The set up

The set up
5.46mm jet delivering 0.68 l/s to the pelton which is rotating at 900 rpm and generating 135 watts into the grid.

Thursday, 15 January 2015

To the limit, ... and beyond.

The 'hours total' recorded on my Sunny Boy inverter is now 8,238 hours, which means it has been receiving power from the turbine for 12 days short of a year.  In that time, it has never managed to put out the 750 W which calculation said should have been possible with a flow of 3 lps.  Today's post is to say the 750 W limit has finally been reached and exceeded.

A flow of 3 lps generated 748 W, - ever so close to the target output, but nevertheless falling short and leaving me hankering to see the full ¾ kW displayed on the Wattson monitor. 

Today, by delivering slightly more water with just a slightly bigger nozzle on the top jet (∅ 7.46 vs 7.14 mm), the output is now 765 W.  To the best of my measuring ability, the flow giving this output is 3.12 lps, - so just 4 % more than calculation predicted and possibly within the margin for error anyway.

To obtain this output from the inverter to the grid, the dc input to the inverter from the alternator is as follows:

... near enough 915 W (3 A x 305 v), - a figure qualified by these being cheap meters with limited accuracy.

915 W 'in' and 765 W 'out' means there is a power loss in the inverter of 150 W, - a surprisingly large chunk of power, making it apparently only 83% efficient at this power level.

I can't quite fathom this out for the moment, - it goes against what I have documented in previous posts (see herethat inverter efficiency gets better at higher power levels. Certainly a hand on the inverter to feel its warmth confirms that its grab of 150 W is probably correct.

Perhaps the answer lies in there being a more significant voltage drop over the transmission line at this power level, such that the voltage the inverter sees is not what's displayed on the above meter.  Hmmm - I'll have to sleep on that to work out a way of checking it out. 

I'll sleep more soundly though, knowing the hydro's that little bit more productive. 


James Knights said...

I have not yet got a Hydro Scheme ! Just about to talk to the Environment agency! I have been studying flows from a spring and comparing this with local rainfall. In Devon I am also on sandstone possibly the same strata. In my case flow follows very closely to the average rainfall for the last five weeks. This formulae probably alters with watershed to watershed. Todays flow is 4.0 ltrs/ sec. and minimum annual flow is 1.5 ltrs/sec. At 6.0 ltrs/sec other springs open up in the area. By forecasting weather and use of weather statistics I would expect the flow to remain constant (relatively) for the next 5 days but then start to drop a bit.

Bill said...

Good to hear from you James, I have been wondering how you were getting on.
There's a lot to be said for tapping into a spring source if you have a productive enough one: compared to the more usual run-of-river scheme:
- if you can pick up the flow not too far from the spring 'eye', the trash burden is greatly reduced
- the civil works needed to 'harvest' the flow are more modest
- you are likely to avoid a 'fisheries interest' from the EA
- the silt/gravel burden is likely to be less
- the yield will likely be 'smoothed' between rainfall periods making nozzle changes less frequent and so overall management of your installation easier
So all strength to your elbow as you progress your scheme.

regen said...

Hi Bill,

Nice to see you are back on max generation again

Best Wishes


Bill said...

...but not for long Dave. Downsized one nozzle yesterday and with no rain (or snow) forecast, I'll have to be making another step down soon. Good news is that running total so far this year is well ahead of last year.