Active Power Article – Flywheel energy storage

Summary – this article offers compelling reasons for using a flywheel in combination with a diesel generator for UPS rather than a battery UPS.  Batteries are the weakest point of any generator – their maintenance is easily overlooked, and the flywheel eliminates the need for them, by storing enough energy to start the generator, and to provide no break power whilst the generator is starting.   If battery UPS is used, this has a limited run time – maybe 20 – 30 minutes, after which time, everything is down unless a generator is installed, so why not put in the flywheel and diesel gen set in the first place, since this will give unlimited UPS.

This article is written by and features Active Power who manufacture these systems.

As compared to other energy storage technologies (i.e., flow battery, compressed air, hydrogen, lithium ion battery, etc.), flywheel technology is a very mature, field proven technology. It’s worth noting  Active Power was the first to commercialize a mechanical flywheel energy storage system and soon after patented the integration of UPS electronics with flywheel energy storage. Flywheel operation is very well understood and Active Power alone has more than 2,100 flywheels deployed in the field to date with more than 55 million hours of runtime. Flywheels present the most power dense energy storage technology when used as a bridging device between an outage and on to a generator.


The cost per kW of integrated flywheel UPS is approximately US $330.00. From a delivery standpoint, the integrated flywheel UPS system can deliver 15 seconds of ride-through at 100 percent load and 30 seconds at 50 percent load. From an efficiency stand point, the system consumes 2 percent of the power to motor the flywheel, operate controls and condition utility power at 100 percent load. The system is up to 98 percent efficient at 75 percent load (or 2 percent losses) and up to 96 percent at 40 percent load (or 4 percent losses).


In addition, the system consumes 75 percent less space compared to conventional double conversion UPS systems. And with a 20 year design life, service and maintenance costs are substantially less – as customers do not have to replace hydrogen or compressed air tanks for other energy storage technologies. At seven times less likely to fail compared to a conventional double conversion UPS system with batteries (refer to Active Power whitepaper #103 – “Reliability Assessment

of Integrated Flywheel UPS versus Double-Conversion UPS with Batteries”), the flywheel system is a highly reliable source of energy, delivering consistent, predictable performance with absolutely no degradation in service over the life of the system. From an operating standpoint, flywheel systems are rugged meaning they can operate in a wide ambient temperature range (0 to 40 degrees Celsius) as compared to conventional systems which required air conditioned environments.

In the instance of a 5 MW system deployment at the base of offshore wind turbines for example, it’s difficult to speculate on this as Active Power’s flywheel technology is designed for the power quality market, not off-grid/on-grid alternative demand management, frequency regulation, etc. It’s worth noting renewable energy sources (i.e., wind, photovoltaic, hydro, etc.) require an inverter (or double conversion step like a flywheel) to produce a 208 V/60 Hz or 400 V/50 Hz supply. Renewable sources are highly unstable and require the grid to stabilize its output. A flywheel or any other short term energy storage is not a solid fit because the system could have hours or days with low output or high output. Frequency regulation is suitable for flywheels, but has nothing to do with renewable.

The one thing that can help improve efficiencies at a lower total cost of ownership (TCO) without compromising reliability is simplification of products and solutions. Taking the flywheel UPS system a step further and based on customer and market feedback, Active Power simplified its offering with the introduction of PowerHouse, a complete critical power protection system. Available in a series of formats, the system is pre engineered and factory tested as a complete, repeatable solution versus a legacy component-by-component implementation. PowerHouse can contain diesel generators, Active Power’s CleanSource flywheel UPS systems, generator starting modules, switchgear, power distribution units and more. Systems can be deployed in a number of environments including the roof, redundant loading bays, secure compounds or car parks. PowerHouse is ideal for end users who have limited facility space and want to maximize use of revenue generating floor space. Since its introduction to market, Active Power has already generated traction with the solution in the United Kingdom, Europe and Asia. To date, Active Power has deployed more than 20 megawatts of power via its PowerHouse platform.

Lee Higgins <>Eric Axel Behrendt <>

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  1. dr. somani l.k. - February 26, 2010, 5:08 am Reply

    780 litre of water falling from height of 100 metre provide 1 kw of energy.
    i have a formula to lift water onthis level by only 2 ox without expending any energy by the help of farmer. so that farmer can also get job and we can solve the energyproblem of the world.
    if your company intrested in this project,please contact on my email

  2. BOUDALI - May 28, 2012, 1:14 pm Reply

    veuillez nous faire parvenir par émail un dossier technique complet concernant un système groupe no break avec flywheel de 60kva pour un éventuel achat.
    sincères salutations

  3. Flywheel vs. Battery UPS: Which Should You Choose? | - November 20, 2015, 3:56 pm Reply

    […] substantially less than a battery UPS.  Active Power, a leading manufacturer of flywheel systems, states that the average flywheel UPS configuration should consume 75% less space compared to a […]

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