Over the past decade, the electrical grid has improved operational efficiencies, reliability, and resilience thanks to the deployment of smart grids across the nation. To date, according to the 2018 Smart Grid System Report to Congress, “U.S. utilities invested approximately $144 billion in electricity generation, transmission, and distribution infrastructure in 2016 (the latest year of available data).” However, even with all the investment in improving the power grid, the U.S. is still plagued by power outages, costing $30 billion to $50 billion in 2015, according to a 2017 study conducted by Lawrence Berkeley National Laboratory on Projecting Future Costs to U.S. Electric Utility Customers from Power Interruptions. In S&C’s 2018 State of Commercial & Industrial (C&I) Power Reliability Report, 50 percent of C&I customers surveyed reported experiencing a power outage that lasted more than 1 hour (see Fig. 1).
Harsh weather, equipment failure, wildlife, vegetation management, and human error all play important factors in power outages. Clearly, state-of-the-art power protection infrastructure is required now more than ever—especially for mission-ready applications.
Protecting the Mission-Critical Environment
The traditional means of achieving continuous power during a power event has involved the use of lead-acid batteries with uninterruptable power systems (UPSs). Although a tried and tested solution, batteries come with a heavy environmental and operational cost. When one considers the toxic nature of chemicals used in batteries, this situation is not ideal. Lead-acid batteries are heavy and slow to recharge. They also require continual and expensive maintenance, spill containment equipment, and environmentally safe disposal. Battery life is also an issue, as most battery manufacturers state that battery life can be maintained as advertised for at least four years if, and only if, they are kept at a constant 75°F in a temperature-controlled room and experience no excessive cycling. The uncertainty of battery health is a major issue—especially during longer duration power outages. For healthcare facilities, the National Fire Protection Association’s (NFPA) NFPA 99 regulations for emergency power systems require that, in the event of a power outage, generators must assume the energy load within 10 seconds.
Data centers, medical facilities, and industrial plants across the globe have realized that the use of flywheels in conjunction with, or instead of, batteries significantly increases power reliability and uptime.
During a power outage, a flywheel system provides backup power instantaneously, bridging the critical gap in power until a generator comes online. Fortunately, flywheels can be used with or without batteries. When used with batteries, the flywheel energy storage system is the first line of defense against damaging power outages—protecting against the frequent cycling of the batteries and prolonging their life.
Jeff Filliez, the datacenter manager for UC San Diego’s Supercomputer Center (SDSC), needed more efficient solutions for protecting its critical computer systems as traditional methods could not advance SDSC’s efficiency goals.
To further efficiency goals, a cogeneration plant with natural gas turbines, as well as a redundant power source with dual electrical feeds from San Diego Gas & Electric, provides power to the campus. For the data center’s power protection equipment, Filliez wanted a system that would provide much longer service life and considerably less maintenance overhead. “Our UPSs were nearing the end of their life and the lead-acid batteries were 10 years old. I wanted to see if there was a better approach that would ensure the highest reliability, reduce maintenance and battery replacement costs, and give us an overall lower total cost of ownership.”
After seeing the flywheels and hearing the positive feedback about flywheel operation and very low maintenance, Filliez replaced all SDSC’s lead-acid batteries with the highly efficient VDC flywheel units from VYCON (see Fig. 2). They specified a configuration pairing a one-megawatt 9900C Mitsubishi UPS with three 300 kW VYCON VDC flywheel units in an N+1 configuration.
When there is a power outage, the VDC flywheel seamlessly transfers the full electrical load to SDSC’s Caterpillar generator within 20 seconds. The generator has a dual starter with a 10-second window. “If the load is critical, you can’t repair it on the fly. So, even if you have 15 or 20 minutes of traditional battery backup, you won’t be able to get back online in that short of time. Quickly transferring the load to the generator just makes sense.”
How Flywheels Work
A flywheel system operates like a dynamic battery that stores energy kinetically by spinning a mass around an axis. Electrical input spins the flywheel rotor up to speed, and a standby charge keeps it constantly spinning until it is called upon to release the stored energy. The amount of energy available and its duration are proportional to its mass and the square of its revolution speed. For flywheels, doubling mass doubles energy capacity, but doubling rotational speed quadruples energy capacity.
As seen in Figure 3, flywheel systems interface 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. Upon loss of utility power to the UPS, up to 450 kW of regulated DC power per flywheel unit is instantly delivered to the UPS. This provides the backup power needed to start up and transition to the emergency generators during a prolonged utility outage. Multiple flywheels can be paralleled for longer run times or N+1 redundancy.
Microgrids and Renewables
The majority of microgrids use internal combustion engines to supplement renewable sources during times of limited sun exposure or wind generation and to handle step load situations. Diesel combustion engines produce power and are kept running as “spinning reserves” to the renewable plant, increasing fuel consumption cost and generating greenhouse gases. Conversely, flywheels not only provide increased storage capacity but also deliver power conditioning for grid stabilization and reduction of high generation costs. Flywheels can be configured to accommodate step load changes and sudden peak demands, allowing operators to start-up the generator on demand and/or run fewer generators (see Fig. 3). Not only does this dramatically reduce the cost of genset fuel and maintenance, it can also reduce or eliminate the need for redundant gensets.
For electric rail, flywheels store energy generated by today’s modern trains during the braking phase of operation, much like an electric vehicle. A braking train generates megawatts of power within 15 to 20 seconds, which would normally be wasted as heat on braking resistors. The flywheel system can store this energy and deliver it back to the train during the acceleration phase and can repeat this cycle hundreds of times a day without degradation (see Fig. 4). Using this type of smart energy recycling can result in energy savings of 20 percent or more.
System uptime and availability are prime concerns to those responsible for operating localized power generating projects, facilities, equipment, and systems. The green technology of today’s flywheel systems offers this reliability as well as cost savings. For example, using a flywheel versus a five-minute VRLA battery bank can offer $100,000 to $200,000 in reduced costs per flywheel deployed. Lower total cost of ownership along with environmental benefits make flywheels a very green alternative that helps lower carbon footprints, thus expanding the role of today’s advanced flywheel energy storage solutions.