Patent Application
20130307273
The present disclosure relates generally to the energy production using solar insolation, and, more particularly, to storage of solar energy using at least three thermal storage reservoirs.
Insolation can be used to heat a working fluid (e.g., water or carbon dioxide) for use in generating electricity (e.g., via a steam turbine). During periods of relatively higher insolation, there may be excess heat energy (i.e., enthalpy) than that needed for electricity generation. In contrast, during periods of relatively lower insolation (e.g., cloud cover or at night), the enthalpy in the working fluid may be insufficient to generate electricity. In general, during the periods of relatively higher insolation, the excess enthalpy may be stored in a thermal storage system for use, for example, during periods of relatively lower insolation or at times when supplemental electricity generation is necessary (e.g., during peak power periods). The thermal storage system can include at least three separate reservoirs at different temperatures above the melting point of a thermal storage fluid (e.g., a molten salt or metal) contained therein. Enthalpy transfer between the thermal storage fluid and the working fluid occurs by way of a heat exchanger in thermal communication with a flow path of the storage fluid between each of the reservoirs.
In one or more embodiments, a method of generating electricity using insolation can include at least first and second operating periods. At a first operating period, the method can include generating steam using insolation and using a portion of the generated steam to drive a turbine so as to produce electricity. Another portion of the generated steam can be directed to a heat exchanger in thermal communication with first through third thermal reservoirs, and at a same time, a storage fluid can be flowed from the first reservoir through the heat exchanger to the second reservoir and from the second reservoir through the heat exchanger to the third reservoir such that enthalpy in the another portion of the generated steam is transferred to the storage fluid by way of the heat exchanger. At a second operating period, the method can include reverse-flowing the storage fluid from the third reservoir through the heat exchanger to the second reservoir and from the second reservoir through the heat exchanger to first reservoir such that enthalpy in the storage fluid is transferred by way of the heat exchanger to generate steam. The steam generated by the reverse-flowing can be used to drive the turbine to produce electricity. A temperature of the third reservoir can be maintained higher than a temperature of the second reservoir, and a temperature of second reservoir can be maintained higher than a temperature of the first reservoir.
In one or more embodiments, a system for generating electricity from insolation can include a solar collection system, a thermal storage system, an electricity generating system, and a heat exchanger. The solar collection system can be constructed so as to generate steam from insolation. The thermal storage system can include first through third thermal storage reservoirs. The electricity generating system can include a turbine that uses steam to generate electricity and can be coupled to the solar collection system so as to receive generated steam therefrom. The heat exchanger can thermally couple the solar collection system and the thermal storage system such that enthalpy in fluid in one of the solar collection and thermal storage systems can be transferred to fluid in the other of the solar collection and thermal storage systems. The first through third storage reservoirs can be connected in order such that fluid flowing between the first and second reservoirs and between the second and third reservoirs passes through the heat exchanger.
In one or more embodiments, a method for thermal storage for electricity generation can include, during a first time, producing electricity using steam generated by discharging stored enthalpy from a thermal storage system via a heat exchanger. The thermal storage system can include three storage reservoirs that can contain storage fluid at different temperatures. A temperature of storage fluid in the first reservoir can be less than a temperature of storage fluid in the second reservoir. A temperature of storage fluid in the second reservoir can be less than a temperature of storage fluid in the third reservoir. The first through third reservoirs can be connected together in order such that storage fluid can flow between the first and second reservoirs and between the second and third reservoirs. The stored enthalpy can be derived from steam generated using insolation.
In one or more embodiments, a method can include, at some times, using insolation to generate saturated steam from pressurized liquid water at a pressure P and subjecting some of the saturated steam to a heat transfer operation whereby enthalpy of the saturated steam is conductively and/or convectively transferred to a thermal storage fluid to heat the storage fluid to the evaporation temperature Tev and to condense the saturated steam. The pressurized steam can be substantially at the evaporation temperature Tev of water for the pressure P. In addition, insolation can be used to superheat some of the saturated steam by a least 50° C. to obtain superheated steam whose temperature is Tsup, and subjecting some of the superheated steam to a heat transfer operation whereby enthalpy of the superheated steam is conductively and/or convectively transferred to the thermal storage fluid at the evaporation temperature Tev to further heat the thermal storage fluid to substantially the temperature Tsup. Some of the superheated steam can be used to drive a steam turbine. The method can further include, at other times, transforming enthalpy from the thermal storage fluid at the temperature Tev to liquid water pressurized to the pressure P to generate saturated steam at the pressure P and to cool the thermal storage fluid, and transforming enthalpy from the thermal storage fluid at the temperature Tsup to the saturated steam to heat the steam to substantially Tsup.
