Finally! After a lot of trial and even more error over the last 2 years, it looks like we have the hydro generator we need for this site. As I write, it’s contributing power to the batteries, something that none of the previous generators have managed to achieve. Not a lot, because of the present meagre flow of water – for the second winter in succession there has so far been very little rain – but the wheel IS contributing for the first time.
Not only that, but it’s a supremely funky addition to our power generation capacity and is also, like the water wheel, proudly made in Benfeita! (Benfeita means ‘well made’.)
Following our experiences, sometimes disastrous, with 3 other permanent magnet alternators/generators we were already thinking along the lines of making one since it was clear off-the-shelf solutions weren’t appropriate for the marginal nature of this site. I was consequently more than excited to hear another local friend was going to be experimenting with making Hugh Piggot design axial flux alternators.
João completed the first one before Christmas and after a coat of epoxy paint, it came here for testing today. This is a high voltage version (many configurations are possible) of the 1kW nominal power rating specification. It has very low cut-in speeds which is exactly what we’re wanting when flow rates here are low. Coupled with an MPPT charge controller which can convert excess voltage into amps, the alternator is able to produce a useful input when most others would fail.
At the moment we have it on a 3:1 gear ratio which slows the wheel down quite a lot under load. The resistance creates some splash-back which equates to power loss, so we might need to adjust the delivery chute. There’ll be a lot more fiddling with different sprockets and the charge controller tomorrow to find the ideal ratio and settings, but what we could really do with is RAIN. The current weather forecast though is predicting temperatures in the low 20s by the end of the week and no rain before next Wednesday …
3:1 proved the optimum gear ratio of those we had available to test. We figure the splash-back is going to be pretty inevitable when we only have 1 litre per second of flow to drive the wheel. These are summer flow levels, when it was never envisaged making use of the wheel anyway since we have more than enough solar capacity for our needs once the sun reappears from behind the hill to the south.
At these flow rates, the wheel is making around 21W after the charge controller has transformed the voltage – 0.5kWH in 24 hours. Around 20% of the power we could expect from ‘normal’ winter flow levels. This may sound paltry, and it is, but to me it’s vindication of the decision to stick doggedly by the wheel against the advice of hydropower experts on various internet forums who, pretty much without exception, all advised the installation of a turbine. Why? Because having run our data through the online calculator for the output of one of the more efficient turbines available, we would be making no more electricity with a turbine. The wheel is as efficient. It just needed the right alternator.
But our present flow rates highlight a different problem to address.
This is the second year in succession the winter rains have failed to materialise, so I am now considering how best to optimise what we can produce from the water even at these low levels. We can make 1.3kWH from the 1 hour 50 minutes of sun the solar panels get at winter solstice (if the sun is shining). If I can double that from the hydro component even at 1 litre per second, then we can limit the use of our propane generator to cloudy days only, which are not that common without rain as well. To do this, the only option open to us is to increase the head, so the next project is to re-site the wheel another 6-7m lower in the barroco and lay 150mm plastic guttering into the stream bed. This will channel the entire flow at these low volumes into the wheel chute with the minimum of friction, but still leave the system open to cope easily with the torrents of water, mud, debris and rocks which fly down this channel after a heavy downpour.
Reducing friction losses and re-siting the wheel will allow us to effectively double our head. Double the head equals double the power. Plus a little bit extra for the fact that the alternator will be operating at greater efficiency once we can increase its rpm to comfortably within its operating range rather than right on the edge as it is now.