Patent Application
20160156309
Described herein are systems, methods and apparatus relating generally to the collection of solar energy to provide electrical energy, thermal energy, or electrical energy and thermal energy.
Solar energy supply is sufficient in many geographical regions to satisfy energy demands, in part, by provision of electric power and useful heat. Solar energy systems may be used to replace or augment traditional energy sources powered by fossil fuel. Improved solar energy systems are needed to satisfy increasing worldwide energy demands. Improved solar energy systems incorporating energy storage are needed. In particular, improved solar energy systems that are capable of delivering substantial dispatchable electrical energy (for example, during low solar output periods or during peak demand times) are desired.
Systems, methods, and apparatus in which solar energy is collected and converted to electrical energy, thermal energy, or a combination of electrical energy and thermal energy are described herein. These systems, methods and apparatus may provide solar-generated dispatchable useful work (e.g., electrical energy) as demanded.
Solar energy systems according to a first aspect of the invention comprise a concentrating photovoltaic-thermal solar energy collector capable of generating electrical energy e1 and heat h1 for use in one or more applications. At least a portion of the solar-generated electrical energy e1 may be used to drive a heat pump to draw heat h2 from a cold reservoir. A hot reservoir may be heated at least in part using at least a portion of heat h1 from the photovoltaic-thermal solar energy collector and at least a portion of heat h2 generated by the heat pump. A heat engine may be used to convert thermal energy in the hot reservoir to electrical energy e2. Electrical energy e2 is dispatchable energy that may be used as demanded, for example, during low solar output times, or during high demand times.
Some variations of the systems may be configured or operated so that electrical energy e2 is generated from the hot reservoir at a time delayed relative to the generation of electrical energy e1. For example, thermal energy may be stored for a desired time period in the hot reservoir and, upon demand, the thermal energy in the hot reservoir may be converted to electrical energy e2. In some cases, systems may be configured or operated so electrical energy e2 is generated from thermal energy in the hot reservoir during generation of electrical energy e1 by the photovoltaic-thermal solar energy collector. Some systems may be configured or operated so that electrical energy e2 is generated from thermal energy in the hot reservoir when no electrical energy e1 is being generated by the photovoltaic-thermal solar energy collector.
Any suitable heat engine may be used in the systems to convert thermal energy of the hot reservoir to electrical energy e2. In some cases, the heat engine is or comprises the heat pump run in a reverse direction, so that heat flows from the hot reservoir to the cold reservoir. In some cases, the heat engine comprises an organic Rankine cycle engine. In some variations, the heat engine comprises an organic Rankine cycle engine and the heat pump, which may be configured as separate stand-alone units or integrated into a combined unit.
In some variations, the systems may be configured or operated so that the dispatchable electrical energy e2 generated from the hot reservoir is about equal to the electrical energy e1 generated by the photovoltaic-thermal solar energy collector. In some variations, the systems are configured or operated so that e2 is at least about 0.5 times e1, at least about 0.6 times e1, at least about 0.7 times el, at least about 0.8 times e1, or at least about 0.9 times e1. In some cases, e2 may be greater than e1.
Any of these systems may employ one or more heat transfer fluids for carrying heat. For example, systems may comprise a heat transfer fluid for carrying heat h1 generated by the photovoltaic-thermal solar energy collector and/or a heat transfer fluid for carrying heat h2 drawn from the cold reservoir. For example, in some variations, a system comprises a heat transfer fluid HTF1 that, in operation, flows through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect heat h1. In some variations, a system comprises a heat transfer fluid HTF2 that carries heat h2 produced by the heat pump. In some variations, a system comprises a heat transfer fluid HTF1 for carrying heat h1 and a heat transfer fluid HTF2 for carrying heat h2.
During operation of some variations of the systems, a heat transfer fluid HTF1 heated by the photovoltaic-thermal solar energy collector and carrying heat h1 has a temperature T1 that is greater than a temperature T2 of the heat transfer fluid HTF2 heated by the heat pump and carrying h2. In some cases, a heat transfer fluid HTF1 carrying heat h1 has a temperature T1 that is less than a temperature T2 of a heat transfer fluid HTF2 carrying heat h2. In some cases, a temperature Ti of a heat transfer fluid HTF1 carrying heat h1 is approximately equal to a temperature T2 of a heat transfer fluid HTF2 carrying heat h2.
Optionally, any of the systems may employ one or more heat exchangers. For example, a system may comprise any one of or any combination of two or more of the following heat exchangers: a) a heat exchanger for transferring heat h1 from the photovoltaic-thermal solar energy collector to the hot reservoir; b) a heat exchanger for transferring heat h2 from the heat pump to the hot reservoir; and c) a heat exchanger for transferring heat between a heat transfer fluid HTF1 carrying heat h1 and a heat transfer fluid HTF2 carrying heat h2.
A variety of system configurations may be used for heating the hot reservoir with heat h1 and heat h2 using one or more heat transfer fluids. In one variation, a heat transfer fluid HTF1 flows through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect heat h1. A heat transfer fluid HTF2 carries h2 from the heat pump. The heat transfer fluid HTF1 passes through a heat exchanger to transfer heat h1 to a heat transfer fluid HTF3. Heat transfer fluid HTF3 carrying heat h1 and heat transfer fluid HTF2 carrying h2 are used to heat the hot reservoir. For example, the heat transfer fluids HTF2 and HTF3 may be combined in the hot reservoir. Optionally, the heat transfer fluid HTF1 may be recirculated in a closed or open recirculation loop through one or more fluid channels in the photovoltaic-thermal solar energy collector and the heat exchanger.
In some variations of the systems, the photovoltaic-thermal solar energy collector is used to boost thermal energy of a heat transfer fluid carrying heat h2 from the heat pump. In one example, a heat transfer fluid HTF1 carrying heat h1 from the photovoltaic-thermal solar energy collector and having temperature T1 transfers thermal energy via a heat exchanger to a heat transfer fluid HTF2 carrying heat h2 from the heat pump having temperature T2 that is less than T1. Following heat exchange, the heat transfer fluid HTF2 carries heat h1+h2 (minus possible heat loss due to transfer inefficiency) that is used to heat the hot reservoir. Optionally, the heat transfer fluid HTF1 may be recirculated through one or more fluid channels in the photovoltaic-thermal solar energy collector in an open or closed recirculation loop. In another example, a heat transfer fluid HTF2 heated by the heat pump and carrying heat h2 flows through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect additional heat h1. Following boosting by the photovoltaic-thermal solar energy collector, the heat transfer fluid HTF2 carries heat h2+h1 which is used to heat the hot reservoir.
In other variations of the systems, the heat pump is used to boost the thermal energy of a heat transfer fluid carrying heat h1 from the photovoltaic-thermal solar energy collector. In one example, a heat transfer fluid HTF2 carrying heat h2 from the heat pump and having temperature T2 transfers thermal energy via a heat exchanger to a heat transfer fluid HTF1 carrying heat h1 from the photovoltaic-thermal energy solar collector having temperature T1 that is less than T2. Following heat exchange, the heat transfer fluid HTF1 carries heat h1+h2 (minus possible heat loss due to transfer inefficiency) that is used to heat the hot reservoir. In another example, a heat pump draws heat h1 from a heat transfer fluid HTF1 that collects heat from the photovoltaic-thermal solar energy collector. The heat pump draws heat h2 from the cold reservoir. A heat transfer fluid HTF2 carrying h1+h2 from the heat pump is used to heat the hot reservoir.
Any suitable cold reservoir may be used in the systems. In some cases, at least a portion of the cold reservoir is the ambient environment. In some cases, the cold reservoir is the ambient environment. In some cases, the cold reservoir may be passively cooled by the ambient environment. In some cases, the cold reservoir may be actively cooled (e. g., using a portion of electrical energy e1 and/or an external cooling source). The negative heat (cold) in the cold reservoir may in some variations be allowed to dissipate to the environment, and in some variations the cold may be stored for use. For example, the cold reservoir may comprise a vessel containing a thermal storage medium (for example, water, ice, or a mixture of water and ice) from which heat may be drawn. The cooled thermal storage medium may be used for one or more cooling applications. In some cases, the cold reservoir from which heat is drawn may be used for cooling one or more applications internal to the system or external to the system. For example, the cold reservoir may be utilized for cooling the heat engine, e. g., a condensing portion of the heat engine. In certain variations in which the heat engine comprises an organic Rankine cycle engine, the cold reservoir may be used for cooling the organic Rankine cycle engine, e. g., a condensing portion of the organic Rankine cycle engine. In some systems, the cold reservoir may be used to cool one or more photovoltaic cells in a receiver in the photovoltaic-thermal solar energy collector.