In one or more embodiments, a multi-reservoir thermal storage system for storing a molten salt and/or molten metal thermal storage fluid can include a plurality of substantially insulated reservoirs and a control system. The plurality of substantially insulated reservoirs can include first, second, and third reservoirs. The reservoirs can be in fluid communication with each other. The control system can be configured to regulate flow of the thermal storage fluid between the reservoirs to transform the thermal storage system from a substantially uncharged state to a substantially charged state. In the substantially uncharged state, substantially all of the storage fluid in the thermal storage system is in the first reservoir at a first temperature T1 that exceeds a melting point of the thermal storage fluid. The thermal storage fluid can travel between reservoirs and be heated en route by at least partial thermal contact with solar-generated steam and/or subcritical carbon dioxide. In the substantially charged state, at most a small minority of the storage fluid in the thermal storage system is in the first reservoir, a majority of the storage fluid in the thermal storage system is in the second reservoir at a second temperature T2 exceeding the first temperature T1, and a minority of the storage fluid in the thermal storage system is in the third reservoir at a third temperature T3 exceeding the second temperature T2. The third temperature T3 can be below a boiling point of the thermal storage fluid. When in the charged state, a ratio between an amount of storage fluid within the second reservoir and an amount of storage fluid in the third reservoir is at least 1.5 and at most 10, a difference between T2 and T1 is at least 20° C., and a ratio between (T3−T2) and (T2−T1) is at least 1.5 and at most 10.
In one or more embodiments, a method of storing enthalpy in a thermal storage fluid can include harvesting enthalpy of a quantity of supercritical steam whose temperature exceeds the critical temperature of water by TDiff
In one or more embodiments, a thermal energy storage system can be configured to store enthalpy received from a steam system. The thermal energy storage system can include first, second, and third reservoirs, a thermal storage fluid, and a control apparatus. Each of the second and third reservoirs can be in fluid communication with the first reservoir. The thermal storage fluid can include at least one of molten salt and molten metal. The control apparatus can be configured to regulate flow parameters and/or heat transfer parameters of the thermal storage fluid so as to effect a state transition between the first and second states of the thermal storage system using enthalpy. The first state can be a lower-enthalpy state in which substantially all of the thermal storage fluid is located in the first reservoir at a first temperature T1. The second state can be a higher-enthalpy state in which substantially none of the thermal storage fluid is located in the first reservoir. A first fraction, F1, of the thermal storage fluid can reside in the second reservoir at a second temperature, T2, in the second state, and a second fraction, F2, of the thermal storage fluid can resides in the third reservoir at a third temperature, T3, in the second state. T3 can be greater than T2, which can be greater than T1. T1 can exceed the freezing point of the thermal storage fluid. The sum of F1 and F2 can be substantially equal to 1. F1 can be greater than F2. The control apparatus can be configured such that the enthalpy for the transition between the first and second states is supplied in a heat exchange process whereby steam of said steam system is cooled into pressurized water.
In one or more embodiments, a thermal energy storage system can include three reservoirs of a liquid. When the system is substantially uncharged, a first reservoir can contain substantially all of the liquid at a first temperature. When the system is substantially charged, the first reservoir can be substantially empty, a second reservoir can contain a first portion of the liquid at a second temperature, and a third reservoir can contain a second portion of the liquid at a third temperature. The first and second portions can comprise substantially all of the liquid in the system. When the system is charging or discharging, the liquid can be in thermal communication with a pressurized working fluid by way of a heat exchanger. The pressurized working fluid can be in a liquid phase at the end of the charging or at the beginning of the discharging. The pressurized working fluid can be in a gas phase at the end of the discharging and supercritical at the beginning of charging. The first temperature can be above the freezing point of the liquid, the second temperature can be greater than the first temperature, and the third temperature can be greater than the second temperature. The first portion of the liquid can be greater by mass than the second portion of the liquid.
Objects and advantages of embodiments of the disclosed subject matter will become apparent from the following description when considered in conjunction with the accompanying drawings.
Embodiments will hereinafter be described with reference to the accompanying drawings, which have not necessarily been drawn to scale. Where applicable, some features may not be illustrated to assist in the illustration and description of underlying features. Throughout the figures, like reference numerals denote like elements.
