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NETWORK / 36 / OCTOBER 2016 Superfast next generation? A Lancaster engineering undergraduate has created a superfast design for a flywheel energy store as part of her degree. Rather than being electromagnetically levitated, the rotor is permanently levitated, without requiring additional control mechanisms. Abigail Carson initially aimed to achieve a rotation speed of 100,000rpm, but simu- lations and calculations reveal the design can easily rotate at 144,000rpm without any adjustment, far quicker than aver- EnErgy storagE Flywheels Flywheels store energy through movement. Electric energy input accelerates a spinning mass to speed via an integrated motor-gen- erator, where it is stored as kinetic energy. The rotor continues to spin in a vacuum on magnetically levitated bearings until the energy is needed again, at which point the same motor-generator discharges the energy back into the grid. Flywheels are low main- tenance, have a long life cycle and negligi- ble environmental impact. Now: Early deployment Flywheels are being used as one half of a new hybrid energy storage system in Rhode, County Offaly in Ireland. Irish company Schwungrad Energie has developed the sys- tem in collaboration with the Department of Physics and Energy at the University of Limerick. The project has been funded by a €2.55 million grant from the European Com- mission Horizon 2020 fund. The system includes two 160kW gen- erators by US manufacturer Beacon and a Hitachi 160kW/576kWh deep-cycle lead-acid battery. These batteries work in tandem with the flywheels to provide a complete solu- tion for grid stability, including both rapid frequency response and longer-term storage discharge, which allows for higher levels of renewable energy on the grid. Axes of rotation Motor/ generator a b c Vacuum pump Upper magnetic bearings Protective shield Lower magnetic bearings Rotor Lithium-air Lithium-air batteries are touted as a highly promising technology for powering electric vehicles (EVs) because of their potential for delivering a high energy output in propor- tion to their weight, but they have serious drawbacks. They degrade quickly, waste up to 30% of electrical energy as heat in charg- ing, and require expensive extra compo- nents to pump oxygen in and out. But scientists at MIT in the US have cre- ated a new fully sealed battery that over- comes these problems. In the nanolithia cathode battery the same kind of electro- chemical reactions take place between the lithium and oxygen, but without the oxygen being allowed to revert back to a gas. This is achieved through the creation of miniscule (billionths of a metre) scale parti- cles, which contain both lithium and oxygen in the form of a glass, embedded within a cobalt oxide matrix to maintain stability. The process reduces the voltage loss by a factor of five, so only 8% of electrical energy is lost to heat. This increased efficiency means faster charging for cars, but also slower degradation of the battery and there- fore a longer life span. These new batteries are also inherently protected from overcharging because the chemical reaction is self-limiting, whereas irreversible structural damage can be caused to normal lithium-air batteries when overcharged. They can even explode. The scientists behind the battery at MIT tested its resilience by overcharging it for 15 days at a hundred times its capacity without it suf- fering any damage. Cycling tests also revealed that on a 120 charging-discharging cycle less than a 2% capacity loss was observed. In the future the lightweight design means EV batteries could have twice the amount of capacity for the same weight, and with refinement this could be increased still further. These scalable, cheap and safer batteries could also be used for grid-scale applications. The team at MIT expects to have a practical prototype of the nanolithia within a year. age existing designs which spin at around 60,000rpm. The design is ideally suited to domes- tic uses, being the size of a football, but it can be scaled up for industrial applica- tions using a stacking approach. Multiple individual units also means if one unit suf- fered a fault the entire system would not be required to shut down. Carson currently has a patent pending for the design and is seeking investment oppor- tunities to implement the FES. An electromagnetically levitated flywheel Courtesy of the researchers