Generator for microhydroelectric power generation station?
Generator for microhydroelectric power generation station?
(OP)
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People That Know Electricity,
I am working on the design for a new microhydroelectric power generation station. The station will be located at an existing pond in a small, urban watershed. The pond has an existing dam with 9+/- feet of available head. The base streamflow is 3+/- cfs and the maximum flow that will be utilized is 23+/- cfs. This translates to roughly 1.5kW base power potential and 14kW maximum power potential.
The proposed system schematic is as follows:
Reservoir --> Waterwheel --> Generator --> Inverter --> Grid
The most suitable power converter in terms of overall performance (cost, efficiency, maintenance) is a breastshot waterwheel (18+/- ft diameter). Breastshot waterwheels are most efficient when converting potential energy into 'mechanical rotational energy' (as opposed to kinetic energy to 'mechanical rotational energy') – in practical terms, this means the waterwheel is most efficient at slow rotational speeds. Ideally, I'd like to have a base waterwheel rotation of 1 RPM, which would roughly result in a maximum rotation speed of 7 RPM. Assuming I could achieve a 40:1 gear ratio, this would be a base generator shaft speed of 40RPM and a maximum generator shaft speed of 280 RPM. As this is an urban watershed, the flow (and thus power output) is highly variable. (I could go beyond the 23+/- cfs input, but I am limiting it to this due to various civil/mechanical reasons).
With all that, I have the following questions:
1) Is the "[DC] Generator --> [DC-to-AC] Inverter" portion of the system schematic what I should be looking at or is there a better system? I've seen various systems, but this seems to be the most straightforward, efficient, and (assuming I can find the generator) least expensive and most viable option.
2) Does anyone have a suggestion for the generator I should use? I've looked around, but haven't found much. I am guessing that I will need to find a high torque / low speed (multi-pole) DC motor used for mixing or grinding operations and run it as a generator.
I've searched the posts and haven't found anything covering this...
Any help is greatly appreciated!
.
People That Know Electricity,
I am working on the design for a new microhydroelectric power generation station. The station will be located at an existing pond in a small, urban watershed. The pond has an existing dam with 9+/- feet of available head. The base streamflow is 3+/- cfs and the maximum flow that will be utilized is 23+/- cfs. This translates to roughly 1.5kW base power potential and 14kW maximum power potential.
The proposed system schematic is as follows:
Reservoir --> Waterwheel --> Generator --> Inverter --> Grid
The most suitable power converter in terms of overall performance (cost, efficiency, maintenance) is a breastshot waterwheel (18+/- ft diameter). Breastshot waterwheels are most efficient when converting potential energy into 'mechanical rotational energy' (as opposed to kinetic energy to 'mechanical rotational energy') – in practical terms, this means the waterwheel is most efficient at slow rotational speeds. Ideally, I'd like to have a base waterwheel rotation of 1 RPM, which would roughly result in a maximum rotation speed of 7 RPM. Assuming I could achieve a 40:1 gear ratio, this would be a base generator shaft speed of 40RPM and a maximum generator shaft speed of 280 RPM. As this is an urban watershed, the flow (and thus power output) is highly variable. (I could go beyond the 23+/- cfs input, but I am limiting it to this due to various civil/mechanical reasons).
With all that, I have the following questions:
1) Is the "[DC] Generator --> [DC-to-AC] Inverter" portion of the system schematic what I should be looking at or is there a better system? I've seen various systems, but this seems to be the most straightforward, efficient, and (assuming I can find the generator) least expensive and most viable option.
2) Does anyone have a suggestion for the generator I should use? I've looked around, but haven't found much. I am guessing that I will need to find a high torque / low speed (multi-pole) DC motor used for mixing or grinding operations and run it as a generator.
I've searched the posts and haven't found anything covering this...
Any help is greatly appreciated!
.
tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com





RE: Generator for microhydroelectric power generation station?
