Pumps as Turbines have many advantages.

If you are good with welding you may want to consider making your own 'turbine' case to replace the pump case and use only the impeller, shaft, seals and bearings from a split case pump. This will allow you to design the turbine case with a much larger inlet to eliminate the restrictive pump outlet.  Note that pump outlet = turbine inlet. This will get you a little more efficiency in converting the energy in the water ( head X flow ) to mechanical shaft energy.

You could even buy just the parts you need. Example shown here. This is a project I'm considering, at least on paper. Another approach might be to modify a split case pump housing with a second outlet. (inlet with respect to turbine operation) Since these housings are mostly made of cast steel it would involve welding of cast steel or cast iron. I'm not sure it would be worth it for maybe a 5% boost in efficiency. But if you like to tweak and optimize ...

Pumps as Turbines (PaT) Motors as Generators

I have been using Pumps as Turbines and motors as generators very successfully for almost four years now. The optimum (maximum power) speed of a PaT is around 1/2 of its no load speed. So to test,run your PaT and generator with the available head but no electrical load or excitation. Then, for maximum power, you should load the system so it runs at 1/2 this No Load speed. So let's assume you have a six pole electric motor running as a generator at 1200 RPM (nominally). You would be looking for a No Load speed of (approximately) 2400 RPM at the generator shaft. If the PaT is direct coupled the only thing that can be tuned is the impeller diameter assuming the head is fixed. Cut down (on a lathe) the impeller diameter to increase the No Load RPM. If the generator is coupled to the PaT by a V belt the shiv ratios can be changed to give the correct RPMs.


How can I estimate roughly the maximum no load speed when impeller diameter and the net head are known?


No Load RPM= (19.1)(SQRT(64 H))/D
Where H= Head in feet, D= impeller diameter in feet (not inches)

So if H = 200 feet and Impeller Diameter is 7 inches we get a No Load RPM = 3699
This is a little high for a 4 pole (1800 RPM) generator, I'd rather be on the low end for better efficiency (less friction due to lower velocities). I would choose an 8" impeller. Or, (even better) go to a 6 pole 1200 RPM (direct coupled) motor, bring the no load speed down to 2400 RPM and calculate the required impeller diameter as below.


More often, you would know the full load normal operating speed of the generator to produce 60Hz from the name plate or the number of poles. Also the head is fixed and known. So you'll want to know what the impeller diameter should be for a direct coupled setup:


Impeller Diameter in inches = 230(SQRT(64 H)/R


Where H = head in feet, R = No Load RPM and SQRT = Square root


So if H = 200' and R = 2400, we get an impeller diameter of 10.8 inches.


These admittedly rough calculations work well with Pelton wheels as well as Francis type runners.


By the way, larger pumps are well designed and optimized to be very efficient. When run in reverse as turbines they perform just like Francis type turbines and are every bit as efficient, assuming you match up head, impeller diameter and operating speed.
The graph above shows how I reverse engineered the pump curves for for operation as a turbine. This analytical approach is not as easy to understand as the empirical approach described above. Note the U shaped > 73 % efficiency region. This is where you want to be operating this particular PaT with a 12 inch impeller, 230 ft of head, and using 750 Gpm with expected output of 25 Hp mechanical energy. BTW, pumps are designated by their outlet X suction inlet X impeller diameter. So this is a 3X4X12 end suction pump with a 30HP, 1800 RPM 3 Phase electric motor.

Best little Hydro House in NY, 20 KW of renewable energy.

A quick overview of the building process. Picked up some inspiration in Costa Rica where pelton wheels could be seen laying around in yards, as ornaments, like wagon wheels here in the US. This is my first attempt at creating a video with music composition. So keep in mind, I'm an engineer not a liberal artist.



It appears my video's no longer play since Google takeover.

Pump as Turbine (PAT)

This is the latest addition to the powerhouse. This split case PAT, 5X6X9 driving a 30HP 3 phase motor as generator will be able to take advantage of the much higher winter flows of the stream. The pump/turbine has been mounted at a 45° angle to eliminate 2 right angle bends in the powerhouse plumbing and there is enough room to accommodate a large flywheel on the generator shaft to enhance mechanical momentum. This will improve voltage regulation and large motor starting capability.

I have a number of Distributed Load Controllers on 1.5kW space heaters in the winter months when there is plenty of water. Then the turbine control valve is wide open all the time and DLC's will have the heaters going full blast until a refrigerator or well pump comes on. Then the DLC's will proportionally reduce the power to the heating loads to keep the voltage constant and allow the motor loads to start up. The 3KW dump load and DLC in the power house penstock is set to a slightly (5V)higher voltage to react to over-voltage situations that might arise if the valve is wide open and loading suddenly decreases. That dump load will absorb the extra power and give the (slow) motorized butterfly valve a chance to close and reduce the power. It is when we are lightly loaded in the spring and fall that I think the flywheel idea will help to regulate the voltage better. I have also just put a few DLC controlled electric heaters outside! Such a waste, but it keeps everything stable.

We are still in drought conditions and waiting for more rain before I can run at full power with the valve wide open. (Our drainage area is only 1.5 square miles) I'm thinking about adding a small efficient pelton to use around 1 gal/sec @ 210' of head so we can keep running through the summer months. Of course none of this would be necessary if we were grid connected on net metering. We are just getting started on the paperwork to get grid connected. To me it seems a bit daunting because I don't like to do paperwork or deal with bureaucrats.