The year to September 30th has seen the most generation in the eleven years my Powerspout has been running. The total energy generated was 5254 kWh.
Understanding that this figure is really quite good for a small turbine is best captured by considering what is called capacity factor.
Capacity factor is the energy generated in a year divided by the energy that could have been generated if the turbine had run everyday for 365 days at the rating specified in its technical specification.
The rating specified for my turbine is 750 watts, which means the maximum power it is meant to be able to produce is 750 W. And using this figure, the maximum energy that could be produced in a year is 6,570 kWh (calc: 0.75 x 24 x 365).
So the capacity factor for the 2023-24 water year turns out to be near enough 80% (calc: 5254 / 6570 = 0.799).
But there is a slight deception in this figure. And this is because the maximum power my Powerspout can actually produce is more than 750 W, and this is evident in the first of the plots below.
There is a reason why there is this deception: the figure of 750 W had to be specified before the turbine had even been commissioned and was a figure derived purely from theoretical calculation. This theoretical calculation had to make assumptions about a lot of things such as friction loss in the pipeline, the efficiency of the 3 phase alternator, the efficiency of the dc/ac grid-tied inverter, ...and many more factors, - all of which were little more than educated guesses.
When the turbine actually got to run, many of the guesses turned out to be on the pessimistic side and the turbine actually was found to produce nearer 800 W at full flow, and even 900 W if slightly more water than the specified maximum flow of 3 l/s was used.
So the 80% capacity factor figure is inflated, and if the true maximum power of 900 W is used to calculate it, the figure drops to 66%. But since officially my turbine is rated at 750 W, that's the figure I'm going to continue to use for my capacity factor calculations. But I will point out that in the interests of 'honesty and transparency' you'll notice that I do say in the Scheme Details section in this blog where each year's capacity factor is given, that the figures are "taking as datum DNC 750 W" (DNC = Declared Net Capacity).
For those who like to appreciate how a small scale hydro works out in the real world, here are the figures for this past year's generation. The year 2023-24 is the black plot line, and previous years are coloured lines:
2 comments:
There's no question but that your waterpower operation is documented to utility standards. I notice that this year's peak output is consistently lower than prior years. If this is due to wear, what system components do your suspect?
Thanks for commenting Craig, - and commenting with an observation that has been frustrating me for some time.
As you have pointed out, peak generation in the most recent water year is down on previous years. The actual figures are that in the past water year, it never got above 896 W whereas in previous years, using exactly the same nozzles, and therefore the same flow, I recorded as much as 929 W.
I don't think it is down to wear in the components, though it could be as the pelton runner has not been changed and its splitter ridges are getting to be less sharp.
My own thinking is there are three possible explanations:
1. In August 2023, I changed the shaft bearings and seals because they had done 6 years. After changing, there was noticeably more 'stiffness' when the shaft was turned by hand, and I suspect that more power is lost to friction when new bearings and seals are put in, - especially new seals.
2. Over the past 4 water years (20/21 to 23/24) I have been 'tweaking' the turbine curve in the SMA inverter connecting my Powerspout to the grid.
See https://water-to-wire.blogspot.com/2023/06/optimising-my-inverter-turbine-curve.html
The aim of doing this was to improve the efficiency of the conversion of hydraulic power to grid ac electrical power, - but much to my consternation, the turbine curve which I am now using seems to be LESS efficient rather than more efficient, at least when power is at the ~900 W level. At lesser flows / lower power levels, the curve I'm using now does show an improvement. Because of the poorer performance at the top-end of the range of flows I use, I have seriously considered swapping back to the original SMA curve, which consistently gave > 900 W. I may yet do so, just to have the satisfaction of generating a bit more.
3. The power generated is very sensitive to the temperature inside the back of the Powerspout,
see https://water-to-wire.blogspot.com/search/label/Temperature%20effect
Winters here in Wales have not been nearly as cold as they used to be and I do wonder whether this might be contributing to why peak generation never reaches the levels of 10 years ago.
Well, - that's enough of an answer, - thanks for giving me the opportunity to write about an issue which has been troubling me !
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