If I understand your breast wheel correctly, it does indeed produce a torque that increases with available water.
Simple, good efficiency, low cost.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Generator for microhydroelectric power generation station?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator for microhydroelectric power generation station?
18ft to a 2in pulley would be 108 ratio.
You'd want the alternator to turn about 8,000rpm.
8000/108 = 74rpm. Still too fast for the desired ~4rpm.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Generator for microhydroelectric power generation station?
The necessary jackshaft could drive an arbitrary number of alternators with poly-v belts, located remote from the water spray.
You might need two jackshafts to get the ratio.
And a fairly serious frame to deal with all the tensions.
1 rpm is pretty slow, and 9 ft is not a lot of head. The jackshafts and such add a lot of complexity and cost to a low power system.
OR
To reduce the number of very large and expensive wheels to be fabricated, you might make the first pass a car tire pressed against the rim of the waterwheel, at the top. You'll need a good rain tire to get wet traction, and a pretty decent weight on the tire's axle to get enough normal force. From there you can use chains or timing belts to the jackshafts as appropriate.
OR
Build a written-pole generator into the rim of the waterwheel. Maybe the patent holders could be interested. The presence and uncertain nature of the water presents a serious challenge, as does a development cycle in both time and money.
Mike Halloran
Pembroke Pines, FL, USA
RE: Generator for microhydroelectric power generation station?
The induction machine would work well with a regenerative drive. A regen-capable drive at (say) 15kW rating is not a common product although there are certainly options.
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If we learn from our mistakes I'm getting a great education!
RE: Generator for microhydroelectric power generation station?
I have heard descriptions of old flour mills converted into dwellings with the water wheel restored. Many used suitable gearing to spin an induction motor/generator as Gunnar describes. The controls are fairly simple and an inverter is not needed.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator for microhydroelectric power generation station?
Water Wheel 30 to 300 RPM
1500 Watts = 2 HP
35 lb-ft at 30 RPM
3.5 lb-ft at 300 RPM
Generators like high RPM-10 to 1 step up transmission. Two small automotive gearboxes in series in low gear, driven "Backwards."
Generator: Brushless Permanent Magnet Motor runing at 300 to 3000 RPM.
Three phase full wave rectify gives 30 to 300 VDC. Current is 50 Amps at 30 VDC.
Boost paower supply converts 30 to 300 VDC to 300 VDC.
Finally, a commercially available Inverter to get AC Power. Possibly a Delta Electronics unit.
ht
RE: Generator for microhydroelectric power generation station?
For this water wheel application, I envision a segmented stainless steel (non-mnagnetic) ring in either a radial or an axial configuration. Welded to this ring are steel teeth. This assembly is attached to the periphery of the wheel, and rotates with it.
Engaging with this rotor is a generator package that resembles a disc brake caliper; it does not need to wrap entirely around the circumference, and probably would need to be only a couple of feet long. It contains the entire magnetic circuit.
Permanent magnets are arranged along one side of the 'caliper', and the generator coils along the other side of the rotor gap. The 'backbone' of the caliper wraps the magnetic circuit back around to the permanent magnets. The coils and associated cores are arranged at the same pitch as the rotor teeth; the permanent magnets are of consistent orientation, and create what would be a continous magnetic 'curtain' field.
The rotor teeth concentrate this field into a area of a coil width, and 'steer' it to successive coils.
This type of alternator has some drawbacks; it requires more copper as half the coils are idle at any given time, and it is a bit more lossy than the usual, but the extra losses in the alternator seem unlikely to exceed the heavy losses requisite with high-ratio step up gearing. And, the mechanical simplicity could be very appealing; the caliper contains all electrics, and can be readily potted. The rotor carries no circumferential magnetic flux, and so can be constructed of segments.
Now if I could only remember what this type of alternator is supposed to be called...
RE: Generator for microhydroelectric power generation station?
