity of said first zone's packing elements exceeds the individual thermal conductivity of said second zone's packing elements by at least 10 percent; and (c) an electrical generating station connected to said thermal storage component, wherein said thermal transfer fluid transfers heat at a constant rate, measured as joules per hour, and a constant temperature to said generating station.

11. The system of claim 10 wherein the individual mass of said first zone's packing elements exceeds the individual mass of said second zone's packing elements by at least 10 percent.

12. The system of claim 10 wherein the individual heat capacity of said first zone's packing elements exceeds the individual heat capacity of said second zone's packing elements by at least 10 percent.

13. An apparatus, for receiving solar radiation at a variable rate and dispensing heat at a constant rate, comprising: at least a first thermal storage zone and a second thermal storage zone, said storage zones comprise ceramic packing elements, wherein said first zone's heat transfer coefficient per unit volume exceeds said second zone's heat transfer coefficient per unit volume by at least 10 percent.

14. The apparatus of claim 13 wherein said first zone's specific heat capacity exceeds said second zone's specific heat capacity by at least 10 percent.

15. The apparatus of claim 13 wherein the geometric surface area per unit volume of said first zone's packing elements exceeds the geometric surface area per unit volume of second zone's packing elements by at least 10 percent.

16. The apparatus of claim 13 wherein said first zone's mass per unit volume exceeds said second zone's mass per unit volume by at least 10 percent.

17. The apparatus of claim 15 wherein the geometric surface area per unit volume of said first zone's packing elements exceeds the geometric surface area per unit volume of second zone's packing elements by at least 15 percent.

18. The apparatus of claim 14 wherein said first zone's specific heat capacity exceeds said second zone's specific heat capacity by at least 15 percent.

19. The apparatus of claim 13 further comprising a thermal transfer fluid disposed within said storage zones.

20. The apparatus of claim 13 wherein said first thermal storage zone comprises a plurality of pipes having the same inside diameter, each pipe comprising ceramic media disposed therein.

21. The apparatus of claim 13 wherein said first thermal storage zone comprises at least a first pipe having a length to width ratio of at least 5:1, said first pipe comprising packing elements disposed therein, said apparatus further comprising a fluid distribution system connected to said pipe and a fluid collection system connected to said first pipe.

22. The apparatus of claim 13 wherein said zones comprise randomly oriented ceramic packing elements.

23. The apparatus of claim 21 wherein said second thermal storage zone comprises a second pipe having a length to width ratio of at least 5:1, said second pipe comprising packing elements disposed therein, wherein the diameter of said second pipe is at least ten percent larger than the diameter said first pipe, said second pipe connected to said fluid distribution system and said fluid collection system.

24. The apparatus of claim 23 further comprising a third zone comprising a third pipe having a length to width ratio of at least 5:1, said third pipe comprising packing elements disposed therein, wherein the diameter of said third pipe is at least ten percent larger than the diameter said second pipe, said third pipe connected to said fluid distribution system and said fluid collection system.

25. The apparatus of claim 21 further comprising a heat transfer fluid disposed within said first pipe and in contact with said packing elements.

26. An apparatus, for receiving solar radiation at a variable rate and dispensing heat at a constant rate, comprising: at least a first thermal storage zone and a second thermal storage zone, said storage zones comprise ceramic packing elements, wherein the individual thermal conductivity of said first zone's packing elements exceeds the individual thermal conductivity of said second zone's packing elements by at least 10 percent.

27. The apparatus of claim 26 wherein the individual heat capacity of said first zone's packing elements exceeds the individual heat capacity of said second zone's packing elements by at least 10 percent.

28. The apparatus of claim 26 wherein the individual mass of said first zone's packing elements exceeds the individual mass of said second zone's packing elements by at least 10 percent.