Insolation can be used by a solar tower system to generate solar steam and/or for heating molten salt. In
The solar energy receiver system 20 can be arranged at or near the top of tower 50, as shown in
More than one solar tower 50 can be provided, each with a respective solar energy receiving system thereon, for example, a solar power steam system. The different solar energy receiving systems may have different functionalities. For example, one of the solar energy receiving systems may heat water using the reflected solar radiation to generate steam while another of the solar energy receiving systems may serve to superheat steam using the reflected solar radiation. The multiple solar towers 50 may share a common heliostat field 60 or have respective separate heliostat fields. Some of the heliostats may be constructed and arranged so as to alternatively direct insolation at solar energy receiving systems in different towers. In addition, the heliostats may be configured to direct insolation away from any of the towers, for example, during a dumping condition. As shown in
More than one solar receiver can be provided on a solar tower. The multiple solar receivers in combination may form a part of the solar energy receiving system 20. The different solar receivers may have different functionalities. For example, one of the solar receivers may heat water using the reflected solar radiation to generate steam while another of the solar receivers may serve to superheat steam using the reflected solar radiation. The multiple solar receivers can be arranged at different heights on the same tower or at different locations (e.g., different faces, such as a north face, a west face, etc.) on the same tower. Some of the heliostats in field 60 may be constructed and arranged so as to alternatively direct insolation at the different solar receivers. As shown in
Heliostats 70 in a field 60 can be controlled through a central heliostat field control system 91, for example, as shown in
At a lowest level of control hierarchy (i.e., the level provided by heliostat controller) in the illustration there are provided programmable heliostat control systems (HCS) 65, which control the two-axis (azimuth and elevation) movements of heliostats (not shown), for example, as they track the movement of the sun. At a higher level of control hierarchy, heliostat array control systems (HACS) 92, 93 are provided, each of which controls the operation of heliostats 70 (not shown) in heliostat fields 96, 97, by communicating with programmable heliostat control systems 65 associated with those heliostats 70 through a multipoint data network 94 employing a network operating system such as CAN, Devicenet, Ethernet, or the like. At a still higher level of control hierarchy a master control system (MCS) 95 is provided which indirectly controls the operation of heliostats in heliostat fields 96, 97 by communicating with heliostat array control systems 92, 93 through network 94. Master control system 95 further controls the operation of a solar receiver (not shown) by communication through network 94 to a receiver control system (RCS) 99.
In
Insolation can vary both predictably (e.g., diurnal variation) and unpredictably (e.g., due to cloud cover, dust, solar eclipses, or other reasons). During these variations, insolation may be reduced to a level insufficient for heating a working or heat transfer fluid, for example, producing steam for use in generating electricity. To compensate for these periods of reduced insolation, or for other reasons disclosed herein, thermal energy produced by the insolation can be stored in a fluid-based thermal storage system for use later when needed. The thermal storage system can store energy when insolation is generally available (i.e., charging the thermal storage system) and later release the energy to heat a working fluid (e.g., water or carbon dioxide) in addition to or in place of insolation. For example, it may be possible at night to replace the radiative heating of the working fluid in the solar collection system by insolation with conductive and/or convective heat transfer of thermal energy (i.e., enthalpy) from thermal storage system to the working fluid in the solar collection system. Although the term working fluid is used herein to refer to the fluid heated in the solar collection system, it is not meant to require that the working fluid actually be used to produce work (e.g., by driving a turbine). For example, the working fluid as used herein may release heat energy stored therein to another fluid which may in turn be used to produce useful work or energy. The working fluid may thus act as a heat transfer fluid. Working fluid and heat transfer fluid has been interchangeably used herein to refer to the fluid heated by the solar collection system
In one or more embodiments, the thermal storage system includes at least three separate thermal storage reservoirs, which can be substantially insulated to minimize heat loss therefrom. A thermal storage fluid can be distributed among the three storage reservoirs. For example, the thermal storage fluid can be a molten salt and/or molten metal and/or other high temperature (i.e., >250° C.) substantially liquid medium. The thermal storage fluid can be heated by convective or conductive heat transfer between the working fluid and the thermal storage fluid in a heat exchanger. This net transfer of enthalpy to the thermal storage fluid in the thermal storage system is referred to herein as charging the thermal storage system. At a later time when insolation decreases, the direction of heat exchange can be reversed to transfer enthalpy from the thermal storage fluid to the working fluid via the same or a different heat exchanger. This net transfer of enthalpy from the thermal storage fluid of the thermal storage system is referred to herein as discharging the thermal storage system.
Each thermal storage reservoir can be, for example, a fluid tank or a below-grade pool. Referring to
During the charging phase (flow directions illustrated by dash-dot lines in the figure), thermal storage fluid can be transferred from the colder reservoirs of the thermal storage system to the hotter reservoirs of the thermal storage system, as designated by the block arrow in
During the charging or discharging modes, enthalpy can be exchanged between the working fluid and the thermal storage fluid as the thermal storage fluid passes between the reservoirs. The fluid conduits or pipes can be in thermal communication with the working fluid by way of a heat exchanger to allow the transfer of enthalpy as the thermal storage fluid flows between reservoirs (i.e., while the thermal storage fluid is en route to a destination reservoir). For example, conduit 608 connecting the first reservoir 602 to the second reservoir 604 can pass through a heat exchanger 612 such that the thermal storage fluid can exchange enthalpy 614 with the working fluid. Similarly, conduit 610 connecting the second reservoir 604 to the third reservoir 606 can pass through heat exchanger 612 such that the thermal storage fluid can exchange enthalpy 616. The direction of enthalpy flow depends on the mode of operation, with enthalpy flowing from the working fluid to the thermal storage fluid during the charging phase and from the thermal storage fluid to the working fluid during the discharging phase. Portions of the fluid conduits can be insulated to minimize or at least reduce heat loss therefrom.
