Another parameter to consider is the flywheel's standby losses of the float charge. Energy consumption is required to spin the mass. Depending on the manufacturer, the energy needed to power the flywheels could range from a few hundred watts to a few thousand watts.
Another key evaluation point when comparing flywheels is cycle time/recharge time. The flywheel needs to reach a high enough speed to produce enough DC electricity to support the load. After a discharge, how soon can the flywheel discharge again? Voltage sags typically come in waves, so it's important to know if the flywheel takes seconds or minutes to get back up to speed.
The last point for evaluation doesn't even relate to flywheels, but to the UPS instead. Some flywheels come integrated inside a UPS while others are UPS vendor neutral. It is necessary to understand the UPS topology used with the flywheel, as the UPS itself is also a critical component of protecting availability.
What's the catch?
The initial purchase price of a flywheel is higher than the cost of lead acid batteries. That initial investment can be difficult to swallow, but it's essential to remember the 20-year life of the system. By the time the first battery replacement comes along in three years, the flywheel will have paid for itself. When factoring in all the expected life, cost components, capital price, maintenance energy costs, and battery replacement cycles, a flywheel can save more than $150,000 versus a comparable battery string. It's important to analyze long-term, total cost of ownership.
Another concern about a flywheel is its unfamiliarity, as some facility or IT managers are hesitant of utilizing new technology. Batteries have been around since the first UPS was manufactured, and a comfort level comes along with that familiarity. But just because the battery is sitting on the rack or in the cabinet doesn't mean it will work when the time comes. Being able to check the status monitor and know the flywheel is spinning, and that it will be there when needed, should restore comfort and confidence in your energy storage systems.
For those managers who prefer the comfort of batteries but want the reliability of a flywheel system, there is always the strategy of using flywheels in conjunction with batteries. Many facilities use the flywheel to absorb the frequent, small and short voltage sags that occur every day while saving the batteries for those longer outages that exceed the flywheels' capabilities. This approach extends battery life close to design claims by eliminating battery cycling for short discharges.
A great alternative
IT and critical systems are everywhere in hospitals and their availability is essential in delivering positive patient outcomes. The use of a UPS with a flywheel for energy storage can provide maximum availability at a lower total cost of ownership and with a more environmentally friendly profile. And that's no spin. HBI
Critical questions to ask when considering flywheels
Does the cost make sense? How often are you replacing UPS batteries?
Would you benefit from using a flywheel in conjunction with batteries?
What is the UPS design topology attached to the flywheel?
Will flywheel implementation help the hospital with its green initiatives?
What is the flywheel's standby power draw?
What maintenance is required? How often is maintenance performed?
What is the flywheel bearing type and how does that impact maintenance?
What is the recharge/cycle time? How many discharges can I get in five minutes?