After a few of the other posts, I was thinking that you could install some strong permanent magnets around the rim of the wheel with a "caliper" type 3-phase generator encompassing a portion of this rim of permanent magnets. Rectify the output to produce a DC output which would be proportional to the wheel speed. Then, it might be possible to use a solar inverter or a Windyboy inverter to produce grid power.
RE: Generator for microhydroelectric power generation station?
So far we haven't had a synchronous machine and a torque converter to drive it suggested, but I'll throw that in with the other 'interesting' ideas!
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If we learn from our mistakes I'm getting a great education!
RE: Generator for microhydroelectric power generation station?
Mike Halloran
Pembroke Pines, FL, USA
RE: Generator for microhydroelectric power generation station?
Not far behind would be any other dc generator that includes brushes simply due to the maintenance required.
The simplest way to achieve grid tied is an induction generator and to forget about allowing the wheel speed to vary. You could also do a 2-speed motor if you really wanted to allow different speeds.
A purpose built permanent magnet generator would also work very well.
If you look at wind power the solutions used there would be similar for the same reasons (relatively low speed, varying speed, varying power levels).
RE: Generator for microhydroelectric power generation station?
People That Know Electricity,
I appreciate all your comments and expertise. It is very beneficial, to say the least. A few bits of information:
1) It is possible to design and install a waterwheel which would have constant speed over the input flow ranges, but in practice it would be rather difficult (given the complexity of the fluid phenomena involved) and very expensive (given the relative precision required and limited skill set in machining such a beast). Active governing would work, but that would unnecessarily reduce efficiency if a direct generator solution can be found. So, a 'fixed speed' waterwheel would be outside the range of cost-effectiveness for this project, though potentially feasible for higher power projects or projects with a much higher likelihood of being reproduced elsewhere.
2) If a suitable brushed DC motor with pretty good efficiency could be found, the maintenance would likely be acceptable.
3) Off-the-shelf combinations of components are very much preferred, though a 'custom' generator would fit the bill if such could be had for a reasonable price. I am clueless as to what such a custom generator would cost.
4) I've looked at wind power solutions. The small turbines are too high rotational speed and the large turbines are too low rotational speed (and way high power and cost).
5) I am thinking that two or more lower power generators/motors connected along a single shaft might be a viable solution. These seem to be more readily available, though I haven't seen many with shafts that run all the way through the equipment - so each would probably have to be driven by gears off a main shaft.
Any additional guidance is more than welcome.
Thanks again!
.
tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com
RE: Generator for microhydroelectric power generation station?
That was an "Inductor" type of AC generator made by the Stanley Electric Co. in Pittsfield Mass., up to around ? 1910 or so. It had a large statioery DC field coil all round the outside of the machine between two stators, the stator coils
were in slots in the cores and in non-magnetic tubes between the stators. There were no slip rings or brushes. It was also built as a synchronous motor typically driving a DC generator (MG set) in substations.
It was used in many hydro plants in California, one unit still exists at a small plant known as Centerville Power House (P. G. & E.) about a 900Kw unit.
Google "Electra Power House" (shut down around 1950)and you will see historic photos of that plant which had five Inductor generators installed about 1902, which transmitted power to San Francisco at 60KV, over a hundred miles...
Yes, I am a historian, anybody else like that out there??
rasevskii
RE: Generator for microhydroelectric power generation station?
If it's a low-head application, you could achieve a 240 rpm and utilize a jackshaft to bring speed to 1800rpm.
Example:
turbine-side gear = 62 teeth,
jackshaft = 21-52 teeth; and
driven induction motor -generator shaft = 21 teeth
Final generator rpm = 240 X 62/17 X 52/17 = 1800rpm!
As mentioned, employing a jackshaft brings the generator away from the water spray! And most of all, you can find a lot of 1800rpm motors. Hope this helps.
RE: Generator for microhydroelectric power generation station?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator for microhydroelectric power generation station?
