[RE-wrenches] PV excellent battery charger

[R Ray Walters]

I understand and use MPPT in most of my systems. I agree, its a great idea. 
My point is whether you have more modules and no MPPT, or fewer modules and MPPT is the same from the battery's point of view.
We were comparing solar vs. traditional AC battery chargers. (MPPT doesn't apply to AC chargers)
As well, we could compare PFC (power factor corrected) AC chargers to traditional chargers.
Manzanita Micro makes some excellent grid chargers for electric vehicles, that have 3 stage tapered charging ,temp comp, and with PFC, get about twice the charging current
for the same power input. They can be used with Lithium Ion batteries, but are also very spendy.

R. Walters
ray at solarray.com
Solar Engineer




On Mar 25, 2010, at 8:21 PM, Starlight Solar Power Systems wrote:

> Hi Ray and Drake,
> 
> Ray, I'm not sure I follow your statement that MPPT does not do much for a
> battery. With today's higher voltage modules, there can be a dramatic
> improvement in the amount of power reaching the battery by using MPPT charge
> circuits. Simply put, MPPT circuits convert all the available PV power
> (remember power is expressed as watts or the ability to do work) into
> current and voltage. The higher the differential between battery and array
> voltage, the more current that can be produced by MPPT circuits. A non-MPPT
> circuit simply connects the battery to the PV array thus pulling down the
> operating voltage and wasting power.
> 
> Consider a single Evergreen 205 watt module. The Vmp is 18.2 volts and Imp
> is 11.4 amps. If you use a non-mppt controller like the old C-40, the
> operating voltage of the module will be just above battery voltage. If the
> battery is at 12.4 volts, you will only capture about 145 watts of the
> available power. The module can do 205 watts of work so you are wasting 30%
> of the power. As battery voltage rises and PV modules heat up, the
> difference will decrease but there will most always be a benefit with well
> designed MPPT circuits. So, Drake, you are wise to use MPPT if there is
> sufficient differential voltage. Since it is a percentage of improvement,
> the larger the PV array, the greater the benefit.
> 
> A PWM controller is a method of controlling voltage, not pulsing off
> sulfation. When a battery reaches 100% SoC then the lead sulphate has been
> recombined into lead, lead dioxide and sulphuric acid. There are pulsing
> circuits available but the PWM in a charge controller does not perform that
> function.
> 
> So, why is PV power an excellent battery charger? Because it uses Starlight
> power! But you knew that.
> 
> Larry Crutcher
> Starlight Solar Power Systems
> (928) 342-9103
> 
> Mailing Address:
> 11881 S. Fortuna Road, #210
> Yuma, AZ 85367
> 
> Retail Store & Shipping Address:
> 2998 Shari Ave.
> Yuma, Az 85365
> 
> 
> ----- Original Message ----- 
> From: "R Ray Walters" <ray at solarray.com>
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Sent: Wednesday, March 24, 2010 10:51 PM
> Subject: Re: [RE-wrenches] PV excellent battery charger
> 
> 
>> MPPT doesn't really do that much for the battery, it just makes the PV
> modules more effective.
>> The real magic is:
>> 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.
>> 
>> R. Walters
>> ray at solarray.com
>> Solar Engineer
>> 
>> 
>> 
>> 
>> On Mar 24, 2010, at 7:04 PM, drake.chamberlin at redwoodalliance.org wrote:
>> 
>>> 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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