Patent Publication Number: US-2013240188-A1

Title: Method and apparatus for a delayed and prolonged air cooling condensation system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and benefit of U.S. Ser. No. 61/533,551, filed Sep. 12, 2011, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     STATEMENT OF GOVERNMENTAL SUPPORT 
     [Not Applicable] 
     BACKGROUND 
     In electrical power plants, large amounts of latent heat carried by low temperature steam from the steam turbine exhausts needs to be removed and condensed into water to complete the Rankine cycle for electricity generation. Similar situations exist in other heat engines and appliances, such as central air-conditioning systems. Typically, the low quality (temperature) latent heat was removed by the use of a large amount of cooling water, which is a method used by the majority of coal fired power and nuclear power plants. However, this so called “wet-cooling” method consumes extremely large amounts of water, accounting for almost 50% of total industrial water usage and 20% of total water consumption. 
     For water resource scarce areas, “dry-cooling” methods were developed to directly dissipate the latent heat into ambient air without using a lot of water. There are two major types of air-cooling condensation methods, one is direct air-cooling condensation and the other is indirect air-cooling condensation. These two methods are distinguished from each other by whether the heat transfer process occurs between low temperature steam and ambient air directly or through other heat transfer media. 
     The heat transfer efficiency of air-cooling condensation strongly depends on the temperature difference between the exhaust steam and the environment ambient air, and the speed of the air that blows onto the condensation heat exchanger surfaces. To dissipate the latent heat of exhausted steam instantaneously requires a larger temperature difference between the exhausted steam and the ambient air, typically as much as 30° C. to 40° C. in “dry-cooling” methods, and 10° C. to 15° C. in “wet-cooling” methods. Moreover, since the volume heat capacity of the air is almost a thousand times smaller than that of the water, an extremely large amount of cooling air is blown upon the heat exchanger surfaces for the cooling. The large temperature difference between the exhaust steam and the ambient air results in higher exhaust steam pressure. For example, in a typical dry-cooling system, the exhaust steam pressure is typically about 25 to 50 kPa instead of 5 to 7 kPa for a typical wet-cooling system. This exhaust steam pressure increase results in a drop in heat to electricity conversion efficiency for the steam turbine generator. For example, the heat to electricity conversion efficiency would decrease from 40% to 35% when “dry-cooling” is used instead of a “wet-cooling” for a typical 600 MW coal-fire power generator. 
     On the other hand, during a “dry-cooling” process, the heat dissipation rate depends on the surface area of the condenser&#39;s heat exchanger and the wind blowing speed that passes through the heat exchanger surfaces. Due to cost considerations, the heat exchanger&#39;s surfaces cannot be too large otherwise the wind speed has to be very large to achieve effective cooling. According to the aerodynamics, the power consumption of a wind-blowing machine used for dry-cooling varies as the 3rd power of the wind speed it generates. The higher the wind speed it requires, the more electricity it consumes. Therefore, the dry-cooling approach may consume a few percent up to more than 10 percent of the electricity that the same power plant generates. 
     SUMMARY 
     To overcome above mentioned shortcomings of an air-cooling condensation process, it was discovered that it is beneficial to use an indirect air-cooling approach while dividing the cooling process into two time periods or “cycles”: 1) A condensation period where the low temperature exhaust steam transfers its latent heat to a low temperature thermal storage material while being condensed into water, e.g., during a time period when ambient air temperature is relatively high; and 2) A dissipation period where the heat is dissipated from the thermal storage material to the ambient air by air-cooling, e.g., during a time period when ambient air temperature is relatively low. If these two stages are separated in time it is possible to reduce the shortcomings of the above mentioned dry-cooling methods. This two stage (time period) method can also be applied partially, e.g., in certain embodiments, during the high temperature period, only a part of the generated latent heat is stored in thermal storage materials, and dissipated into ambient air during the cool time period; while other part is still dissipated using conventional cooling methods. This is especially useful to modify and improve existing power plants. 
     It is even more beneficial for a concentration solar thermal power (CSP) plant to use a dry-cooling method because in most cases, CSP power plants are constructed in desert areas where water resources are very limited. In this case, a separated two-stage dry-cooling can bring even more advantages compared to the traditional dry-cooling methods because the temperature differences between day and night are normally larger in desert areas than in other locations. 
     The apparatus and methods described herein have been developed in view of the above points. Accordingly, in various embodiments, methods and apparatus are described that provide delayed and prolonged dry-cooling condensation methods, that take the advantage of different ambient air temperatures during the day and night to lower the energy consumption for cooling (e.g., for a wind blower) while decreasing the condensation temperature of the exhaust steam so that the overall thermal to electricity conversion efficiency can be improved for dry-cooling. 
     Let the starting time of the first condensation stage to be t 1 , and the duration of the stage 1 to be Δt 1 ; the starting time of the second heat dissipation stage from the thermal storage media to be t 2 , and the duration of stage 2 to be Δt 2 . If t 1  equals t 2  and Δt 1  equals to Δt 2 , the entire cooling process becomes a normal indirect air-cooling condensation process. For a delayed and prolonged indirect air-cooling condensation, t 2  (the starting time of the dissipation stage) is typically later than t 1  (e.g., at a cooler time of a given day), and in certain embodiments, Δt 2  is not equal to Δt 1 . In this way, effectiveness of the condensation process can be optimized independently from the subsequent heat dissipation process, thereby improving the effectiveness of the air-cooling process. 
     In certain embodiments by taking advantage of the fact that the ambient air temperature during the night is lower than that during the day, one can use low temperature thermal storage materials to store the latent heat of exhausted steam during the day while condensing the turbine exhaust steam into water, and then dissipate the stored thermal energy into the ambient air during the night when the ambient temperature is lower, using a wind blower to drive the ambient air through the packaged thermal storage material surface to release the latent heat stored therein into the environment. In certain embodiments low temperature phase change materials (PCMs) are used to store the latent heat from the exhaust steam (during Δt 1  time period). The stored thermal energy is then dissipated into the ambient air during the night when the ambient air temperature is lower than temperature during the day via wind blower in a pre-determined time duration Δt 2 . 
