Number Crunching

[SparWeb]

Now that I have built a datalogger, I finally get some numbers to pore over.  I probabaly enjoy doing this more than normal people do.


Laptop collecting data from datalogger (black with LCD)

The logger pours out a continuous stream of RPM, voltage and current data.  Occasionally record it.  Number crunching takes some time so it's worth recording only when I have some time to sit down with it.  When I do, I learn stuff.  But, I should start at the beginning.

My first turbine (2007) had 8-foot blades and an axial alternator, which burned out pretty quick, because the blades were oversized for it.  Then I converted a very old GE 3HP 3 phase motor (2008) and used the same blades.  They were were still a bit oversized bu it didn't matter because the furling system worked and the GE motor could withstand a LOT of heat.  Later (2011) I did a much better motor conversion on a Baldor 3-phase, and mated it up to the 8-foot blades.  Once I got that one running, I noticed it behaved differently.  The blades were quieter so it seemed an improvement from day 1.

Somewhere around 2012, I had the irresistable (and unexplainable) urge to do a lot of analysis, and figured out that the blades might be under-sized for the Baldor.  Huh.  That explained a lot, because after watching it for a year, even in strong winds they didn't really seem to be turning that fast, even if the furling was about to activate.  At the time, I didn't have a tachometer, so no way to know how fast the blades were actually turning.  Now that I have a datalogger, it turns out that the blades are stalled most of the time.  They rarely go above 300 RPM and I have yet to record 400 RPM, even during some pretty strong winds.  I could probably run it safely with no furling at all.


Power Coefficient and TSR, Spirit of Zubbly with 8-foot blades, 9 May 2018

Here's how I figured it out.  I collected RPM data simultaneously with the wind speed from the weather station, which is right next to the WT tower.  With the RPM and the wind speed, averaged for a minute or 10 minutes (same result either way) I get the TSR plot shown above.  While I have always known that the TSR around cut-in speed is pretty high (they spin unloaded up to cut-in), I am still surprised to see that the TSR of the blades continues to drop as the wind gets stronger.  The TSR is not leveling off, like the analysis predicted, either.  Anything below TSR=4 and my blades are mostly stalled, because they were carved for TSR=7.  In the plot above, the Cp drops drastically when the wind is greater than 20 kph (12 mph).  This is a pretty drastic mismatch between blades and generator.

So it's time I made some 10 foot blades for the Spirit of Zubbly.  Stay tuned for some wood carving.

[OperaHouse]

Unrelated, but still number crunching.  I've been in discussion as to how much a battery costs per KWH of actual use over its lifetime.  I've seen the figure of 12 cents/KWH. No one actually collects this data.  Care to put in your vote?

I used to look at those numbers collected.  Now I just have a couple flashing LED.  If the beer is cold and the milk doesn't stink, I'm satisfied.

[SparWeb]

Hello Grommit,

My economics are pretty skewed. The batteries were free, the energy usage is (still) unmonitored, and most of my energy production comes from solar, not wind.
Nobody would purposefully set out to build a system like the one I've ended up with

Your question leaves a lot of room for debate and other questions about "what do you include".
A rooftop array of solar panels that charge a suitably-sized battery bank that powers a very well insulated house with no electric appliances, very few peak loads, and most consumption during the daylight hours, plus grid tie to shave the peaks, would probably see the maximum utilization of their batteries.  How that could break down in terms of $/kWh would require even more assumptions than the 5 or 6 I just rattled off.

FWIW, my bank is a set of very old Absolyte IIIp backup batteries, which I inherited used at the end of their warrantied service life.  I have reconditioned them a little, monitored their relative SOC, kept them in an insulated box, and at float charge every day, for 10 years.  As a group they show only minor signs of degradation.  There are a few "bad" ones, but they're only a few points below the rest of the group.

[bigrockcandymountain]

I have 8 surrette rolls s-550 that were $3000 canadian gor the set.  The chart yells me at 50% dod i will get 1400 cycles.  They store 10.25 kwh is 50% so 14350 kwh over their life. 3000÷14350= 21 cents per kwh. 

 All the power you use while generating solar costs nothing so actual cost of power is much lower.  For example, we do all our clothes washing, vacuuming, cooking with electric etc while the sun is shining.  Actual power cost will be lower than 10cents. 

We live in the super insulated (16 inch walls) etc house.  No large loads really.  I think off grid is the best thing ever.  No outages in 2 years and counting. 

[frackers]

I've run about 2.5MW through my 1000-hr battery bank (just over 100,000 amp-hrs @ 24v) since 2013.

The bank is 20 x 12v 100A-hr sealed UPS lead acid batteries which I bought second hand for NZ$500 for the lot. Retail cost at the time would have been about NZ$7000

I reckon that works out at about NZ20c per KW-hr for the price I paid for the batteries, approaching NZ$3 per KW-hr if I had bought new.

They still have capacity that is perhaps 70% of when I got them when they had about 70% of new!!