Have a look at the website: www.hydrowatt.de for examples of delivered systems by that company involving classic waterwheels and small turbines. (I am not connected with them). The German you can translate using babelfish if needed.
rasevskii
RE: Generator for microhydroelectric power generation station?
Lionelhutz: A flying magnet type of design was my first thought as well, but two problems arise... The permanent magnets are the most expensive part of the build, and it would use a lot. Also, the first bit of scrap steel that came along would bring the whole rig to a crunchiing stop.
You are right about the one-off wind turbine generators serving as a model. Where commercial products are not readily available that provide a good match to the input parameters, the clever builder steps outside the box and finds a way to roll his own. Some of the home-built wind generators are extremely simple yet effective.
ScottyUK: Certainly a home-brew generator will give up some efficiency points to a commercial product. I would argue that it would be beneficial to give up those efficiency points in a direct-drive generator than in a step-up gear train as it would result in much reduced system complexity.
Tsgrue: A breastshot wheel uses the weight of the falling water to load the downhill buckets to create a torque. Can the buckets be deepened to contain most of the peak flow? It seems that this would increase torque with greater flow more than increase speed. This more constant speed would in turn seem to work better with an induction generator.
Overall folks, it seems to me that if the intent of this exercise is to generate the most electricity, some form of turbine might be better as it would be inherently of much higher speed. If the intent is for aesthetics, the wheel is more attractive, but I wouldn't plan on getting large amounts of electricity out of it.
To make use of the wheels energy via a commercial product is going to require step up gearing on the order of 1:1800. Intuitively, I'd think one would be hard pressed to attain 15% efficiency on the gear train. I would also think that a great deal of changing final ratios to get the wheel speed tuned to the just over synchronous induction generator speed required.
I would also worry about torque pulsations... The impact of the flowing water against the wheel buckets will create periodic torque variation. That pulsation, multiplied by the huge step up ratio would seem to spin up the generator which could then overrun the slop in the gear train slamming the inertial load of the high-speed generator back and forth against the drive train slop.
One could always use the wheel to winch a series of heavily weighted magnets to the top of a tower whereupon the magnets would be released to fall through coils, and the resulting electricity stored in a battery. Non-turbine waterwheels are inherently low speed devices. Electrical generators are inherently high-speed devices. To get them to play together is going to require extraordinary effort.
RE: Generator for microhydroelectric power generation station?
RE: Generator for microhydroelectric power generation station?
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Electric Wizards,
A few notes:
1) Properly designed and installed overshot, backshot, and breastshot waterwheels are very efficient, with 70% to 95% able to be realized over a wide power band. These are not worse or better than turbines, each appropriate on a site-by-site case-by-case basis. I am estimating an average of 75% efficiency at the shaft for system design purposes. As these are 'potential energy converters', the key to the better efficiencies is keeping the water input velocity low and minimizing fluid losses (especially turbulence losses at the entrance and exit).
2) I am fairly familiar with the crossflow and most other turbine types. The crossflow is an option, but for a variety of reasons - including aesthetics, visibility, and education - the breastshot waterwheel was chosen. The breastshot is also expected to be somewhat less expensive and more robust than the crossflow. Interestingly, the crossflow works partially in the same manner as the breastshot waterwheel, but with much more of the power conversion from kinetic and not potential energy in the crossflow.
3) The potential for pulsing is fairly minimal. With 60 buckets likely for the final design - which will be determined in part by the generator selected - the flow effect is relatively continuous.
4) The buckets are sized to accommodate the median and peak flows. It is possible to partition the buckets with dividers (similar to crossflow turbines) to maintain constant speed while torque increases, but - as mentioned before - that level of effort and cost is probably not feasible for this project.
5) I am familiar with the primary current German (around 3) and American (around 1-1/2, the 1/2 being wooden) manufacturers of waterwheels, as well as the 'historical' American manufacturers (mainly Fitz and Campbell) and have reviewed information available from them - especially the German. It's the generator for this site that has me stumped. There used to be various generators produced that would do the job for this scenario - especially from 1900 to 1950 - but these don't seem to be around anymore. It may be no coincidence that power converter speed increased significantly during that time along with mechanical system advances - also the era during which most waterwheels were phased out.
