Friction Head Losses in Hydro Design

I know it's the stock answer, but did you Google "Friction Head loses hydro" I came up with these:

http://hydropowerstation.com/?p=467

http://www.canyonhydro.com/guide/HydroGuide11.html

http://www.exmork.com/how-to-measure-water-head.htm

You have information on the "flow rate per month", but that is a problem since as it represents units of volume.

Here is why this is relevant. Friction head losses vary instantaneously proportional to the square of flow velocity. In one average month there are 43,200 minutes. Say the flow velocity at time T1 = 0 is 100 gpm, but at T2 = 120 minutes (2 hours later), is now 150 gpm. The head loss at time T2 will be significantly higher than at time T1. But with only a monthly flow-rate (meaningless) known, your design does not take into account the fact that the friction head loss varies widely.

Likewise the energy generated will vary widely.

You need to take into account the flow variation and head variation with respect to time.

Thanx guys but I think I mentioned that we are at feasibility stage were we just need to establish whether we will be able to extract the energy from the existing dam. The real nitty grities will come at the detailed design stage. Any rule of thump percentage that I can use to assume the loss.

If you're using it strictly for feasibility, I can suggest a quick and dirty thumb rule.

Knowing only the available head and estimated flow ... a hydro turbine-generator output capacity can be roughly estimated with the following...

Electrical output = 0.127 watts / ( gpm * ft)

for example 10 gpm flow at 25 ft of head would be ...

0.127 watts (per gpm per ft) * 10 gpm * 25 ft = 31.75 watts

Again this is rough and should NOT be used for final design, but it should get you in the ball park.

Large hydro projects can attain ~90% or even up to ~95% efficiency. For a medium project I would guess ~80-85%, for a small project ~70-75%. (?) It would depend on the quality of design and equipment.

I'd agree with only the caveat that those efficiencies are strictly for the turbine (i.e. not the system as a whole).

My thumb rule above assumes a turbine hydraulic work efficiency of 75%, mechanical work efficiency of 75%, and a generator efficiency of 90%.

20%.