# Micro hydro turbine calculations

1. Apr 25, 2014

### Baggy1

Hi!

I'v been looking into this for way too long and have come to that point where nothing makes sense, hoping you guys could help me out!

Basically i have been given a net head of 20m and need to provide a micro hydro turbine with 5kW of power for over one minute. What i want to find out is what gross head i would need to produce this and the diameter of the pipe to supply it.

I'v selected a pipe diameter of 193.67mm schedule 80 PVC for now, and these are the calculations i made:

Flow rate = 5000/0.8x1000x9.81x20 = 0.032m3/s at 80% efficiency(turbine)

Velocity = Flow rate/0.25∏x0.19^2 = 1.12 m/s

From Bernoulli's equation i have this:

sqrt(2xgx20)= 19.81 m/s is what i get for velocity

Could someone be kind enough to explain the differences in these results?

Also...

How would i work out the pipe diameter if the one i have written is incorrect? The reason i selected this size was because it would have less friction resulting in a reduced gross head length. Id have to work out the friction losses to find the gross head, this is what i did... not sure its the right way... again

I calculated the friction factor to be 0.04

Gross head - 0.04x20x1.12^2 / 0.19x2x9.81 = 20

Gross head = 20 + 0.27

Any help would be greatly appreciated

2. Apr 25, 2014

### AlephZero

The difference is because your pipe diameter is bigger than you need to generate 5kW.

You could find the "correct" diameter (ignoring friction) by solving
Flow rate/0.25∏ x D^2 = 19.81 m/s
for D.

This is assuming that your turbine can extract all the kinetic energy (OK, 80% of it) from the water at that flow rate and velocity.