Re: segway- whatever happened to it

Pikachu wrote:
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"?


1 gallon of gasoline has about 131 MJ of energy. This is equivalent to 36.4 kWh. Assuming the rate of electricity is $0.15* per kWh for the end consumer, the energy equivalent of 1 gallon of gasoline is $5.50. To achieve equivalence to the national average price of $4 per gallon of gasoline, electricity need to cost $0.11 per kWh.

* This figure was used for convenience. It may be significantly lower than peak rates in CA, but it also may be significantly higher than off-peak rates.

This comparison is not valid. The energy content of fuel is not converted to mechanical work at anywhere near 100% efficiency in an internal combustion engine in a car, 25% is more typical. The electrical energy can be converted to mechanical work at much higher efficiency, around 90% if used directly in an induction motor, and less if it must be converted to DC, stored in batteries, and then used in DC motors. The electrical power plant may burn fuel such as natural gas or coal, but efficiency of the plant may be well over 50%.

When you buy energy from a power company, you're buying it after the thermal efficiency losses have already been taken. When you buy fuel, you have yet to take the thermal efficiency losses.

Dave Lehnen

.

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