29. A process, for using solar radiation to produce electricity, comprising: (a) receiving solar radiation at a variable rate and converting said radiation to heat; (b) within a twenty-four hour period, storing at least twenty-five percent of said heat in a thermal storage component comprising a first storage zone and a second storage zone; and (c) transferring said heat at a constant rate, measured as joules per hour, and a constant temperature to an electrical generating station.

30. The process of claim 29 wherein, within a 24 hour period, step (a) comprises receiving said solar radiation for at least 2 hours and no more than 18 hours.

31. The process of claim 29 wherein step (c) comprises transferring said heat solely from said first thermal storage zone and then solely from said second thermal storage zone.

32. The process of claim 29 wherein step (c) comprises transferring said heat simultaneously from said first thermal storage zone and said second thermal storage zone.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/104,885 filed Oct. 13, 2008.

BACKGROUND OF THE INVENTION

This invention generally relates to the equipment and process used to capture solar radiation at a variable rate, store the radiation as heat and then transfer the heat at a constant rate and temperature. More particularly, this invention is concerned with a solar power plant and a thermal storage component usable in the power plant.

Examples of patents and published patent applications that disclose capturing solar energy and using it to produce electricity include U.S. Pat. No. 4,286,141 and WO 2008/108870.

SUMMARY

Embodiments of the present invention provide the ability to capture solar radiation as it becomes available, convert the radiation to heat and to deliver the heat at a constant rate. The ability to deliver heat at a constant rate enables the reliable production of electricity. In one embodiment, this invention is a system for using solar radiation to produce electricity. The system includes: (1) a solar collector that receives solar radiation at a variable rate, when measured as joules per hour, and uses the radiation to heat a thermal transfer fluid; (2) a thermal storage component connected to the collector; and (3) an electrical generating station connected to the thermal storage component wherein the thermal transfer fluid transfers a constant amount of heat, measured as joules per hour, at a constant temperature to the generating station. The thermal storage component includes at least a first thermal storage zone and a second thermal storage zone. The zones include ceramic packing elements. The first zone's heat transfer coefficient per unit volume exceeds the second zone's heat transfer coefficient per unit volume by at least 10 percent.

In another embodiment this invention is a system for using solar radiation to produce electricity. The system includes: (1) a solar collector that receives to solar radiation at a variable rate, when measured as joules per hour, and uses the radiation to heat a thermal transfer fluid; (2) a thermal storage component connected to the collector; and (3) an electrical generating station connected to the thermal storage component wherein the thermal transfer fluid transfers a constant amount of heat, measured as joules per hour, at a constant temperature to the generating station. The thermal storage component includes at least a first thermal storage zone and a second thermal storage zone. The zones include ceramic packing elements. The individual thermal conductivity of the first zone's packing elements exceeds the individual thermal conductivity of the second zone's packing elements by at least 10 percent.

Another embodiment also relates to an apparatus for receiving solar radiation at a variable rate and dispensing heat at a constant rate. The apparatus includes a first thermal storage zone and a second thermal storage zone. The zones include ceramic packing elements. The first zone's heat transfer coefficient per unit volume exceeds the second zone's heat transfer coefficient per unit volume by at least 10 percent.

In another embodiment, the invention relates to an apparatus for receiving solar radiation at a variable rate and dispensing heat at a constant rate. The apparatus includes a first thermal storage zone and a second thermal storage zone. The zones include ceramic packing elements. The individual thermal conductivity of the first zone's packing elements exceeds the individual thermal conductivity of the second zone's packing elements by at least 10 percent.

Yet another embodiment relates to a process for the capture of solar radiation to produce electricity. The process may include the following steps. Receiving thermal radiation at a variable rate and converting the radiation to heat. Within a twenty-four hour period, storing at least twenty-five percent of the heat in a thermal storage component that includes at least a first storage zone and a second storage zone. Transferring the heat at a constant rate, measured as joules per hour, and a constant temperature to an electrical generating station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a first embodiment of a system for using solar radiation to produce electricity;

FIG. 2 is a schematic drawing of a second embodiment of a system for using solar radiation to produce electricity;

FIG. 3 is a perspective view of an embodiment of a packing element; and

FIG. 4 is a process flow chart.

