# Hydroelectricity - salt vs fresh water

I am doing doing a science project for school and I didnt get the results i was expecting so I was wondering if somebody would help me :)
I wanted to test whether salt water or fresh water would produce more hydroelectric voltage. I expected the salt water to produce more because it is heavier. It was the opposite - can somebody help me understand why that is? Thx!

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gneill
Mentor
I am doing doing a science project for school and I didnt get the results i was expecting so I was wondering if somebody would help me :)
I wanted to test whether salt water or fresh water would produce more hydroelectric voltage. I expected the salt water to produce more because it is heavier. It was the opposite - can somebody help me understand why that is? Thx!
This is pretty vague. How was the comparison made? What kind of test was done?

We built a mini hydroelectric plant. A stream of water flows to a wheel that spins which is attached to a DC motor. A voltage meter is attached to the motor so we can measure the output. We made sure the water always hits the wheel at the same place by gluing the container in place. We got results in the mid 40s for the fresh water and low 40s, some 30s for the salt water.

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gneill
Mentor
We built a mini hydroelectric plant. A stream of water flows to a wheel that spins which is attached to a DC motor. A voltage meter is attached to the motor so we can measure the output. We made sure the water always hits the wheel at the same place by gluing the container in place. We got results in the mid 40s for the fresh water and low 40s, some 30s for the salt water.
Nifty. Was there any attempt to make sure that the temperature of the water(s) was the same for each run? How about the starting level for the water in the reservoir?

It's possible I suppose that some other property of the water is affecting the results. Some things to consider:

1. Velocity of water existing the reservoir port. What affects it? (Look up Bernoulli equation)
2. Dynamic Viscosity of seawater versus fresh water (probably a 7% difference!)

Yes, the water was at room temperature for both, and we measured the flow at a certain point on the jar. Thanks for the response :)