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Thermal energy storage systems and methods

Thermal energy storage systems and methods description/claims

This application claims priority to U.S. provisional patent application 60/939,426 which was filed on May 22, 2007. U.S. provisional patent application 60/939,426 is hereby incorporated by reference in its entirety.

The claimed invention generally relates to energy storage and, more particularly, to thermal energy storage systems and methods thereof.

Worldwide, there are ever-growing demands for electricity due to increasing populations, technology advancements requiring the use of electricity, and the proliferation of such technology to more and more countries around the world. At the same time, there is an increasing push to harness reusable sources of energy to help meet these increasing electricity demands and offset and/or replace traditional carbon-based generators which continue to deplete natural resources around the world.

Many solutions have been developed to collect and take advantage of reusable sources of energy, such as solar cells, solar mirror arrays, and wind turbines. Solar cells produce direct current energy from sunlight using semiconductor technology. Solar mirror arrays focus sunlight on a receiver pipe containing a heat transfer fluid which absorbs the sun's radiant heat energy. This heated transfer fluid is then pumped to a turbine which heats water to produce steam, thereby driving the turbine and generating electricity. Wind turbines use one or more airfoils to transfer wind energy into rotational energy which spins a rotor coupled to an electric generator, thereby producing electricity when the wind is blowing. All three solutions produce electricity when their associated reusable power source (sun or wind) is available, and many communities have benefited from these clean and reusable forms of power.

Unfortunately, when the sun or wind is not available, such solutions are not producing any power. In the case of solar solutions, non-reusable energy solutions are often turned-to overnight. Similar issues arise for wind turbines during calm weather. Therefore, some form of energy storage is needed to store excess energy from the reusable power sources during power generation times to support energy demands when the reusable power source is unavailable or unable to meet peak demands for energy.

Solar mirror arrays generate and transfer heat as an inherent part of their operation. Solar cells and wind turbines which typically generate electricity can also selectively be used to drive heaters to generate heat and/or transfer heat from windings to a heat transfer fluid. Several solutions have been developed to store heat from these renewable energy sources for use in non-energy-generating times.

FIG. 1 illustrates a two-tank direct energy storage system. Heat transfer fluid is heated by mirrors in a solar field 30 and stored in a hot oil tank 32. The heat transfer fluid is then pumped through a steam generator 34 as needed to generate steam and power a turbine 36 to meet energy demands. Even if the solar field 30 is not producing newly heated heat transfer fluid for the hot oil tank 32, the hot oil tank 32 has a certain capacity to provide stored hot transfer fluid to the steam generator 34 for power generation. After passing though the steam generator 34, the cooled heat transfer fluid is then pumped into and stored in a cold oil tank 38. When the solar field 30 is active, cooled heat transfer fluid is pumped from the cold oil tank 38, through the solar field to be heated-up, and back to the hot oil tank 32 where the process can begin again. While the two-tank direct energy storage system of FIG. 1 helps to store energy for non-generation times, it is unfortunately complex, requires two expensive tanks, and is limited in the amount energy it can store due to limitations in the heat storage capacity of the heat transfer fluid.

FIG. 2 illustrates a two-tank indirect energy storage system. Relatively cold molten salt is pumped from a cold salt tank 40 out to a heat exchanger 42 where it is heated by proximity to counter-current running hot heat transfer fluid from the solar field 44. The newly-heated molten salt is then pumped from the heat exchanger 42 into a hot salt tank 46 where it is stored until needed. When energy needs to be reclaimed from the hot salt tank 46, the hot molten salt is pumped out of the hot salt tank 46 and to a turbine system 48 whereby the heat from the hot molten salt is used to generate steam to drive the turbine system 48. Relatively cold molten salt exits the turbine system 48 and is pumped back into the cold salt tank 40. Alternatively, the hot molten salt from the hot salt tank 46 may be pumped out of the hot salt tank 46 and back through the heat exchanger 42 to heat the heat transfer fluid from the solar field 44 before being pumped back into the cold salt tank 40. In this alternate setup, the reheated heat transfer fluid would then be pumped through the turbine system before being recirculated to the solar field. Taking advantage of the heat storage capacities of salt in this indirect two-tank system, more energy may be stored than in the direct system. Unfortunately, this system still requires two expensive tanks. Furthermore, the system of FIG. 2 will be subjected-to complexities and issues arising from the need to pump and transport molten salt. The system may have the need to keep the salt molten at all times and therefore may require the addition of heaters not powered by the solar field. If the salt is allowed to solidify within the transport pipes, the natural expansion of the salt when transitioning to a solid state may cause stress cracks in the pipes. Furthermore, if the salt is allowed to solidify, the system may take an undesirable amount of time to come on-line as it waits for the salt to liquefy to become pumpable. Corrosion is also an issue when pumping molten salt.

