I also emailed Nesscap the night this was posted and got a prompt reply from Marketing. It was nice that they responded, but the person who wrote the email didn’t seem to be well versed in things battery.

After digging I think here’s the story….

Energy denisity (as Nesscap uses it) a measure of how much electricity can be stored in a given area (w/l – watts per liter) or in a given weight (w/kg – watts per kilo) of a particular product.

Power density is a measure of how “fast” energy can be withdrawn from a given area (wH/l) or given weight (wH/kg) of a particular product.

On Nesscap’s web page I found “The 5000F/2.7V Nesscap ultracapacitor exhibits energy densities of 5.8Wh/kg & 7.1Wh/l and power densities of 5.2KW/kg & 6.4KW/l.”

On another site (below) I found that today’s best batteries store energy at around 150 wH/kg. That translates into ultracapacitors being very inefficient in terms of power stored per kg (5.8 vs. 150 wH/kg).

Their advantage is in how quickly they can release or regain stored electricity. That makes them very useful for very rapid acceleration and regenerative braking. And suggests a valuable role as a hybrid ultra/battery pack for EVs.

In my searching around I found what I think is a very useful article for those of us trying to understand EVs beyond “you plug them in”….

http://www.designnews.com/article/10574-Auto_Industry_Working_Hard_to_Make_an_Electric_Vehicle_Battery.php?text=slam+dunk

Also, this came out today. Panasonic has found a way to fuse standard PC batteries together to be used in EVs.

“The new technology will likely enable Panasonic to make electric car batteries at half the cost of lithium-ion batteries that are developed solely for electric cars, since it can use existing battery plants and production expertise, the company said.”

That’s the 50% drop in battery price promised by moving to large scale battery production.

http://www.reuters.com/article/rbssConsumerGoodsAndRetailNews/idUST21755220091001

The Wikipedia definition you’ve quoted clearly stated that energy density can be measured by “per unit volume, or PER UNIT MASS”.

“Basically, we are an ultracapacitor manufacturer, so we barely have any idea on Hp or associated electronics requirement for the vehicle.
“However, we can provide you pricing and array of the module if you tell me electrical requirement of ultracapacitor module in your application.
“Please see attached file and send it back to me after filling out so that I can ask our engineer to review it.”

They could be Martians and I’d be impressed after how some companies respond, or never do! Engineer review it? oh, my! some body might actually want to sell product and not just get grants….continuing…

Ultracapacitor

Discharge Time 1~30 sec
Charge Time 1~30 sec
Energy Density (Wh/kg) 1~10
Power Density (W/kg) 10,000
Charge / Discharge Efficiency ~10
Cycle Life > 500,000

Battery

Discharge Time 0.3~3 hrs
Charge Time 1~5 hrs
Energy Density (Wh/kg) 20~100
Power Density (W/kg) 50~200
Charge / Discharge Efficiency 0.7~0.85
Cycle Life 500~2,000

Now I could use some help understanding these numbers.

Energy density. From Wikipedia:

“Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context.”

But the number listed above is in watt hours per kilogram. Not a volume measurement.

Clearly ultas win when it comes to charge times. They make shorter range EVs more practical. A 100 mile range which would cover at least 85% (perhaps 90%+) of US daily driving along with a few quick charge stops would make occasional longer trips possible.

They also win big in terms of lifetime cycles. One could buy a set of ultras once and move them to new cars for life and then pass them to ones children and grandchildren.

Ultras also win in terms of charge efficiency.

So, energy density. Should the measurement be one of volume? And if so are we talking about a solution that is superior in every aspect except the space it would take up inside the vehicle?

And if power density/energy per pound is 5+x greater than batteries are we not just looking at bulk but not extra weight to haul around?