The particular arrangement and configuration of fluid conduits 608 and 610 in
Although illustrated as substantially the same size, each of the reservoirs can be a different size depending on, for example, the anticipated loading capacity. For example, the first reservoir (i.e., the cold tank) could be larger than both the second reservoir (i.e., the warm tank) and the third reservoir (i.e., the hot tank). As explained in more detail below, at the beginning of the charging phase, the first reservoir may contain substantially all of the thermal storage fluid in the thermal storage system. At the end of the charging phase, the thermal storage fluid may be transferred completely (or nearly completely) out of the first reservoir. The thermal storage fluid may thus be distributed between the second reservoir and the third reservoir, with the second reservoir holding the majority of the thermal storage fluid.
One or more pumps (not shown) can be included for moving the thermal storage fluid between reservoirs. Additional flow control components can also be provided, including, but not limited to, valves, switches, and flow rate sensors. Moreover, a controller (for example, see
The thermal storage system can include a total quantity, Xtot, of thermal storage fluid distributed between the different thermal storage reservoirs depending on the particular mode of operation and time within the mode. For example, the thermal storage system may be constructed to accommodate a total quantity of fluid of at least 100 tons, 500 tons, 1000 tons, 2500 tons, 5000 tons, 10000 tons, 50000 tons, or more. In the fully discharged state (which may be at the beginning of a charge phase), the distribution of thermal storage fluid in the thermal storage system may be such that substantially all of the storage fluid is in the cold reservoir. The cold reservoir thus has a quantity of fluid, XC, that is substantially equal to Xtot while the quantity of fluid in the warm reservoir, XW, and the quantity of fluid in the hot reservoir, XH, are approximately 0. In the fully charged state (which may be at the beginning of a discharge phase), the distribution of the thermal storage fluid in the thermal storage system may be such that substantially all of the storage fluid is in the warm and hot reservoirs. In particular, the warm reservoir may contain most of the thermal storage fluid. The quantify of fluid in the cold reservoir, XC, is thus approximately 0, while the warm reservoir quantity, XW, and the hot reservoir quantity, XH, together add up to Xtot, with XW being greater than XH. For example, in the fully discharged state, a ratio of XC to Xtot is at least 0.7, 0.8, 0.9, 0.95, 0.98, 0.99, or higher. In the fully charged state, a ratio of XC to Xtot is at most 0.2, 0.1, 0.05, 0.01, or less. In the fully charged state, a ratio of XW to Xtot is at least 0.5, 0.6, 0.7, 0.8, or higher. In the fully charged state, a ratio of XW to XH is at least 1.2, 1.5, 1.75, 2, 2.5, 3, 3.5 or higher. Alternatively or additionally, in the fully charged state, a ratio of XW to XH is at most 10, 5, 4, 3, or less.
The first reservoir 602 is connected to the third reservoir 606 by way of the second reservoir 604 and the fluid conduits between the reservoirs in the configuration of
A method for operating the thermal storage system in combination with a solar collector system and an electricity generation system is shown in
At 806, the insolation is used to heat a working fluid to induce a phase change therein. For example, when the working fluid is water, the insolation can be used to produce steam from pressurized water. Such steam production may be done in a two-stage process, with a first stage of insolation serving to evaporate the pressurized water into steam and a second stage of insolation serving to superheat the steam. To produce the steam from insolation, a concentrating solar tower system as described above with regard to
At 810, it is determined if the thermal storage system should be charged. The determination may take into account the amount of excess heat energy available and/or the current state of the thermal storage system. For example, during solar collection system startup (e.g., during the early morning hours), there may be insufficient insolation to support both electricity generation and charging of the thermal storage system. The charging may thus be delayed until sufficient insolation levels are present. In another example, charging may be unnecessary if the thermal storage system is considered fully or adequately charged. If charging of the thermal storage system is desired, the process can proceed to 812. Otherwise the process returns to 804 to repeat.
At 812, at least a second portion of the heated working fluid (i.e., a different portion from the first portion) can be directed to a heat exchanger, which is in thermal communication with the thermal storage system. Simultaneously or subsequently, the process can proceed to 814, where thermal storage fluid is flowed in the thermal storage system. In particular, the thermal storage fluid can be flowed from the first reservoir (i.e., the cold reservoir) through the heat exchanger to the second reservoir (i.e., the warm reservoir), and/or from the second reservoir through the heat exchanger to the third reservoir (i.e., the hot reservoir). Simultaneously or subsequently, the process can proceed to 816, where the enthalpy in the working fluid is transferred to the flowing thermal storage fluid by way of the heat exchanger. When the working fluid is water, superheated steam can enter the heat exchanger at one end and leave the heat exchanger at the other end as pressurized water. Enthalpy lost by the superheated steam in the phase change transition is transferred to the flowing thermal storage fluid, thereby heating the storage fluid. The heated storage fluid accumulates in the reservoirs at respective different temperatures until the first reservoir is substantially depleted. A majority of the storage fluid accumulates in the second reservoir at a lower temperature than a minority of the storage fluid in the third reservoir. At this point, the thermal storage system may be said to be fully charged and can await subsequent discharge to accommodate a low insolation condition. The process can return to 804 to repeat.