DETAILED DESCRIPTION

The need to extract heat from a fluid has been recognized for many decades. Procedures and equipment needed to accomplish the same have been developed. In industrial processes, such as regenerative thermal oxidizers, which are used to improve the thermal and therefore economic efficiency of many processes that generate heat which would be wasted if not recovered, the ability to extract heat from a first fluid and transfer the heat to a second fluid has been well developed as demonstrated in the patent literature including U.S. Pat. No. 6,669,562 and U.S. Pat. No. 7,354,879. Regenerative thermal oxidizers are typically designed to receive a heated flowing fluid such as a hot waste gaseous effluent from an industrial process. Due to the controls exerted over the process that generates the effluent, the temperature of the effluent may be maintained within a relatively constant temperature range. The thermal oxidizer receives the effluent and absorbs the heat. The heat is absorbed by directing the hot gas to flow over, around and through the ceramic media that are contained within the oxidizer. The media, which may be referred to herein as packing elements or packing media, are designed to have sufficient mass and surface area to quickly absorb a large percentage of the heat in the fluid. The amount of time needed for the absorption of heat to occur depends upon the type of media used and various other to parameters such as the desired thermal efficiency of the process. A bed of media absorbs heat from a hot fluid and then desorbs heat to a fluid that is cooler than the media. The absorption and desorption of heat is then repeated. The time from the beginning of a first absorption cycle to the beginning of the next absorption cycle may be referred to as the duty cycle. Duty cycles for many regenerative thermal oxidizers may last from a few seconds in one process to several minutes in a different process. Longer duty cycle times may not be feasible because the process that generates the effluent may be a continuously running process and the flow of effluent into the regenerative thermal oxidizer cannot be interrupted for extended periods of time without disrupting the process that generates the effluent.

In contrast to regenerative thermal oxidizers which have duty cycles that typically last less than thirty minutes, power plants that utilize solar radiation stored as heat in a thermal storage component have one duty cycle per day and the duty cycle lasts twenty-four hours. The inventors of this application recognized that this dramatic difference in the length and frequency of the duty cycles of solar power plants compared to conventional regenerative thermal oxidizers requires the creation of unique systems for using solar radiation to produce electricity and thermal storage components that are specifically tailored to the duty cycle of solar power plants.

Solar power plants may be designed to include a solar collector and thermal storage component that are capable of capturing and storing enough solar radiation as heat to provide heat at a constant rate to the electrical generating station for sustained periods of time up to and including twenty-four consecutive hours. The generating station may contain an expandable fluid, such as water, that reversibly converts from a liquid to a gas in response to increases in the temperature of the expandable fluid caused by the transfer of heat to the expandable fluid. The expansion of the generating station's expandable fluid drives the generator which produces electricity. The heat supplied to the to generating station needs to be provided at a constant rate, measured as joules per hour, and at a constant temperature in order to power the turbine. As used herein, the rate at which heat is supplied to a generating station is defined to be at a “constant rate” for a defined period of time if the rate at which heat is supplied in every hour during the defined period of time does not vary more than five percent above or below the average amount of heat supplied per hour during the same period. Similarly, the temperature at which heat is supplied to a generating station is defined to be “constant” for a defined period of time if the temperature at which heat is supplied in every hour during the defined period of time does not vary more than five percent above or below the average temperature during the same period. For example, within a ten hour period, if the average amount of heat supplied to the generating station by the thermal transfer fluid is 10,000 joules per hour at a temperature of 300° C., then the amount of heat supplied in any single hour during the same ten hours cannot be less than 9,500 joules nor greater than 10,500 joules and the temperature cannot drop below 270° C. nor exceed 330° C. If the heat is not supplied to the generating station at a constant rate and temperature, the generator may slow down or speed up an unacceptable amount thereby changing the electrical characteristics of the electricity generated by the generating station.

