I think you're right: it's hot enough there that the Voc never hits
the 57 v BLue Sky death point. Problem is, if you rewire those
modules for parallel, their mpp won't match the SB50. According to
Blue Sky's Tech bulletin #100214, it wants to track MPP between 33 v
-37 v. YOu could add some special jumper (which doesn't help in
Senegal) that would allow it to track between 24v -28 v.
This is why we quit using Blue Sky for the most part: the range of
voltages they'll work with is extremely limited. Not like an Outback
which seems to be able to MPPT almost anything up to 100 v or so, and
step it to any battery voltage.
Might have to just leave it alone. Tell them not to wash the modules!
the dust is probably keeping the Voc down a bit, and if they cooled
them with water on a sunny day, it could all be over.....as the Voc
could exceed 57v.
Whoever "designed" that system was a hack. Probably just throwing
whatever module they were trying to get rid of, with an SB50, and had
no experience with off grid systems.
Seems the Africa scams go both ways, and one of our fellow Americans
ripped some very poor people off.
In the heat there, the actual MPP for the module series is probably
down at 50 v, so the SB 50 is probably running the array at 37 v.
Pretty inefficient, but better than nothing.
R. Walters
Solarray.com
NABCEP # 04170442
On Jun 26, 2009, at 4:22 PM, Walt Ratterman wrote:
Hello,
I am in a very remote part of Senegal, (near the Guinea and Mali
borders…) and I have come across some prefabricated “plug and
play” American made systems installed for educational institutions.
The systems use two Sharp panels that are 220Watts, 33.6 Voc, 29.2
Vmp, wired in series, using #10AWG home run wire from the panels
back to the charge controller.
Charge Controller is a Solar Boost 50.
Batteries are Dekka AGM – two strings of 250AH, 12V batteries.
(four batteries total).
My specific question is about the controller. This is a 24V in /
24V out charge controller with MPPT. I have not used this before,
so I am not familiar with the details of operation.
The data sheet that I downloaded says that the maximum open circuit
voltage is 57 VDC. But, this system is hitting the charge
controller with two panels of 33.6 VDC wired in series for
73.2VDC. So, why is the controller not fried, or what am I seeing
wrong here. I suppose with the panel temperature being elevated
maybe 35 degrees above 25 degrees and a resulting 17.5% loss,
coupled with some voltage drop, the system may actually be seeing
less than the 57 volts.
But…..isnt this a dangerous way to design a system? (it will get
cooler here ….)
Or am I missing something?
What would be the appropriate application here….
Sorry, I cant do a lot of internet research from here – limited
download capability on the satellite….
Thanks!!
Walt
Walt Ratterman
SunEnergy Power International
11 Laurel Lane South Washougal, WA 98671
(360)-837-3680 ▪ fax (360)-837-1315 ▪ Skype Walt-Mobile
wratter...@sunepi.org ▪ www.SunEPI.org
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