If at 804 it is determined that there is insufficient insolation, the process proceeds to 818. At 818, working fluid from a working fluid source can be directed to the heat exchanger. For example, when the working fluid is water, a pump can pressurize water from a feedwater source to the heat exchanger. Additionally or alternatively, water output from the turbine can be directed to the heat exchanger. Simultaneously or subsequently, the process can proceed to 820, where thermal storage fluid is reverse-flowed in the thermal storage system. In particular, the thermal storage fluid can be flowed from the third reservoir (i.e., the hot reservoir) through the heat exchanger to the second reservoir (i.e., the warm reservoir), and from the second reservoir through the heat exchanger to the first reservoir (i.e., the cold reservoir). Simultaneously or subsequently, the process can proceed to 822, where the enthalpy in the flowing thermal storage fluid is transferred to the working fluid by way of the heat exchanger. When the working fluid is water, pressurized steam can enter the heat exchanger at one end and leave the heat exchanger at the other end as superheated steam. Enthalpy lost by the flowing thermal storage fluid in progressing from the third reservoir to the first reservoir is transferred to the pressurized water to effect a phase change and superheating thereof. The process can then proceed to 824, where the heated working fluid from the heat exchanger can be used to produce useful work, for example, the production of electricity. When the working fluid is water, the steam from the heat exchanger can be used to drive a turbine to obtain useful work, for example, to drive an electricity generator. Such electricity production may continue until the thermal storage system is fully discharged, i.e., when a substantial majority of the thermal storage fluid is located in the first reservoir. The process can return to 804 to repeat.
Referring to
A solar collection system 902 can receive insolation and use the insolation to evaporate pressurized water received via input line 922. The resulting steam (which may be further superheated in solar collection system 902 using the insolation) can be output from the solar collection system 902 via output line 904. The steam may be split into at least two portions: a first portion designated for thermal storage and a second portion designated for electricity generation. The relative proportions of the first and second portions may be based on a variety of factors, including, but not limited to, the amount of enthalpy in the generated steam, current electricity demand, current electricity pricing, and predicted insolation conditions. A control system 924 can be provided for regulating the operation of the solar collection system 902, the thermal storage system 912, the electricity generation system 916, the heat exchanger 910, and/or other system or flow control components (not shown). For example, the control system can be configured to execute the method shown in
The first portion of the steam can be directed via line 908 to an electricity generation system 916. The electricity generation system 916 can use the first portion of the steam to produce electricity and/or other useful work at 918. The steam may be condensed in the electricity generation process to produce water, which can be directed via line 920 back to the inlet line 922 of the solar collection system 902 for subsequent use in producing steam. Meanwhile, the second portion of the steam can be directed via input line 906 to a heat exchanger 910. The heat exchanger 910 is in thermal communication with a thermal storage system 912, which includes at least three thermal storage reservoirs, as described herein. Steam entering the heat exchanger 910 via input line 906 releases enthalpy (via conduction and/or convection) to the thermal storage system 912, thereby undergoing a phase change. The steam thus exits the heat exchanger 910 as water at output line 914. The water may be directed via line 914 back to the inlet line 922 of the solar collection system 902 for subsequent use in producing more steam.
When insolation is insufficient or non-existent, the setup of
Steam enters the second solar receiver 1108 and is further heated by at least 50° C. (or at least 100° C., 150° C., or higher) so as to generate pressurized superheated steam (or further heated supercritical steam). A first portion of the pressurized superheated steam is sent to turbine 1124 of electricity generation system 916, for example, to generate electricity. Steam and/or water at a reduced temperature and/or pressure may exit the turbine 1124 and be returned to the solar collection system 902 for re-use. A conditioner 1122 may be provided to convert the output from the turbine into pressurized water for use by the solar collection system. A second portion of the pressurized superheated steam is sent to heat exchanger assembly 910, which can include one or more heat exchangers. Within the heat exchanger assembly 910, enthalpy of the pressurized superheated steam is used to heat the thermal storage fluid in thermal storage system 912. Storage fluid in the thermal storage system 912 may flow from first reservoir 1120 to second reservoir 1118 by way of the heat exchanger assembly 910 and from second reservoir 1118 to third reservoir 1116 by way of the heat exchanger assembly 910. After the pressurized superheated steam transfers enthalpy to the thermal storage fluid, it is at a lower thermal potential. For example, water leaving the heat exchanger assembly 910 can be pressurized liquid water having a temperature below its boiling point at that pressure. One or more pumps 1112, which may be reversible, can be used to return the pressurized water exiting the heat exchanger to the solar collection system 902 for further use. When the solar collection system is configured to generate supercritical steam, the output from the heat exchanger may be sufficiently pressurized for use by the solar collection system without pump 1112 or pump 1110. Pump 1112 may thus be omitted and/or pump 1110 may be bypassed in embodiments employing supercritical working fluid.
