[RE-wrenches] PV excellent battery charger

[Drake Chamberlin]

Hi Dave,

At 10:44 AM 3/26/2010, you wrote:
>Is the answer here (at least the one that NABCEP intends) just that 
>the VMP of a "12V module" is higher than the voltage of a 12V 
>battery? With the higher voltage it will charge the battery with its 
>corresponding current based on the I-V curve. The objective reads 
>"Explain why PV modules make excellent battery chargers based on 
>their I-V characteristics


This may be the answer they want.  The "Objectives" deals with the 5 
key points on the IV curve, Vmp, Imp, Voc, Isc and Pmp.  From a study 
of the curve, the obvious "excellent" load is one that takes power 
from Pmp, which direct battery charging doesn't do.  When I draw the 
curve, the Vmp of the module is above the resulting voltage on the curve.

What you say about the power loss not being released as heat in the 
batteries,  just not produced, makes sense to me.  I've never seen 
any real documentation about what happens to the power not gained in 
a non MPPT battery charging system.

We can definitely agree that "excellent battery charger" is an exaggeration.

Thanks,

Drake


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM  Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648  
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