FIG. 3 illustrates a single-tank thermocline energy storage system. The thermocline tank 50 holds a hot molten salt on the top of the tank 50 and a relatively cool molten salt in the bottom of the tank 50. When the solar field 52 is active, a hot heat transfer fluid is pumped from the solar field to a heat exchanger 54. The relatively cool molten salt is pumped out of the bottom of the thermocline tank 50 out to the heat exchanger 54 where it is heated by proximity to the hot heat transfer fluid from the solar field. The heated molten salt is then returned to the top of the thermocline tank 50. When the solar field 52 is not active, the flow to and from the thermocline tank 50 is reversed. Heated molten salt is pumped out of the top of the thermocline tank 50 to the heat exchanger 54, where it transfers its heat to the heat transfer fluid. The heat transfer fluid is pumped to a turbine system 56 for generating electricity. The molten salt which gave up some of its heat in the heat exchanger 54 is then returned to the bottom of the thermocline tank 50. While this system takes advantage of a vertical temperature gradient within the thermocline tank to move down to a single tank, the tank itself may still be expensive when properly sized for industrial and/or community demands, and the system continues to have the corrosion and solidification concerns mentioned above when pumping molten salt.

Therefore, there is a need for a thermal energy storage system which can take advantage of the high energy storage capacities of phase change media, such as salts, while avoiding corrosion and solidification issues in an inexpensive, easy-to-construct, control, and maintain fashion.

A thermal energy storage apparatus is disclosed. The thermal energy storage apparatus has a phase change medium, an inner header having at least one inner feed port, and an outer header having at least one outer feed port and fluidically coupled to the inner header. The inner header and the outer header are configured to be substantially immersed in the phase change medium.

A thermal energy power system is also disclosed. The thermal energy power system has a phase change medium, an inner header, an outer header, and a collection header. The thermal energy power system also has one or more inner tubes coupled between the inner header and the collection header. The thermal energy power system further has one or more outer tubes coupled between the outer header and the collection header, wherein the inner header is fluidically coupled to the outer header via the one or more inner tubes, the collection header, and the one or more outer tubes. The thermal energy power system also has a brick structure configured to contain the phase change medium such that the inner header and the outer header are substantially immersed in the phase change medium and wherein the bricks are configured to have a cooling zone which encourages the phase change medium to solidify in gaps defined by the bricks. The thermal energy power system also has a base which supports the brick structure, a pump, a renewable heat collector, and a turbine plant. The inner header and the outer header are reversibly connected in a series closed loop with the pump, the renewable heat source, and the turbine plant. The closed loop carries a thermal fluid.

A method of constructing a thermal energy storage system is also disclosed. A base is formed. At least one heat exchange system is substantially aligned over the base, the at least one heat exchange system comprising an inner header and an outer header. A brick wall is dry-laid substantially on the base to surround the at least one heat exchange system. An area defined by the base and the brick wall is filled with a phase change medium such that the phase change medium substantially covers the at least one heat exchange system.

A method of controlling a thermal energy storage system is also disclosed. When a renewable heat source is available: i) the renewable heat source is thermally and fluidically coupled to an inner header of a heat exchange system which is substantially immersed in a phase change medium and which is further coupled to an outer header of the heat exchange system which is also substantially immersed in the phase change medium; and ii) the outer header is thermally and fluidically coupled to a turbine plant and then back to the renewable heat source in a closed-loop heating mode which provides a remaining renewable energy source heat to the turbine plant. When the renewable heat source is not available: i) the renewable heat source is thermally and fluidically coupled to the outer header; and ii) the inner header is thermally and fluidically coupled to the turbine plant and then back to the renewable heat source in a closed-loop cooling mode which provides a stored heat to the turbine plant. A heat exchanger for a thermal energy storage system is also disclosed. The heat exchanger has

an inner header having at least one inner feedport. The heat exchanger also has an outer header having at least one outer feedport and fluidically coupled to the inner header. The inner and outer feedports are configured to enable a heat transfer fluid to reversibly flow from the inner header to the outer header when the inner header and the outer header are substantially immersed in a phase change medium.

• Provisional Patent
• Utility Patent

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