Flywheel Versus Supercapacitor for Running a Small Electric Ferry

by Emil Morhardt

When we think of all-electric cars, we think lithium-ion batteries because they are lightweight and have a high power density. For ships, light-weight doesn’t matter so much, and it turns out there are types of shipping routes that don’t need very much energy storage: think ferries, specifically the plug-in ferry Ar Vag Tredan (the “electric boat” in Breton), a zero-emission passenger ferry crossing the Lorient roadstead 56 times a day. When parked between trips it can recharge its supercapacitor more-or-less instantly (that’s a main feature of supercapacitors—that and their ability to discharge their power equally quickly to meet any need for power the ship may have.) How would a flywheel energy storage system work compared to the existing supercapacitor? That’s the question asked in a new paper by Olivier et al. (2014). Continue reading

Hybrid Energy Storage for CubeSats

by Emil Morhardt

CubeSats are cool. No, actually very cold, since they’re out in space. But they are reproducing like rabbits. There are well over 200 of these little 10 cm X 10 cm X 10 cm cube satellites have been launched into orbit by tucking them into the nooks and crannies in the launch vehicles around much larger satellites. (Some are multiples of cubes, 10 cm X 20 cm, or 30 cm.) They need energy. Until now they have been powered in the main by lithium ion batteries like those in your computer, and charged by the photovoltaic panels that make up a CubeSat’s skin. The thing is that these batteries don’t work very well when they are cold; the speed of electrochemical reactions, just like those of every other chemical reaction, are modulated by temperature—the colder the slower. The current Li-ion batteries don’t work at all below –10°C, yet CubeSats headed for deep space are expected to encounter temperatures of –40°C some of the time. So if you have a CubeSat process that needs power at low temperatures or a short-term burst of power faster than the batteries can provide, you need help. Continue reading

Supercapacitors save Windpower Batteries


by Emil Morhardt

Windpower, because it is intermittent, works best on the electrical grid if it has some energy-storage facility connected to it. Batteries are the simplest approach, and the low cost of lead-acid batteries makes them good candidates, but they resent being randomly charged and discharged (especially deeply discharged) at the will of the wind, and die prematurely. Enter the supercapacitor; it can be charged by wind turbines much faster than a battery, can deliver its stored energy to the grid much faster as well, and doesn’t resent it at all, even being deeply discharged at every cycle. Engineers at Kocaeli University connected a supercapacitor in parallel with a battery (see diagram above) so that it would buffer transient current surges, saving the battery to do what it does best. The system worked just like one might expect, but there are some graphs in the paper showing just how the current flowed, and I think it is a nice example of an experimental setup to look into these types of hybrid energy storage systems. (The diagram is from their paper. There’s a link to it below.)

Erhn, K., Aktas, A., Ozdemir, E., 2014. Analysis of a Hybrid Energy Storage System Composed from Battery and Ultra-capacitor, 7th International Ege Energy Symposium & Exhibition, June 18-20, 2014, Usak, Turkey

Please send suggestions for other recent papers appropriate for this blog to