ST versus Sunny boy [RE-wrenches]

[William Miller]

Pals:

Earlier I had written about some ST inverters that I thought might be
providing low output.  It was asked that I provide more information on
array, location, etc.  I investigated more thoroughly, measuring
insolation, input current and voltage versus output current and voltage.
During this process I gained access to the Sunny Boy 2500 watt inverters.
I had a chance to perform a "side-by-side" comparison today--at least as
close as side to side as one can.  I had the Sunny Boy installed and was
able to switch over to the ST in about 40 minutes.  Here are the results:

Array: 24 Siemens SR100 panels on two fixed, top of pole racks.
Azimuth: Approx. true south
Tilt: Approx. 16 degrees
Temperature: Approx. 70 degree F
Output Amp measurements: Averaged over 5 minutes with a Fluke 87 on one
pole of 2 pole output breaker.
Input amp measurements: Averaged over 5 minutes with a Fluke 87 on input DC
lead (after combiner for ST)
Array and AC voltage measurements: Beckman DVM

Results:

SB2500:
8/13/01 1:10 pm
7.00 avg @ 242 v ac (1, 694 watts)
Insolation: 45 w/m2

ST2500:
8/13/01 1:53 pm
6.31 @ 245 v ac (1, 545 watts)
Insolation: 45 w/m2

As you can see, the SB is about 10% better.

I would note these other differences:

The SB is quieter (no fan)
The SB is string wired (smaller wire size, more flexibility where to locate).
The ST has input and output and GFI breakers built in.
The ST has metering built in.
The SB offers optional remote metering and free monitoring and control
software.
ST clients are complaining about the ST shutting down periodically
throughout the day, even after installing the latest chip upgrade.  One
client found that after the chip upgrade, his system stopped shutting down,
but the output dropped by about 10%.

Any suggestions on testing procedures and any questions are appreciated.


William Miller

PS: I also checked efficiency of both inverters, comparing input watts
against output watts.  They both range about 90%.  I can only surmise that
the higher output on the SB is because it has a better MPPT circuit (loads
the panels better).


WM



__________________________________________________________________
William Miller
SLO Communications: Communications and Power Systems Consulting
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
License No. C-10-773985
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