Building a Hydroelectric Dam Project for Grade 7 Students

[FA22raptero]

Howdy folks,

I took a course way back in undergrad on the fundamentals of energy sustainability, so I have a good preconception how how hydropower works in general, but not in detail. So when my little sister (grade 7) came to me asking for help on a hydroelectric dam project, then I thought it would be fun as I could learn something and then teach her, and she could get a good grade as well.

So I want to power some 12V, 20W lightbulbs in order to demonstrate that the dam is working. Using the basic hydroelectric dam equation (P=npQgh), I am estimating that to produce 20 watts of power with an estimated 70% efficiency, I need a 'dam' that is about 15cm or so tall. However, I am having trouble converting the theoretical to the real with a DC motor.

The motor I am using is:http://www.riorand.com/electronics/motors/riorand-mini-12v-dc-60-rpm-high-torque-gear-box-electric-motor.html

The lights: https://www.amazon.com/gp/product/B009S1BF2Y/?tag=pfamazon01-20

Now, I may be wrong, but in my primitive research I learned that most dam generators spin at about 30-90RPM, however, I realized that most don't use a pelton wheel, and a pelton wheel spins optimally at about half of the speed as the velocity of the water that is shooting out to hit the pelton wheel, so I might have picked a motor that spins too slow (I also assumed that if the output is 60rpm at 12V, I assumed that an input of 60rpm will produce an output of 12v).

So here are the issues I'm running into

1. I have no idea what the amperage of my motor is... and so I don't know how many lights I will be able to run. Obviously watts is a function of volts and amps, so I can always spin my wheel faster and slower to get the right power, but I'm not sure how. Is there something I am missing here?

2. I don't know how to calculate water flow. For most electric dams, there is a flow from the river. Now, since we're in the classroom they will just have a tub filled with water that they can just keep filling up with a jug, and I sort of imagine they can keep refilling the tub at a rate of ~1L per minute. Is this actually a flow? Now, I was thinking of using a half inch diameter PVC pipe as the penstock with a nozzle on the end to fire at the pelton wheel we will be using as the turbine for the generator. However, I don't know what the ideal nozzle diameter is, and how this will affect the flow/velocity of the pipe overall. Any help on how to think about this?

3. I thought it would be cool to show that dropping water from different heights will generate different amounts of power (thus spinning the turbine at different speeds). This means that I have to predict the individual heights for different watts of electricity production (e.g., with 20watt 12V lightbulbs, I'm going to need to calculate the dam height for 20, 40 and 60 watts ect. as I add lights to the grid).

So could I grab any help from you guys? Thanks so much!

 

[Spinnor]

So I want to power some 12V, 20W lightbulbs in order to demonstrate that the dam is working. Using the basic hydroelectric dam equation (P=npQgh), I am estimating that to produce 20 watts of power with an estimated 70% efficiency, I need a 'dam' that is about 15cm or so tall. However, I am having trouble converting the theoretical to the real with a DC motor.

Power is energy per time or mass of water that falls some distance in some time. You just gave a distance, you also need the mass per time that falls that distance. It's going to be large. Unless you have a lot of water you won't make much power for very long, consider using energy efficient led lights. Check this out,



Simple and it works. From, https://www.youtube.com/results?sea...ate+a+small+hydroelectric+energy+demo+project

Your motor would not work well if used like the above video because it is highly geared down and requires a lot of torque to turn. Keep it simple.

Good luck!

 

[sophiecentaur]

The bicycle 'Dynamo' is one of the best methods for generating low power Electricity. It is far more efficient than a DC motor, that's not actually designed for that purpose. If you could get hold of one, you might find it interesting to compare, I think you may be a bit optimistic to expect 20W from your motor so have some lower power LED bulbs available too.
Good luck.