Solutions to the first 3 numerical problems of the last homework.


1.  Total electricity produced = 1.2 Terrawatts = 1.2 x 10^12 watts

    US population in round numbers is 300 million

    Per capita is then 1.2 x 10^12/3 x 10^8 = 4000 = 4KW produced per person

    Now note those that wanted to google this:  This the electricity *produced*
    per person not the electricity *consumed* per person.  Consumption is about
    45% of production when you integrate overall energy efficiencies.

2.  The monthy cost of production is then

    4KW x .09 cents per KWH x 720 hours per month  or about $250 per person.  This
    then gives you a good baseline for understanding the costs associated with
    electricty production.

3.   Gasoline powered car obviously uses 3 gallons to go 120 files so that's $9.00

     Electric vehicle:
   
     60 KWH is required to go 120 miles

     72 KWH of electricity is required to charge up your battery so that it holds 60KWH

     72 KWH x 7.5 cents per KWH = $5.40

     so in this example, the EV has lower operating cost.

     Note however, that if the EV were heavier, equivalent to the size of a typical
     passanger car it would average about 1 KWH per mile and the cost would therefore
     double.

     Bottom Line:  The operating costs of an EV depend more on its weight than typical fluctuations
     in the price of gas