Dear Solar Guy,

        Someone told me that the total amount of energy in sunlight that
falls on my house dwarfs my total energy consumption.  How much solar energy
does fall on my house, and how does this compare to the energy that I buy
from the gas and electric company ?  

 I.M. Small,  Acre Homes, TX.

----------------------------------------------------

Dear I.M.,

        A typical single story house of say 1800 square ft of living space
will have a roof area of about 2200 square ft, or about 200 square meters.
In central Texas the average daily solar radiation in the summer on a
horizontal surface is about 6.5 kWh/m2-day, and in the winter about 2.5
kWh/m2-day.  For the entire roof this means about 500 kWh/day in the winter
and about 1300 kWh/day in the summer.  Depending on whether a home is gas
electric or all electric, the demand will vary, but assuming an all-electric
house, the winter and summer consumptions would be about 70 and 80 kwh/day
in the winter and summer respectively.  In the Spring and Fall seasons the
energy use is lower.  So one sees that the available solar energy is in the
range of 7 to 16 times greater than the solar energy falling on the roof.
If one takes into account the efficiency of photovoltaic (solar) cells,
which are typically about 12 to 15%, this means the potential
solar-electrical energy is still about equal to or greater than the demand
of the building for all seasons of the year.   

The Solar Guy.