[RE-wrenches] PV excellent battery charger

[Dave Click]

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."

 > My understanding is that the voltage, in excess of battery voltage, from
 > the array, represents energy that is dissipated as heat in the 
batteries.

Feel free to correct me- the battery would present a load to the module 
and then the module would be producing at some point on the I-V curve. 
There's no real "excess voltage" lost here; by dropping the operating 
voltage of the module you're just not producing your max power out of 
the module. The power's never produced- it's not that it's lost as heat 
anywhere.

I think we can agree that "excellent battery chargers" is a bit of an 
exaggeration unless it's "why PV systems with the magic that Ray 
mentioned** make excellent battery chargers."

**A) the 3 stage charging (compared to traditional single stage AC chargers)
B) Temperature compensation
C) PWM that helps pulse off sulfation
D) Slower charge rates let batteries charge more fully without damage 
from overheating.


-------- Original Message --------
Subject: [RE-wrenches] PV excellent battery charger
From: drake.chamberlin at redwoodalliance.org
To: RE-wrenches at webmail8.g.dreamhost.com, 
<RE-wrenches at lists.re-wrenches.org>@webmail8.g.dreamhost.com
Date: 2010/3/24 21:04

> Can anyone tell me why PV is considered an excellent battery charger? I
> think it is, only after the addition of a MPPT charge control.  Otherwise,
> the battery drags the PV voltage below Vmp.
>
> One of the NABCEP objectives for the entry level class is to explain why
> PV modules make excellent battery chargers and show this through the IV
> curve.
>
> Thank you,
>
> Drake
>
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