The systems may employ a variety of schemes by which the heat pump is driven. The heat pump may be driven at least in part using electrical energy e1. In some cases, substantially all of the electrical energy e1 generated is used to drive the heat pump. In other cases, a portion of the generated electrical energy e1 is used to drive the heat pump, and a portion of e1 is used for another application that may be an internal application within the system or an external application outside of the system. In some situations, external energy e3 from an external energy source is used in combination with electrical energy e1 to drive the heat pump. External energy e3 may be from any type of supplemental energy source, including mechanical energy, energy derived from burning fossil fuels or plant-based fuels, or electrical energy (e. g., from the power grid, a generator, a battery, another solar energy collector, a wind turbine, a hydroelectric source, or the like). The energies e1 and e3 may be used in any suitable relative amounts and may be combined in any manner to drive the heat pump. For example, e1 and e3 may be used in a parallel operation so that both e1 and e3 are supplied simultaneously to the heat pump in any relative amounts. The relative amounts of e1 and e3 need not stay constant with time, and may be adjusted according to operating conditions (e. g., time of day, weather, season and/or demand). In other instances, e1 and e3 may be supplied in an alternating manner to the heat pump. The alternating scheme may be at regular intervals, or may be irregular intervals determined by an operator based on operating conditions. If e1 and e3 are alternated at regular intervals, the frequency at which they are alternated may be any suitable frequency and the frequency of alternating may be adjusted during operation to accommodation conditions, for example time of day, weather, season and/or demand. For example, e1 may be used during peak sunlight hours and e3 may be used during darkness. The duration of alternating intervals may be adjusted, for example, seasonally.
In these systems, at least a portion of heat h1 and at least a portion of heat h2 are used to heat the hot reservoir, but it is not required that heats hl and h2 be used continuously or simultaneously to heat the hot reservoir, and instead any combination of heat h1 and h2 may be applied intermittently, or heat h1 and heat h2 may be alternately used to heat the hot reservoir. In some variations, the systems employ an external heat source h3 to supply supplemental heat to the hot reservoir.
In these systems, the photovoltaic-thermal solar energy collector may be capable of generating any suitable relative quantities of heat h1 and electrical energy e1. For example, in some variations, heat h1 is approximately four times e1. The systems may be capable of heating a hot reservoir using heat h1 from the photovoltaic-thermal solar energy collector and heat h2 drawn from the cold reservoir by the heat pump so that the thermal energy in the hot reservoir is, for example, about 6 times e1, about 7 times e1, about 8 times e1, about 9 times e1 or about 10 times e1.
A system may be operated at any suitable operating temperature to achieve a desired temperature difference between the hot reservoir and the cold reservoir that is used by the heat engine to generate electrical energy e2. In some variations, the hot reservoir in operation may have a temperature TH of about 100° C.-120° C. and the cold reservoir may have a temperature TC of about 25° C.-40° C. A photovoltaic receiver in the photovoltaic-thermal solar energy collector in the system may utilize any suitable type of photovoltaic cells that demonstrates sufficient efficiency at the desired operating temperature. In some cases, one or more photovoltaic cells that are capable of demonstrating a desired efficiency at a temperature of about 100° C., about 120° C., or even higher are used. In some cases, one or more heterojunction intrinsic thin film photovoltaic cells may be used in the receiver.
One variation of a system for generating dispatchable electrical energy according to the first aspect of the invention comprises one or more concentrating photovoltaic-thermal solar energy collectors comprising a reflector for focusing incident solar radiation on a receiver. The receiver comprises one or more photovoltaic cells that generate electrical energy e1. The system comprises a cold reservoir and a heat pump driven at least in part by electrical energy e1 that draws heat h2 from the cold reservoir. The system comprises a hot reservoir that, in operation, is heated at least in part with heat h1 and h2. The system comprises an organic Rankine cycle engine that converts thermal energy in the hot reservoir to electrical energy e2 using the temperature difference between the hot and cold reservoirs. The system may be capable of generating electrical energy e2 that is at least about 0.5 times e1, at least about 0.6 times e1, at least about 0.7 times e1, at least about 0.8 times e1, at least about 0.9 times e1, about e1, or greater than e1. In some variations, the system may be configured for generating electrical energy e2 at a time delayed relative to the generation of electrical energy e1. In some variations, the system may be operated so that the hot reservoir is at temperature in a range from about 100° C. to 120° C. and the cold reservoir is at a temperature in a range from about 25° C. to about 40° C.
Methods for generating dispatchable useful work (e.g., dispatchable electric energy) according to a second aspect of the invention comprise generating electrical energy e1 and collecting heat h1 using a concentrating photovoltaic-thermal solar energy collector, drawing heat h2 from a cold reservoir using a heat pump optionally powered at least in part by electrical energy e1, heating a hot reservoir with heat h1 and heat h2, and generating electrical energy e2 from thermal energy in the hot reservoir. Electrical energy e2 is dispatchable energy that may be used as demanded, for example, during low solar output periods, or during high demand times.
In certain variations, the methods are used to generate electrical energy e2 at a time delayed relative to the generation of electrical energy e1, for example, a method may comprise storing thermal energy for a time period in the hot reservoir, and upon demand, converting the stored thermal energy to electrical energy e2. In some cases, a method may comprise generating electrical energy e2 from the hot reservoir while generating at least some electrical energy e1 using the photovoltaic-thermal solar energy collector. In some cases, a method may comprise generating electrical energy e2 from the hot reservoir during a time period in which no electrical energy e1 is being generated by the photovoltaic-thermal solar energy collector.
The methods may utilize any suitable means, apparatus, or scheme to convert thermal energy in the hot reservoir to electrical energy e2. In some cases, a method comprises using a heat engine to convert thermal energy of the hot reservoir to electrical energy e2. In some variations, the methods comprise operating the heat pump in a reverse direction so that heat flows from the hot reservoir to the cold reservoir to generate electrical energy e2. In some methods, an organic Rankine cycle engine is used to convert thermal energy in the hot reservoir to electrical energy e2. In some variations, an organic Rankine cycle engine is used in combination with the heat pump to convert thermal energy in the hot reservoir to electrical energy e2.
The methods may be adapted for generating any suitable quantity of dispatchable electrical energy e2 relative to a quantity of electrical energy e1 generated by the photovoltaic-thermal energy solar collector. For example, the methods may be adapted for generating dispatchable electrical energy e2 that is at least about 0.5 times e1, at least about 0.6 times e1, at least about 0.7 times e1, at least about 0.8 times e1, at least about 0.9 times e1, or about equal to e1. In some cases, the methods may be adapted to generate e2 that is greater than e1.
In any of these methods, one or more heat transfer fluids may be used for transferring heat h1 generated by the photovoltaic-thermal solar energy collector and/or heat h2 drawn from the cold reservoir to the hot reservoir. For example, in some variations, a heat transfer fluid HTF1 may be flowed through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect heat h1. In some methods, a heat transfer fluid HTF2 may be heated by the heat pump to carry h2. In some methods, a heat transfer fluid HTF1 may be flowed through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect heat h1 and a heat transfer fluid HTF2 may be heated by the heat pump to carry heat h2.
Optionally, any of these methods may employ one or more heat exchangers. For example, a method may use any one of or any combination of two or more of the following heat exchangers: a) a heat exchanger for transferring heat h1 from the photovoltaic-thermal solar energy collector to the hot reservoir; b) a heat exchanger for transferring heat h2 from the heat pump to the hot reservoir; and c) a heat exchanger for transferring heat between a heat transfer fluid HTF1 carrying heat h1 and a heat transfer fluid HTF2 carrying heat h2.
In some variations of the methods, a heat transfer fluid HTF1 heated by the photovoltaic-thermal solar energy collector and carrying heat h1 has a temperature T1 that is greater than a temperature T2 of the heat transfer fluid HTF2 heated by the heat pump and carrying heat h2. In other variations of the methods, a heat transfer fluid HTF1 carrying heat h1 has temperature T1 that is less than temperature T2 of a heat transfer fluid HTF2 carrying h2. In still other variations of the methods, a heat transfer fluid HTF1 carrying heat h1 has temperature Ti that is approximately equal to temperature T2 of a heat transfer fluid HTF2 carrying h2.