In some applications, a supplemental heat source may be used to precisely increase the temperature of the thermal transfer fluid to a desired final temperature prior to the thermal transfer fluid flowing into the generating station. The supplemental heat source could be, for example, a natural gas fired burner assembly. Instead of, or in addition to, a supplemental heat source, the thermal transfer fluid may be directed into a large thermal equilibration tank prior to the thermal transfer fluid flowing into the generating station. The function of the thermal equilibration tank would be to moderate swings in the temperature of the fluid by allowing the temperature of the fluid to equilibrate before exiting the tank.

During a twenty-four hour period, the heat supplied to the generating to station may be (a) completely supplied directly from the solar collector; (b) a combination of heat supplied directly from the solar collector and heat from the thermal storage component; (c) completely supplied by heat from the thermal storage component; or (d) a combination of heat supplied by a supplemental heat source and heat directly from the solar collector and/or the thermal storage unit. In a typical twenty-four hour period, which is defined herein as beginning one hour after sunrise, heat supplied to the generating station may be provided by a combination of heat flowing directly from the solar collector and heat which had been captured the previous day and is now flowing from the thermal storage compartment. The period of time during which heat is provided by both the solar collector and the thermal storage component may be referred to herein as the morning transitional period. The morning transitional period begins when heat provided directly from the solar collector begins to supplement heat provided by the thermal storage compartment and ends when the quantity of heat provided directly from the solar collector exceeds the amount of heat needed to power the generating station. The excessive heat is then diverted to the thermal storage component where it may be stored in thermal storage media. The amount of heat captured by the solar collector between mid-morning and mid-afternoon must be sufficient to provide all of the heat needed by the generating station during that period of time while also capturing and storing excess heat in the thermal storage component. Between approximately mid-afternoon and sunset, the heat supplied directly from the solar collector to the generating station may need to be supplemented by heat supplied from the thermal storage component. During this transitional period, the amount of heat from the thermal storage component may need to be gradually increased until all of the heat provided to the generating station flows directly from the thermal storage component. Beginning at approximately sunset, all of the heat supplied to the generating station must be supplied by the thermal storage component because the solar collector is no longer capturing solar radiation from the sun. From sunrise to approximately mid-morning, heat supplied directly from the solar collector begins to increase and heat supplied from the thermal storage component may be decreased.

To supply heat to an electrical generating station as described above, the solar power plant's thermal storage component may need to absorb and retain large quantities of thermal radiation at a rapid rate for several hours (between mid-morning and mid-afternoon), and then release the heat at a variable rate for a few hours (the afternoon transitional period), a constant rate for several hours after sunset, and a variable rate for another few hours (the morning transitional period). This unusual thermal regime may be difficult to achieve using (a) conventional thermal storage media such as rocks or a bed of ceramic media designed for use in regenerative thermal devices; and (b) a single thermal storage zone such as a vessel filled with homogenous thermal storage media. The inventors of this application have recognized that the demands of a solar power plant's thermal regime can be met by providing a thermal storage component that has at least a first thermal storage zone and a second thermal storage zone provided the thermal storage zones differ in at least one thermal characteristic that allows the rate and/or quantity of heat provided by each zone to be controlled so that the combination of heat from the first storage zone, the second storage zone, the solar collector and the supplemental heat source can be combined to supply the thermal regime described above. A system for capturing and using solar radiation to produce electricity is disclosed in FIG. 1 and described below.

