The Unexpected Result From Our Analysis of Battery Versus Flywheel UPS

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The ongoing focus from the public sector and large organizations to improve their ”green” image and reduce their carbon footprint has triggered an ongoing debate about possible alternatives to lead-acid batteries. Flywheels in particular have been a part of that discussion, and there are advantages and disadvantages of each approach. For example, flywheels take up a smaller footprint than VRLA batteries and operate over a wider temperature range, while VRLA batteries provide longer runtime, and more efficient operation.

Of course, the answer to which technology is “greener” depends largely on the definition of green. Is it based on energy efficiency, carbon footprint, recycled raw materials, hazardous materials? Green washing and hype has made it difficult to get to the bottom of this and understand the differences. That’s why we thought it necessary to conduct a lifecycle carbon footprint analysis of flywheels vs. VRLA batteries.


Flywheels vs. Batteries: By The Numbers

Schneider Electric has launched a free online Flywheel vs. Battery Carbon Footprint Calculator that can allow data center operators to compare energy storage for static UPSs. You put in details about your location and capacity requirements, and the tool provides guidance on what you can expect in terms of carbon impact from raw materials, maintenance & delivery, energy to operate, and energy to cool,


The results may come as a surprise to many. In almost all cases, VRLA batteries had a lower overall carbon footprint, primarily because the energy consumed to operate the flywheel over its lifetime is greater than that of the equivalent VRLA battery solution, and the carbon emissions from this energy outweighs any carbon emissions savings in raw materials or cooling. Of course, the tool lets users conduct their own comparison to see for themselves.


This analysis and tool are a good reminder that decisions around energy storage needs to factor in a number of variables. The feature set of a UPS needs to be tailored to businesses on a case-by-case basis, and that includes considerations around carbon footprint. In some scenarios, there may be reasons for batteries and flywheel storage units to coexist. And ultimately, the one thing that’s common across all data centers is the goal to eliminate the risk of downtime.


Flywheel vs Battery


For years now, experts have been discussing this topic. Continuing to build awareness with tools such as our new carbon calculator will ultimately lead to more innovative solutions to business challenges.

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  • Vidyadhar Joshi

    9 years ago

    Good Article Wendy, You have highlighted only the carbon foot print, what about the real-estate. Look at the weight comparison. Flywheel is 3 times lighter. So one has to be careful while making a choice. I would rather see the third choice which is not mentioned. ie. not use both at all.

  • BROUSSET frederic

    9 years ago

    Hi Wendy. Very interesting article and tool in order to compare both technologies. Now, it will be great to include Li-ion batteries on the analysis, which become very competitive, for short back up time autonomy. They may cost more, but will last about twice as long as VRLA batteries. Li-ion batteries also have a far smaller footprint, which drives down both space and cooling requirements (finaly carbon emissions) and delivering further cost savings.

  • Ferran Biosca

    6 years ago

    Good report Wendy. Very interesting insights about the operating costs of both devices. It seems though that there’s no consideration on the recycling cost of either. It’d be good to understand the whole life cycle including the dismantling and reuse/revalue/recyclability of material used.

  • LuckyLuke

    6 years ago

    I am not sure if the cost of replacing the batteries every 3 years and the 2 yearly maintenance, against the maintenance every 10 years for the flywheel has been taken into consideration …? Also, while the Flywheel consumes power while idling, the batteries will consume power since only 50% of the input will be available to output and every cycle erodes the capacity to charge the batteries fully … ?

    • Wendy Torell

      6 years ago

      The tool does consider the maintenance activity and raw materials of replacement batteries in the total carbon emissions. For maintenance, we assume transportation of 200 miles (322 km) for the service personnel. The tool allows you to set the frequency of maintenance and service life so you can see the impact this has. I hope this helps.

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