Several variations of the methods may be employed for heating the hot reservoir with heat h1 and heat h2 using one or more heat transfer fluids. In one variation, the methods comprise flowing a heat transfer fluid HTF1 through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect heat h1, and collecting heat h2 from the heat pump with a heat transfer fluid HTF2. The methods may comprise passing the heat transfer fluid HTF1 through a heat exchanger to transfer heat h1 to a heat transfer fluid HTF3, and using the heat transfer fluid HTF3 carrying h1 and the heat transfer fluid HTF2 carrying heat h2 to heat the hot reservoir. In some variations, the heat transfer fluids HTF2 and HTF3 may be combined in the hot reservoir. Optionally, the methods may comprising recirculating the heat transfer fluid HTF1 in a closed or open recirculation loop through one or more fluid channels in the photovoltaic-thermal solar energy collector and the heat exchanger.
In some variations of the methods, the photovoltaic-thermal solar energy collector is used to boost thermal energy of a heat transfer fluid carrying heat h2 from the heat pump. In one example, the methods comprise transferring heat via a heat exchanger from a heat transfer fluid HTF1 carrying heat h1 from the photovoltaic-thermal solar energy collector and having temperature T1 to a heat transfer fluid HTF2 carrying heat h2 from the heat pump having temperature T2 that is less than T1. Following heat exchange, the methods comprise using the heat transfer fluid HTF2 carrying heat h1+h2 (minus possible heat loss due to transfer inefficiency) to heat the hot reservoir. Optionally, the methods comprise recirculating the heat transfer fluid HTF2 through one or more fluid channels in the photovoltaic-thermal solar energy collector and the heat exchanger in an open or closed recirculation loop. In another example, the methods comprise passing a heat transfer fluid HTF2 carrying heat h2 from the heat pump through one or more fluid channels in the photovoltaic-thermal solar energy collector to collect additional heat h1. Following boosting by the photovoltaic-thermal solar energy collector, the methods comprise using the heat transfer fluid HTF2 carrying heat h2+h1 to heat the hot reservoir.
In other variations of the methods, the heat pump is used to boost the thermal energy of a heat transfer fluid carrying heat h1 from the photovoltaic-thermal solar energy collector. In one example, the methods comprise transferring heat a via heat exchanger from a heat transfer fluid HTF2 carrying heat h2 from the heat pump and having temperature T2 to a heat transfer fluid HTF1 carrying heat h1 and having temperature T1 that is less than T2. Following heat exchange, the methods comprise using the heat transfer fluid HTF1 carrying heat h1+h2 (minus possible heat loss due to transfer inefficiency) to heat the hot reservoir. In another example, the methods comprise using the heat pump to draw heat h2 from the cold reservoir and to draw heat h1 from a heat transfer fluid HTF1 that collects heat from the photovoltaic-thermal solar energy collector. The methods comprise using a heat transfer fluid HTF2 carrying heat h1+h2 from the heat pump to heat the hot reservoir.
Any suitable cold reservoir may be used in the methods. Some methods use the ambient environment as at least a portion of the cold reservoir. Some methods use the ambient environment as the cold reservoir. In some methods, the cold reservoir may be actively cooled (e. g., using an external energy source and/or using a portion of electrical energy e1 generated by the photovoltaic-thermal energy solar collector) or may be passively cooled using the ambient environment. Some methods use a vessel containing a thermal storage medium (for example, water, ice, or a mixture of water and ice) as the cold reservoir from which heat may be drawn by the heat pump.
Negative heat (cold) in the cold reservoir may or may not be stored for use. In some cases, the cooling is not stored, and is allowed to dissipate into the environment. In other cases, the methods may comprise storing a cooled thermal energy storage medium (e.g., water, ice, or a mixture of water and ice) in the cold reservoir for use. Some variations of the methods may use the cold reservoir for a cooling application in a photovoltaic-thermal energy solar collector, heat pump, heat engine, or other system components used in the methods. For example, certain methods may comprise using the cold reservoir for cooling a heat engine, e. g., a condensing portion of the heat engine, that is used to convert thermal energy in the hot reservoir to electrical energy e2. In those variations in which an organic Rankine cycle engine is used to convert thermal energy in the hot reservoir to electrical energy e2, the methods may comprise using the cold reservoir for cooling a condensing portion of the organic Rankine cycle engine. Some methods may comprise cooling one or more photovoltaic cells in a receiver in the photovoltaic-thermal solar energy collector using the cold reservoir. Certain method may comprise using the cold reservoir to cool a heat engine and cooling one or more photovoltaic cells. Variations of the methods comprise using the cold reservoir to cool an application external to the photovoltaic-thermal solar energy collector, heat pump, heat engine, and associated components.
The methods may employ a variety of schemes by which the heat pump is driven. The heat pump may be driven at least in part using electrical energy e1. Some methods comprise using substantially all of the electrical energy e1 generated to drive the heat pump.
Other methods comprise using a portion of the generated electrical energy e1 to drive the heat pump, and using a portion of e1 for one or more additional applications. Certain variations of the methods comprise using external energy e3 from an external energy source and electrical energy e1 to drive the heat pump. External energy e3 may be from any type of supplemental energy source, including mechanical energy, energy derived from burning fossil fuels or plant-based fuels, or electrical energy (e. g., from the power grid, a generator, a battery, another solar energy collector, a wind turbine, a hydroelectric source, or the like). The energies e1 and e3 may be used in any suitable relative amounts and may be combined in any manner to drive the heat pump. For example, in some methods, e1 and e3 are used in a parallel operation so that both e1 and e2 are supplied simultaneously to the heat pump in any relative amounts. The relative amounts of e1 and e2 need not stay constant with time, and may be adjusted according to operation conditions (e. g., time of day, weather, season and/or demand). In other variations of the methods, e1 and e3 are supplied in an alternating manner to the heat pump. The alternating scheme may be at regular intervals, or may be at irregular intervals determined by an operator based on operating conditions. If e1 and e3 are alternated at regular intervals, the frequency at which they are alternated may be any suitable frequency and the frequency of alternating may be adjusted during operation to accommodate conditions, for example time of day, weather, season and/or demand. For example, e1 may be used during peak sunlight hours and e3 may be used during darkness. The duration of alternating intervals may be adjusted, for example, seasonally.
In these methods, at least a portion of heat h1 and at least a portion of heat h2 are used to heat the hot reservoir, but it is not required that heats h1 and h2 be used continuously or simultaneously to heat the hot reservoir, and instead any combination of heat h1 and h2 may be applied intermittently, or heat h1 and heat h2 may be alternately used to heat the hot reservoir. Some variations of the methods may comprise using a supplemental heat source h3 to heat the hot reservoir.
These methods may be adapted for generating any suitable relative quantities of heat h1 and electrical energy e1 using the photovoltaic-thermal solar energy collector. For example, the methods may produce heat h1 that is approximately e1, about 2 times e1, about 3 times e1, about 4 times e1, about 5 times e1, about 6 times e1, about 7 times e1, about 8 times e1, about 9 times e1, or 10 times e1. In some cases, the methods produce h1 that is about 4 times e1. The methods may be adapted for heating the hot reservoir using heat h1 from the photovoltaic-thermal solar energy collector and heat h2 drawn by the heat pump from the cold reservoir so that the thermal energy in the hot reservoir is about e1, about 2 times e1, about 3 times e1, about 4 times e1, about 5 times e1, about 6 times e1, about 7 times e1, about 8 times e1, about 9 times e1 or about 10 times e1.
In these methods, the receiver in the photovoltaic-thermal solar energy collector may operate at any suitable temperature. In some cases, the methods include operating a photovoltaic portion of the receiver at temperatures of about 100° C.-120° C. Photovoltaic cells may be selected to have optimal efficiencies over the desired operating temperature range. For example, in methods in which the receiver is operated at a temperature of about 110° C.-120° C., one or more heterojunction intrinsic thin film photovoltaic cells may be used in the receiver.
Solar energy systems according to a third aspect of the invention comprise a concentrating photovoltaic-thermal solar energy collector capable of generating electrical energy We and collecting heat Q1 for use in one or more applications. The systems comprise a cold reservoir and a hot reservoir that is configured to be heated at least in part using solar-generated heat Q1. The systems comprise a heat pump that may be configured to be powered at least in part using solar-generated electrical energy We. The heat pump (e.g., a chiller) is configured to draw heat from the cold reservoir, thereby reducing a temperature of the cold reservoir. The heat pump may exhaust the heat drawn from the cold reservoir to the ambient environment, for example. The systems comprise a heat engine that is configured to operate between the hot reservoir and the cold reservoir to generate useful work. In some variations, the heat engine is configured to generate electrical work.
