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Xantrex: Nice efficiency, fun with fishbowl
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Author:  Mark Lopez [ Thu Mar 27, 2003 1:24 am GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Ron Schroeder:


1. the ability to select logging once every 1, 2, 3, 4, 5, or 6 seconds and possably also once per minute instead of just every second to allow for smaller files/ day. (Excel limits files to 32,000 records for graphing which is less than 12 hrs at once per second.)
<HR></BLOCKQUOTE>

One workaround I have done is to do a quick filter for power < X Then I delete those rows. This usually results in less then 32K rows left.

Also, there is a program here http://www.timnolan.com/hparticle/hparticle.htm called decimate.exe which will extract every x number of rows. For example, every fifth row.
Author:  Gordon Shackelford [ Thu Apr 03, 2003 3:47 pm GMT ErdGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Hi Henry et al,

On Monday, my system (48 SP75s and a ST2500 XR/GP set at 22 degrees, pointing due south in San Diego County) produced a System Best 19.82 kWh! My best result with the old ST2500 was 18.8 kWh in late April 2002.

However, I'm starting to think that my SP75 are underperforming. As I see it, DC current from the array is almost entirely proportional to insolation. I have observed, during times when the inverter is NOT power limiting and insolation is over 1000 watt per meter squared (clear day insolation chart and actual insolation measurements) that my DC current is 48 amperes (as measureed by fishbowl) when, the name plate current ratings should produce 53 amps at Max. Power Point* with 1000 watts per meter squared insolation. Important Point: This is not an issue of DC power, that falls as PV temperatures climb due to reduced voltage -- simply current that isn't strongly related to temp.

The ST2500XR/GP is working so well that the real characteristics of PV array are showing through quite clearly.

Gordon

* The MPPT as shone on fishbowl matched up very well with MPP from IR Measurements and calcuation of MPP.
Author:  Solar Guppy [ Thu Apr 03, 2003 5:48 pm GMT ErdGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Hi Gordon,

Isn't it fun , now instead of spending your time with the inverter , you now get to focus at other parts of the system [img]images/smiles/icon_biggrin.gif[/img] [img]images/smiles/icon_biggrin.gif[/img]

Your panels angle will match the sun angle about the 3rd week of april , since your fixed mounted , this will be the only time you will get STC current.

Also , get up on the roof and wash the panels once a month and spray down once a week.

If you do the wash next week , you will get a good idea of the panels ability for maximum output.

Having said all that , I'm not sure how you can make this measurement on your system (peak current) since if they really are putting out the maximum STC power , your inverter would be needing to make 2700-2800 watts , which it can't do.

For the current measurement , I would pull a string to get the STC watts below the limit of the inverter. Also , you not taking into account wire losses , the FishBowl DC amps will be net , not gross

Henry [img]images/smiles/icon_razz.gif[/img] [img]images/smiles/icon_razz.gif[/img]
Author:  Gordon Shackelford [ Thu Apr 03, 2003 8:01 pm GMT ErdGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Henry,

Wire losses don't produce a loss of current, only voltage -- current proportionality to insolation is where my concern is.

Since DC power is voltage x current, when the cells are hot, the loss in performance is due to the loss of voltage -- that is a lower MPP, not current falling off.
I figure it like this:
Each cell's voltage falls by 2.3 mV per degree C above their nameplate MPP rating at a cell temp. of 25 degrees C. So, if the cells are at 55 degrees C (as per my IR thermometer measurement) this is 30 degrees above the rating temperature.
So I calculate as follows:
Voltage Fall = 0.0023 x 144 x 40 = 9.9 volts.
The 144 is the number of cells in each circuit. The voltage fall of 9.9 volts puts MPP at about 58 volts -- which matches the operating MPPT on the XR/GP at the time. This calculation yields an almost 15% power fall below nameplate rating.

Current, however, has only a slight change (actually upwards) with temp. So, current ratings should be observed. That said, it would be best, for array testing, to measure its short circuit current (58 amperes for my system) rather than MPP current (53 amperes).

As for sun angle, I was measuring at the plane of the array.

One of the great things about your work on the inverter is that I can now turn my attention to physics/performance of the PVs. This is great.

Gordon
Author:  Solar Guppy [ Thu Apr 03, 2003 10:56 pm GMT ErdGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Me Bad , your right only the voltage is effected on IR loss. Heat actually increase current in SI panels, by about 1/10th the effect of the voltage drop

Unless your getting edge of cloud effect I doubt your getting 1kWmsq, in clear conditions , you will not usally see 1kWmsq , typical clear conditions here in Florida would be in the 930-950 range.

As for the drop off , it is the COS off the angle difference

Henry
Author:  arnolddeleon [ Fri Apr 04, 2003 3:52 am GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Gordon:
Hi Henry et al,

On Monday, my system (48 SP75s and a ST2500 XR/GP set at 22 degrees, pointing due south in San Diego County) produced a System Best 19.82 kWh! My best result with the old ST2500 was 18.8 kWh in late April 2002.

<HR></BLOCKQUOTE>

I had 19.67 kWh from 44 BP585s last Friday. It's been partly cloudly recently so I haven't had "perfect" days. I'm about 30 degrees east of south in Silicon Valley.

arnold
Author:  Solar Guppy [ Fri Apr 04, 2003 10:44 am GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
First one to 20 kWr and sends me the FishBowl Log get a gold star!!

Looks like Gordon has some competition !

Henry [img]images/smiles/icon_biggrin.gif[/img] [img]images/smiles/icon_biggrin.gif[/img]
Author:  Gordon Shackelford [ Mon Apr 07, 2003 1:24 pm GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Henry et al,

Two Items:
Yesterday my system 9 (a cool day) produced 19.89 kWh -- ever closer!

By my calculations, PV current climbs with temperature at a rate to negates only about 3% of the power loss due to reduced voltage. The power loss due to temperature is large enough that it really should be considered in the mapping of the country for PV generation potential. As an example, a location rated at 6 solar hours (annual average) in a very hot location may not actually be better than my 5.5 solar hour location.

Gordon
Author:  arnolddeleon [ Mon Apr 07, 2003 10:01 pm GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
I have one inverter 19.94 kWh for the day. I don't think there is enough daylight left for it to make it to 20.

arnold
Author:  Gordon Shackelford [ Tue Apr 08, 2003 2:26 pm GMT EthGMT ]
Post subject:  Nice efficiency, fun with fishbowl
Hotter day, less energy yesterday 19.4 kWh. MPPT ran 2 to 3 volts lower than the day before (April 6) due the higher air temps and less wind. The inverter works so well that the physics of the array is really showing through.

Gordon
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