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Homework Help: Thermo problem causing me to hemerage

  1. Nov 10, 2008 #1
    1. The problem statement, all variables and given/known data

    The light energy that falls on a square meter of ground over the course of a typical sunny day is about 20 MJ The average rate of electric energy consumption in one house is 1.0 kW

    one of the questions was:
    On average, how much energy does one house use during each 24 hr day?
    That I was able to figure out to be 86 MJ

    But the one that is really pissing me off is this one.
    If light energy to electric energy conversion using solar cells is 5 \% efficient, how many square miles of land must be covered with solar cells to supply the electrical energy for 250,000 houses? Assume there is no cloud cover.

    2. Relevant equations

    Figure meter^2 to miles^2
    efficiency (what you get/what you pay)

    3. The attempt at a solution

    I need just help where to start
  2. jcsd
  3. Nov 10, 2008 #2

    250000 houses require 250000*86MJ of energy a day. The energy obtained is 1/20 the total energy released, so 250000 houses require 5000000*86MJ/day.

    There is 20MJ/m^2 coming from the sun and 2589988.11m^2/mi^2... Solve.
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