Re: Hydro Electric Power As a Viable Alternative?

Hi Linda,

  I hate to dampen your entheusiasm, but there is not a lot of energy in the rainwater even from the top of the roof...

  The potential energy is given by the equation Ep = MGH.  So to light a 100W lightbulb you'd need 100J / second

we'll solve for water flow... M = Ep/GH 

Ep = 100J/sec (where J = kg*m)

H =  10 meters or 30 ft (the peak of a 2 story colonial)

G = 9.8m/sec^2 (we'll say 10)

M = 1.02 kg/sec (~> 1 liter/second or 16.1 gal/min)

16 gal/min falling from the rooftop... that's a lot of water for just one 100W lightbulb! That's why dams are as tall as they are, and the pipes are tens of feet in diameter...

  Now if you get a tiny little "grain of wheat" or even smaller "grain of rice" lightbulb, or an even more efficient LED, you can probably do a nice demonstration for the science fair.   Or you can drive a "solar" electric motor...

Good luck with tyour project!  It's great that you're teaching some of the real principles of energy at such a young age.  :-)  So many kids are completely ignorant to the reality...  They've never hauled firewood, never seen a gas stove, barely see the heating elements in an electric, and the microwave is just a magic box with a pushbutton.