     In addition, when circumstances require it, one can choose time durations for the condensation stage Δt 1  and the heat dissipation stage Δt 2  so that the heat dissipation rate can be slower than that of a typical indirect dry-cooling system. In certain embodiments one can chose a time duration Δt 2 &gt;Δt 1 . Thus, the exhaust steam condensation temperature can be significantly decreased. It should be noted that for every 10° C. of higher condensation temperature for a steam turbine generator, the heat to electricity conversion efficiency would be lower by 4.5%. This is a very significant loss of efficiency because normally a “dry-cooling” approach raises the condensation temperature up to 30° C. higher than that of a “wet-cooling” approach. 
     In certain embodiments if the delay and prolonged indirect dry-cooling approach described herein is used, in the stage of condensation for the exhausted steam from the steam turbine or other heat appliances, the low temperature exhausted steam transfers its latent heat to the low temperature thermal storage media via an efficient heat exchanger while condensing the steam into water. The exhaust steam condensation temperature (typically a few degrees higher than the low temperature thermal storage material&#39;s phase change temperature) can be set at only a few degrees higher than the ambient air temperature at night. During the heat dissipation stage, the phase change material would have enough temperature difference relative to the ambient air temperature so that the stored latent heat can be dissipated into the environment, as described in detail below. This is how the new approach described herein can lead to an improvement for the heat to electricity conversion efficiency. 
     As described in detail below, the large amount of heat exchange area of our apparatus described herein ensures that the steam can be condensed into water at close to phase change temperature during the condensation stage, and that the stored latent heat can be dissipated into the environment during the night, resulting in a drop of wind speed required for effective cooling. This can reduce the electricity consumption significantly due to the third power relationship between the power needed to drive a wind blower and the wind speed that is created by that blower. 
     Accordingly, in various embodiments, device for steam condensation and delayed dissipation of the heat produced by the condensation is provided. In certain embodiments the device comprises a combined condensation/thermal storage chamber, the chamber comprising: one or more valved ports for receiving steam from a steam source; one or more containers containing a thermal storage material; one or more valved ports for applying a vacuum to the thermal storage chamber; one or more valved ports for introducing ambient pressure air into the chamber; one or more valved ports for removing condensed water from the chamber; and a valve system operably coupling the chamber to a source of ambient temperature air. In this context a valved port indicates that flow of fluid or gas through the port is under the control of one or more valves, however, the valves need not be located at the site of the port and can be remote (e.g., disposed between a vacuum source and a vacuum port, between a steam source and a steam port, and the like). In certain embodiments the one or more containers containing a thermal storage material is a plurality of containers each containing a thermal storage material. In certain embodiments the thermal storage material is a phase change thermal storage material (PCM). In certain embodiments the thermal storage material is a liquid/solid phase change thermal storage material. In certain embodiments the thermal storage material comprises a material selected from the thermal storage materials shown in Table 2 (e.g., Na 2 CO 3 .10H 2 O, and the like). In certain embodiments the phase change material contains glass microfibers or nanofibers. In certain embodiments the device further comprises an apparatus to cause mixing of liquid phase thermal storage material in the containers containing the thermal storage material. In certain embodiments the containers (containing the thermal storage material(s)) are attached to a frame structure (see, e.g.,  FIG. 3 ) and the apparatus comprises a motor configured to cause rotation of the structure and the attached containers. In certain embodiments the one or more valved ports for applying a vacuum to the thermal storage chamber are operably coupled to a vacuum pump. In certain embodiments the one or more valved ports for applying a vacuum to the thermal storage chamber and the one or more valved ports for introducing ambient pressure air into the chamber are controlled by separate valves. In certain embodiments the one or more valved ports for applying a vacuum to the thermal storage chamber and the one or more valved ports for introducing ambient pressure air into the chamber are controlled by the same valve(s). In certain embodiments the valve system operably coupling the chamber to a source of ambient temperature air comprises a butterfly valve (or a flange cover, or other functionally equivalent structure). In certain embodiments the source of ambient air is a fan and/or blower and/or one or more ducts configured to receive ambient wind. In certain embodiments the device is one of a plurality of the devices configured in a parallel configuration. In certain embodiments the one or more valved ports for receiving steam from a steam source are operably coupled to the low temperature steam output from a turbine (e.g., a turbine in a power plant selected from the group consisting of a coal-fired power plant, a gas-fired power plant, a nuclear power plant, and a solar thermal power plant). In certain embodiments the device is sited in a desert or a non-desert region with limited water availability. 
     Also provided are systems for delayed heat dissipation from the condensation of waste steam, said system comprising a plurality of devices for steam condensation and delayed dissipation of the heat produced by the condensation, e.g., as described herein. In certain embodiments the devices are configured in a parallel configuration, e.g., as illustrated in  FIG. 2 . In certain embodiments the system comprises at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 70, or at least 80, or at least 90, or at least 100, or at least 150, or at least 200 of said devices. In certain embodiments the system is operably coupled to the low temperature steam output from a turbine. In certain embodiments the turbine is a turbine in a power plant (e.g., a coal-fired power plant, a gas-fired power plant, a nuclear power plant, a solar thermal power plant, etc.). In certain embodiments the system is sited in a desert or a region with limited water availability. 
