Supercapacitor as Prius 'battery'

I'm guessing the non-linear voltage could be dealt with using appropriate control circuitry.

And now that winter is here and I'm seeing severely degraded battery performance in cold weather, I see another advantage of capacitors: presumably they'd be just as efficient at 30 below zero as they are at 70 above.

 

The following would be a great read for you with misinformation or not on ultracapacitors. This IEEE Spectrum article contains the newest development of them.

http://www.spectrum.ieee.org/WEBONLY/publi...5/0105wcap.html


To summarize the main reason ultracapacitors cannot be used in hybrid cars is due to its low energy density. Commercially available UC (ultra capacitor) can store 3 to 4 Wh/kg while compared with 60 to 70 Wh/kg of NiMH or 130 to 140 Wh/kg or Li-Ion batteries. Some lab claims hugh advances in energy density but they are not yet verified independently by others. Long way to go but with hopes from nano-technology, especially nanotubes.

 

If they had been ready now they'd be in our Prius now. But you can bet Toyota is monitoring advances and will use them when it becomes practical, if ever, unless something better comes along first.

 

Capacitors have been around for a long, long time. They used to be called "condensers." They have a lot of use in electrical power generation and distribution, in addition to power supplies and VFD's.

As far as the "misinformation" about ultracapacitors, I would suggest a good part of that misinformation is from the developers themselves. In the URL referenced above, there is a quote:

"In comparison with batteries, ultracapacitors can put out much more power for a given weight ..."

But Joel Schindall of MIT is quoted as saying: "In all ways other than energy density, an electric field is superior to chemistry for storing energy regeneratively."

According to the article, the best commercially available ultracapacitors have an energy density of 4 Wh (Watt hour)/kg. This is in contrast to 70 Wh/kg for NiMH and 130 Wh/kg for Li.

Like any other developing technology, I'm sure we'll see advances that will make the technology feasible in the "near" future. I'm particularly intrigued by carbon nanotubes.

 

<div class='quotetop'>QUOTE(jayman @ Jan 18 2005, 07:37 AM) [snapback]64362[/snapback]</div>

That's not misinformation. They can put out much more power per unit weight. However they have much lower energy capacity per unit weight. You're confusing power and energy. Power is in Watts (W), whereas energy is power expended over some time, expressed for example in Watt-hours (Wh). (I use those latter units here -- the proper units are Joules for energy, kg m^2/s^2, and Joules per second or Watts, kg m^2/s^3 for power. A Wh is 3600 Joules.)

A 1 kg super-capacitor and a 1 kg Ni-MH battery might each hold, let's say, 4 Wh and 45 Wh of energy respectively. However the battery would be limited to a discharge rate, or power, of 100 W, whereas the super-capacitor could discharge at a much higher rate of 3000 W. So the battery has ten times the energy density of the super-capacitor, whereas the super-capacitor has 30 times the power density of the battery.

A typical engineering tradeoff. What you use depends on what you need.

mark

 

<div class='quotetop'>QUOTE(KTPhil @ Jan 17 2005, 07:31 PM) [snapback]64249[/snapback]</div>

HAY, yeah, I'm with KTPhil................ :lol: :lol:

 

I believe this subject was previously posted in the Technical forum - or maybe that was in PriusOnline.

 

<div class='quotetop'>QUOTE(naterprius @ Aug 11 2004, 11:08 AM) [snapback]31946[/snapback]</div>

Nate, even though you missed on how capacitors work, you are corrrect about them sometimes exploding. Most high value capacitors are electrolytic, so they contain a paste-like electrolyte rolled up between plates. This makes for the cylindrical shape so often found in power capacitors. If the electrolyte is overheated, it will expand and explode the cylinder. Most cylindrical capacitors are scored on one end to allow for a controlled release of pressure rather than turning the thing into a tiny hand granade. Other types, such as tantalum, go off with a cracking report.

Tom

 

BMW have been working on this:

http://www.greencarcongress.com/2005/08/bmw_to_show_sup.html

Seems to add a ridiculous amount of torque. They aren't brave enough to shrink the engine though it seems.