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California Energy Commission Begins Final-Stage Field Trial Testing of Beacon Power Flywheel System

A 250 kWh flywheel matrix.

The California Energy Commission, in partnership with the US Department of Energy and the California Independent System Operator (ISO), has begun the formal field trial testing of a flywheel-based frequency regulation system from Beacon Power Corporation.

Conventional approaches to frequency regulation—balancing power generation with load—vary the power output from fossil-fuel or hydro generators connected to the electric grid. The flywheel system, however, is a storage-based approach, and thus is of particular interest for use in conjunction with renewable power generation (wind, solar) where the primary power output is variable.

A flywheel energy storage system draws electrical energy from a primary source and stores it in a high-density rotating flywheel. Upon power loss, the motor driving the flywheel acts as a generator. As the flywheel continues to rotate, this generator supplies power to the customer load.

The scale-power Smart Energy Matrix demonstration system is located at a Pacific Gas & Electric substation in San Ramon, California. The field trial is the final stage of evaluation and is expected to be completed before the end of 2006. Beacon also has a system undergoing formal field testing in new York.

Current markets for frequency regulation services. The open market is about 22% of US generation.

Beacon plans to build megawatt-scale flywheel-based frequency regulation plants around the US and to own and operate them on an independent merchant basis, or in conjunction with partners. In 2005, the value of frequency regulation services in the open and accessible US markets was more than $600 million.

The Smart Energy Matrix is a multi-flywheel-based energy storage systems based on Beacon’s Co-mingled Rim Technology (PCRT) flywheel design. The core component of both Smart Energy Matrix systems will be 25 kWh/100 kW flywheels optimized to perform frequency regulation services.

Beacon houses sets of flywheels in a transportable shipping container that can then be aggregated nearly anywhere on the grid.

(A hat-tip to Bob!)




I once looked over Beacon Power's site and found that their system seemed to have rather high parasitic losses.

It's not all bad, though.  The losses might be acceptable if the storage units were sited near bus stops and EV fast-charging stations, so that the stored energy could give a very fast energy bump to a vehicle without loading the grid.

Success of this scheme might push investment toward superflywheels operating in vacuum, reducing the losses.

Rafael Seidl

I thought all modern flywheel energy storage designs are based on composite fiber rotors revving at very high speeds (50k RPM and above) in a high vacuum on magnetic bearings. The rotors are even manufactured in a vacuum to prevent outgassing during the device's lifetime.

The biggest problem with flywheels is the risk of delamination, due to overrevving (no rotor is *perfectly* balanced), loss of vacuum (i.e. aerodynamic friction heating) or a bearing failure. The sudden release of energy requires a robust containment structure, e.g. reinforced concrete walls or composite panels designed to resist explosions, cp.

Such containmment structures are feasible in stationary applications. Possible applications include not just the general electricity grid but specialized ones for (light) rail and even high-rise elevators (eliminating the pulley and counterweight and enabling vertical-to-horizontal transitions).

Btw: in the mid-90s, Rosen Motors (a technology startup) proposed using a superflywheel in a revolutionary series hybrid car whose prime mover was to be a single-stage microturbine. The flywheel was gimball-mounted and connected to the chassis using Kevlar straps. Investors got cold feet when they figured out that when fully charged, the energy stored in the flywheel was equivalent to that need to lift the vehicle about 20 floors straight up. That would not happen in a crash, it merely illustrates the need for containment.

Btw 2: a less efficient but more easily contained form of mechanical energy is hydraulic pressure. It might be attractive for stationary applications as well as large mobile ones:


I guess a bearing failure is less catastrophic if there are many smaller flywheels. I read where a Japanese grid would not accept windpower from a producer unless the output was smoothed. Four of the shipping containers could store a megawatt-hour which I presume can be fully drawn down unlike most batteries. There is no mention of cost or if maintenance staff are required onsite 24/7. Whether this is the needed breakthrough for intermittent energy sources all depends on cost and reliability.

allen Z

Frequency and power smoothing aside, batteries look better than this system as pertains to efficiency. 90%+ in, 90%+ out (for 81%-86%+ 2way), over days and weeks, repeated over years and decades. Next gen high power desity ultra caps and li-ion batteries look even better.
Hydraulic hybrids would work well on vehicles with largely stop and go driving patterns, as well as those that stop/slow regularly and frequently from high speeds. Air hybrids work too, but not as well. The only advantage is the lower weight vs. hydraulics.


