Hello all!!! I am hoping to install a hydro plant this fall. I have some major questions. First I'll explain my site, then the questions.
We have a creek running along our property on a pretty steady grade. We have 26.4ft of head and an 825ft run of penstock. I'm planning on running my penstock down the creek to avoid freezing. I have a 3kw turbine from china, supposedly rated for 236gpm - 394gpm. Because the penstock follows essentially the same route is the dream, the water in the pipe will be moving at essentially the same speed as the water in the river. Correct? So far so good.
The question I have is the penstock. The pipes. How big do they need to be???
The Chinese dealer is telling me that 110mm pipe is plenty, thats about 4.5inches. BUT, at our water speed, according to the friction chart for poly pipe (the kind of pipe I want to use) the output is only 5l per second when I need at least 15l per sec (236gpm).
So my question is, whose wrong, me or my Chinese dealer, and why?!!
Sounds like what you need to be able to do is increase the penstock pressure at the turbine.
I would think about having the pipe larger at the head and neck down to increase the pressure and thus the speed of the water.
What size pipe is the turbine set up for?
that will be the determining factor for the feed pipe at the turbine.
I disagree with the above. Reducing the pipe size will increase the pressure loss, not the pressure, and eat up some of the energy you want for your turbine in friction. Your starting pressure is 29.4ft of head and you can't make that go up.
At the outset I have no hydro power experience, but I do know water and pressure quite well.
I also disagree with your dealer. Over short distances 110mm pipe may be fine (say 100ft), but your run of penstock is fairly long for that diameter pipe at those flow rates. I think you are right. My working is in metric as that is what I know, apologies.
29.4 ft is 8.96 metres head.
825 ft is 251 metre run of penstock.
236 gpm is 14.9 L/s (lower value given)
In Australia we have two types of the black poly pipe (I assume this is what you are talking about) - Rural grade (called green line) which is 800kPa (~80 metre) maximum pressure and the internal diameter is the same as the nominal diameter in this case 110mm. The metric stuff has a wider range of pressure ratings but the internal diameter changes depending on the pressure rating. It may depend on what you have available. PN 2.5 is the lightest and has an internal diameter of 104.6mm with a max pressure of 2.5 bar, about 25m. You could probably get away with that with a safety factor, or PN4 for a bit more. PN4 has an internal diameter of 101.6mm. The higher the pressure rating, the thicker the wall, the longer it will last.
I have a little calculator here. PN2.5 black poly pipe at 14.9 L/s is going to use up 5.74 metres of head in friction, more when joiners and such and such are taken into account. You will have about 8.96-5.74 = 3.2m head left, or ~10.5ft. You will have to work your turbine power out with that. this is the lower value you give. You could use larger pipe, perhaps PVC to lose less head. Plastic pipe like black poly or PVC of 150mm internal diameter (160mm metric poly) would only lose about 1m, a bit over 10% of the pressure at the lower flow rate. Bigger is even less.
Or you could find a small turbine that needed less flow. A 3kW turbine (assuming your dealer isn't exaggerating a little) makes 72 kWh a day, that is quite a bit depending on what you are using it for. 72 kWh would last me nearly two weeks of electricity consumption. Heating will chew up a bit though. Hope that helps.
Hi Justus; Few things, I have lived with micro hydro for the last 20 years. Steve's description of pressure and volume was spot on. From my experience in northern Montana, running water does not freeze, but your waste water after the hydro can and will freeze . So how you run your pipe to the hydro is much less important than how you funnel the waste water back into the creek. (In fact having your pipe next to the creek rather than in the creek makes it much easier to work on.) You haven't given us much info about your creek. 26.4 ' of head with 825' of pipe, what is your flow rate ? In comparison my system has 300' of head with 2200' of pipe.... I have 125 psi at the hydro, however I have a very small flow and only run apx. 3-4 gal a minute . My system is known as high head, low flow. Your system would be a low head, high flow. How much water is flowing ... is it seasonal at all ? You need to know how large a pipe your stream can fill and keep full when your hydro is running. With a low head system flow (volume) is everything ! Set up a test system (pipe only) use the 4.5" pipe and a barrel of known size and time how long it takes to fill, this will give you a flow rate, if can your stream easily fill and flow a 4.5" pipe ... can it do the same with a bigger pipe ? The more water you can run and still keep the pipe full the more power you will make !
Not all who wander are lost... J.R.R. Tolkien
posted 2 years ago
Thomas! And everybody!!! Thank you! I have a flow rate of about 25itl/sec using a 200mm pipe. My stream is spring fed by two independent springs and some snow pack. Seasonal fluctuations are minimal.