     In various embodiments a dry-cooling methods are provided. It will be recognized that the methods, as described herein provide methods of condensing waste steam while delaying heat dissipation from said condensation; and can be used to complete a Rankine cycle at enhanced efficiency. Accordingly, in certain embodiments a dry-cooling condensation method is provided where the method comprises: receiving steam from a source of steam; condensing the steam into water while transferring the latent heat of said steam into the latent heat of a thermal storage material; and dissipating the latent heat from said thermal storage material at a later time when the ambient temperature is lower than the ambient temperature at the time the steam was condensed into water. In certain embodiments the thermal storage material is a phase change thermal storage material (PCM). In certain embodiments the thermal storage material is a liquid/solid phase change thermal storage material. In certain embodiments the thermal storage material comprises a material selected from the thermal storage materials shown in Table 2 (e.g., Na 2 CO 3 .10H 2 O, and the like). In certain embodiments the source of steam is the steam output from a turbine. In certain embodiments the turbine is in a power plant selected from the group consisting of a coal-fired power plant, a gas-fired power plant, a nuclear power plant, and a solar thermal power plant. In certain embodiments the receiving and condensing comprises receiving and condensing during daylight hours. In certain embodiments the receiving and condensing comprises receiving and condensing peak temperature hours (e.g., between noon and 3:00 pm). In certain embodiments the dissipating comprises dissipating the latent heat from the thermal storage material during cooler hours (e.g., the late afternoon, and/or evening, and/or night). In certain embodiments the method is performed using one or more devices for steam condensation and delayed dissipation of the heat produced by the condensation, e.g., as described herein. In certain embodiments the receiving and condensing comprises: opening said one or more valved ports for applying a vacuum to a thermal storage chamber to reduce the ambient pressure in the thermal storage chamber; opening one or more valved ports for receiving steam to introduce steam from a steam source (e.g., a turbine) into the chamber, whereby the steam condenses transferring latent heat of steam into a thermal storage material; and operating one or more valved ports for removing condensed water from the chamber to return the condensed water to the system providing the steam. In certain embodiments the dissipating comprises: restoring the pressure in the thermal storage chamber to atmospheric pressure; operating a valve system operably coupling the chamber to a source of ambient temperature air to pass ambient temperature air through the thermal storage chamber to transfer heat from the thermal storage material to the air. In certain embodiments the passing ambient temperature air comprising operating a fan and/or blower or to force air through the chamber, and/or coupling the chamber to a duct system that channels wind through the chamber. In certain embodiments the dissipating further comprises operating an apparatus to provide mixing of fluid thermal storage material in chambers containing the fluid thermal storage material. In certain embodiments the method comprises operating a motor to rotate a structure frame to which the chambers containing the thermal storage material are attached. In certain embodiments the method is performed using a system comprising a plurality of In certain embodiments the method is performed using one or more devices for steam condensation and delayed dissipation of the heat produced by the condensation, e.g., as described herein. In certain embodiments the devices are configured in a parallel configuration. In certain embodiments substantially all of the devices in said system perform said receiving and condensing at the same time. In certain embodiments substantially all of the devices in said system perform said dissipating at the same time. In certain embodiments some of the devices perform said receiving and condensing at the same time that other devices are dissipating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of the apparatus  100  operably linked to a steam source (e.g., a steam turbine  101 ). An efficient condensing heat exchanger is used to convert the latent heat of exhausted steam (e.g., from a power plant) into the latent heat of a thermal storage medium while the exhausted steam is condensed into water during a “condensation stage”. During a second “heat dissipation stage”, the valves (e.g., butterfly valves, or flange covers) are opened and the stored heat in thermal storage medium is dissipated into the ambient air by an air stream (wind) by a blower or other wind source. The labeled parts are described as follows: steam source (e.g., turbine)  101 ; steam exhaust valve  102  that connects the steam turbine and the condensing heat exchanger/thermal storage tank; vacuum pump  103  that is used to pump the air inside the tank out to create a vacuum (reduced pressure) in the tank; a vacuum valve  104  that connects the vacuum pump and the tank; micro pole  105  for the vacuum pathway; valves  106  (e.g., butterfly valves, flange covers, or other functionally comparable structure(s)) that seal the vacuum during the “condensation stage”; wind blower  107  (or other source of an ambient temperature air stream); a thermal storage tank  108 ; a supporting base  109  for the thermal storage tank; packaging containers  110  (e.g., pipes) for the thermal storage materials (e.g., phase change materials (PCMs); supporting structure  111  for the phase change material packaging pipes (e.g., as illustrated in  FIG. 3 ) that, in certain embodiments, is supported by an rotates on bearing  117 ; condensed water passage way  112  from the tank; shutoff valve  112 A for use during a “heat dissipation stage”; an apparatus (e.g., a motor)  113  that rotates the entire phase change packaging system (e.g., comprising a structure frame  115  attached to the packaging containers containing the thermal storage material), e.g., via a helical drive system  116  to mix the phase change thermal storage materials inside the thermal storage packaging pipe to prevent the possible phase separation inside the pipes; air release valve  114  to vent the air into the tank until the valve  106  can be opened at the beginning of the “heat dissipation stage”. 
         FIG. 2  schematically illustrates another embodiment of the device, where multiple steam condensation tank/heat dissipation devices (e.g., as illustrated in  FIG. 1 ) are configured in a parallel system/structure  200  operably coupled to a steam source  201 . The labeled parts are described as follows: steam source (e.g., turbine)  201 ; N number of similar modules  202  as described in  FIG. 1  (illustrated with N=5); wind path pipes  207  that connect the condensing tanks together to the source of the air stream; the wind blower  204  (or other source of a cooling air stream); the valve  205  (e.g., a butterfly valve, flange cover or other functionally equivalent structure) that allows air from the blower to enter the thermal storage chamber  108  (when operating as a heat dissipation apparatus); valve  206  (e.g., a butterfly valve, flange cover or other functionally equivalent structure) that allows the air to blow out of the heat dissipation apparatus; the parallel wind path pipes  203  to allow the air stream to flow out of system; valve  208  that connects the steam source (e.g., steam turbine exhaust) with the condensation/heat dissipation system. Vacuum pump  213  connects (e.g., is operably coupled) via vacuum valve  214  and pipe  215  connects with the main exit pipe  203 . Its function is to reduce pressure in the entire parallel condensation/heat dissipation system before the turbine exhaust steam is released into the system for condensation. 
         FIG. 3  illustrates a structure frame  115  in a cross section view for the packaged thermal storage pipe fixture and arrangement.  110  is the cross section of the packaged thermal storage pipes;  116  is the structure frame to hold the storage pipes in the storage tank. The center distance between packaged pipes can be optimized to allow the air stream to pass through the pipes along the length direction of the storage tank. 
     