Shown in FIG. 1 is a general schematic of a system that captures and uses solar radiation to produce electricity. The system may include a concentration solar collector 20, thermal storage component 22 and generating station 23. Optionally, supplemental heat source 25 and/or thermal equilibration tank 27 may be inserted between thermal storage component 22 and generating station 23. Thermal transfer fluid, which flows throughout the system, may move from the solar collector 20 to one or more of the thermal storage zones, through the electrical generating station and then back to collector 20. Alternately, the transfer fluid may flow directly from mechanism 20 to generating station 23 and then back to mechanism 20. By-pass line 29 may be used to route the heat transfer fluid around the supplemental heat source and thermal equilibration tank. In one embodiment, a solar collector includes an elongated concave shaped trough lined with a reflective material that focuses the solar radiation onto tubing that contains thermal transfer fluid and is located at the convergence of the reflected thermal radiation. Absorption of the solar radiation by the fluid in the tubing increases the energy content, measured as joules per kilogram, of the fluid. The rate at which the solar radiation is absorbed by the fluid may be measured as joules per hour. When solar radiation is provided by allowing the sun to shine on the reflective material, the mechanism inherently receives the solar radiation at a variable rate throughout a 24 hour period. As used herein, the rate at which solar radiation is received is defined to be at a “variable rate” if the rate at which radiation is received in any hour during a twenty-four hour period of time varies more than fifty percent above or below the average amount of radiation received per hour in the same twenty-four hour period. In a solar application, the rate at which solar radiation is received may vary from zero joules per hour during portions of the night to a maximum rate, which may be kilojoules per hour, during the middle of the day.

As shown in FIG. 1, collector 20 is connected to thermal storage component 22 which may include all of the items shown within dotted line 24. The thermal storage component includes at least first thermal storage zone 26, second thermal storage zone 28 and may include additional thermal storage zones such as third thermal storage zone 30. The thermal storage zones may contain packing elements made from materials, such as ceramics, which are capable of absorbing and desorbing heat. The packing elements may be individual elements that are randomly loaded into a thermal storage zone and are commonly known as randomly oriented packing elements. An example of a suitable randomly oriented packing element is shown in FIG. 3 and described below. Alternately, packing elements known as monoliths may be loaded into a thermal storage zone by manually placing each element beside another element so that the passageways in to one element align with the passageways in the adjoining element. The first thermal storage zone may differ from the second thermal storage zone in at least one of the following thermal or physical characteristics. The first characteristic is heat transfer coefficient per unit volume of the thermal storage zone. When exposed to the same operating conditions, such as the incoming heat transfer fluids having the same temperatures and flow rates, the first zone's heat transfer coefficient exceeds the second zone's heat transfer coefficient by at least 10 percent. For example, if the second zone's heat transfer coefficient is 40 W/m2K, then the first zone's heat transfer coefficient must be at least 44 W/m2K. The second characteristic is the geometric surface area per unit volume of the thermal storage zone. This characteristic is determined by measuring: the geometric surface area of an individual packing element; the number of elements within a fixed volume, such as one cubic meter; and then multiplying the number of elements by the geometric surface area per element. The units of measurement used may be expressed as square meters per cubic meter. The first zone's geometric surface area per unit volume exceeds the second zone's geometric area per unit volume by at least 10 percent. The third characteristic is the thermal storage zone's specific heat capacity. The first zone's specific heat capacity exceeds the second zone's specific heat capacity by at least 10 percent. The fourth characteristic pertaining to the storage zones is mass per unit volume. The first thermal storage zone's mass per unit volume exceeds the second thermal storage zone's mass per unit volume by at lest 10 percent.

Instead of differences between thermal or physical characteristics of the storage zones, the packing elements in the zones may differ in one or more of the following thermal or physical characteristics. A packing element characteristic is the individual mass of a zone's packing elements. The individual mass of the first zone's packing elements exceeds the individual mass of the second zone's packing elements by at least 10 percent. Another packing element characteristic is the individual thermal conductivity of a zone's packing elements. The to individual thermal conductivity of the first zone's packing elements exceeds the individual thermal conductivity of the second zone's packing elements by at least 10 percent. Yet another packing element characteristic is the individual heat capacity of a zone's packing elements. The individual heat capacity of the first zone's packing elements exceeds the individual heat capacity of the second zone's packing elements by at least 10 percent.

