DGDanforth wrote:

Hey Student,

How about a little algebra?

Write everything out without numbers and then at the end, specify the values of the variables in a table and then put those values into the expression to give you the final result. Makes reading and understanding much easier.

It's fairly easy to follow. If you want the calculations then blow up all the spoilers.

A lot simpler than thermodynamics.

If you're still having trouble then I suppose I can work something out.

Basically:

(EPA kWh used/km at the plant) x (grams CO2/kWh on U.S. grid) = EPA grams CO2/km using electricity off the U.S. grid.

(EPA grams CO2/km using electricity off the U.S. grid.)/(Siry's 0.7 adjustment factor) = Adjusted EPA grams CO2/km using electricity off the U.S. grid.

I gave a low end average emissions per kWh (470g/kWh) and a high end emissions per kWh (700g/kWh) of electricity off the grid. I also provided the actually U.S. average emissions per kWh (~612g/kWh per the EIA).

All three calculations have been shown.

I also did all three of those calculations for three different Tesla Roadster kWh/km numbers: first the advert number (0.110kWh/km at wheels), second the typical EV number (31kWh/100miles at the plug), and third the EPA number (28kWh/100miles at the plug).

Only the advert number, 0.110kWh/km at the wheels, needed to utilize the plug-to-battery and battery-to-wheels efficiency numbers. All three were taken out to the plant using the EIA 93.5% grid efficiency number.

Last edited Tue, 04 May 2010, 5:14am by student

Bill Nye says limits for a dielectric are simply what have been demonstrated to date.

student scale: 1.5%