Re: segway- whatever happened to it

In article <s-adnVoPHK73YRrVnZ2dnUVZ_r7inZ2d@xxxxxxx>,
"David L. Johnson" <david.johnson@xxxxxxxxxx> wrote:

Ryan Cousineau wrote:

Durability of the battery packs is a big deal, because electricity is
way cheaper per joule than the common fuels (gas, diesel, propane, CNG).

I don't get this. How can that be? Seeing as how electricity is often
generated by burning common fuels. In the US, that fuel is often coal
or natural gas, While it might be that coal is much cheaper per joule
than gasoline in an internal combustion engine, it's hard to see why
natural gas would be. And in the US, there is precious little
electricity generated by wind, direct solar, or nukes.

With most of the energy coming from the same process, and a lot more
inefficiency in battery-powered cars, how does it end up "way cheaper"?

There are a few reasons:

-internal combustion engines are not 100% efficient, and a fair amount
of your fuel's energy goes to heating the engine, at which point a bit
more energy goes to pumping the water that cools the engine. Electric
motors are much more efficient at turning electrical inputs into power
on the ground. (conversely, the energy density of gasoline or diesel is
better than any battery technology, and refuelling is more convenient).

-coal (and to a lesser extent, natural gas) costs less per joule than
gasoline, and is conveniently burnable in large stationary plants. There
are transmission losses, but there are efficiency gains from the large
stationary plants.

http://en.wikipedia.org/wiki/Energies_per_unit_mass

Fascinating tables and data. In comparing energy densities, it does
include batteries (an energy storage device) alongside stuff like coal
and gasoline (actual sources of energy), but the numbers are useful for
comparing stuff like the space or weight of batteries you'd need to
match the energy capacity of your gas tank. The energy density of
gasoline is listed as 46.9 MJ/kg on that table, or 34.6 MJ/l.

By comparison, the energy density of current LiIon batteries comes in at
about .72 MJ/kg, or 2 MJ/l. EEStor capacitors, with specs exceeding
those of any battery in production, are targeting numbers like 2.5 and
5.5. On the other hand, EEStor capacitors may not actually exist. There
appear to have been no outside tests of the technology, which puts it
close to Moller Skycar territory.

In fairness to electric cars, Gas cars give up much of their energy
density advantage by needing big engines. By comparison, the motor part
of a Tesla Motors Roadster is 115 pounds and looks about the size of a
car transmission. On the other hand, the battery system is huge.

http://www.teslamotors.com/design/under_the_skin.php

Getting back to your question...

http://www.eia.doe.gov/cneaf/electricity/epm/tablees1a.html

Last year the US generated about half its power using coal, and about
1/5 its power using nuclear sources, just a bit more than was generated
by natural gas. But nonetheless, your electric company can deliver
joules to you surprisingly cheaply, and gas cars throw away much of
their energy density advantage by burning the fuel in such a way that
only about 20% of gasoline's energy goes to turning the rear wheels.
Electric cars are much better at turning stored joules into motion, so
you don't need to take on as many joules in the first place.

Despite all these inherent advantages, current electric cars still suck.
Instead of buying one, I bought a new bike frame today, which brings me
up to something like 10 bikes that are either rideable or in the process
of being built up into rideable bikes. The maintenance time alone makes
this fleet size unsustainable.

--
Ryan Cousineau rcousine@xxxxxxxxx http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."
.

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