[RE-wrenches] Solar Boost Controller in Senegal

Tue Jun 30 10:01:08 PDT 2009

Walt,

I would also offer that in a hot climate, MPPT in general is only useful in a case where odd cell counts take the Vmp away from 24V nominal specs. That is, MPPT was originally developed to harvest the voltage headroom between Voc and Vmp, which was greatest in cold ambient temperatures. There is little benefit to MPPT in a tropical climate, unless it’s being used (incorrectly in this case) to adapt a particular module with odd cell count.

Walt, I would suggest that you consider pursuing replacing the Sharps with any 12Vnom or 24Vnom module commonly in use there, and then either keep the SB50 because it’s already there, or replace it with the most reliable non-MPPT PWM controller you can bring in or find in country. This maximizes the likelihood that the system can be kept in operation even if the SB50s fail (and experience says that some will in time) and the locals can’t get service or replacement product. It seems to me that the SB50 is an unnecessarily complex component for this application, and a standard PWM replacement controller will match poorly and inefficiently to the Sharps.

FYI, I called Earthwalk and spoke with “Joey” there. I copied him on Rick’s email, and got a read response. So Earthwalk is aware of this situation, although Joey was a computer tech, not one of the “solar experts”. If they have integrity, they’ll contact you and start making arrangements to get this resolved. Perhaps they can wire you the funds to purchase compatible modules locally? 

I have copied Joey on this message as well.

Allan Sindelar

Allan at positiveenergysolar.com

NABCEP Certified Photovoltaic Installer

EE98J Journeyman Electrician

Positive Energy, Inc.

3201 Calle Marie

Santa Fe, New Mexico 87507

505 424-1112

www.positiveenergysolar.com

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Bob-O Schultze
Sent: Tuesday, June 30, 2009 8:14 AM
To: wratterman at sunenergypower.com; RE-wrenches
Subject: Re: [RE-wrenches] Solar Boost Controller in Senegal

alt,

In addition to those possible replacement controllers you mentioned, you might add the BZ MPPT 500 to the list. I've had a few issues with them but that seems to have mostly sorted itself out. Very reasonably priced for a MPPT controller, 100 Voc input. The catch is you've got a 500W output limit.

Bob-O

On Jun 30, 2009, at 1:26 AM, Walt Ratterman wrote:

Hello all,

Thanks to all of your responses, and particularly Rick’s confirmation of the appropriate ranges for the SB50, it has become clear that these panels can not be made to work with the SB50, and that the SB50 was the wrong choice for these pre-fabricated systems, or perhaps better phrased, the panels were the wrong choice for the controller.  Actually, it is probably more accurate that the panels were the wrong choice because their characteristics severely limit the possible options of what to do next.

I would like your input on what you think should be done here.

Nine systems were purchased from Earthwalk.  One has been deployed for four months.  A second unit is being deployed now.  This leaves seven in the warehouse.  (And we wont even get into the fact that we have AGM batteries here instead of the advertised GEL batteries, and the voltage is so low they might not even work……I will deal with that separately…..)

While it is clear that the panels do not match up with the controller, it is not clear why they are still working (other than the heat and dirt) and if they will continue to work. 

One solution would be to just leave everything alone and tell them what they should do if the system(s) fail.  In some cases, this might be the right action to take.  But in this case, I think the folks who sold the prefabricated unit should be held accountable, and provide a system that is designed to work properly.  The schools paid good money for this equipment and they should at least have a running start at success, which is difficult to come by in this part of the world on a good day.

So – when we tell the schools to insist that the system be fixed, what do you think we should tell them?

Due to the characteristics of the panel (not being either 12V or 24V nominal) they need a MPPT controller.  I suppose we could tell them to change to a controller that will accept the output of the panel.  This would be either Outback, Midnite Solar, or possibly the new Morningstar 15A controller.  Any suggestions?

The other route would be to have them change the panels, and keep the prefabricated system as it is.  Rick:  what would you recommend the best voltage / current combination to replicate the need for a 440 to 500 watt peak array output with the SB50?  

Given the relative cost of the panels versus the controller, the manufacturer may likely decide to switch the controllers, but it is not as easy as it sounds.  If either the Outback or Midnite controllers are used, they will not fit into the small space the cabinet allowed for the SB50.  But I will deal with that another way.  (We will just build an all new cabinet here in Senegal).

So – any ideas or thoughts I have missed are welcome!!

Thanks so much for all of the great feedback.  I think, like most of us, every day is a learning experience, even if we think we have done this 100 times before. 

Take care,

Walt

From: Rick Cullen - Blue Sky Energy, Inc. [mailto:rick at blueskyenergyinc.com] 
Sent: Monday, June 29, 2009 10:14 AM
To: wratterman at sunenergypower.com; 'RE-wrenches'
Subject: RE: [RE-wrenches] Solar Boost Controller in Senegal

Hello Everyone,

The SB50's maximum input voltage spec it 57VDC. This should be considered an absolute maximum above which the controller will be damaged in a manner not covered by warranty. Our recommendation is to not apply a total Voc at STC of more than 57V/1.25= 45.6V. There are transient voltage protection diodes on both battery and PV inputs on ALL Solar Boost charge controllers. These are not "tell tail" indicators but real protection devices designed/selected to protect down stream electronics from transient voltage damage resulting from ESD, lightning, etc. On the PV side of the SB50 the protection diodes will begin to clip at about 58-60V. They can eat a 1 millisecond 3000W transient without damage, but will burn up if they receive more than about 10W continuously. These two diodes are located right behind the PV terminals.

In the application described below I would expect the SB50 to be damaged. What typically happens with excess over voltage is the diodes fail short, and then clamp PV voltage low and protect the down stream electronics. If PV current is sufficiently high the diodes will burn open and the SB50 may continue to operate since down stream devices have somewhat higher voltage withstand capability, or it may suffer catastrophic damage.

Why these systems continue to operate must be due to actual Voc not getting high enough long enough to cause catastrophic damage. If the controllers were to not switch to Float (unloading the PV's), the brief Voc sample as part of MPPT may not have burned up the diodes and they are successfully eating the excess voltage transients which would seem to occur during the Voc sample. It may also be that the modules are so hot that their actual Voc & Vmp are low enough that when PV voltage is clamped to 60V by the SB50's protection diodes insufficient power is delivered at 60V to burn up the diodes...

Needless to say, this is a situation that need to be corrected. Technical Bulletin #100214 available on our web site describes proper voltage, current and power sizing for all Solar Boost charge controllers.

Regards, 
Richard A. Cullen 
Blue Sky Energy, Inc. 
760-597-1642 x102 
fax 760-597-1731 
 <mailto:rick at blueskyenergyinc.com> rick at blueskyenergyinc.com 
 <http://www.blueskyenergyinc.com/> www.blueskyenergyinc.com 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Walt Ratterman
Sent: Friday, June 26, 2009 3:22 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Solar Boost Controller in Senegal

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

wratterman at SunEPI.org   ▪   www.SunEPI.org <http://www.sunepi.org/> 

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