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# Solar Energy: Energy And The Enviornment? (7/22/2012)

A solar Panel is used to make electricity on a moderate scale. The panel ruuns a pump that puts water into a 10-meter high reservoir. The water then falls to turn a generator. on a particular day the solar pael averages 15,000 watts output for 24 hours. A. how much water in kg is pumped into the resivoir on a given day? B. what are the advantages and/or disadvantages of setting up the system this way rather than just generating and using directly the electricity from the solar cells.

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Just_gone July 22, 2012 at 9:23 pm

That depends upon motor wattage and efficiency, and pump capacity and efficiency.
The method would store water for power at night and cloudy days. There are power losses as described (efficiency).

Engineer July 22, 2012 at 9:51 pm

A) First of all to make this calculation you need to make some assumptions. I will assume a perfectly efficient pump. The pertinent equations are:

Force = mass * acceleration
Work = force * distance
Energy = power * time
Work = Energy (no losses)

We need to solve these equations for mass.

Mass = (power * time) / (distance * acceleration)

Acceleration in this problem is the acceleration of gravity with is 9.8 in MKS units.
Power is 15,000 watts
Time is 24 hours
Distance is 10 meters

Therefore mass = (15000*24)/(10*9.8) = 3673.5 kg

B) The reason you might want to set up a system like this is because a solar panel does not produce power when there is no sun. You can think of the reservoir as like a battery. It is a place to store energy that can be recovered on demand whether the sun is shining or not.