Variable flow Hydro Generation

Thanks for the response.  Is my idea the best way, or is there a better way (different turbine, or?)?  I have about 5 gpm in the summer, and probably  4 times that in the winter.

Hi, I'm actually working on an abandoned project that no one remembers much about.  There is an existing pipe, and an old timer remembers the head to be about 120 psi.  It's possible we would rebuild the line to start at a lower elevation that might only have about 60 psi.  I'm information gathering, to see what would be practical to persue.  What do you think?

Hi Richard:

The first thing I would recommend is that you get a copy of the stream engine manual, if you do not already have one. It is available here off the Alt-E store site, or directly from
http://www.microhydropower.com/e-literature/May-SEmanual.pdf
It has a real good section on determining head and flows, as well as other system design info.
Next is an article on installing a stream engine.
http://www.homepower.com/files/hp67-68.pdf
Both of these documents make good general references, in addition to being specific for the stream engine.

In your specific case, I think that the stream engine will be the best “out of the box” solution. Something else could be built up one piece at a time, but the efficiencies gained would be marginal. Your biggest problem is low flow.

Assuming that the flows and pressures you gave are correct, the 4 nozzle machine makes some sense. By plumbing it with individual nozzle shutoffs, you will have a neat way to avoid switching larger and smaller nozzles. You are actually lucky in that aspect. With different flows or head, you could have ended up having to switch nozzles to maximize the unit, even with the 4 nozzle model. In that case, I would have said go with 2 nozzles, because it will be cheaper and easier to change 2, rather than 4.

You did not say if you are planning to re-use the old pipe.  If that is part of the plan, you need to get out there and get the pipe functioning ASAP.  Not only will it confirm the pressure and flow (which I think is critical), but it will prove whether the pipe has any problems.  The age/condition varies, but the phrase “old pipe” scares me. Scaling of the pipe can give you repeated nozzle problems, even if the pipe does not leak. It could takes weeks or even months of periodic flushing, before you know if the water will clean up enough, not to cause problems.
If you can get it flowing water in a day or two, great. Otherwise I would write it off and re plan from scratch.  That could be just new pipe from this source, or it could allow you take another look at the other sources. 

Combining sources at different pressures is difficult. The easiest way and often the least expensive, is to run them as separate hydro sources and then combine them electrically.

The 5 gpm 120 psi source has both advantages and disadvantages. It is a very low flow source 5 gpm, but it is at least 280 feet high( based upon the 120 psi). The stream engine manual doesn’t even show 5 gpm flows. You can check with the mfg, but I think you will find that it will only produce about 75 watts at this flow. This is about 1.8 kilowatt hours a day.  When the flow picks up to 10 gpm, it will produce about 190 watts, 4.5kwh a day. When the flow picks up to 20 gpm, it will produce about 510 watts or 12.2kwh a day. 

That is going to raise heck with your electrical system, particularly your battery bank sizing/operation. I think I would take a look at your electrical needs, get a rough idea of the daily usage and the size bank you need, and then look at how much generation you can really use. There could be an argument made to size the thing based on the 10 gpm flow and just let the excess water go. There is no reason to generate a bunch of power, if most of it goes to your dump load. And it could reduce the total capital cost of the installation. But that is just one factor of the cost/benefit analysis.

Power transmission from the turbine/gen to the battery bank/inverter may become an issue depending on the distance between them, and the dc voltage, particularly at the 20 gpm flow.

Regardless of the end size of the bank, you need to figure out how to top the batteries off several times a week, during the 5 gpm flows.

I hope this helps,
Ken

Hi Richard - good luck with the project.  In many ways it is similar to the large scale projects you are familiar with, but the smaller scale makes it much easier to implement. One thing I've found is that because they tend to be small physically, people forget about the engineering part.  Obviously you won't make that mistake since you are an engineer!

Keep us posted on how things turn out!

Regards -

Tom Hardy, PE
HVTA, Inc.