6) The easy answer seems to be speed the thing up, but I need higher efficiencies to make the combination of aesthetics, visibility, education, and life cycle cost work out. You know - everything!
As before – thanks very much!
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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com
RE: Generator for microhydroelectric power generation station?
Where copper is available, drug-fueled thieves will arrive. They will bring tools, and persistence, and LN2 if needed.
Plan on a total enclosure around whatever electrics you choose, and plan on welding it shut. Ordinary locks will not suffice.
Mike Halloran
Pembroke Pines, FL, USA
RE: Generator for microhydroelectric power generation station?
Compound sprocket chain drives would be practical up to perhaps a hundred rpm, they could run fairly loose in an oil bath with very little frictional loss. Fairly easy to make too.
The ever experimenting do it yourself wind power guys are now using home constructed alternators with neodymium magnets.
These can easily be fabricated as a large diameter non magnetic disc with the neodymium magnets (facing axially) studded around the periphery, then have a very large numbers of stationary field windings arranged on either side.
Many windings running in phase, are connected in series right around the disc, so that the turns count per pole need not be very high, but even at low rpm, the output voltage and frequency becomes very usable.
The wind guys find that doing it that way requires no gearing, and with air cored coils (!) there are no eddy current core losses, and it is far easier and cheaper to make.
All rather surprising if you have never seen this approach before, but it seems to work rather well.
RE: Generator for microhydroelectric power generation station?
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Thanks to all who posted. The information has been very helpful. It looks like the system will employ an asynchronous generator.
Thanks again!
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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com
RE: Generator for microhydroelectric power generation station?
http://f
RE: Generator for microhydroelectric power generation station?
Although not an off-the-shelf device, it would seem to be mechically and conceptually simple enough to home build.
RE: Generator for microhydroelectric power generation station?
They have the particular problem of "cogging" which may be much less troublesome with a water wheel.
What happens is, the permanent magnets align themselves with the iron pole pieces of the electromagnets, and the whole thing strongly resists initial turning.
The result is the alternator locks up stationary, and the initial break away torque can be high enough to prevent the wind turbine from starting up at all at very gentle wind speeds.
The drive torque also fluctuates massively as each iron pole piece and magnet pass each other when it does start up. That is the evil "cogging" effect.
The solution is to use AIR CORED COILS in your calipers. There is then zero cogging effect, and the alternator turns completely freely where there is no load current.
Now it might be thought that this massively reduces efficiency, and it certainly does from the size, packaging, and power density aspect.
But amazingly it has almost no effect on the efficiency of mechanical power in versus electrical power out.
In fact, the complete elimination of hysteresis and eddy current loss that always occurs in an iron magnetic path
is actually a bonus.
So what you end up with is an inconveniently large machine, of excellent overall energy efficiency. This is real fringe engineering, but it sure is interesting.
Here is a link to how a home constructor in Italy went about building a 1Kw machine. The air cored alternator pictures begin half way down page two:
http://w
RE: Generator for microhydroelectric power generation station?
RE: Generator for microhydroelectric power generation station?
Here is a good site showing different wind power construction teqniques. You can see the general evolution over time if you go through the links in the boxes from the bottom to top, with the newest projects being 20', 5kW turbines.
http://www.otherpower.com/otherpower_wind.shtml
Gearing up to a few 100 rpm would be a lot easier than gearing up to 1800rpm or 8000rpm.
RE: Generator for microhydroelectric power generation station?
There have been a great many amateurs all over the world working on these low rpm axial flux disc alternators, and even the crudest built examples seem to work amazingly well.
This definitely seems to be the way to go.
An internet search will give you plenty of ideas of how to do this, and your goal of 1.5Kw is right in the ball park.