The solar energy systems may be configured for storing energy in the hot and cold reservoirs and operating the heat engine at a time delayed relative to the generation of electrical energy We to generate dispatchable useful work, e. g., dispatchable electrical energy. The dispatchable useful work may be produced as demanded, for example, during low solar output times, or during high demand periods. In some variations, the systems may be configured for generating an amount of dispatchable electrical energy that is at least 0.5 times the solar-generated electrical energy We, at least 0.6 times We, at least 0.7 times We, at least 0.8 times We, or at least 0.9 times We. In some cases, the systems may be configured for generating an amount of dispatchable electrical energy that is about equal to the solar-generated electrical energy We. Some systems are configured for generating an amount of dispatchable electrical energy that is greater than the solar-generated electrical energy We.
The heat pump or chiller used in these systems may be any suitable type of heat pump or chiller. Non-limiting examples include vapor-compression chillers, absorption chillers, and adsorption chillers.
The heat engine used in the systems may be any suitable type of heat engine. Non-limiting examples include organic Rankine cycle heat engines, Stirling heat engines, Brayton cycle heat engines, and thermoelectric devices. In some variations, the heat engine comprises an organic Rankine cycle heat engine.
In some variations of the systems, the heat pump and the heat engine may share one or more common components. In some cases, the heat engine comprises the heat pump operated in a reverse direction. In certain variations of the systems, the heat pump and the heat engine may be integrated into a combined unit.
Certain variations of the systems comprise a controller configured for controlling during operation a portion of solar-generated electrical energy We that is used to power the heat pump and a portion of electrical energy We that is supplied to an electrical grid based on a time-dependent market value of electricity.
Although the heat pump in these systems may be configured to be powered at least in part using solar-generated electrical energy We, at certain times during operation the heat pump may be powered in part or completely by an external energy source e3 (e.g., an electrical power grid). At various times during operation, the heat pump may be powered by any one of: a) electrical energy We; b) external energy source e3; c) electrical energy We alternated with external energy source e3; and d) electrical energy We in parallel with external energy source e3. In some operational modes, substantially all of electrical energy We is used to drive the heat pump. In other modes, a portion of We is used for another application that may be an internal application within the system, or an eternal application outside the system (e.g., a portion of We may be delivered to the grid). If external energy source e3 is used to drive the heat pump, external energy e3 may be from any type of supplemental energy source, including the power grid, a generator, a battery, another solar energy collector, a wind turbine, a hydroelectric source, mechanical energy, energy derived from burning fossil fuels or plant-based fuels, and the like. If external energy e3 is used in combination with all or a portion of We to drive the heat pump, any suitable relative amounts of We and e3 may be used, and We and e3 may be combined in any manner to drive the heat pump.
In these systems, at least a portion of solar-generated heat Q1 is used to heat the hot reservoir, but it is not required that all of heat Q1 be used to heat the hot reservoir. In some variations, substantially all of heat Q1 is used to heat the hot reservoir, and in other variations, a portion of heat Q1 is diverted for a use other than heating the hot reservoir. In some variations, the systems may employ a supplemental heat source to heat the hot reservoir.
The systems comprise a photovoltaic-thermal solar energy collector configured for providing any suitable ratio of heat Q1 to electrical energy We. In some cases, the ratio Q1:We is in a range from about 3 to about 6, or in a range from about 3 to about 5. In some cases, the ratio Q1:We is about 3. In some cases, the ratio Q1:We is about 4. In some cases, the ratio Q1:We is about 5.
The photovoltaic-thermal solar energy collector in the systems may be operated at any suitable temperature. In some cases, the photovoltaic-thermal solar energy collector operates at a temperature of about 100° C.-120° C., or about 110° C.-120 ° C. In those cases, photovoltaic cells may be selected that have useful efficiencies at an operating temperature of about 120° C. For example, the photovoltaic-thermal solar energy collector may comprise one or more heterojunction intrinsic thin film photovoltaic cells capable of generating electrical energy at an operating temperature of about 120° C.
A system may be operated to achieve a desired temperature difference between the hot reservoir and the cold reservoir so that the heat engine operating between the hot and cold reservoir operates with a desired efficiency. For example, if the heat engine is an organic Rankine cycle heat engine, the hot reservoir may be operated at about 110° C.-120° C. (e.g., about 110° C., about 115° C., or about 120° C.) and the cold reservoir may be cooled to a temperature of about −5° C. to about 10° C., e.g., about −5° C., about −3° C., about 0° C., about 1° C., about 2° C., about 3° C., about 5° C., about 6° C., about 7° C., about 8° C., about 9° C., or about 10° C. In some cases, the heat engine is an organic Rankine cycle heat engine and the hot reservoir is operated at about 120° C. and the cold reservoir is cooled to a temperature in a range from about 0° C. to about 7° C., e.g., about 0° C., about 1° C., about 2° C., about 3° C., about 5° C., about 6° C., or about 7° C.
One variation of a system according to the third aspect of the invention comprises one or more concentrating photovoltaic-thermal solar energy collectors, each comprising one or more reflectors for focusing incident solar radiation on a receiver. The receiver comprises one or more photovoltaic cells that generate electrical energy We, and one or more fluid channels through which a heat transfer fluid flows and collects heat Q1 produced in the receiver. The system comprises a cold reservoir and a hot reservoir. The system comprises a chiller configured to draw heat from the cold reservoir, thereby lowering a temperature of the cold reservoir, and an organic Rankine cycle heat engine configured to operate between the hot reservoir and the cold reservoir to generate useful work. The chiller may be configured to be driven at least in part by electrical energy We. In some variations of the system, the organic Rankine cycle heat engine is configured for generating electric work. The system may be configured for operating the heat engine to generate useful work at a time delayed relative to the generation of electrical energy We, so that energy is effectively stored in the hot and cold reservoirs.
Methods for generating dispatchable useful work (e.g., dispatchable electrical energy) according to a fourth aspect of the invention comprise generating electrical energy We and collecting heat Q1 using a concentrating photovoltaic-thermal solar energy collector, drawing heat from a cold reservoir to reduce a temperature of the cold reservoir, heating a hot reservoir at least in part using heat Q1, and operating a heat engine between the hot reservoir and the cold reservoir to generate useful work, e.g., electrical work. The heat drawn from the cold reservoir may be exhausted to the ambient environment, for example. In certain variations, the methods comprise powering a heat pump at least in part using electrical energy We to draw heat from the cold reservoir.
In certain variations, the methods are used to generate dispatchable useful work at a time delayed relative to the generation of electrical energy We. For example, a method may comprise storing energy for a time period in the hot and cold reservoirs, and upon demand, operating the heat engine to convert the stored energy in the hot and cold reservoirs to generate useful work (e.g., electrical work). The dispatchable energy may be produced upon demand, for example, during low solar output periods or during high power demand periods. In some cases, the methods comprise generating an amount of dispatchable electric energy that is at least about 0.5 times We, at least about 0.6 times We, at least about 0.7 times We, at least about 0.8 times We, or at least about 0.9 times We. In certain cases, the methods comprise generating an amount of dispatchable electric energy that is approximately equal to We. In some cases, the methods comprise generating an amount of dispatchable electric energy that is greater than We.
The methods may employ any suitable type of heat pump or chiller for drawing heat from the cold reservoir to reduce the temperature of the cold reservoir. Non-limiting examples include vapor-compression chillers, absorption chillers, and adsorption chillers.
The methods may employ any suitable type of heat engine to operate between the hot reservoir and the cold reservoir to generate useful work. Non-limiting examples include organic Rankine cycle heat engines, Stirling heat engines, Brayton heat engines, and thermoelectric devices. In some variations, the heat engine comprises an organic Rankine cycle heat engine.
At certain times during operation the methods may employ an external energy source e3 (e.g., an electric power grid) to drive the heat pump. At other times during operation, the methods may comprise driving the heat pump solely using solar-generated We. In some modes of operation, the methods may comprise using We in combination with an external energy source e3 to drive the heat pump, where We and e3 may be delivered in parallel or in an alternating scheme. If external energy source e3 is used to drive the heat pump, external energy e3 may be from any type of supplemental energy source, including the power grid, a generator, a battery, another solar energy collector, a wind turbine, a hydroelectric source, mechanical energy, energy derived from burning fossil fuels or plant-based fuels, and the like. If external energy e3 is used in combination with all or a portion of We to drive the heat pump, any suitable relative amounts of We and e3 may be used, and We and e3 may be combined in any manner to drive the heat pump.
In these methods, at least a portion of solar-generated heat Q1 is used to heat the hot reservoir, but it is not required that all of heat Q1 be used to heat the hot reservoir. In some variations, substantially all of heat Q1 is used to heat the hot reservoir, and in other variations, a portion of heat Q1 is diverted for a use other than heating the hot reservoir. In some variations, the methods may employ a supplemental heat source to heat the hot reservoir.
