Diverting stream flow or keep turbine in main channel?
I am asking b/c we have a stream that can flow really heavy after the rain.
We have a year round stream that can be 10' across and 2' deep with 10' of head during normal flow.
However, during rains, which can be every couple days in a wet summer, the stream can grow to 35'-40' across and 6' deep.
Which might blow out anything placed in the stream.
If one has the option, is is better to divert the stream in a metal sluice and install the turbine here?
I would like to be able to shut off or regulate flow when super heavy rains occur and also diversion of stream might help with filtering are my thoughts.
A lot of things come out of nowhere, so look everywhere.
Every site has many unique factors. Once water gets into the pipe, microhydro project development can be pretty straightforward job of plumbing and wiring. However, getting water into the pipe can be daunting, and expensive. Some water sources are not practical for hydro because of intake difficulties.
However, people have been taking water out of streams since forever and there are many ingenious methods to deal with variations of flow. The less water you use, the less demanding the intake will be. See what other people do locally to divert water from streams. Copy them.
About putting the generator in the channel...don't. It will, as you fear, be damaged from floods. Divert water away from the channel so that the machinery is above the flood mark. In some terrains, a ditch might be the best thing. Just see what they do locally, as I said...
I'm got a year round stream with good flow but its only got 4' head and its at the bottom of a 15' channel that floods full every other year or so. There really isn't any way to get the equipment out of the flood plain. Should I just give up on it?
It does sound like you have multiple challenges. It all depends upon how much you need the power. Off grid, power is very valuable indeed. You might break down and use an under shot waterwheel on an arm so that it can be lifted out of the stream as required, but the flooding issue sounds pretty ferocious.
Don't know where you live, but there's a farm called Long Branch Educational Center that looks like it has diverted a stream in front of their houses to get power. They have 4 houses on microhydropower, I think. They are in Weaverville NC. I have been meaning to check out their power setup because it looks so much like my own place.
As you are wondering, equipment in the stream itself is likely to be washed away during high water event. Thus diversion is necessary. The water needs to be cleaned of debris that could damage or clog the turbine, anyhow, with some kind of screening mechanism.
People have been taking water out of streams for irrigation and other purposes since forever, and have worked out many ingenious methods of fluming and directing water hither and yon. Miners divert water lots, as well. You have to know that if you divert water into a ditch, it will eventually fill up with gravel and mud, which means that you should make it possible to clean out the ditch every so often. Depending upon the volume, people have used removable boards to dam ditches, removing them and letting the water carry away the debris for cleaning. Some streams require little cleaning, some require lots.
Not all streams can be developed for hydro potential in a cost effective manner, so each case has many unique elements. Energy Systems and Design has a nice, 10 foot turbine that's worth investigating. There is a turbine called "Powerpal" that uses 5 feet of head and could also work at your site, it sounds like.
In many ways, low head turbines require less by way of civil works than higher pressure systems, and if you have the water flow, may indeed be the best alternative even if more head is available. Practicality is all about cost effectiveness, and so one answer doesn't fit all situations by any means...
Placing hydro in the stream is not a problem when a block of concrete is involved. Straight sided into the bed, and domed top. Longer horizontal sides like river pylons stop any rear erosion. Inside your block of concrete is a Kaplan horizontal turbine. Lead in pipe is covered with mesh to stop intrusions, though most debris surface float and only becomes a problem when water levels drop to be lipping the intake pipe.
When diverting the flow do so by PVC or other pipe not open channel. Bury the turbine and generator in a water proof housing. A flow regulator to the turbine sees no need for shut down during flood events.