    
    
     DETAILED DESCRIPTION 
     In various embodiments devices are described that provide delayed and prolonged dry-cooling condensation methods that take advantage of different ambient air temperatures during the day and night to reduce energy consumption for cooling (e.g., for operating a wind blower in a dry-cooling system) while decreasing the condensation temperature of the exhaust steam so that the thermal to electricity conversion efficiency can be improved for dry-cooling. 
     Methods are described in here in detail with reference to devices examples of which are illustrated in the accompanying drawings. The methods and devices are intended to be illustrative and not limiting. Using the teaching provided herein variations of the illustrated devices and methods will be readily available to one of skill in the art. 
     Aspects of the innovations, such as those set forth in some of the implementations below, may relate to systems and methods of air-cooling. However, it should be understood that the inventions herein are not limited to any such specific illustrations, but are defined by the scope of the claims and full disclosure. 
     As illustrated in  FIG. 1  a vacuum can be applied to the chamber  108  by running a vacuum pump  103  (or other source of vacuum) after opening of vacuum valve  104  of the thermal storage tank  108  via a micro pole  105 . Low temperature exhaust steam from a steam source  101  (e.g., from a power plant turbine) enters thermal storage tank  108  via opened valve  102 , to release the latent heat of the stem to containers  110  (e.g., packaged pipes) holding thermal storage materials (e.g., phase change thermal storage materials (PCMs)). This transfer of latent heat from the steam to the thermal storage material is accompanied by condensation of the steam into water. The water drains out from the tank  108  via water path (e.g., optionally valved ports)  112  to complete the Rankin cycle for the power (e.g., electricity) generation. Where the thermal storage material is a phase change material, the phase change material (PCM) thermal storage material inside containers (e.g. pipes)  110  absorbs the latent heat of steam and changes its phase from solid form into liquid form, which means the phase change material (PCM) melts and keeps (stores) the latent heat. This process comprises the “condensation stage”. 
     The maximum temperature difference required for the exhaust steam and the phase change temperature of the thermal storage material can be described by the following equation: 
     
       
         
           
             
               
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           where 
         
       
       
         
           
             
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     where T w  is the wall temperature for the packaging pipe, which is also very close to the exhaust steam temperature for the thermal storage material, T m  is the phase change temperature, ρ cs  (ρ c ) is the phase change material density in the solid state, γ c  is the heat of fusion of the phase change material (or latent heat during phase change), λ cs  is the thermal conducting coefficient for the solid state phase change material, V c  is the total volume; d o  is the diameter for the phase change material&#39;s packaging container (e.g., pipe), Φ 1  is the amount of latent heat for the turbine exhaust steam that needs to be condensed per hour; as defined before, and Δt 1  is the time duration for the “condensation stage”, and Q 1  is the total latent heat condensed during the condensation stage. One can find that if the time duration for the “condensation stage” Δt 1  is larger, the maximum temperature difference is smaller because longer time is used to transfer the steam latent heat to the PCMs. 
     The following illustrates the use of this equation for a real world example: Consider small scale CSP power plant with 10 MW e  peak capacity. With the help of the delay and prolonged dry-cooling apparatus described herein, the exhaust steam condensation temperature for the steam turbine can be 35° C. or below. In this case, its heat to electricity conversion efficiency would be 35%. Therefore, about 65% of the total thermal energy produced by a solar thermal field needs to be eventually condensed into ambient air during power generation. Assume such a CSP system would work six hours to produce electricity per day. The amount of latent heat for the turbine exhaust would be 15 MW th . To apply the delay and prolonged dry-cooling approach described herein 26 individual storage/dissipation units, similar to those illustrated in  FIG. 1  can be used to complete the task. In one illustrative embodiment, each storage unit comprises a cylindrical container about 5 meters in diameter and 16 meters in length, made from fiber-glass material with a steel enhancement frame structure. Inside each container, 5200×3 thin glass tubes (with 25 mm diameter and 0.5 mm wall thickness, 5 meter in length with 3 identical sections to fill the 16 meter long tank, as illustrated in  FIG. 1 ) are placed in parallel with the long dimension of the container in a supporting a structure such as the one illustrated in  FIG. 3 , where the frame structure is designed to hold the thin glass tubes in such a way that the distance between glass tube centers is about 62.5 mm. This distance is an optimized value for the storage tank design after considering the density of the storage pipes in the tank and the wind resistance when the wind is blown along the pipes to dissipate the heat from the storage pipe. An illustrative thermal storage material is Na 2 CO 3 .10H 2 O compound, whose phase change temperature is at 32° C. with the latent heat (heat of fusion) of 267 kJ/kg. The total amount of thermal storage material that is packaged inside the glass tubes in the container is 50 ton, with total latent heat capacity about 3.6 MWh. To store all the turbine exhaust steam latent heat of the CSP plant into the phase change material during the “condensation stage”, which is 6 hours in this case, applying the equation above, the temperature difference of T w  and T m  would be 2.6° C. As mentioned before, 26 such storage units configured in parallel, e.g., as illustrated in  FIG. 2 , would be sufficient to condense all the exhaust steam from the 10 MW CSP plant into water during 6 hours of “condensation stage”, store all the latent heat into these storage tanks, and wait until in the night time to be dissipated into ambient air. 
     During the “heat dissipation stage”, e.g., during the nighttime or cooler daylight periods, when the ambient air temperature is significantly lower than the phase change temperature of the thermal storage materials in the storage tank, a vent valve  114  is opened to release the air into the tank  108  until the pressure inside the tank reaches atmospheric pressure, the two butterfly valves  106  are opened, and a fan (wind blower)  107  is started to drive the ambient cooling-air flow through the thermal storage package pipe surfaces via the spaces between the package pipes  110 . The ambient cooling air-flow carries the latent heat of the phase change material (PCM) from the package pipes  110  surfaces into the environment. After releasing its latent heat the phase change material (PCM) of the thermal storage medium returns to its solid form again. 
     In certain embodiments, in order to avoid the nucleation of the phase change material (PCM) inside its container (e.g., pipe) an agitator or mixer can be provided to facilitate mixing of the PCM inside the container(s). In certain embodiments the agitator/mixer can be fixed at the bottom of the thermal storage tank  108 . In certain embodiments the agitator/mixer comprises a motor  113  that can drive rotation of the heat pipes attached to structure frame  111  via for example, a helical drive  116  when the thermal storage materials are in liquid phase. As a result, this motion effectively mixes the liquid phase change thermal storage materials inside the pipes to avoid the possible nucleation and phase separation of the thermal storage medium. In various embodiments other agitators/agitation systems can be contemplated. Such systems include, for example acoustic/ultrasound agitation, mechanical vibrators (e.g., piezoelectric vibrators), and the like. 
     An alternative method to avoid the possible nucleation and phase separation of the thermal storage medium is to mix super thin (e.g., 5-50 μm, or 10-30 μm, or 10-20 μm, etc.) glass fibers (e.g., about 0.1 to about 10%, or 0.5% to about 5%, or about 1% in volume) into the phase change material inside the packing containers (e.g., pipes). Other suitable materials will be recognized by one of skill in the art. Typically, any matrix materials with low density to prevent solids from precipitating to the bottom are suitable. 
     As noted above, the methods and devices described herein are particularly advantageous because of the separation of the “dry-cooling” process into the “condensation stage” and the “heat dissipation stage”. During the “condensation stage”, the turbine exhaust steam enters the storage tank and convert its latent heat (from vapor to water) into thermal storage material&#39;s latent heat with phase change process. 
     However, the heat dissipation process involves entirely different heat exchange mechanism because it utilizes a forced convection process with air to dissipate the heat inside the packaged thermal storage pipes into the environment. 
     Consider the process of “heat dissipation stage” in the following illustrative example. Taking the temperature variation in a typical day into account, assume that the lowest temperature of that day equals to (a° C.) and the highest temperature equals to (a+b° C.). Furthermore we propose a hypothesis that the temperature variation within one day can be described as a Sine function, and the summit of this curve (the highest temperature) appears at 14:00 o&#39;clock. We can then use the following formula to describe the ambient air temperature: 
     