In some operational modes, the methods comprise using substantially all of electrical energy We to drive the heat pump. In other operational modes, the methods may divert essentially all or a portion of We for another application that may be an internal application within the system, or an external application outside the system. At certain times during operation, essentially all of We, or a portion of We (e.g., the balance of We that is not used to drive the heat pump) may be supplied to the grid. The methods may comprise controlling the portion of electrical energy We that is used to power the heat pump and the portion of electrical energy We that is supplied to the power grid based on a time-dependent market value of electric energy.
The methods may comprise operating the photovoltaic-thermal solar energy collector at any suitable temperature. In some cases, the photovoltaic-thermal solar energy collector is operated at a temperature of about 100° C.-120° C., or about 110° C.-120° C. In those cases, photovoltaic cells in the photovoltaic-thermal solar energy collector may be selected that have useful efficiencies at an operating temperature of about 120° C. For example, the photovoltaic-thermal solar energy collector may comprise one or more heterojunction intrinsic thin film photovoltaic cells capable of generating electrical energy at an operating temperature of about 120° C.
The methods may comprise heating the hot reservoir and cooling the cold reservoir to achieve a desired temperature difference between the hot reservoir and the cold reservoir so that the heat engine operating between the hot and cold reservoir operates with a desired efficiency. The methods may comprise reducing the temperature of the cold reservoir to a temperature TL, where TL is selected to optimize energy stored in the hot and cold reservoirs from which dispatchable energy is produced by operation of the heat engine. In certain methods utilizing an organic Rankine cycle heat engine, the methods may comprise heating the hot reservoir to a temperature of about 110° C.-120° C. (e.g., about 110° C., about 115° C., or about 120° C.) and cooling the cold reservoir to a temperature of about −5° C. to about 10° C., e.g., about −5° C., about −3° C., about −2° C., about −1° C., about 0° C., about 1° C., about 2° C., about 3° C., about 5° C., about 6° C., about 7° C., about 8° C., about 9° C., or about 10° C. Some methods employing an organic Rankine cycle heat engine comprise storing water in the hot reservoir at a temperature of about 120° C. and cooling water in the cold reservoir to a temperature TL that is in a range from about −5° C. to about 10° C., or from about −3° C. to about 7° C., or from about 0° C. to about 7° C., or from about 0° C. to about 5° C. For example the temperature of the hot reservoir may be about 120° C. and TL may be about −3° C., about −2° C., about −1° C., about 0° C., about 1° C., about 2° C., about 3° C., about 4° C., about 5° C., about 6° C., or about 7° C.
In certain modes of operation, the methods comprise alternating operation of the heat pump with operation of the heat engine, so that the heat pump and the heat engine are not operated at the same time.
The methods comprise generating electric energy We and collecting heat Q1 using a photovoltaic-thermal solar energy collector, where a ratio of Q1:We may be any suitable amount. For example, in some cases, the photovoltaic-thermal solar energy collector produces a ratio Q1: We in a range from about 3 to about 6, or in a range from about 3 to about 5. In some cases, the ratio Q1:We is about 3. In some cases, the ratio Q1:We is about 4. In some cases, the ratio Q1:We is about 5.
One variation of a method according to the fourth aspect of the invention comprises generating electrical energy We and collecting heat Q1 using a concentrating photovoltaic-thermal solar energy collector, drawing heat from a cold reservoir to reduce a temperature of the cold reservoir using a chiller, heating a hot reservoir at least in part using heat Q1, and operating an organic Rankine cycle heat engine between the hot reservoir and the cold reservoir to generate useful work, for example, electrical work. The chiller may be powered at least in part using We. The method may comprise effectively storing energy in the hot and cold reservoirs and operating the heat engine to generate useful work at a time delayed relative to the generation of electrical work We.
In the systems and methods summarized above for the first, second, third, and fourth aspects of the invention, all, some, or none of the electricity generated by the solar energy collector may be used to drive the heat pump (e.g., chiller), and the heat pump may additionally or alternatively be driven by, for example, electricity supplied from an external grid. In one mode of operation, for example, during daytime hours all or substantially all of the electricity generated by the solar energy collector is supplied to an external use such as, for example, an external commercial electric power grid. During evening hours, the heat engine (e.g., ORC) runs off stored heat to generate electricity that is also supplied to an external use. In late evening to early morning hours the heat pump (e.g., chiller) is driven with electricity drawn from an external commercial electric power grid. In this scheme the system supplies electricity to an external use during periods corresponding to peak demand and/or high electricity prices, and draws electricity from the external grid during periods in which electricity prices are typically lower and in which low ambient temperatures make operation of the heat pump more efficient.
These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following more detailed description of the invention in conjunction with the accompanying drawings that are first briefly described.
The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise.
Described herein with reference to
Described herein with reference to
The systems, methods and apparatus described herein comprise or use one or more photovoltaic-thermal solar energy collectors. A photovoltaic-thermal solar energy collector collects solar energy from which it generates electricity and also collects useful heat. A concentrating photovoltaic-thermal solar energy collector uses reflectors or other optics to concentrate solar energy onto one or more solar energy receivers. A receiver comprises one or more photovoltaic cells for generating electricity and one or more fluid channels through which a heat transfer fluid flows to collect heat. The electricity generating and heat collecting portions of the photovoltaic-thermal solar energy collector may be integrated with each other in some variations, or separated from each other in other variations. A concentrating photovoltaic-thermal solar energy collector may comprise, for example, a photovoltaic-thermal receiver and a solar thermal booster receiver arranged in series, where a heat transfer fluid is first used to actively cool and collect heat from the photovoltaic-thermal receiver, and the heat transfer fluid is subsequently passed through the solar thermal booster receiver to further increase the temperature of the heat transfer fluid. In such a scheme, the solar thermal booster receiver may lack any solar cells. Non-limiting examples of configurations of suitable photovoltaic-thermal solar energy collectors that may be used with the systems, apparatus and methods described herein include trough collectors, dish collectors, linear Fresnel collectors, heliostat collectors, and central tower collectors.
Certain photovoltaic cells may be selected for use in a receiver of a photovoltaic-thermal solar energy collector that permit useful operation at temperatures as high as 120° C. For example, heterojunction with intrinsic thin layer (HIT) silicon solar cells, which may, for example, be obtained from Sanyo Corp., may be operated with usable efficiency at 120° C. Additional non-limiting examples of photovoltaic solar cells that may be used in the systems and methods described herein include high efficiency solar cells manufactured by Silevo (Fremont, Calif.), Gallium Arsenide thin film photovoltaic cells (e.g., those manufactured by Alta Devices, Sunnyvale, Calif.), and multijunction (e.g., III-V material system) photovoltaic cells.
Non-limiting examples of suitable photovoltaic-thermal solar energy collectors that may be employed with the systems, apparatus and methods disclosed herein are described in the following publications: U.S. patent application Ser. No. 12/712,122 filed Feb. 24, 2010 and entitled “Designs for 1-D Concentrated Photovoltaic Systems”; U.S. patent application Ser. No. 12/788,048 filed May 26, 2010 and entitled “Concentrating Solar Photovoltaic-Thermal System”; U.S. patent application Ser. No. 12/622,416 filed Nov. 19, 2009 and entitled “Receiver for Concentrating Solar Photovoltaic-Thermal System”; U.S. patent application Ser. No. 12/774,436 filed May 5, 2010 and entitled “Receiver for Concentrating Solar photovoltaic-thermal System”; U.S. patent application Ser. No. 12/781,706 filed May 17, 2010 and entitled “Concentrating Solar Energy Collector”; U.S. patent application Ser. No. 13/079,193 filed Apr. 4, 2011 and entitled “Concentrating Solar Energy Collector”; U.S. patent application Ser. No. 13/291,531 filed Nov. 8, 2011 and entitled “Photovoltaic-Thermal Solar Energy Collector with Integrated Balance of System; U.S. patent application Ser. No. 13/371,790 filed Feb. 13, 2012 and entitled “Solar Cell with Metallization Compensating for or Preventing Cracking”; U.S. patent application Ser. No. 13/590,525 filed Aug. 21, 2012 and entitled “Maximizing Value form a Concentrating Solar Energy System”; and U.S. patent application Ser. No. 13/837,604 filed Mar. 15, 2013 and entitled “Concentrating Solar Energy Collector”, each of which is incorporated by reference herein in its entirety.