Within heat exchanger assembly 910, a first portion of the enthalpy transferred from the steam to the thermal storage system 912 can be used to heat a first quantity of thermal storage fluid from an initial temperature to a first destination temperature, while a second portion of the enthalpy transferred from the steam to the thermal storage system 912 can be used to heat a second quantity of thermal storage fluid from an initial temperature to a second destination temperature As the thermal storage fluid is heated, it travels between the reservoirs. For example, heating of storage fluid by the first portion of the enthalpy may occur when the storage fluid is en route from the first reservoir 1120 to the second reservoir 1118. At least some of the heating by the second portion of the enthalpy may occur when the storage fluid is en route from the second reservoir 1118 to the third reservoir 1116, and/or from the first reservoir 1120 to the third reservoir 1116 (e.g., by way of a bypass line).
When discharging is necessary, for example, due to a low insolation condition, pump 1112 may reverse direction so as to pump pressurized water from feedwater supply 1114 and/or turbine 1124 to heat exchanger 910. Within the heat exchanger assembly 910, enthalpy of the thermal storage fluid in the thermal storage system is used to heat the pressurized water. Storage fluid in the thermal storage system 912 may flow from the third reservoir 1116 to the second reservoir 1118 by way of the heat exchanger assembly 910 and from the second reservoir 1118 to the first reservoir 1120 by way of the heat exchanger assembly 910. The resulting steam can be conveyed to the turbine 1124 for use in generating electricity, for example. The steam may be at a lower pressure than that obtained via insolation generally but at substantially the same temperature obtained via insolation. The turbine 1124 may thus be configured to use the lower-pressure steam. For example, the turbine 1124 can be designed for a higher swallowing capacity so as to handle an increased steam flow rate to compensate for the decreased steam pressure. Alternatively, the turbine can include an additional steam inlet port for receiving lower pressure steam at a higher flow rate. The turbine may have a power capacity of 1 MW, 5 MW, 10 MW, 50 MW, 100 MW, 250 MW, 500 MW, or higher.
The heat exchange process with heat exchanger 910 can be a substantially isobaric process. For example, the pressure of water/steam in the heat exchanger 910 may be less than 500 bar, 400 bar, 350 bar, 300 bar, or less (but sufficiently high enough to exceed the critical point pressure for supercritical embodiments). Referring to
Referring to
The first destination temperature at 1310 may be substantially equal to the boiling temperature, T1, for example. In another example, the first destination temperature at 1310 may be within a tolerance of 50° C., 25° C., 10° C., or less of the boiling temperature, T1. In still another example, the first destination temperature at 1310 may be at or within the boiling temperature, T1, with a tolerance of at most 30%, 20%, 10% or less of a difference between an initial temperature of the steam, T3, and a final temperature of the water, T4. In yet another example, the first destination temperature at 1310 may be within the boiling temperature, T1, with a tolerance of at most 30%, 20%, 10% or less of a sum of the absolute values of ΔT12 and ΔT15. For example, ΔT13/ΔT12 can be at least 0.3, 0.5, 0.7, 0.9, or higher and/or ΔT14/ΔT15 can be at least 0.3, 0.5, 0.7, 0.9, or higher. Alternatively or additionally, the sum of the absolute values of ΔT13 and ΔT15 and/or the difference between the second destination temp, T2, and the initial temperature, T5, can be at least 100° C., 125° C., 150° C., 175° C., 200° C., or higher.
In one or more embodiments, the pressure of the steam produced during the discharge phase is less than the pressure during the charging phase. In one particular example, the charging can be at supercritical pressures while the discharging is at subcritical pressures. Another example of a temperature-heat flow curve for charging and discharging processes is shown in
Although a single heat exchanger has been illustrated in
Referring to
Referring to
In one or more embodiments, the thermal storage system can include a control system, either as a shared component with the solar collection system and the electricity generation system (i.e., as part of an overall system controller) or a separate module particular to the thermal storage system (i.e., independent from but potentially interactive with other control modules). The control system can be configured to regulate flow of thermal storage fluid within and between the different storage reservoirs. For example, the control system may regulate a rate of fluid flow between the reservoirs, a timing of the fluid, an allocation parameter governing relative quantities of fluid in the reservoirs, or any other aspect governing the distribution of thermal storage fluid within the system. The flow parameters may be governed in accordance with heat transfer parameters of the flow path between reservoirs. For example, the flow parameters may be based, at least in part, on the heat transfer parameters of the heat exchanger, a temperature of the working fluid flowing through the heat exchanger, a flow rate of the working fluid flowing through the heat exchanger, or any other aspects or conditions affecting the heat transfer between the thermal storage system and the working fluid.
