5 ms·

Piggybacking, does anyone know where we are with capacitors? Everyone focuses on batteries, but I've always wondered about supercaps. They can't hold a charge f

Piggybacking, does anyone know where we are with capacitors? Everyone focuses on batteries, but I've always wondered about supercaps. They can't hold a charge for years, but 12-48hrs is possible. Size is not an issue, and I had thought even fancier caps are pretty simple and environmentally friendly. Unlike molten salt and many other storage tech, they have no moving parts. Obviously the energy density is not incredible, but these are land-based installations we're talking about, not Teslas.

metalliqaz 9y ago
Don't they have particularly catastrophic failure modes?
- sliverstorm 9y ago
  If you're thinking of electrolytic caps (the common barrel shaped ones), not all caps share that failure mode.
philipkglass 9y ago
I've wondered myself why supercapacitors haven't been used more for stationary energy storage. If you search the academic literature, it looks like there are many supercapacitor chemistries that can match or surpass the specific energy of lead-acid batteries (~40 Wh/kg), they all manage incredible charge/discharge rates compared to batteries, and almost all of them have incredible cycle life compared to batteries. They can sustain thousands or tens of thousands of charge/discharge cycles with only modest capacity fade. Here are my guesses why supercapcitors haven't been used for bulk energy storage: 1) The reported specific energy numbers are fudged somehow, so that if you wanted a supercap Powerwall equivalent it'd be much larger/heavier than the reported numbers suggest. Maybe they're excluding e.g. mass of electrolyte? 2) It just takes a long time to industrialize laboratory discoveries. It took 30 years for quantum dots to make their way from laboratory curiosity to consumer display devices. It took 20+ years for the high-efficiency PERC solar cell structure to make its way from the University of New South Wales to the commercial mainstream.
- ac29 9y ago
  Lithium-ion is an order of magnitude better in Wh/L vs supercaps [0]. There simply isn't room to get 100+ kWh of supercaps into a ~car-sized vehicle. [0] https://en.wikipedia.org/wiki/Energy_density#Energy_densities_of_common_energy_storage_materials https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...
  - philipkglass 9y ago
    That table gives a value of 9 Wh/kg for electrochemical supercapacitors. I've seen a lot of researchers claim values over 30 Wh/kg in research papers over the past few years. That's still not adequate for mobile applications that currently use lithium ion batteries, but what we're wondering is why supercapacitors aren't being used for stationary applications where cycle life is more important than density. It could just be, as I speculated before, that these improved supercapacitor designs take a long time to move from lab to factory.
collinmanderson 9y ago
I believe there might be an issue with capacitors requiring rare-earth materials so therefore can't scale. http://www.sciencedirect.com/science/article/pii/S0272884212004774 http://www.sciencedirect.com/science/article/pii/S0272884212... It sounds like the energy density still doesn't match batteries though there may be breakthroughs that might fix it: http://www.teslarati.com/supercapacitor-breakthrough-evs-charge-in-seconds/ http://www.teslarati.com/supercapacitor-breakthrough-evs-cha...

metalliqaz 9y ago

Don't they have particularly catastrophic failure modes?

sliverstorm 9y ago
If you're thinking of electrolytic caps (the common barrel shaped ones), not all caps share that failure mode.

philipkglass 9y ago

I've wondered myself why supercapacitors haven't been used more for stationary energy storage. If you search the academic literature, it looks like there are many supercapacitor chemistries that can match or surpass the specific energy of lead-acid batteries (~40 Wh/kg), they all manage incredible charge/discharge rates compared to batteries, and almost all of them have incredible cycle life compared to batteries. They can sustain thousands or tens of thousands of charge/discharge cycles with only modest capacity fade. Here are my guesses why supercapcitors haven't been used for bulk energy storage: 1) The reported specific energy numbers are fudged somehow, so that if you wanted a supercap Powerwall equivalent it'd be much larger/heavier than the reported numbers suggest. Maybe they're excluding e.g. mass of electrolyte? 2) It just takes a long time to industrialize laboratory discoveries. It took 30 years for quantum dots to make their way from laboratory curiosity to consumer display devices. It took 20+ years for the high-efficiency PERC solar cell structure to make its way from the University of New South Wales to the commercial mainstream.

ac29 9y ago
Lithium-ion is an order of magnitude better in Wh/L vs supercaps [0]. There simply isn't room to get 100+ kWh of supercaps into a ~car-sized vehicle. [0] https://en.wikipedia.org/wiki/Energy_density#Energy_densities_of_common_energy_storage_materials https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...
- philipkglass 9y ago
  That table gives a value of 9 Wh/kg for electrochemical supercapacitors. I've seen a lot of researchers claim values over 30 Wh/kg in research papers over the past few years. That's still not adequate for mobile applications that currently use lithium ion batteries, but what we're wondering is why supercapacitors aren't being used for stationary applications where cycle life is more important than density. It could just be, as I speculated before, that these improved supercapacitor designs take a long time to move from lab to factory.

collinmanderson 9y ago

I believe there might be an issue with capacitors requiring rare-earth materials so therefore can't scale. http://www.sciencedirect.com/science/article/pii/S0272884212004774 http://www.sciencedirect.com/science/article/pii/S0272884212... It sounds like the energy density still doesn't match batteries though there may be breakthroughs that might fix it: http://www.teslarati.com/supercapacitor-breakthrough-evs-charge-in-seconds/ http://www.teslarati.com/supercapacitor-breakthrough-evs-cha...