My chart for optimum Powerspout operation.

Powerspout owner / operators who rely on a water source that is seasonal will be familiar with the challenge of needing to optimise the output of the turbine when using different sized nozzles for the different seasons.

In this blog, I'm posting the chart I use to help me with this challenge.

For me, the variables are the type of rotor, the amount of rotor packing, and the type of stator. 

When flows are good and a big nozzle is in use, so much torque is produced by the jet hitting the pelton that the more highly magnetised Type 2 + rotor is needed to keep turbine speed down to a speed where maximum power is produced.

At the other extreme, when flows are least and there is a small nozzle, the torque lost in overcoming the attraction between the rotating magnets and the iron cores of the stator is such a large proportion of the total torque being produced by the pelton that the number of poles in the stator has to be reduced from 42 to 18 in order to keep shaft speed up.

Between these two extremes, the chart gives me a system, which I've built up from experience over 8 years, to guide as to when to change from one type of rotor or stator to the other, and as to how much packing to place beneath the rotor for each of the 13 nozzles I employ.

The chart also has a column for efficiency, and this is 'whole system' or 'water-to-wire' efficiency. Numerous factors contribute to this figure, and these include: how good the penstock is; how good is the alignment of the jet on the splitter ridges of the pelton cups; how well cut are the nozzles to give a good jet profile; how much drag effect there is from grease in the bearing housing; how much transmission loss there is between turbine and inverter, (this will vary with the current); how good the efficiency of the inverter is at different input voltages; and how inefficient the Smart Drive alternator becomes by packing off the rotor. 

Peak efficiency can be seen to be 56.8% and this is achieved with nozzle XII, delivering 2.43 l/s at 1102 rpm, generating 723 watts leaving the inverter.

As I write this, the nozzle in use is number VII and the Powerspout is producing 321 watts; for this time of year this is exceptionally good and is a reflection of the rather wet summer we are having so far; unlike most people, I'd quite like it to continue that way !