Extracting as much energy as possible from a small turbine is part of the fun of operating one.
As described in the last post, installing the reduced core stator actually had the opposite effect: power output decreased. Disappointing as that was, I'm anticipating the time, which hasn't come yet as water flows are still holding up quite well through this past week, when the reduced core will generate more productively than the full core.
Another investigation to see if more power could be extracted involved using a rotor from which the cooling fins had been removed. It was supplied as a 'one-off' by EcoInnovation in New Zealand:
The idea was that some energy must be consumed in rotating the vanes of the rotor against the resistance imposed by air, and that by removing them, increased electrical output might be seen.
The degree of benefit was never going to be very great so a really sensitive way of measuring power / energy output was needed.
The study involved running the turbine without interruption at constant flow and head for several days, first with the usual, finned, rotor and then with the new, de-finned rotor. For each rotor, energy output was measured with an Elster A100C kWh meter over a very precise period of time, precise enough to be measured to the nearest second after a minimum of 2 days of recording. By converting kWh to watt-seconds and dividing this figure by the duration of the recording period in seconds, the mean power output for each rotor was obtained.
Well, the findings were not very impressive: the study was done on two separate occasions, the first demonstrated a gain of 0.96 W and the second 1.51 W. So the conclusion has to be that removing the fins is not a worthwhile thing to do.
As a side investigation, the temperature inside the Smart Drive housing was measured with each of the two rotors in use:
This demonstrated that when the fins have been removed the lack of circulating cooling air raises the differential temperature between inside and outside by a factor of 2 or more. So the fins do achieve their desired effect and removing them could make the Smart Drive compartment too warm, especially if high power outputs are being generated, if ambient temperature is high or if the turbine is situated in the direct glare of the sun. It has to be remembered that LDPE, the plastic of the Powerspout casing, is a thermo-plastic !
The next investigation into how more power can be squeezed out of a Powerspout will look at using different bearings, starting with SKF's Energy Efficient type of deep groove ball bearings. Watch this space.