A previous post reported on the acquisition of Beacon Power, formerly the largest flywheel player, after the company went bankrupt.

One of the technical hurdles faced by designers of these whirling rotational energy storage devices is that spinning masses have a natural “wobble.”  Most flywheel designers have employed expensive bearings, magnets, and materials in attempts to minimize this wobble to better align the flywheel’s axis of rotation with the rotation of a generator.

Enter Velkess, a Silicon Valley developer of new flywheel technology, which has invented a self-stabilizing design.  Velkess owns U.S. Patent Application Publication No. 2012/0096984, entitled “Flywheel system” (’984 Application).

The ’984 Application is directed to a flywheel system in which the wheel is suspended in a non-symmetric damped gimbal system (9) (a gimbal is a pivoted support that allows the rotation of an object about a single axis, commonly used in gyroscopes).  The shaft of a motor/generator (20) is attached to a flexible coupling (13), which is also attached to a rigid shaft (14).

 The rigid shaft (14) is attached at its other end to a super-circular bare filament flywheel rotor (16).  The shaft (14) can transmit high levels of torque and will not suffer the destabilizing displacement common in traditional flywheels.

According to the ’984 Application, the invention allows one axis of the gimbal to dampen the resonant frequencies in the other axis:

[T]he non-symmetric damped gimbal system 9 of embodiment 15 has two different resonant base frequencies established by the differing lengths of the pendulum that each axis 10 and 11 create. This allows one axis 10 or 11 of the non-symmetric gimbal 9 to damp the resonant frequencies in the other axis 10 or 11.

As explained nicely by Chris Nelder in a recent Scientfic American piece, this feature minimizes resonant disturbances and permits more control of the device:

The gimbal in the Velkess is asymmetrical, so the two axes of rotation—the flywheel axis as well as that of the rotor, which drives the brushless, inducting DC motor—are not on the same plane, and have different periods of frequency. This dampens the resonance effects that make traditional flywheels hard to control (a resonant disturbance in one of the planes can intensify until the device shatters). With the gimbal, resonance in one plane is translated into the other, which is nonresonant at the same frequency. Accordingly, only very loose engineering tolerances—about one sixteenth of an inch—are required to build the device.

According to Nelder, the Velkess flywheel has significant advantages over previous devices like those made by Beacon Power, including slower, longer discharge of stored energy, and scalability.  More info on the Velkess technology can be found on the company’s technology page.

LightSail Energy (LightSail) is a Berkeley, California, company that has developed compressed air energy storage technology which may be used for grid-scale storage. 

The company’s central innovation is the injection of a mist of water spray into a compressed air system so the spray rapidly absorbs the heat energy of compression and provides the energy during expansion.

According to Cleantech PatentEdge™, LightSail owns at least 52 US, international, and European patents and published applications.  U.S. Patent No. 8,240,142 (’142 Patent) is one of a family of patents relating to the company’s compressed air energy storage system.

The ’142 Patent is entitled “Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange” and directed to a compressed air energy storage system (20) including a cylinder device (21) defining a chamber (22), a piston device (23) in the chamber, and a pressure cell (25).  The cylinder (21) and pressure cell (25) together form a one stage reversible pressure compression/expansion mechanism (24).

Air enters the system (20) via pipe (10), passes through a filter (26) and enters the cylinder chamber (22) via pipe (30) where it is compressed by the action of the piston (23).  Before compression begins, a liquid mist is introduced into the chamber (22) using an atomizing nozzle (44).  The volume of mist injected into the chamber (22) is predetermined to be the volume required to absorb all the heat generated during that piston stroke.

As the mist condenses, it collects as a body of liquid (49e) in the cylinder chamber (22).  The compressed air/liquid mixture is then transferred into the pressure cell (25) through outlet nozzle (11) via pipe (51). 

According to the ’142 Patent, that is when the critical heat exchange occurs, followed by storage of the air:

In the pressure cell 25, the transferred mixture exchanges the captured heat generated by compression to a body of liquid (49f) contained in the cell.  The air bubbles up through the liquid and on to the top of the pressure cell, and then proceeds to the air storage tank 32, via pipe 33.

According to this Greentech Media piece, LightSail’s system is more efficient because it captures and stores both the mechanical energy and the thermal energy used in compressing air.  The article reports the company has received a recent funding round by some big name investors, including Bill Gates and Khosla Ventures.

Isentropic is a UK company that has developed an energy storage system called Pumped Heat Electricity Storage (PHES).

Isentropic owns several international and U.S. patents and applications.  U.S. Application Publication No. 2010/0257862 (’862 Application) describes and claims the PHES technology.

Entitled “Energy storage,” the ’862 Application is directed to an energy storage system (10) comprising compressor/expander means (20) including a compressor (21), an expander (22), and power input/output means (40).

The energy storage system (10) also includes a first heat storage means (50), a second heat storage means (60), high pressure transfer means (70, 71) and low pressure transfer means (80, 81).

To charge the system (10), a low pressure gas enters the compressor (21) through inlet (23) and passes into a compression chamber (24).  The low pressure gas is compressed by a compression piston (25) and transferred via the high pressure transfer means (70) to the first heat storage means (50) where it transfers thermal energy to the first thermal store (53).

The gas then passes through the high pressure transfer means (71) and enters the expander (22) through inlet (27).  The gas is then expanded in the expansion chamber (28) and is transferred by the low pressure transfer means (81) to the second heat storage means (60) where it receives thermal energy from the second thermal store (63).

Finally, the gas passes through the low pressure transfer means (80) and can start the process again by entering the compressor (21).

According to Isentropic’s PHES technology web page, each heat storage means contains mineral particulates as a storage medium to interact with the pumped gas.

The company says the PHES system provides very high (72-80%) round trip efficiency comparable with pumped hydro, high reversibility, i.e., the system can function as both an engine and a heat pump, and no geographical restraints.

Isentropic should be able to showcase all of these advantages soon.  This GTM piece reports that a UK public-private partnership called the Energy Technologies Institute is investing $22 million to build a full-scale PHES demo system.