A thermal storage component that has two or more thermal storage zones which differ in one of more of these thermal or physical characteristics can be used to supply all or some of the heat to the electrical generating station. Within a single system for using solar radiation to produce electricity, the rates and quantities of heat obtained from two or more thermal storage zones that have different thermal and/or physical characteristics may be coordinated to supply heat at a constant rate and temperature to the generating station. For example, a system may be designed to have a first thermal storage zone and a second thermal storage unit wherein the first storage zone has a relatively small specific heat capacity compared to the specific heat capacity of the second thermal storage zone. The first storage zone may be quickly heated to its maximum specific heat capacity by the solar collector while the second zone may require a much longer time to reach its maximum specific heat capacity. The first zone may then be used to provide a rapid infusion of heat to the thermal transfer fluid if the amount of solar radiation transferred directly from the solar collector should suddenly decline due to clouds temporarily blocking direct sunshine from reaching the collector. In this example, the first storage zone could be used as a quick charge/discharge zone while the second zone, which would take longer to heat to maximum specific heat capacity, would be used to provide a constant rate of heat over a much longer period of time.

Some of the thermal storage component's physical parameters that may be controlled in order to maintain the differences in the thermal storage zones' thermal characteristics described above will now be addressed by comparing thermal storage zones 26 and 28. As shown in FIG. 1, the length of the second thermal storage zone is at least ten percent greater than the length of the first thermal storage zone. If the first and second zones are pipes that have the same inside diameter and are filled with the same randomly oriented ceramic media, then the specific heat capacity of the second zone will be at least 10 percent greater than the specific heat capacity of the first zone. Zones having different specific heats of capacity could also be accomplished by using different thermal storage media in zone 26 versus in zone 28. For example, if the geometric surface area per unit volume of the randomly oriented packing media in zone 28 was 20 m2/m3 and the geometric surface area per unit volume of the randomly oriented packing media in zone 26 was 15 m2/m3, the geometric surface area per unit volume of the randomly oriented packing media of the two zones would differ by more than ten percent of the geometric surface area per unit volume of the randomly oriented packing media of zone 26. Yet another way to achieve the same objective is to construct the thermal storage component so that zone 28 includes a pipe which has a constant inside diameter that is at least 10 percent greater than the diameter of the pipe in zone 26. If the lengths of the pipes are the same, the heat storage media in each pipe are the same and the diameters of the pipes differ by at least 10 percent, then the specific heat capacities of the zones must differ by at least 10 percent. Yet another way to achieve the same objective is to construct the thermal storage components so that the interior volume of zone 28 is equal to the interior volume of zone 26 and the individual heat capacity of the thermal storage media in zone 28 exceeds the individual heat capacity of the thermal storage media in zone 26 by at least 10 percent.

While the basic concept of using a thermal storage component was explained with reference to only two thermal storage zones, the same principles apply to a thermal storage component that includes three or more thermal storage zones. The existence of a third zone would provide even greater flexibility and control over the amount of heat provided by the thermal storage component. In one embodiment of a three zone thermal storage component, the mass per unit volume of thermal storage zone 30 could be made at least ten percent larger than to the mass per unit volume of zone 28 which could be made at least ten percent larger than the mass per unit volume of zone 26.

If desired, the thermal storage component could include more than three zones. Each zone may be connected by a network of valves (not shown) and pipes which function to deliver heat transfer fluid from the solar collector to the zones and may be referred to herein as fluid distribution system 34. Each of the zones may also be connected by a network of valves (not shown) and pipes which function to collect and deliver the heat transfer fluid from the zones to the generating station and may be referred to herein as fluid collection system 36. Delivery pipe 21 allows the heat transfer fluid to flow directly from solar collector 20 to the generating station. Return pipe 32 allows the heat transfer fluid that exits the generating station to return to the solar collector.