The control system may be configured to control other aspects of the overall system, including, for example, one or more parameters of the working fluid. For example, the control system may be configured to regulate the temperature and/or flow rate of the working fluid, at least partly in thermal communication with the heat exchanger. The control system can include any combination of mechanical or electrical components for accomplishing its goals, including but not limited to motors, pumps, valves, analog circuitry, digital circuitry, software (i.e., stored in volatile or non-volatile computer memory or storage), wired or wireless computer network(s) or any other necessary component or combination of component to accomplish its goals.
The temperature of the thermal storage fluid can also be monitored within any of the thermal storage reservoirs or combination thereof. The control system can regulate flow parameters according to the measured temperature. For example, the control system can use the measure temperatures and regulate responsively thereto in order to ensure that the temperature(s) of storage fluid in the reservoirs provide any feature disclosed herein. The measurement can be accomplished by any device known in the art. For example, the measurement can be direct (e.g., using a thermocouple or infrared sensor) or indirect (e.g., measuring a temperature in a location indicative of the fluid temperature within a reservoir).
The control system may control the various flow rate through the heat exchanger (or plurality of heat exchangers) during the charging and discharging phases to effect efficient heat transfer between the working fluid and the thermal storage fluid. For example, during the charging phase, steam at a temperature of approximately 585° C. and a pressure of approximately 170 bar may enter the heat exchanger and flow therethrough at a flow rate of approximately 317 tons per hour (tph). The steam may be reduced in temperature and/or condense in the heat exchanger so as to emerge at a temperature of approximately 295° C. and a pressure of approximately 160 bar. During the charging phase, thermal storage fluid from the cold reservoir to the warm reservoir may be controlled to flow at a higher rate than the thermal storage fluid from the warm reservoir to the hot reservoir. For example, thermal storage fluid at a temperature of approximately 290° C. from the cold reservoir may flow through the heat exchanger (or portions thereof) at a flow rate of approximately 4370 tph and arrive at the warm reservoir at a temperature of approximately 347° C. In addition, thermal storage fluid at a temperature of approximately 347° C. from the warm reservoir may flow through the heat exchanger (or portions thereof) at a flow rate of approximately 900 tph and arrive at the hot reservoir at a temperature of approximately 560° C. Of course, other temperature, pressures, and flow rates are also possible according to one or more contemplated embodiments.
Moreover, the flow rates of the thermal storage fluid can be also controlled for the bypass line (as discussed with respect to
The teachings disclosed herein may be useful for increasing solar energy generation efficiency during days of intermittent cloudy periods, maximizing electricity production and/or revenue generation of a solar electric facility, and/or meeting reliability requirements of an electric transmission network operator. In one non-limiting example, during daylight hours, (i) sub-critical or super-critical steam is generated by subjecting pressurized liquid water to insolation; (ii) a first portion of the steam (e.g., after superheating/further heating) is used to drive a turbine; and (iii) a second portion of the steam is used to heat thermal storage fluid of the thermal storage system via heat conduction and/or convection to charge the thermal storage system. At night or other period of relatively low insolation, enthalpy of the thermal storage system (i.e., when the thermal storage system is discharged) is used to evaporate and/or superheat pressurized liquid water via heat conduction and/or convection between the hotter thermal storage fluid and the cooler pressurized liquid water. This steam generated by enthalpy from the thermal storage system may be used to drive the same turbine (or any other turbine) that was driven during daylight hours by steam generated primarily by insolation. In some embodiments, the turbine driven by enthalpy of the thermal storage system operates at a lower pressure than when drive by insolation alone.
Various embodiments described herein relate to insolation and solar energy. However, this is just one example of a source of intermittent energy. The teachings herein may be applied to other forms of intermittent energy as well, according to one or more contemplated embodiments. Steam may be generated by other sources of energy and used to charge a thermal storage system. For example, fossil fuels, electricity heaters, nuclear energy, or any other source could be used to generate steam for thermal storage. Although aspects of the present disclosure relate to the production of steam using insolation for the production of electricity, it is also contemplated that the teachings presented herein can be applied to solar thermal systems that convert insolation into any of a heated working fluid, mechanical work, and electricity. Although panel-type heliostats with a central solar tower are discussed above, the teachings of the present disclosure are not limited thereto. For example, redirection and/or concentration of insolation for heating a working fluid can be accomplished using an elongated trough apparatus.