Energy isn't cheap enough where these people would just arbitrarily go with a less efficient system. They must be pursuing this design because other options aren't viable/cost effective.

Allen Z
Funny you mention air hybrids. Formula 1 is considering implementing rules that would allow teams to develop/use air hybrid systems for regenerative breaking.


The idea of power regulation using flywheel is very attractive.

Usually, for large scale renewable energy, the source of power and the users of these power are physically in 2 different places.

And therefore, if at the source of power (e.g. wind turbine), can be stored with flywheel systems, then from the users point of view, the fluctuation of the wind power can be smoothed out.

Furthermore, if at the user side (maybe at city), one can install flywheels (underground) for storage of power. For example, in the daytime, maybe the transmission grid between the wind site and the city is too congested to transmit extra power. Then one can transmit power at night and store at the flywheel for next day use. Also, there maybe small wind turbines or solar panels in the city, where extra power can be either delivered to the grid or to the city located flywheel.

I think for high energy storage, high roundtrip effiency, non-mobile usage, flywheel is definitely the answer to go.


I think frequency modulation and smoothing are the prime motivation for this system.It is not intended to contribute a significant percentage of stored power.

Starting up gas fired plants during peak periods causes frequency range problems.Storage shemes will be easier to plug in if these modulators are distributed throughout the system.

Im no engineer but this is the thrust I got from an article that I believe I saw on the energy blog.


Energy Blog now has a post of the sale by VRB of a battery storage system to be coupled with windmills in Ireland.

Hydrogen production during off peak to be used in a ice engine during peak demand was another option posted here recently.

A plethora of distributed generating processes demands a smoothing sheme to avoid cascading failures.


I always think, is it possible to get these 6kwh flywheel battery cheap enough for residential use?

That would really offset the time to manage those lead-acid battery. (the product sheet said it's mean time failed average is 20 years)

Also, one can install these flywheel battery and connect it with solar panel and wind turbines at those off-grid homes.

And it may even possible to put these flywheels in electric railway system (may need a bigger flywheels), where these batteries can be stored at stations. When the train starts, it sucks it lot of electric power from the grid, and when it stops it wastes a lot of electric power. That's a lot of power going in and out from the grid, if these power can be put into the flywheel batteries (they are very good at taking in and loads out lot of power in a short amount of time), that may reduce costs to the whole railway system. (reducing fluctuation of the loads, reducing wearing to the brakes, reducing electric bills, etc.)

There is another reason to use flywheels instead of conventional chemical energy: scalability. since amount of energy stores in a flywheel is proportional to the square of the angular speed times mass whereas the energy stores in a chemcial energy is proportional to its mass, when one wants to store more energy in a flywheel through "mainly" increasing the speed, the size may become a little bit bigger (increase the diameter of the flywheel, use better casing), however for chemical batteries, you mainly need to increase its volumn. Sometimes, in practical usage, you don't really have that space to put in, and that's a good selling point of flywheel based battery system.

And more importantly, flywheel battery systems can be an important amercian based industries. (I don't know whether they are able to make these flywheels battery in China, considering the quality....)


Stress in flywheel materials rises as the rotation speed squared; the energy storage is proportional to the tensile strength divided by the density.  Energy scales as volume, like everything else.


Other advantage over batteries, these can be discharged many more times than batteries and are environmentally


Sounds similar in concept (if not in execution) to the old motor-generator systems we used to smooth power to our Control Data mainframes back in the day. Even if the lights flickered, the systems never noticed a thing.

Charles Ivie

What is the current status of this project? I work for a wind energy company and we are looking for energy storage systems.

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