With reference to FIG. 1, thermal storage zones 26, 28 and 30 could be three pipes, three vessels or a combination of pipes and vessels. If a pipe is used as a thermal storage zone, the pipe may have an inlet, an outlet and ceramic heat transfer media disposed within the pipe. The media could be randomly oriented or secured within the pipe. An example of media secured to the pipe is one or more ceramic tubes that have been inserted into and fit closely within the pipe so that the tube's smooth outer circumferential surface abuts the interior surface of the pipe and the tube's interior surface is grooved and contoured to facilitate a circular, turbulent flow of transfer fluid through the pipe. Fluid distribution system 34 may be connected to the pipe at the inlet and fluid collection system 36 may be connected to the pipe at the outlet. The pipe may have a length to width ratio of at least 5:1 and a constant inside diameter between the inlet and outlet.

As described above, thermal transfer zones in thermal storage components may use heat transfer media, such as ceramic media, to reversibly store heat. Ceramic media used in heat transfer applications may be designed to accommodate one or more of the following design parameters. First, the thermal conductivity of the ceramic material. Second, the thermal capacity of the ceramic material. Third, the thermal efficiency of the media. Fourth, pressure drop across a bed of the media. Depending upon the heat transfer application, the media may need to be modified to increase one thermal characteristic, such as thermal conductivity. Unfortunately, the modification made to increase the thermal conductivity may inherently and undesirably decrease another one of the media's thermal characteristics such as the media's thermal capacity. In a specific application, such as a regenerative thermal oxidizer, media may be designed to minimize pressure drop due to the high fluid flow through the oxidizer. In contrast, the rate at which the thermal transfer fluid moves through a typical solar collector may be much slower than the rate of fluid flow through a thermal oxidizer. Consequently, heat transfer media that have been designed for use in a regenerative thermal oxidizer may not be appropriate for use in a system that captures and converts thermal radiation to electrical energy.

Shown in FIG. 2 is a second embodiment of a system for using solar radiation to produce electricity. Part numbers in FIGS. 1 and 2 identify the same parts unless otherwise noted. Relative to FIG. 1, FIG. 2 has been modified by connecting fluid collection system 36 to return pipe 32 via extension 38. As indicated by arrow 40, extension 38 allows thermal transfer fluid in one or more of the thermal storage zones to flow back to collector 20 for additional heating by solar radiation before flowing to the generating station. This setup is particularly useful if the quantity of heat in a thermal storage zone has dropped below an acceptable level and the temperature of the thermal transfer fluid needs to be increased without using supplemental heat source 25.

Referring now to FIG. 3, there is shown a perspective view of a first embodiment 60 of a ceramic packing element, also referred to herein as ceramic media and heat transfer media useful in a system of this invention. This particular embodiment includes peripheral wall 62, first end face 64 and second end face 66. The packing element may be manufactured as described in U.S. Pat. No. 6,699,562 which generally discloses the use of any suitable ceramic materials such as natural or synthetic clays, zeolites, cordiertes, aluminas, zirconia, silica or mixtures of these. The formulation can be mixed with bonding agents, extrusion aids, pore formers, lubricants and the like.

Shown in FIG. 4 are process steps for converting thermal radiation to electrical energy. Step 100 represents receiving thermal radiation at a variable rate and converting the radiation to heat. Step 102 represents, within a twenty-four hour period, storing at least twenty-five percent of the heat in a thermal storage component that includes at least a first storage zone and a second storage zone. In step 104, the heat is transferred at a constant rate, measured as joules per hour, and a constant temperature to an electrical generating station. Within a twenty-four hour period of time, the heat may be received for at least 2 hours and no more than 18 hours. In many applications, much more than twenty-five percent of the heat received may be stored in the thermal storage component. For example, forty percent, fifty percent or as much as seventy-five percent of the radiation received may be stored as heat in the thermal storage component. Heat may be transferred to the generating station for much more than two hours, such as eight, ten or twelve hours in a single day. The heat transferred from the thermal storage component may flow solely from the first thermal storage zone to the generating station and then solely from the second thermal storage zone to the generating station or the heat may be transferred simultaneously from both zones.

The above description is considered that of particular embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and are not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents.