Thermal energy storage system

Abstract

A variety of energy storage and retrieval systems are described. Generally “hot” and “cold thermal reservoirs are provided. The “hot” reservoir holds both liquid and saturated vapor phase working fluid. The “cold” reservoir holds working fluid at a lower temperature than the hot reservoir. A heat engine/heat pump unit: (a) extracts energy from vapor passing from the hot reservoir to the cold reservoir via expansion of the vapor in a manner that generates mechanical energy to facilitate retrieval of energy; and (b) compresses vapor passing from the cold reservoir to the hot reservoir to facilitate the storage of energy. In some embodiments, the heat engine/heat pump takes the form of a reversible positive displacement heat engine that can act as both an expander and a compressor. To facilitate the storage and retrieval of electrical energy, an electric motor/generator unit may be mechanically coupled to the heat engine/heat pump unit.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Patent Application No. 61 / 559,318, filed Nov. 14, 2011, which is hereby incorporated by reference in its entirety for all purposes.BACKGROUND[0002]The present invention relates generally to thermal energy storage systems. More particularly, it relates to systems that store thermal energy making use of a phase change such as liquid water / steam.[0003]There are many circumstances in which it is desirable to store electrical energy in order to resolve temporal mismatches between energy supply and demand. By way of example, the availability of some alternative energy sources such as solar energy and wind energy can vary significantly over the course of a day and the output of devices that harvest such energy, (e.g., photovoltaic collectors or wind turbines) is often mismatched with the demand for the electrical energy that such devices produce. Another example of the mismatch between supply ...

AI Technical Summary

Benefits of technology

[0009]In order to facilitate the storage and retrieval of electrical energy, an electric motor / generator unit may be mechanically coupled to the heat engine / heat pump unit. The electric motor / generator is arranged to drive the heat engine / heat pump unit during the compression of working fluid and to generate electricity during the expansion of the working fluid. The electric motor / generator may be implemented as a single reversible unit or as separate motor and generator devices.

[0010]The hot and cold reservoirs may take the form of pressure vessels or unpressurized reservoirs. When an unpressurized reservoir is used, a sub-atmospheric pressure chamber may be provided to facilitate sub-atmospheric flashing of working fluid to vapor (e.g., liquid water to steam) and / or sub-atmospheric condensation of vapor to a liquid. When a pressurized vessel is used as the hot reservoir, the working fluid in the hot reservoir may be stored at a pressure substantially above ambient atmospheric pressure.

[0011]In some alternative embodiments, the cold store may be replaced by the combination of a condenser arranged to condense steam and a separate low temperature thermal energy source arranged to provide steam having a lower temperature than the hot reservoir.

Problems solved by technology

By way of example, the availability of some alternative energy sources such as solar energy and wind energy can vary significantly over the course of a day and the output of devices that harvest such energy, (e.g., photovoltaic collectors or wind turbines) is often mismatched with the demand for the electrical energy that such devices produce.

Although batteries tend to work well for relatively small-scale energy storage applications, they tend to be cost prohibitive in larger scale energy storage systems.

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