Systems and methods for energy storage and recovery using gas expansion and compression

Abstract

In various embodiments, energy-storage systems are based upon an open-air arrangement in which pressurized gas is expanded in small batches from a high pressure of, e.g., several hundred atmospheres to atmospheric pressure. The systems may be sized and operated at a rate that allows for near isothermal expansion and compression of the gas.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 13 / 154,996, filed on Jun. 7, 2011, which (A) is a continuation-in-part of U.S. patent application Ser. No. 12 / 639,703, filed Dec. 16, 2009, which (i) is a continuation-in-part of U.S. patent application Ser. No. 12 / 421,057, filed Apr. 9, 2009, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61 / 148,691, filed Jan. 30, 2009, and U.S. Provisional Patent Application No. 61 / 043,630, filed Apr. 9, 2008; (ii) is a continuation-in-part of U.S. patent application Ser. No. 12 / 481,235, filed Jun. 9, 2009, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61 / 059,964, filed Jun. 9, 2008; and (iii) claims the benefit of and priority to U.S. Provisional Patent Application Nos. 61 / 166,448, filed on Apr. 3, 2009; 61 / 184,166, filed on Jun. 4, 2009; 61 / 223,564, filed on Jul. 7, 2009; 61 / 227,222, filed on Jul. 21, 2009;...

AI Technical Summary

Benefits of technology

The invention is an energy storage system that uses a high-pressure open-air arrangement to expand and compress gas. The system can be designed to operate at a near isothermal temperature, and can be scaled up by adding more accumulator circuits and storage tanks as needed. The invention allows for efficient and high-energy density compression and expansion.

Problems solved by technology

In certain parts of the United States, inability to meet peak demand has led to inadvertent brownouts and blackouts due to system overload and deliberate “rolling blackouts” of non-essential customers to shunt the excess demand.

However, these units burn expensive fuel sources, such as natural gas, and have high generation costs when compared with coal-fired systems, and other large-scale generators.

Accordingly, supplemental sources have economic drawbacks and, in any case, can provide only a partial solution in a growing region and economy.

The most obvious solution involves construction of new power plants, which is expensive and has environmental side effects.

In addition, because most power plants operate most efficiently when generating a relatively continuous output, the difference between peak and off-peak demand often leads to wasteful practices during off-peak periods, such as over-lighting of outdoor areas, as power is sold at a lower rate off peak.

The array may generate well for a few hours during the day, but is nonfunctional during the remaining hours of low light or darkness.

However, such generators are often costly, use expensive fuels, such as natural gas or diesel fuel, and are environmentally damaging due to their inherent noise and emissions.

The flywheel units are expensive to manufacture and install, however, and require a degree of costly maintenance on a regular basis.

Many large-scale batteries use a lead electrode and acid electrolyte, however, and these components are environmentally hazardous.

Batteries must often be arrayed to store substantial power, and the individual batteries may have a relatively short life (3-7 years is typical).

However, a large array of such capacitors is needed to store substantial electric power.

Ultracapacitors, while more environmentally friendly and longer lived than batteries, are substantially more expensive, and still require periodic replacement due to the breakdown of internal dielectrics, etc.

The main drawback of CAES is probably the geological structure reliance, which substantially limits the usability of this storage method.

In addition, CAES power plants are not emission-free, as the pre-compressed air is heated up with a fossil fuel burner before expansion.

Moreover, CAES plants are limited with respect to their effectiveness because of the loss of the compression heat through the inter-coolers, which must be compensated during expansion by fuel burning.

The fact that conventional CAES still rely on fossil fuel consumption makes it difficult to evaluate its energy round-trip efficiency and to compare it to conventional fuel-free storage technologies.”

In general, the use of highly compressed gas as a working fluid for the motor poses a number of challenges due to the tendency for leakage around seals at higher pressures, as well as the thermal losses encountered in rapid expansion.

While heat exchange solutions can deal with some of these problems, efficiencies are still compromised by the need to heat compressed gas prior to expansion from high pressure to atmospheric pressure.

That is, the amount of compression possible is limited by the size of the tank space.

In addition, since the gas does not completely decompress when the fluid is removed, there is still additional energy in the system that cannot be tapped.

To make a closed air system desirable for large-scale energy storage, many large accumulator tanks would be needed, increasing the overall cost to implement the system and requiring more land to do so.

Disadvantages of open-air systems can include gas leakage, complexity, expense and, depending on the intended deployment, potential impracticality.

As demand for renewable energy increases, the intermittent nature of some renewable energy sources (e.g., wind and solar) places an increasing burden on the electric grid.

However, most of the discussed methods for converting potential energy in the form of compressed air to electrical energy utilize turbines to expand the gas, which is an inherently adiabatic process.

An ideally adiabatic energy-storage cycle would also have 100% thermodynamic efficiency, but there are many practical disadvantages to the adiabatic approach.

These include the production of more extreme temperatures and pressures within the system, heat loss during the storage period, and inability to exploit environmental (e.g., cogenerative) heat sources and sinks during expansion and compression, respectively.

However, the need to burn fossil fuel (or apply another energy source, such as electric heating) to compensate for adiabatic expansion substantially defeats the purpose of an otherwise clean and emission-free energy-storage and recovery process.

While it is technically possible to provide a direct heat-exchange subsystem to a hydraulic / pneumatic cylinder, an external jacket, for example, is not particularly effective given the thick walls of the cylinder.

An internalized heat exchange subsystem could conceivably be mounted directly within the cylinder's pneumatic side; however, size limitations would reduce such a heat exchanger's effectiveness and the task of sealing a cylinder with an added subsystem installed therein would be significant, and make the use of a conventional, commercially available component difficult or impossible.

Thus, the prior art does not disclose systems and methods for rapidly compressing and expanding gas isothermally in a manner that allows maximum use of conventional, low-cost components, and which operates in a commercially practicable yet environmentally friendly manner.

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