4 ms·

Centrifugal storage systems would be more efficient, AND last 100 years with only needing new bearings every 20years.

gandreani 9y ago
You mean like flywheels? What's their efficiency like? I always thought that they needed magnetic bearing to get to higher (70+) efficiencies. But they seem cheap over the course of decades when compared to battery lifecycles and maintenance of other storage methods
ridgeguy 9y ago
I assume you mean flywheels. Flywheel energy storage seemed appealing until I worked on it in an energy storage startup. Flywheels require expensive protection against catastrophic failure. The costly part isn't fragment containment, that's affordable. But angular momentum is conserved. That means when a flywheel crashes, it will exert a very large torque on its containment structure. If the containment breaks loose, it can do a lot of damage in moments. Containment that's safe against torque failure is very expensive. Flywheels also have to run in a vacuum. If the rotor is s composite material, there has to be an active vacuum pump because composites outgas forever. Additional system cost and failure point. If you don't use composite rotors, the energy storage density goes down because tensile strength of metals is so low compared to composite fiber materials. Low energy density increases overall cost/MWHr. Rotor life is limited by static fatigue and by high cycle fatigue, which have different failure mechanisms. For carbon, glass, or aramid fibers, you can count on a rotor MTTF of ~20 years if the rotor is operated so it never exceeds ~35% of the fiber's ultimate tensile strength. But that cuts into energy storage efficiency, driving the cost up more. There are some niches that flywheels can serve with competitive economics (grid intersection phase matching, for example). But overall, it's hard to see how flywheel economics can beat the declining cost curve of electrochemistry. The foreseeable cost floor, set by some of the system issues I listed, is too high.
- basicplus2 9y ago
  In-ground installations protect against failure This mob seem to have it all worked out "http://beaconpower.com/" http://beaconpower.com/"
  - ridgeguy 9y ago
    In-ground gives additional protection, but things can still get away. Beacon Power is AFAICT the leader in deployed flywheel electrical energy storage. Their units are all underground. One of their failures dislodged a heavy concrete and steel lid on the unit [1]. Part of their emergency shutdown routine is a water dump into the flywheel chamber to dissipate energy. The water flashed to steam and blew a multi-ton lid partly off the unit. The spinning rotor did not escape, so all was well. More about Beacon Power technology: [2]. [1] http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/ http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon... [2] http://www.sandia.gov/ess/docs/pr_conferences/2014/Thursday/Session7/02_Areseneaux_Jim_20MW_Flywheel_Energy_Storage_Plant_140918.pdf http://www.sandia.gov/ess/docs/pr_conferences/2014/Thursday/...

You mean like flywheels? What's their efficiency like? I always thought that they needed magnetic bearing to get to higher (70+) efficiencies. But they seem cheap over the course of decades when compared to battery lifecycles and maintenance of other storage methods

ridgeguy 9y ago

I assume you mean flywheels. Flywheel energy storage seemed appealing until I worked on it in an energy storage startup. Flywheels require expensive protection against catastrophic failure. The costly part isn't fragment containment, that's affordable. But angular momentum is conserved. That means when a flywheel crashes, it will exert a very large torque on its containment structure. If the containment breaks loose, it can do a lot of damage in moments. Containment that's safe against torque failure is very expensive. Flywheels also have to run in a vacuum. If the rotor is s composite material, there has to be an active vacuum pump because composites outgas forever. Additional system cost and failure point. If you don't use composite rotors, the energy storage density goes down because tensile strength of metals is so low compared to composite fiber materials. Low energy density increases overall cost/MWHr. Rotor life is limited by static fatigue and by high cycle fatigue, which have different failure mechanisms. For carbon, glass, or aramid fibers, you can count on a rotor MTTF of ~20 years if the rotor is operated so it never exceeds ~35% of the fiber's ultimate tensile strength. But that cuts into energy storage efficiency, driving the cost up more. There are some niches that flywheels can serve with competitive economics (grid intersection phase matching, for example). But overall, it's hard to see how flywheel economics can beat the declining cost curve of electrochemistry. The foreseeable cost floor, set by some of the system issues I listed, is too high.

basicplus2 9y ago
In-ground installations protect against failure This mob seem to have it all worked out "http://beaconpower.com/" http://beaconpower.com/"
- ridgeguy 9y ago
  In-ground gives additional protection, but things can still get away. Beacon Power is AFAICT the leader in deployed flywheel electrical energy storage. Their units are all underground. One of their failures dislodged a heavy concrete and steel lid on the unit [1]. Part of their emergency shutdown routine is a water dump into the flywheel chamber to dissipate energy. The water flashed to steam and blew a multi-ton lid partly off the unit. The spinning rotor did not escape, so all was well. More about Beacon Power technology: [2]. [1] http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon-power-frequency-flywheel-plant/ http://eastwickpress.com/news/2011/07/a-mishap-at-the-beacon... [2] http://www.sandia.gov/ess/docs/pr_conferences/2014/Thursday/Session7/02_Areseneaux_Jim_20MW_Flywheel_Energy_Storage_Plant_140918.pdf http://www.sandia.gov/ess/docs/pr_conferences/2014/Thursday/...