[RE-wrenches] Solar Boost Controller in Senegal

[Walt Ratterman]

Hello,

 

Why do you say that AGM batteries are a better choice?

 

I have been reading about the differences, and all I see (comparing DEKA Gel versus DEKA AGM is that the cycle life of the AGM (at 50% DOD) is 500 cycles versus 1000 cycles for the Gel.

 

The AGM seems to have better resistance to freezing, but of course that is not a concern here.

 

What are the benefits of AGM that I am missing here?  (This could be important, because I was going to jump all over the fabricator for shipping AGM when the literature quotes GEL, and I was thinking GEL would have been a better choice.  Maybe they were trying to right think, but I would need to be educated more here…

 

Thanks!!

 

Walt

 

From: Wind-sun.com [mailto:windsun at wind-sun.com] 
Sent: Tuesday, June 30, 2009 7:30 AM
To: wratterman at sunenergypower.com; RE-wrenches
Subject: Re: [RE-wrenches] Solar Boost Controller in Senegal

 

The AGM batteries are probably a better choice than gelled, but the fact that some are down to 5 volts is the real problem.

 

A typical AGM will lose around 1-2% charge per month at 25 degrees C. If they are at 5 volts, that indicates that they either sat around for over a year unused and uncharged, and possibly in a very high temperature environment. The 2nd possibility is that there is some kind of constant load on them, even when the units are not turned on - which would be poor design.

 

The Midnite controller is not available yet, so your only real choices with the panels you have are the Outback FM60 or the Xantrex XW-SCC - both of them are in the $600 range.

 

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Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
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----- Original Message ----- 

From: Walt Ratterman <mailto:wratterman at sunenergypower.com>  

To: 'Rick <mailto:rick at blueskyenergyinc.com>  Cullen - Blue Sky Energy, Inc.' ; 'RE-wrenches' <mailto:re-wrenches at lists.re-wrenches.org>  

Sent: Tuesday, June 30, 2009 1:26 AM

Subject: Re: [RE-wrenches] Solar Boost Controller in Senegal

 

Hello all,

 

 

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

 

 



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