Zakaj so električni avtomobili prava stvar

Ti izklapljaš ABS? (nevem če je sploh mogoče, pri večini avtomobilov ni)

v vesolju so sateliti, ki delajo s po 250W in več nonstop, noč in dan, par let; pa od kje jim štrom?

# Anatoly Moskalev wrote on December 24th, 2006 at 11:45 am

Comment about fast charge and ultracapacitor energy storage limits.

1. Ability to charge electric car fast is actually fundamentally limited by low power density of electric current compared to gasoline stream into car tank. It is easy to pump gasoline with the rate ~10 gallons / minute. A gallon of gas has ~35 kWh of energy. So at the gas station energy transfer to a car tank comes at 350 kWh / min rate or even faster. With electricity ~1000 V is a practical threshold voltage of dramatic increase of safety problems with electricity. Approximately above that voltage breakdown discharges along typical dielectric flat surfaces appear meaning that no simple electric plugs would work. Currents above 1000 A would also be difficult because they would melt wiring. As a result it is very hard to exceed 1 MW power level in electricity applied for car size objects. Typically threshold is about 100 kW. Anyway even at 1 MW level it would take 20 min of charging to match 1 min of gas pumping.

So fast charge does not look entirely practical regardless how fast electricity storage of the car could charge.

As mentioned trickle overnight charging is a solution. It changes somewhat use model but is entirely convenient if electric car range is above 200 miles for many people and 500 miles for most.

2. I am fairly sceptical about ultracapacitirs because of the following fundamental reason. Chemical energy is a form of electric field energy coming from intermolecular fields. At molecular distances quantum effects rule. It exist well known tunneling effect making electrons move through energy barrier if the barrier is becoming small. Because all matter including all dielectrics is swarming with electrons tunneling exists in all materials. It means that if electric field approaches few percent of intermolecular fields electric breakdown making dielectric to conduct current is absolutely unavoidable. Energy density of electric field per unit of volume is a product of electric field intensity by electric induction. With small fileds electric induction is dielectric constant multiplied by electric filed. People typically use the same relationship for high electric fields approaching breakdown and say, like EEStore company, that they would provide high volume energy density of ultracapacitors. Because understanding physics degraded in a society tremendously compared to 70s-80s investors and public believe such a story.
In fact electric induction is a fraction of intermolecular fields applied to compensate external electric field applied to material. As such this value could never exceed intermolecular fields whatever you do. And because of tunneling electric field could be just a few percent of intermolecular field. So in the product determining chemical energy you multiply intermolecular field by itself. In the product determining ultracapacitor energy of any design and nature you multiply at best intermolecular field for induction by a few percent of it. So in a wildest dream you could come to at most few percent of chemical energy in ultracapacitor. Representative example of chemical energy used for such comparison would be energy density of hydrogen or gasoline but taken together with oxygen used for burning. If taken that way and assuming typical ~1 gram / sm^3 density of a substance you get ~3 kWh / kg of chemical energy. (Taken without oxygen you get ~12 kWh / kg for gas and ~32 kWh / kg for hydrogen.) Take 5 % of 3 kWh / kg and you get ~0.15 kWh / kg absolute limit for any ultracapacitor ever. This limit is fairly close to current Li-ion battery. But theoretical limit for this battery under similar skew of factors considered would be ~1 kWh / kg coming from Li chemistry and extra weight of electrolyte, second electrode etc. Today paremeters are ~0.2 kWh / kg for Li-ion and ~0.03 kWh / kg for ultracapacitors. In both cases we have a factor of ~5 lower achieved capacity against ultimate limit estimated. But from these estimates you could see that ultracapacitors could probably improve 2 - 3 may be 5 times but still would not come even to match available today batteries. Batteries could progress same 2 - 3 may be 5 times. After that you get fundamental limits.

With batteries the only hope to beat this limit would be to use oxygen in a reaction cycle and release it into the air while charging and consume while discharging ( famous by energy density metal - air batteries do that ). Unavoidably this makes your no pollution behavior go away because exaust from charging of such a battery would be bad enough. The only exception is hydrogen fuel cell (basically hydrogen - air battery) and even with it you need to fix chemical pollution problems currently preventing widespread use of such fuel cells because microscopic amount of CO and other gases damage fuel cells.