A photovoltaic-thermal solar energy collector system may comprise components other than a photovoltaic-thermal solar energy collector, such as one or more inverters to convert DC electricity generated by photovoltaic cells in the photovoltaic-thermal solar energy collector to alternating current, one or more heat transfer fluid control systems that circulate heat transfer fluid through the solar energy collector to collect heat, and, optionally, a control system that electrically and/or physically integrates the one or more inverters with the one or more heat transfer fluid control systems. The one or more inverters may in some cases control the current-voltage point at which the photovoltaic cells operate to optimize electrical power output from the photovoltaic-thermal solar energy collector. Heat transfer fluid used in the photovoltaic-thermal solar energy collectors may be any suitable heat transfer fluid, and in some cases is water and/or ice. In other variations, a heat transfer fluid may comprise water mixed with one or more glycols (e. g., ethylene glycol or propylene glycol). In still other variations, a heat transfer fluid may be a fluid other than water (e. g., one or more glycols such as ethylene glycol and/or propylene glycol, or a silicone oil containing heat transfer fluid).
Solar energy systems described herein may comprise more than one solar energy collector and in some cases, more than one type of solar energy collector. In some cases, an array comprising multiple solar energy collectors is used in a solar energy collector system. For example, a system may comprise 1, 2 between 2 and 10, between 10 and 20, between 20 and 30, or any other suitable number of photovoltaic-thermal solar energy collectors capable of generating electrical energy and thermal energy. Each photovoltaic-thermal solar energy collector may comprise, for example, one or more rows of coupled photovoltaic-thermal solar energy collector modules. Any suitable grouping of photovoltaic-thermal solar energy collector systems may be used to provide the desired amount of electrical energy and thermal energy. The electrical and thermal operation of individual photovoltaic-thermal solar energy collectors, or the operation of different groups of photovoltaic-thermal solar energy collectors, may be separately controlled in some cases. Thus, different photovoltaic-thermal solar energy collectors within a system may operate at different current-voltage power points, use different heat transfer fluid flow rates and temperature, or both operate at different current-voltage power points and operate using different heat transfer fluid flow rates and temperatures. It should be understood that the modules collecting thermal energy may be integral with those generating electrical energy or modules collecting thermal energy may be separate from those generating electrical energy.
A heat pump is any apparatus that uses energy to transfer heat from a colder heat source to a higher temperature heat sink. A reversible heat pump is a heat pump that, when operating in a forward direction, uses energy to transfer heat from a colder heat source to a higher temperature heat sink, and when operating in a reverse direction is capable of generating energy (e.g., electrical energy or mechanical energy) by transferring heat from a higher temperature heat source to a lower temperature heat sink. Any suitable type of heat pump may be used in the systems, methods and apparatus described herein. Non-limiting examples of heat pumps that may be used include: an air source heat pump, a water source heat pump, a ground source heat pump (which may use ground, rock, and/or a body of water as the cold reservoir), exhaust air heat pump, a hybrid heat pump using more than one cold reservoir (for example, ground and/or air may be used as the cold reservoir, depending on ambient conditions), and a geothermal heat pump.
A chiller is a heat pump that is employed to transfer heat out of a cold reservoir (colder heat source), thereby lowering the temperature of the cold reservoir. Any suitable type of chiller may be used. In some cases, a vapor-compression (e.g., reverse Rankine cycle) chiller is used. In some cases, an adsorption chiller is used. In some cases an absorption chiller is used. Additional non-limiting examples include air cycle chillers and chillers that utilize a reverse Stirling engine. Wet or dry cooled chillers may be used. In general, dry cooled chillers have lower COP (defined and discussed below).
A heat engine as used herein refers to any device or apparatus capable of generating useful work from thermal energy. The useful work may be in any form, e.g., mechanical work or electrical work. In some cases, the heat engine produces electrical energy or mechanical work that is converted to electrical energy. A heat engine may be the heat pump of the system operating in a reverse direction. A heat engine may comprise the heat pump of the system and additional components. Non-limiting examples of heat engines include Rankine cycle heat engines, e. g., organic Rankine cycle (ORC) heat engines, Brayton cycle heat engines, and Stirling cycle heat engines. Other non-limiting examples of heat engines include any type of thermoelectric device or thermoelectric generator that is capable of converting heat to electrical energy.
The performance of a heat pump may be characterized by a “coefficient of performance” (COP). The COP of a heat pump is the ratio of the heat pumped by the heat pump to the amount of work required to pump the heat. For electrically powered heat pumps, the COP is essentially the amount of heat pumped by the heat pump divided by the amount of electrical energy required by the heat pump to pump that heat. The work dissipated in the heat pump may appear as heat in the heat transfer fluid heated by the heat pump. Thus, the total amount of heat delivered by an electrically powered heat pump to a heat transfer fluid may be approximately equal to the amount of electrical energy used to pump the heat multiplied by (COP+1). That is, the heat delivered by a heat pump is approximately (COP+1) times (electric energy used to pump the heat). For electrically powered heat pumps pumping ambient heat into a heat transfer fluid (for example, water) having a temperature of about 120° C. or less, the value of the COP may be, for example, about 3 to 4. Certain chillers useful for lowering the temperature of water in a cold reservoir (e.g., from about 20° C.-40° C. to about 0° C.-10° C.) may have a COP that is about 4 or greater, about 5 or greater, or about 6 or greater, for example about 6 to 10, or about 6 to 7 (e.g., about 6.3, about 6.4, or about 6.5), or about 7 to 8, or about 8 to 9, or 9 or greater.
Referring again to
In the systems and methods of
In the systems and methods of
Any suitable cold reservoir may be used in the systems and methods. In some cases, at least a portion of the cold reservoir is the ambient environment. In some cases, the cold reservoir is the ambient environment. Optionally, the cold reservoir may be passively cooled by the environment. In some variations, the cold reservoir may be actively cooled (e. g., using a portion of electrical energy e1 and/or an external cooling source). The negative heat (cold) in the cold reservoir may in some variations be allowed to dissipate to the environment. In other variations, the cold may be stored for use. For example, the cold reservoir may comprise a vessel containing a thermal storage medium (for example, water, ice, or a mixture of water or ice) from which heat may be drawn. The cooled thermal storage medium may in some cases be used for one or more cooling applications, which may be internal to the system or external to the system. In some variations of the systems or methods, cold stored in the cold reservoir may be used for cooling a heat engine, for example, a condensing portion of a heat engine. In certain variations in which the heat engine comprises an organic Rankine cycle engine, cold from the cold reservoir may be used for cooling the organic Rankine cycle engine, for example a condensing portion of the ORC. In some systems or methods, cold in the cold reservoir may be used to cool one or more photovoltaic cells in a receiver of the photovoltaic-thermal solar energy collector. For example, the cold reservoir may be used to cool one or more photovoltaic cells to increase their efficiency to a desired level.
In general, the temperature difference between the hot and cold reservoirs affects the efficiency of a heat pump or heat engine that is used to convert thermal energy in the hot reservoir to electrical energy e2. Also, an efficiency of photovoltaic cells decreases with increasing temperature, so that in many cases a photovoltaic solar thermal energy collector is operated at a temperature that is less than 120° C. The operating temperature TH of the hot reservoir and the operating temperature TC of the cold reservoir may be selected to strike a desired trade-off between energy consumption of the heat pump, operation temperature of the photovoltaic-thermal solar energy collector, cost of thermal energy storage, volume of heat transfer fluid used, type and efficiency of heat engine used to convert stored thermal energy to electricity, and type of electrical demand on the final electrical output (e. g., high power bursts of electrical output, or low power extended time electrical output.)
Referring now to
The systems, methods and apparatus of
Certain variations of the systems, methods and apparatus of
Optionally, the systems, methods and apparatus of
A variety of system configurations and methods may be used for combining heat h1 with heat h2 for heating the hot reservoir using one or more heat transfer fluids. In some variations, a heat transfer fluid carrying heat h1 and a heat transfer fluid carrying heat h2 may be mixed in the hot reservoir, or the fluids may be mixed and the combined heat transferred to the hot reservoir via heat exchange. Mixing of the heat transfer fluids may be used to combine heats h1 and h2, for example, in situations in which the temperatures of the heat transfer fluids are similar. In some variations, a heat exchanger is used to transfer heat from a heat transfer fluid HTF1 carrying heat h1 from the photovoltaic-thermal solar energy collector to another heat transfer fluid HTF3, and HTF3 and HTF2 are mixed to combine heats h1 and h2 for use in heating the hot reservoir. This option allows heat transfer fluid HTF1 to be recirculated back to the photovoltaic-thermal solar energy collector in a closed or open recirculation loop. In other variations, a heat exchanger is used to transfer heat from a heat transfer fluid HTF2 carrying heat h2 from the heat pump to another heat transfer fluid HTF4, and HTF4 and HTF1 are mixed to combine heats h1 and h2 for heating the reservoir. This option allows heat transfer fluid HTF2 to be recirculated back to the heat pump in an open or closed recirculation loop. In still other variations, a heat exchanger is used to transfer heat h1 from HTF1 to another heat transfer fluid HTF3, a heat exchanger is used to transfer heat h2 from HTF2 to another heat transfer fluid HTF4, and fluids HTF3 and HTF4 are mixed to combine heats h1 and h2 for use in heating the hot reservoir. This option allows recirculation of heat transfer fluid HTF1 back to the photovoltaic-thermal solar energy collector, and recirculation of heat transfer fluid HTF2 back to the heat pump.