       
         
           
             
               
                 
                   
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     Suppose that the starting time of heat dissipation stage t 2  is later than 2:00 pm, so the duration of the heat dissipation stage t 2  is given by: 
       Δ t   2 =52−2 t   2    (2)
 
     By integration of the temperature variation function over the entire time duration of stage 2, we obtain the average ambient temperature during the heat dissipation stage: 
     
       
         
           
             
               
                 
                   
                     
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     According to the relevant aerodynamics, the Nusselt number Nu, Reynolds Number Re and the heat exchange coefficient h are related by: 
     
       
         
           
             
               
                 
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     where Nu is given by: 
       Nu=0.023×Re 0.8 ×Pr 0.33  
 
     while Reynolds Number Re is in the range of Re=10 4 −1.2×10 5 ; d e  is the equivalent diameter of the thermal storage tank cylinder, λ is the thermal conductivity of the air flow, which is 2.63×10 −2  W/(m K) for air at temperature of 25° C. Reynolds Number Re is given by: 
     
       
         
           
             
               
                 
                   Re 
                   = 
                   
                     
                       ud 
                       e 
                     
                     v 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where μ is the velocity of the air flow and v is the coefficient of viscosity of air, which is 15.53×10 −6  m 2 /s for air at temperature of 25° C. Substituting equation (5) into equation (4), we have: 
         h= 4.04 u   0.613   d   e   −0.382 (W/m 2 K)   (6)
 
     Moreover, the equivalent diameter of cylinder d e  is expressed by: 
     
       
         
           
             
               
                 
                   
                     d 
                     e 
                   
                   = 
                   
                     
                       
                         4 
                          
                         
                           A 
                           c 
                         
                       
                       P 
                     
                     = 
                     
                       
                         
                           D 
                           i 
                           2 
                         
                         - 
                         
                           Nd 
                           o 
                           2 
                         
                       
                       
                         
                           D 
                           i 
                         
                         + 
                         
                           Nd 
                           o 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     where D i  is the internal diameter of the cylinder tank, while d o  is the external diameter of the N pipes. 
     If the heat transfer rate Φ 1  by the exhausted steam from turbine and the time duration of “condensation stage” Δt 1  are known, the requirement of the phase change material (PCM) is then determined. The total volume of the phase change material (PCM) is given by: 
     
       
         
           
             
               
                 
                   
                     V 
                     PCM 
                   
                   = 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         t 
                         1 
                       
                        
                       
                         Φ 
                         1 
                       
                     
                     
                       
                         ρ 
                         PCM 
                       
                        
                       
                         γ 
                         PCM 
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where ρ PCM  is the density of the phase change material (PCM) in units of kg/m 3 ; and γ PCM  is the latent heat of the phase change material (PCM), in unite of J/kg. 
     From the fundamental heat transfer equation: 
     
       
         
           
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         t 
                         1 
                       
                        
                       
                         Φ 
                         1 
                       
                     
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         t 
                         2 
                       
                     
                   
                   = 
                   
                     h 
                      
                     
                         
                     
                      
                     A 
                      
                     
                         
                     
                      
                     Δ 
                      
                     
                         
