Texas’ Lesser Known Green Energy Alternatives


What is a Flywheel?

Texas’ Lesser Known Green Energy Alternatives | The Light Lab

First used during the Industrial Revolution of the 19 Century, flywheels are heavy metal wheels that store energy by converting it into rotational energy. A prime example is the big bronze wheel on display at the Tredegar Ironworks National Park in Richmond, VA. It measures 12 feet across, weighs several tons, and once powered the rolling mill.

Flywheels work because they are mass in motion. Once all their huge mass is spinning, they hold an enormous about of energy, and thus tend to keep spinning — which makes them a cheap and efficient means to store energy. Flywheels, like the example at Tredegar, were made of bronze or steel and mounted in conventional bearings. Because of friction, speed was limited to a few thousand RPMs. Unless the flywheels were manufactured with exact precision, their spin would be unbalanced at higher speeds — with calamitous results. It was a common industrial accident for large-scale flywheels to fly apart or explode if driven too fast. In 1905 at Tredegar, a 25 foot wide flywheel exploded, killing a man, injuring two others, and tore up one of the steel mill’s buildings.

Modern flywheels are hi-tech marvels. Designed for 90% energy efficiency, they are made by stacking carbon-fiber-reinforced-plastic (CFRP) rotors. Different masses can be built to order by vary the number of rotors per flywheel. Superconducting magnetic bearings are used and once refrigerated they create a magnetic field strong enough to levitate the stack of rotors. This allows a 4 ton flywheel to spin with virtually no friction. The flywheel is also connected by its shaft to a motor/generator that can both keep the flywheel spinning and use its motion to generate electricity. Finally, the entire assembly is sealed in vacuum to eliminate any possibility of air-drag or friction that can slow the flywheel. Since a flywheel’s stored energy is in the form of a spinning mass of metal, there’s none of the problems that comes from chemical reactions as in lithium ion batteries.

Flywheels are currently used to regulate electricity frequency and voltage regulation. However, they are also perfectly suited for storing and smoothing output from both solar and wind installations. It’s thought that the technology has the capability to store 50% of grid capacity within 50 years. This is mainly because as a power storage system, flywheels don’t suffer from the limitations of cycling and charging time that batteries face.

Currently there are several flywheel projects in Texas:

Compressed Air Energy Storage (CAES)

Texas’ Lesser Known Green Energy Alternatives | The Light Lab

CAES uses low cost late-night wind power to run giant air compressors to pump air into a salt cavern. In Texas, underground salt domes are a plentiful resource and many have been hollowed out to store huge amounts of natural gas. The compressed air is kept there under pressure until day time when electricity prices rise. At that point, the compressed air is released, heated (usually with natural gas) so that it expands further and is used to spin up turbines to generate electricity at a profit.

One problem with this is that CAES system tend to have a low energy efficiency (50%) because heat is lost during compression. By storing the heat, it can be used to help expand the air upon its release. This reduces the amount of natural gas used to heat and expands the air. Known as an “ Adiabatic system” or A-CAES, studies have shown that they are nearly twice as expensive as conventional CAES process using natural gas as a power supply for production.

For the moment, there are only two commercial CAES plants operating in the world: one in Huntorf, Germany and the other in McIntosh, Alabama, USA. One project by the Iowa Association of Municipal Utilities was terminated by investors in 2012 after studies showed the proposed use of sandstone aquifer northwest of Des Moines was unsuitable.

Two Texas plants are slated to begin construction upon regulatory approval:

  • APEX’s Bethel Energy Center Anderson County is designed for a 317 MW generation capacity and an air/energy storage capacity of 30,000 MWh. The plant is expected to be on-line by 2020.
  • Chamisa Energy proposed a 270 MW facility in Swisher County, Texas. At last word, the company was seeking $400 million for the project.

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