As we reflect on the many goals of the recent UN Climate Change Conference (COP26), two key principles were of special note:

• Encourage more sustainable behaviour.
• Promote the use of responsible sources and responsible use of resources throughout the supply chain.

These values are especially appropriate for the data centre industry. Never in our history have we experienced the unprecedented rapid growth of the digital infrastructure. The global Covid-19 pandemic has certainly accelerated technologies to meet customer demand for all things digital. Large companies are building and expanding their data centre footprints to meet the world’s insatiable digital appetite. 

To illustrate this point, in April of 2021, Microsoft announced it would build 50 to 100 new data centres annually across the globe. And IDC estimates that by 2025, there will be 175 zettabytes of data created each year, resulting in data centres consuming up to 5% of the world’s electricity. 

This growth also means that 24X7 always-on operation has never been as crucial as it is now. Protecting data centre operations against inevitable power disturbances and outages is a critical piece of the data centre infrastructure. The Department of Energy (DoE) has estimated that by 2018 outages cost the US economy $150 billion a year.

UPSs and energy storage

While there has been substantial adoption of alternative energy sources such as solar, wind and geothermal to power large data centres, more can be done to reduce an operations’ carbon footprint. Manufacturers of three-phase Uninterruptible Power Supply systems (UPSs) for protecting data centres have adopted newer technology to improve efficiency and scalability.

However, the energy storage component of the UPS is still dependent on strings of batteries – some of which, like lead-acid batteries – are extremely toxic and hostile to the planet.

Moreover, lead-acid batteries, which are still the preferred energy storage choice due to cost, are unreliable, require expensive cooling, frequent maintenance and replacement, and need a large amount of real estate. And don’t forget environmental mitigation and spill containment.

Relatively new to the scene is the integration of Lithium-Ion (Li-ion) batteries with UPSs. Li-ion batteries have distinct advantages over lead-acid types, like the ability to operate in wider temperature ranges with thousands of charge-discharge cycles over their lifespan. 

However, according to The National Fire Protection Association (NFPA) 855 standard in the US, Li-ion batteries must include an approved battery management system with thermal runaway management. In addition, installations must maintain three feet of clearance all around the battery cabinets to ensure that fire will not spread from cabinet to cabinet unless they are UL9450A tested, and the Authorised Housing Jurisdiction (AHJ) waives cabinet spacing.

Clean energy flywheels to the rescue

A more sustainable approach to energy storage involves incorporating 40kW to megawatt-sized flywheels into power protection configurations instead of heavy, toxic batteries with a large carbon footprint. Configuring a 160kVA UPS with a flywheel clean energy storage system instead of lead-acid batteries can save six metric tons of CO2 over a 20-year life with four battery replacements.

Besides the great environmental benefits, there are also substantial cost savings in adopting flywheel modules with UPSs. Since the flywheel does not use a chemical reaction to produce power, it can be deployed in operating temperature environments of up to 40°C. 

The ability to operate in a wide temperature range saves valuable computer room floor space since the UPS doesn’t have to be in a precise temperature-controlled room, thus reducing the cost of HVAC to cool the system. And the compact footprint of the flywheel is another benefit as one flywheel module only takes up 30in in depth by 30in width of floor space.

Flywheel technology

Because the flywheel operates as a mechanical battery, it holds kinetic energy in the form of a rotating mass. It then converts this energy to electric power within the flywheel system. A high-speed motor generator, active magnetic bearings that levitate and sustain the rotor during operation, and an on-board control system provide vital information on system performance. 

The monitoring system lets users know the exact state of the system in real time – unlike batteries. There are always questions about the batteries’ state of health. Even testing them under load degrades their useful life.

Compatible with all major global brands of three-phase UPSs, the flywheel interfaces with the DC bus of the UPS, just like a bank of batteries, receiving charging current from the UPS and providing DC current to the UPS inverter during discharge. 

When there is a power outage, the flywheel will provide 14 to 45 seconds of backup time to transfer to the on-site generator. This allows plenty of time for the generator to start up, as an average backup generator requires less than 10 seconds to come online. 

For installations where the flywheel is used in conjunction with batteries (either with or without a genset), the flywheel systems will engage first during transients and short power disruptions, preserving the batteries for use in longer-term outages and minimising discharge cycles to prolong overall battery life.

Bottom line

Flywheel energy storage replaces the weak links associated with battery-based backup with a reliable, energy-efficient, instantaneous energy source. Because of maintenance and replacement costs, cooling and space requirements, the traditional operating cost of batteries over a 15-year period is three to four times more than that of a flywheel energy storage solution. 

Users are realising $100,000 to $200,000 USD in savings over using a five-minute lead-acid battery configuration. The flywheel solution is the most reliable and cost-effective bridge to the engine genset during a utility line failure.

As the demands of processing data rapidly increase and become more complex, data centre managers, engineers, and consultants continually assess power solutions that can improve efficiencies while enhancing energy reliability. 

While system availability is always the first requirement, being environmentally friendly and lowering carbon footprint are now must-haves. By augmenting battery strings or replacing them with flywheels, managers can take one more step in reducing their carbon footprint and lowering the cost of ownership.