                     
                      
                     
                       T 
                       m 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     where h is the convection heat transfer coefficient between air flow and outer wall of pipes, in units of W/(m 2  K); A is the heat exchange area for heat dissipation processes, in units of m 2 ; ΔT m  is the average convection heat exchange temperature difference, i.e. temperature difference between the outer diameter of the main tank surface and cooling air temperature, K; Substitute (6) into (9): 
     
       
         
           
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         t 
                         1 
                       
                        
                       
                         Φ 
                         1 
                       
                     
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         t 
                         2 
                       
                     
                   
                   = 
                   
                     
                       A 
                        
                       
                           
                       
                        
                       
                         hT 
                         m 
                       
                     
                     = 
                     
                       4.04 
                        
                       
                           
                       
                        
                       
                         u 
                         0.613 
                       
                        
                       
                         d 
                         e 
                         
                           - 
                           0.382 
                         
                       
                        
                       A 
                        
                       
                           
                       
                        
                       Δ 
                        
                       
                           
                       
                        
                       
                         T 
                         m 
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     When we consider the formula of air specific heat we have: 
       Φ 2 =C p q m ΔT a    (11)
 
     where Φ 2  is the heat dissipation power for the proposed apparatus, C p  is the specific heat at constant pressure of the air flow, in units of J/(kg K); q m  is the mass flow rate of the air in units of kg/s, and ΔT a  is the temperature different of the air flow between inlet and outlet of thermal storage tank  108 . In addition, it is noted that Δt 1 Φ 1 =Δt 2 Φ 2  which means that equation (10) equals equation (11). 
     Another temperature difference that can be taken into account is the difference between the temperature of the phase change material (PCM) and the outer wall of package pipe containing the PCM. This temperature difference relates to the properties of the phase change material (PCM), the external diameter of pipe do and the time duration of stage Δt 1  or Δt 2 : 
     
       
         
           
             
               
                 
                   
                      
                     
                       
                         T 
                         m 
                       
                       - 
                       
                         T 
                         w 
                       
                     
                      
                   
                   = 
                   
                     
                       
                         ρ 
                         PCM 
                       
                        
                       
                         γ 
                         PCM 
                       
                        
                       
                         d 
                         o 
                         2 
                       
                     
                     
                       8 
                        
                       
                         λ 
                         PCM 
                       
                        
                       Δ 
                        
                       
                           
                       
                        
                       t 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     In order to keep the temperature difference between the phase change material (PCM) and the outer wall of the pipes suitable small, the pipes (PCM containers) can be selected such that the outer diameter is less than: 
     
       
         
           
             
               
                 
                   
                     d 
                     o 
                   
                   ≤ 
                   
                     
                       
                         8 
                          
                         
                           λ 
                           PCM 
                         
                          
                         Δ 
                          
                         
                             
                         
                          
                         t 
                          
                         
                            
                           
                             
                               T 
                               m 
                             
                             - 
                             
                               T 
                               w 
                             
                           
                            
                         
                       
                       
                         
                           ρ 
                           PCM 
                         
                          
                         
                           γ 
                           PCM 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     The Power of the blower motor generating the cooling airflow (e.g., wind) is given by: 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     
                       
                         169.6 
                          
                         
                             
                         
                          
                         S 
                       
                       T 
                     
                      
                     
                       u 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     using equation (5), we have: 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     0.019 
                      
                     
                       ST 
                       
                         - 
                         1 
                       
                     
                      
                     
                       
                         
                           d 
                           1.76 
                         
                          
                         
                           ( 
                           
                             
                               Δ 
                                
                               
                                   
                               
                                
                               
                                 t 
                                 1 
                               
                                
                               Φ 
                             
                             
                               Δ 
                                
                               
                                   
                               
                                
                               
                                 t 
                                 2 
                               
                                
                               Δ 
                                
                               
                                   
                               
                                
                               
                                 T 
                                 m 
                               
                                
                               A 
                             
                           
                           ) 
                         
                       
                       4.76 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     where N is the power of the air blower in units of W; S is the cross sectional area of the air duct in units of m 2 ; T is the temperature of the ambient air in units of K; A is the heat transfer area in units of m 2  which is the sum of all the surface areas for the thermal storage package pipe (container) outside surfaces. 
     In certain embodiments, as indicated above the devices described herein can be configured in a “parallel” architecture comprising multiple devices, e.g., as illustrated in  FIG. 2 . In certain embodiments N, the number of devices in such a configuration is greater than 2, more preferably greater than 3, still more preferably greater than 4, 5, or 6, in certain embodiments, greater than 10, 20, 30, 40, or 50, and in certain embodiments, greater than 75, 100, 150 or greater than 200. 
     In this way, the system can handle larger amounts of exhausted steam (for example, larger than 3.6 MWh heat capacity, as in the example storage unit described above) or sustain 24 hours of continuing operation by alternating “condensing/storage” and “heat dissipation” process with different containers. Another advantage with this configuration is that the number of valves that allow ambient air to enter the tank during the dissipation cycle can be reduced significantly to lower the system cost. For example, in certain embodiments, the N containers can share two butterfly valves, one for air entering path and the other for the air exhaust path through the main pipe and parallel pipes configured as described in  FIG. 2 . In addition, one wind blower with larger operation power can be used for the entire system, further simplifying system construction and reducing cost. 
     Continuing with the example described above, and considering the heat dissipation stage. Table 1 lists typical heat dissipation time periods required for each thermal storage tank given the ambient air temperature for a typical year for the said 10 MW CSP power plant. The average ambient air temperatures for each month are for the application location in northern China. It should be noted, however, that because the ambient air temperature during the night is much lower than the phase change temperature relative to the temperature difference of T w  and T m , the required Δt 2  is actually much shorter than Δt 1 . In other words, the “delay” is much more effective than the “prolonged”, especially during the winter season. 
     Table 1. Illustrates typical heat dissipation time periods given the ambient temperature for a typical year and realistic application of the system. 
     
