Low flow high head?

I have a spring on my farm in NE Alabama about 800' feet above the house on the side of Sand Mtn. it is fed to a 1000 gallon holding tank about 100' above the house which supplies all our water. My question is would it be possible to catch the over flow from the holding tank; which is diverted to a pond, to run a hydroelectric generator? The site has about 35' vertical drop from the holding tank to the old grist mill I will be using to house the generator/battery bank were the water can then spill out into my pond (which leaks but thats a different issue). The issue is that of flow rate, the over flow from the tank is about 1/5 of a gallon a minute, is that enough GPM to generate any power with that amount of fall? If not what if I diverted some of the water higher up the mtn. so it had 75' of vertical fall and maybe increased the flow to 1 GPM would that be enough? What do you think would be the minimum flow rate with the amount of vertical fall I have to achieve any substantial output from the hydroelectric generator?

What is the average flow from the spring? What percentage of that flow are you diverting to your storage tank? Are there other users? Would it make a significant negative environmental impact if you diverted more?

You would get the most from your 800' of head if you piped water directly from the spring to your powerhouse.

I found this app that should answer your questions: http://www.energyalternatives.ca/Downloads/MicroHydroCalc.exe

I grew up in that area near Valley Head. Are you on the East or West side of Sand Mountain?

East side in Dear Head Cove.

A few more details - 100% of the water is being captured and piped down the mtn. to the holding tank. My family of 5 are the only ones using the spring, it feeds the tank that supplies all our water, the spring puts out enough water to keep the tank full and over flow the tank into another pipe that feeds our pond at a rate of .25 GPM. So currently I have a 2" pipe running about 100' with 40' of vertical fall and .25 GPM of water running into a pond I want to harness this to create electricity. I guess what I am asking is what is the best setup to extract the most energy from this amount of water i.e. turgo wheel or pelton wheel? What kind of generator would work best at the realativly low RPM I expect to produce? Should I try to run more than one nozzle or do you think that would require more GPM? Does anyone have a hydroelectric setup with similar conditions that would like to share their experiences?

Daniel,

Running your figures for the run from your holding tank to your powerhouse through the calculator gives a generating capacity of .999 watts. Putting a generator on a hamster's wheel might get you more power.

I did a calculation with 700' of head and a 2" pipe with a length of 1750' at .25 gpm (I was guessing at the run from the spring to your holding tank). The output with optimum equipment would be 17.499 watts or .419 Kilowatt hours per day. That is still extremely low for what you would be investing.

You need to get your volume much higher to make it viable. Could you build a tank (500 gallon) at the spring? If you had enough storage at the spring site, I think you could run the generator intermittently and get, if I did the calculations correctly, around 17 Kilowatt hours per day running an optimum 82 gpm for about 4.5 hours a day.

Please run you own calculations to verify mine.

Thanks Andrew that is pretty much what I suspected but wanted make sure someone out there didn't know of some setup that would work. I considered the holding tank at the spring but since it also provides my home with water I am concerned about diverting to much of the water away from the household water supply. I think I might build a pelton wheel and hook it to an old car alternator just to trickle charge some batteries maybe I can at least light my chicken coop and maybe the tractor shed?

Daniel,

Build your powerhouse at your existing holding tank and have the outflow from the turbine fill the tank.

As the saying goes if it were a snake it would have bit me. I dont know why that didnt occue to me that is the perfect answer I can harness 100% of the water for electricity and 100% for house hold use thanks Andrew that is the perfect answer to my delima.

Thanks. That is what forums are for, providing additional perspective. You still need to research equipment and installation and do a cost benefit analysis (or just do it anyway). I hope everything works out for you.

So, I was just getting to sleep when I realized (the snake bit me) I had messed up my calculating. In my last calculation I was thinking gallons per hour, not gallons per minute. At optimum flow you could generate 3.8 kilowatts for 4.4 minutes a day. Sorry to get your/our hopes up.

I just saw this video on youtube, it may be of interest
http://www.youtube.com/watch?v=6LjuZsod4E4&feature=endscreen

maybe a hydro generator similar to this might be something to look into:
http://peswiki.com/index.php/Directory:Zotloterer_Gravitational_Vortex_Power_Plant

it uses the "swirling" of the water to turn the generator, and are designed for low head situations. not sure if your flow is enough, but it may be something to look into.



more info here: http://www.pureenergysystems.com/NEC/conferences/2008/EnvironmentalHallofFame--Chicago/displays/Zotloterer.pdf

I think your flow rate is too low to be practical. A nozzle to deliver 1 gpm is pretty small. leading to inefficiencies because the wheel would be too big for the jet of water to hit properly. In the Serious Microhydro anthology, the lowest flow rates are about 5-10 gallons per minute.

Here's how to calculate the power you'd get from a given head and flow.

flow in gpm times head in feet divided by 14 (10 for larger more efficient systems). Note that the head in this formula is the net head, which includes deducting the frictional losses in the pipe from the gross head.

So if you have 1 gpm at 35 feet of head, you'd only expect a couple or three watts, even if you could find a really tiny turbine. People in the Serious Microhydro anthology find that even a dozen watts is useful in an offgrid setting. 50 to 100 watts delivers a lot of energy, and a 200-300 watt system will deliver a high standard of living. That's off grid. If you already have electricity, hundreds or thousands of watts needs to be generated to make a system pay at a reasonable rate.

Anyway, this will give a good rough estimate of the power output at a given site. I do go into the technie gore details of how to get a pretty good idea of your potential output in Microhydro: Clean Power from Water.

There's a good discussion in the microhydropower buyers' guide, which I helped to create.

Here's the link:


http://canmetenergy.nrcan.gc.ca/renewables/publications/2427

Cheers,

Scotty

Scotty,

Last year, we discussed the possibility of running the turbine for short periods at optimum flow. The calculation I made, using one of those online calculators, put minimum optimum flow at about 82 gpm, which might generate 3.8 kilowatts for about 4.4 minutes a day -- not real hopeful for the money involved. What kind of output can you get at 5-10 gpm with a 700' head and a 2" pipe?

Stew Griffiths,
Your post was moved to a new topic.

Did I go to OIT with you?

Q. McDonald