Although various embodiments of the N-reservoir solar energy storage system are explained in terms of a specific case where N is three, it is noted that greater than three reservoirs can also be used according to one or more contemplated embodiments. Moreover, some of the examples discussed herein relate to a single-phase thermal storage system for a multi-phase power generation systems. However, the teachings presented herein are not to be so limited. Rather, the teachings presented herein may be applicable to multi-phase thermal storage systems and/or single-phase power generation systems, according to one or more contemplated embodiments. Moreover, while specific examples have been discussed with respect to using water/steam as a working/heat transfer fluid, it is further contemplated that other working/heat transfer fluids can be used as well. For example, salt-water and/or pressurized carbon dioxide can be used as a working/heat transfer fluid. Other working/heat transfer fluids are also possible according to one or more contemplated embodiments. In addition, while specific examples have been discussed with respect to using molten salt and/or molten metal as the thermal storage fluid, it is contemplated that other types of thermal storage fluids can be used as well.
It will be appreciated that the modules, processes, systems, and sections described above can be implemented in hardware, hardware programmed by software, software instruction stored on a non-transitory computer readable medium or a combination of the above. A system for controlling the thermal storage system, the solar collection system, and/or the electricity generating system can be implemented, for example, using a processor configured to execute a sequence of programmed instructions stored on a non-transitory computer readable medium. The processor can include, but is not limited to, a personal computer or workstation or other such computing system that includes a processor, microprocessor, microcontroller device, or is comprised of control logic including integrated circuits such as, for example, an Application Specific Integrated Circuit (ASIC). The instructions can be compiled from source code instructions provided in accordance with a programming language such as Java, C++, C#.net or the like. The instructions can also comprise code and data objects provided in accordance with, for example, the Visual Basic™ language, or another structured or object-oriented programming language. The sequence of programmed instructions and data associated therewith can be stored in a non-transitory computer-readable medium such as a computer memory or storage device which may be any suitable memory apparatus, such as, but not limited to read-only memory (ROM), programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random-access memory (RAM), flash memory, disk drive, etc.
Furthermore, the modules, processes, systems, and sections can be implemented as a single processor or as a distributed processor. Further, it should be appreciated that the steps discussed herein may be performed on a single or distributed processor (single and/or multi-core). Also, the processes, modules, and sub-modules described in the various figures of and for embodiments above may be distributed across multiple computers or systems or may be co-located in a single processor or system. Exemplary structural embodiment alternatives suitable for implementing the modules, sections, systems, means, or processes described herein are provided below, but not limited thereto. The modules, processors or systems described herein can be implemented as a programmed general purpose computer, an electronic device programmed with microcode, a hard-wired analog logic circuit, software stored on a computer-readable medium or signal, an optical computing device, a networked system of electronic and/or optical devices, a special purpose computing device, an integrated circuit device, a semiconductor chip, and a software module or object stored on a computer-readable medium or signal, for example. Moreover, embodiments of the disclosed method, system, and computer program product can be implemented in software executed on a programmed general purpose computer, a special purpose computer, a microprocessor, or the like.
Embodiments of the method and system (or their sub-components or modules), may be implemented on a general-purpose computer, a special-purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmed logic circuit such as a programmable logic device (PLD), programmable logic array (PLA), field-programmable gate array (FPGA), programmable array logic (PAL) device, etc. In general, any process capable of implementing the functions or steps described herein can be used to implement embodiments of the method, system, or a computer program product (software program stored on a non-transitory computer readable medium).
Furthermore, embodiments of the disclosed method, system, and computer program product may be readily implemented, fully or partially, in software using, for example, object or object-oriented software development environments that provide portable source code that can be used on a variety of computer platforms. Alternatively, embodiments of the disclosed method, system, and computer program product can be implemented partially or fully in hardware using, for example, standard logic circuits or a very-large-scale integration (VLSI) design. Other hardware or software can be used to implement embodiments depending on the speed and/or efficiency requirements of the systems, the particular function, and/or particular software or hardware system, microprocessor, or microcomputer being utilized. Embodiments of the method, system, and computer program product can be implemented in hardware and/or software using any known or later developed systems or structures, devices and/or software by those of ordinary skill in the applicable art from the function description provided herein and with a general basic knowledge of solar collection, thermal storage, electricity generation, and/or computer programming arts.
Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features.
It is thus apparent that there is provided in accordance with the present disclosure, system, methods, and devices for solar energy storage using three or more reservoirs. Many alternatives, modifications, and variations are enabled by the present disclosure. While specific embodiments have been shown and described in detail to illustrate the application of the principles of the present invention, it will be understood that the invention may be embodied otherwise without departing from such principles. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.
The present application claims the benefit of U.S. Provisional Application No. 61/440,454, filed Feb. 8, 2011, which is hereby incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB11/55357 | 11/29/2011 | WO | 00 | 6/29/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61440454 | Feb 2011 | US |