A non-limiting example of a system in which a heat transfer fluid carrying heat h1 and a heat transfer fluid carrying heat h2 are mixed to heat the hot reservoir is provided in
In some variations of the systems and methods of
Non-limiting examples of systems in which the photovoltaic-thermal solar energy collector is used to boost the thermal energy of a heat transfer fluid carrying h2 from the heat pump are illustrated in
Referring now to
In some variations of the systems and methods of
Non-limiting examples of systems in which the heat pump is used to boost the thermal energy of a heat transfer fluid carrying heat h1 from the photovoltaic-thermal solar energy collector are provided in
Referring now to
In the systems and methods of
The systems and methods of
The systems and methods of
In some cases, substantially all of heat h1 generated by the photovoltaic-thermal solar energy collector and substantially all of heat h2 drawn by the heat pump is used to heat the hot reservoir. In other cases, only a portion of heat h1 and substantially all of heat h2 are used, or substantially all of heat h1 and only a portion of heat h2 are used, or only a portion of heat h1 and only a portion of heat h2 are used. Portions of heat h1 or heat h2 that are not used to heat the hot reservoir may be used for one or more other applications, which may be internal applications within the solar energy system or external applications outside of the system. In certain variations, external heat h3 from an external energy source is used in combination with heat h1 and heat h2 to heat the hot reservoir. External heat h3 may be derived from any type of energy, including mechanical energy, energy derived from burning fossil fuels or plant-based fuels, or electrical energy (e. g., from the power grid, a generator, a battery, another solar energy collector, a wind turbine, a hydroelectric source, or the like). When external heat h3 is used in combination with heat h1 and heat h2 to heat the hot reservoir, heat h1, heat h2 and heat h3 may be used in any suitable relative amounts. For example, heat h1, heat h2 and heat h3 may be used to heat the hot reservoir where (h1+h2) and h3 are used in a ratio (h1+h2):h3 of about 1:1000, about 1:800, about 1:500, about 1:200, about 1:100, about 1:50. about 1:20, about 1:10, about 1:5, about 1:3, about 1:2, about 1:1, about 2:1, about 3:1, about 5:1, about 10:1, about 20:1, about 50:1, about 100:1, about 200:1, about 500:1, about 800:1 or about 1000:1. The relative amounts of heats h1, h2 and h3 need not stay constant with time, and may be adjusted according to operating conditions (e. g., time of day, weather, season and/or demand). When external heat h3 and h1+h2 are used to heat the hot reservoir, the heat sources may be combined in any suitable manner. For example, heat h1, heat h2 and heat h3 may be applied in a parallel operation so that all three heat sources are supplied simultaneously to the hot reservoir in any relative amounts. In other operating modes, heats h1, h2, and h3 may be alternately supplied to hot reservoir, or any combination of any two of heats h1, h2, and h3 may be alternated with the third heat source to heat the hot reservoir. For example, a combined heat h1+h2 may be alternately supplied with heat h3 to the hot reservoir. Any suitable scheme for alternating supply of the various heat sources may be used. The alternating may occur at regular intervals or irregular intervals (e. g., irregular intervals determined by an operator based on operating conditions or demand). Regular or irregular intervals may have any suitable duration, and the frequency of alternating may be constant or non-constant (e. g., adjusted during operation to accommodate operating conditions, such as time of day, weather, season, and/or demand).
Referring now to
Referring now to
The photovoltaic-thermal solar energy collector 905 in the example of
In one example, the efficiency of the solar collector 905 may be about 75% energy production. Of the energy produced, about 15% is in the form of electrical energy e1 and 60% in the form of thermal energy h1, so that h1 is approximately 4 times e1 (using equivalent energy units). In some cases, the heat transfer fluid stream carrying thermal energy h1 from the receiver 907 may have a temperature T1 as high as 120° C. Any portion of or all of a conduit system that carries heat transfer fluid throughout system 905 may be pressurized so that desired temperatures are reached. For example, if water is used as a heat transfer fluid, conduits carrying water may be pressurized to enable operation at 120° C. Heat pump 910, powered by electrical energy e2, may have a COP of about 3 to 4, so about 1 unit of solar-generated electrical energy e1 is used to generate about 4 units of thermal energy h2. Heat pump 910 may be used so that the temperature T2 of the heat transfer fluid HTF2 carrying heat h2 is about 80° C. and a temperature TC of the cold reservoir is about 40° C. Heat transfer fluid HTF2 passes through heat exchanger 930 where heat h1 from the photovoltaic-thermal solar energy collector boosts the thermal energy of HTF2 and boosts its temperature to T2′>T2. T2′ may be as high as T1, so that if T1=120° C., then T2′ may be approximated as 120° C., and the temperature of the hot reservoir TH may be approximated as 120° C. If substantially all the heat h1 collected from receiver 907 is transferred to the heat transfer fluid HTF2 via heat exchanger 930, then heat transfer fluid carries heat h1+h2 to heat the hot reservoir 915. In this particular example, h1+h2 is approximately 8 times the solar-generated electrical energy e1. The thermal energy stored in the hot reservoir at temperature TH may be converted to electrical energy using any suitable means. In some cases, a heat pump (for example, heat pump 910 operating in reverse), a heat engine (for example, an organic Rankine cycle heat engine), or a combination heat pump/organic Rankine cycle (which may comprise a separate heat pump combined with a separate organic Rankine cycle, or which may comprise an integral unit in which the heat pump and organic Rankine cycle are combined) may be used. In a system using water as a heat transfer fluid, if an organic Rankine cycle transfers heat from a hot reservoir having temperature TH=120° C. to a cold reservoir having temperature TC=40° C., an overall efficiency of about 12.5% for conversion of heat to electricity may be achieved, so that the thermal energy h1+h2 which is approximately 8 times e1 may be converted to e1 units of electrical energy. The example in
In the variation shown in
In the system illustrated in
Non-limiting examples of additional systems and methods are illustrated in
ORC 1225 is increased. In some cases, the heat transfer fluid stored in hot reservoir 1215 may be vertically stratified or partially stratified according to temperature (illustrated by dashed line in hot reservoir 1215), with higher temperature fluid residing above lower temperature fluid. In such cases, heat transfer fluid provided from the hot reservoir 1215 to the ORC 1225 may be preferably drawn from the upper higher temperature strata, as shown. In some cases, the heat transfer fluid stored in cold reservoir 1220 may be vertically stratified or partially stratified by temperature, illustrated by a dashed line in cold reservoir 1220, with cooler fluid residing below hotter fluid. In such cases, heat transfer fluid provided from the cold reservoir 1220 to ORC 1225 may be preferably drawn from lower temperature strata, as shown. Heat transfer fluid flow cycles from the heat exchanger 1206 or PVT 1205 through the hot reservoir 1215, from the heat pump 1210 and heat exchanger 1209 through the cold reservoir 1220, and through the ORC 1225 may each operate independently from each other.
In some variations of the systems and methods of
An example of a system in which one or more components are common to both the heat pump and the heat engine is illustrated in
A more detailed example of a system in which the heat engine and heat pump share one or more common components is provided in
During operation of system 1400, photovoltaic-thermal solar energy collector 1405 collects heat Q1 and generates electrical energy We. At least a portion of heat Q1 is transferred to hot reservoir 1415. In some modes of operation, essentially all of heat Q1 is transferred to hot reservoir 1415. In other modes of operation, at least a portion of heat Q1 is diverted for a use other than transfer to hot reservoir 1415.