       
         
           
               
               
               
               
               
             
               
                   
               
             
            
               
                 Phase  
                 Phase 
                   
                 Heat of 
                 Thermal 
               
               
                 change 
                 change 
                 density 
                 fusion 
                 conductivity 
               
               
                 material 
                 temperature 
                 (kg/m 3 ) 
                 (kJ/kg) 
                 (W/m · K) 
               
               
                   
               
               
                 Na 2 C0 3  · 10H 2 0 
                 32° C. 
                 1349 ( l ) 
                 267 
                 0.54 
               
               
                   
                   
                 1447 ( s ) 
               
               
                   
               
               
                   
                   
                   
                   
                 Dissipation 
               
               
                   
                 Ambient  
                   
                   
                 temperature 
               
               
                   
                 temperature 
                 Δt2 
                 Tw − Tm 
                 difference 
               
               
                   
               
               
                 January 
                 −16.1/−7.2° C.  
                 2.37 h 
                 2.6° C. 
                 26.8° C. 
               
               
                 February 
                 −14.3/−3.4° C.  
                 2.45 h 
                   
                 25.7° C. 
               
               
                 March 
                   −1.9/9.9° C. 
                 3.18 h 
                   
                 18.6° C. 
               
               
                 April 
                   5.1/17.7° C.  
                 3.81 h 
                   
                 14.6° C. 
               
               
                 May 
                   9.2/23.1° C. 
                 4.37 h 
                   
                 12.1° C. 
               
               
                 June 
                  14.7/26.3° C. 
                 5.08 h 
                   
                  9.1° C. 
               
               
                 July 
                  17.7/29.6° C. 
                 5.58 h 
                   
                  7.4° C. 
               
               
                 August 
                  15.0/25.2° C. 
                 5.09 h 
                   
                  9.1° C. 
               
               
                 September  
                  10.5/21.9° C. 
                 4.44 h 
                   
                 11.6° C. 
               
               
                 October 
                   2.4/15.1° C. 
                 3.54 h 
                   
                 16.1° C. 
               
               
                 November 
                   −4.6/5.3° C. 
                 2.97 h 
                   
                 20.3° C. 
               
               
                 December  
                 −13.0/−3.4° C. 
                 2.51 h 
                   
                 25.0° C. 
               
               
                   
               
            
           
         
       
     
     It is very easy to control the system operation. During the “condensation stage”, because the heat exchange area is sufficiently large and the required heat exchange temperature difference is relatively small, as described in the above examples, no specific control is needed except to open the control valve  102  to start the “condensation stage” and to close this valve when the condensation stage” is finished. During this stage, the exhaust steam will first condensed onto the packaged thermal storage pipe surface while transferring the latent heat into the phase changing material with very small temperature difference. As time passes, this heat transfer temperature difference gradually increases. However, even at the end of the stage, this temperature difference is still relatively small. In the above described example, this value is only 2.6° C. For the “heat dissipation stage”, as described above, valve  102  is closed, and valve  114  is opened to let air into the storage tank until the pressure inside the tank is at or close to outside pressure. The two valves  106  in  FIG. 1  or valves  205  and  206  in  FIG. 2  are opened. The blower tis turned on, or where a cooling air stream is provided by ducted ambient wind, the ducts are open. When used, the power setting of the blower depends on the ambient temperature, as illustrated in the above example and Table 1. 
     In various embodiments low temperature phase change materials are preferred as the thermal storage material for the delay and prolonged dry-cooling applications. Means of determining suitable parameters for the phase change materials are provided above. Illustrative low temperature phase change materials believed to be suitable for the heat storage material include, but are not limited to those shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Illustrative low temperature phase change materials suitable for exhaust 
               
               
                 steam condensation/thermal storage applications. 
               
            
           
           
               
               
               
            
               
                   
                   
                 Heat of 
               
               
                 Phase Change Thermal Storage Material 
                 Melting point 
                 Fusion 
               
               
                 (molecular formula) 
                 ° C. 
                 (KWh/ton) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 LiClO 3 •3H 2 O 
                 8.1 
                 70.3 
               
               
                 ZnCl 2 •3H 2 O 
                 10 
                 / 
               
               
                 K 2 HPO 4 •6H 2 O 
                 13/14 
                 30.3 
               
               
                 45% CaCl 2 •6H 2 O + 55% CaBr 2 •6H 2 O 
                 14.7 
                 38.9 
               
               
                 NaOH 3½ H 2 O 
                 15/15.4 
                 / 
               
               
                 51-55% Cu(NO 3 ) 2 •6H 2 O + 45-49% 
                 16.5 
                 69.4 
               
               
                 LiNO 3 •3H 2 O 
                   
                   
               
               
                 45-52% LiNO 3 •3H 2 O + 48-55% 
                 17.2 
                 61.1 
               
               
                 Zn(NO 3 ) 2 •6H 2 O 
                   
                   
               
               
                 Na 2 CrO 4 •10H 2 O 
                 18 
                 / 
               
               
                 KF•4H 2 O 
                 18.5-19.0 
                 64.2 
               
               
                 FeBr 3 •6H 2 O 
                 21/27 
                 29.2 
               
               
                 55-65% LiNO 3 •3H 2 O + 35-45% 
                 24.2 
                 63.9 
               
               
                 Ni(NO 3 ) 2 •6H 2 O 
                   
                   
               
               
                 66.6% CaCl2•6H 2 O + 33.4%  
                 25 
                 35.3 
               
               
                 MgCl2•6H 2 O 
                   
                   
               
               
                 45% Ca(NO 3 ) 2 •6H 2 O + 55% Zn 
                 25 
                 36.1 
               
               
                 (NO 3 ) 2 •6H 2 O 
                   
                   
               