A description of the operation of system 1400 during the chilling cycle follows. Compressor 1475 may be configured to be powered at least in part using We during the chilling cycle. In some modes of operation, the compressor 1475 is powered entirely by We, and in some modes of operation an external energy source e3 (e.g., electricity from the grid, as indicated by arrow 1440) may be used alone or in combination with We to power compressor 1475. A cooling loop (working fluid flow {dot over (M)}4) passes from the chiller compressor 1475 to the chiller condenser 1473, from the chiller condenser 1473 to the throttling or expansion valve 1474, from the expansion valve 1474 to the chiller evaporator 1472, which is in thermal communication with cold reservoir 1420 via heat exchanger 1408, and from the chiller evaporator 1472 back to the compressor 1475. During the chilling cycle, chiller compressor 1475 accepts gas flow {dot over (M)}4 from the chiller evaporator 1472 and supplies compressed gas flow {dot over (M)}4 to the chiller condenser 1473. Chiller condenser 1473 accepts compressed gas flow {dot over (M)}4 from compressor 1475, removes heat from flow {dot over (M)}4, rejects heat Q5 and supplies condensed liquid flow {dot over (M)}4 to expansion valve 1474. The chiller condenser 1473 operates by heat exchange and rejects heat in any suitable manner, for example, rejecting heat to air or to liquid (e.g., water). Expansion valve 1474 accepts liquid flow {dot over (M)}4 and expands the working fluid to result, typically, in a mixture of liquid and gas. Operation of throttling or expansion valve 1474 is typically isenthalpic. Gas/liquid flow {dot over (M)}4 from the expansion valve 1474 is supplied to chiller evaporator 1472, where any remaining liquid in flow {dot over (M)}4 is vaporized. In this vaporization step, heat is drawn out of the cold reservoir 1420 by working fluid flow {dot over (M)}3 via heat exchanger 408, thereby cooling cold reservoir 1420. Gas flow {dot over (M)}4 from the chiller evaporator 1472 is returned to compressor 1475 to continue the cooling cycle.
A description of the operation of system 1400 during the work generating cycle follows. During the work generating cycle, at least a portion of We may be diverted to the grid, as indicated by arrow 1440, or used for a purpose other than powering compressor 1475. A work generating loop (working fluid flow {dot over (M)}5) passes from the pump 1476 to the ORC evaporator 1471, from the ORC evaporator 1471 (which is in thermal communication with the hot reservoir 1415 via heat exchanger 1407) to the ORC turbine 1475, from the turbine 1475 to the ORC condenser 1472 (which is in thermal communication with cold reservoir 1420 via heat exchanger 408), and from the ORC condenser 1472 back to the pump 1476. In some modes of operation, the pump 1476 is powered entirely by We, and in some modes of operation an external energy source e3 (e.g., electricity from the grid, as indicated by arrow 1440) may be used alone or in combination with We to power pump 1476. Pump 1476 pumps liquid fluid {dot over (M)}5 to ORC evaporator 1471. Heat from fluid {dot over (M)}2 from the hot reservoir 1415 is transferred to fluid {dot over (M)}5 via heat exchanger 1407 in the ORC evaporator 1471, vaporizing fluid {dot over (M)}5. The heated vaporized fluid {dot over (M)}5 from ORC evaporator 1471 is expanded in ORC turbine 1475 to drive the turbine and generate useful work Wout, which may be electrical work. Expanded gas flow {dot over (M)}5 from turbine 1475 enters ORC condenser 1472, where fluid {dot over (M)}5 is cooled and condensed via heat exchange with working fluid {dot over (M)}3 from cold reservoir 1420. Condensed liquid flow {dot over (M)}5 exits ORC condenser 1472 and returns to pump 1476.
For the systems and methods of
The solar energy systems and methods of
For the systems and methods of
For the systems and methods of
Any suitable type of hot and cold reservoirs may be used in the systems and methods of
In general, the temperature difference between the hot and cold reservoirs affects the efficiency of the heat engine that is used to convert the energy stored between the hot and cold reservoirs to useful work. Also, an efficiency of photovoltaic cells in the photovoltaic-thermal solar energy collector decreases with increasing temperature. An efficiency of the heat pump drawing heat from the cold reservoir decreases as the temperature of the cold reservoir is lowered. The operating temperature of the hot reservoir and the cold reservoir may be selected to strike a desired trade-off between energy consumption of the heat pump, efficiency of photovoltaic cells, and efficiency of the heat engine. In general, the cost of storing energy in the hot and cold reservoirs is very low, unlike battery-based or electrochemical energy storage schemes. Further, the temperature of the hot and cold reservoirs can be cycled indefinitely with no degradation in performance, and without the use of chemicals, unlike battery-based or electrochemical energy storage schemes.
In the systems and methods of
During operation of the systems and methods of
In certain operational modes of the systems and methods of
Certain operating modes of the systems or methods of
Certain variations of the systems and methods of
The systems and methods of
In the systems and methods of
A photovoltaic-thermal solar energy collector collects heat (Q1) and generates photovoltaic electrical energy (We). During operation, it is advantageous to determine an optimal amount of photovoltaic energy We to use to cool the cold reservoir. It is desired to cool the cold reservoir sufficiently to increase the efficiency of the heat engine (e.g., ORC) to optimize electrical output without cooling unnecessarily. Photovoltaic electricity We that is not used to power a chiller to cool the cold reservoir can be supplied to the grid, or put to another valuable use. Heat pump/chillers become less efficient as operating temperature is decreased, so that increasing amounts of energy are required to cool to lower temperatures. At some cooling temperature, the benefit to the ORC efficiency of cooling further does not outweigh the cost of the extra energy needed to power the heat pump/chiller. One method for determining an optimal amount of energy storage given a certain heat (Q1) to photovoltaic electrical energy (We) ratio is described here. R is defined as the ratio of the outputs Q1/ We. The temperature of the low temperature (cold) side of the chiller is TL, which can be used as the chiller cooling set point. Eff(TL) is the efficiency of the ORC as a function of TL. Ch(TL) is the COP of the chiller as a function of TL. The efficiency of the ORC Eff(TL) increases as TL decreases, and as a secondary effect, less heat is rejected. The efficiency of the chiller Ch(TL) decreases as TL decreases. Eout(TL) is the amount of electrical energy (relative to electrical energy used to power the chiller) that can be generated from the hot and cold reservoirs as a function of TL, and is calculated as: Eout(TL)=R×Eff(TL). Ch(TL) provides the amount of energy (relative to the electrical energy used to power the chiller) that is stored in the cold reservoir. To optimize Eout(TL), TL may be selected to balance between increasing efficiency of the ORC and decreasing efficiency of the chiller as the set point temperature TL is lowered. TL may be selected so that Ch(TL)=R×[1−Eff(TL)]. The excess cooling can be calculated as {Ch(TL)−[R×(1−Eff(TL))]}. For one non-limiting example, assume R=4/1 for a representative PVT, TL=5° C., Ch(TL)=4 for a representative chiller, and Eff(TL)=0.125 for a representative ORC, then the excess cooling is calculated as {4−[4×(1−0.125)]}=0.5. The corresponding non-optimized electrical output from the ORC is Eout(TL)=4×0.125=0.5. For another non-limiting example, assuming R=4/1 for a representative PVT, TL=0° C., Ch(TL)=3.333 for a representative chiller and Eff(TL)=0.166 for a representative ORC, then the excess cooling is calculated as {3.333−[4×(1−0.166)]}=0. The corresponding optimized electrical output from the ORC is Eout(TL)=433 0.166=0.667. Optionally, analytic equations describing the function of the chiller COP as a function of TL and the ORC efficiency as a function of TL may be used to find a temperature TL that does not result in excess cooling and optimizes Eout(TL).
In one non-limiting prophetic example, a photovoltaic-thermal solar energy collector is capable of generating 1 kWh electrical energy and collects 4 kWh thermal energy. The PVT operates at about 120° C., so that the hot reservoir has a hot storage temperature of about 120° C. Referring again to
In another non-limiting prophetic example, a photovoltaic-thermal solar energy collector is capable of generating 1 kWh electrical energy and collects 4 kWh thermal energy. The PVT operates at about 120° C., so that the hot reservoir has a hot storage temperature of about 120° C. Referring again to
Still referring to
This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.
This application claims benefit of priority to U.S. Provisional Patent Application No. 61/845,541 titled “Photovoltaic-Thermal Solar Energy Collection System With Energy Storage” and filed on Jul. 12, 2013; and to U.S. Provisional Patent Application No. 61/860,720 titled “Solar Energy Collection System With Energy Storage” and filed on Jul. 31, 2013, both of which are incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/46396 | 7/11/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61845541 | Jul 2013 | US | |
| 61860720 | Jul 2013 | US |