               
                 50% CaCl 2 •6H 2 O + 50%  
                 25 
                 26.4 
               
               
                 MgCl 2 •6H 2 O 
                   
                   
               
               
                 Mn(NO 3 ) 2 •6H 2 O 
                 25.8/25.5 
                 38.9 
               
               
                 48% CaCl 2  + 4.3% NaCl + 0.4%  
                 26.8 
                 52.2 
               
               
                 KCl + 47.3% H 2 O 
                   
                   
               
               
                 50% CH 3 CONH 2  + 50% NH 2 CONH 2   
                 27 
                 45.3 
               
               
                 CaCl 2 •6H 2 O 
                 29 
                 53.0 
               
               
                 CaCl 2 •6H 2 O 
                 29/29.2/29.6/ 
                 50.0 
               
               
                   
                 29.7/30/29.9 
                   
               
               
                 LiNO 3 •3H 2 O 
                 30 
                 82.2 
               
               
                 LiNO 3 •3H 2 O 
                 30 
                 52.5 
               
               
                 67% Ca(NO 3 ) 2 •4H 2 O + 33%  
                 30 
                 37.8 
               
               
                 Mg(NO 3 ) 2 •6H 2 O 
                   
                   
               
               
                 47% Ca(NO 3 ) 2 •4H 2 O + 53%  
                 30 
                 37.8 
               
               
                 Mg(NO 3 ) 2 •6H 2 O 
                   
                   
               
               
                 60% CH 3 COONa•3H 2 O + 40%  
                 31.5 
                 62.8 
               
               
                 CO(NH 2 ) 2   
                   
                   
               
               
                 Na 2 CO 3 •10H 2 O 
                 32 
                 74.2 
               
               
                 Na 2 SO 4 •10H 2 O 
                 32.4 
                 66.9 
               
               
                 KFe(SO 4 ) 2 •12H 2 O 
                 33 
                 48.1 
               
               
                 Na 2 CO 3 •10H 2 O 
                 33/32 
                 74.2 
               
               
                 LiBr 2 •2H 2 O 
                 34 
                 34.4 
               
               
                 CaBr 2 •6H 2 O 
                 34 
                 33.3 
               
               
                 Na 2 HPO 4 •12H 2 O 
                 35.5/36/35/40 
                 77.8 
               
               
                 0.925 mol Ca(NO 3 ) 2 •4H 2 O + 0.075  
                 35.6 
                 43.1 
               
               
                 mol CaCl 2 •6H 2 O 
                   
                   
               
               
                 Zn(NO 3 ) 2 •6H 2 O 
                 36/36.4/36.1 
                 40.8 
               
               
                 FeCl 3 •6H 2 O 
                 37 
                 61.9 
               
               
                 Mn(NO 3 ) 2 •4H 2 O 
                 37.1 
                 31.9 
               
               
                 Na 2 HPO 4 •12H 2 O 
                 40 
                 77.5 
               
               
                 50% CH 3 COONa•3H 2 O + 50%  
                 40.5 
                 70.8 
               
               
                 HCONH 2   
                   
                   
               
               
                 CoSO 4 •7H 2 O 
                 40.7 
                 47.2 
               
               
                 KF•2H 2 O 
                 41.4/42 
                 45.0 
               
               
                 CH 3 COOK•1½H 2 O 
                 42 
                 / 
               
               
                 MgI 2 •8H 2 O 
                 42 
                 36.9 
               
               
                 CaI 2 •6H 2 O 
                 42 
                 45.0 
               
               
                 K 2 HPO 4 •7H 2 O 
                 45 
                 40.3 
               
               
                 K 3 PO 4 •7H 2 O 
                 45 
                 / 
               
               
                 Zn(NO 3 ) 2 •4H 2 O 
                 45/45.5 
                 30.6 
               
               
                 Ca(NO 3 ) 2 •4H 2 O 
                 42.7/47 
                 42.5 
               
               
                 Mg(NO 3 ) 2 •4H 2 O 
                 47 
                 39.4 
               
               
                 Fe(NO 3 ) 3 •9H 2 O 
                 47 
                 43.1 
               
               
                 Na 2 HPO 4 •7H 2 O 
                 48 
                 / 
               
               
                 Na 2 SiO 3 •4H 2 O 
                 48 
                 46.7 
               
               
                 K 2 HPO 4 •3H 2 O 
                 48 
                 27.5 
               
               
                 MgSO 4 •7H 2 O 
                 48.5 
                 56.1 
               
               
                 Na 2 S 2 O 3 •5H 2 O 
                 48/48-49/48.5  
                 58.1 
               
               
                 Ca(NO 3 ) 2 •3H 2 O 
                 51 
                 28.9 
               
               
                 61.5% Mg(NO 3 ) 2 •6H 2 O + 38.5%  
                 52 
                 36.5 
               
               
                 NH 4 NO 3   
               
               
                   
               
            
           
         
       
     
     The foregoing embodiments are intended to bee illustrative an not limiting. Using teachings provided herein, other variations will be available to those of skill in the art. For example, while the system in  FIG. 1  is shown with a fan  107  to drive ambient air through the thermal storage system during the heat dissipation period in various embodiments, a fan is not required. For example, where the system is sited in locations having significant winds, particular at night, the system can comprise ducts to channel ambient winds through the thermal storage system thereby reducing or avoiding the power usage required by a fan. 
     Similarly, a valve  104  is shown to control application of vacuum to chamber  108 , while a separate valve  114  is shown to introduce atmospheric pressure air into chamber  108 . However, in certain embodiments, these need not be separate valves. Thus, for example valve  104  can be configured to switch between a vacuum source and atmospheric pressure air thereby obviating valve  114 . 
       FIG. 1  also shows that in certain embodiments, the device can comprise an agitator/mixer configured to rotate perforated plates to which the chambers containing the thermal storage material are attached. However, numerous other configures to achieve such mixing will be recognized and available to one of skill in the art. 
     Thus, it is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes.