SPAM: Re: UI w/SB50 controllers , was C40's and SW's [RE-wrenches]

[Kirk Herander, VSE]

Bill,

Yes, I agree climate ie. module operating temps make a big difference in
performance. All I really know from personal experience is that MPPT is
worth the investment in my cold climate with the modules I primarily use,
Astropower, Siemens, and Kyocera.

Kirk
----- Original Message -----
From: "Bill Brooks" <billb at endecon.com>
To: <RE-wrenches at topica.com>
Sent: Tuesday, February 04, 2003 4:51 PM
Subject: RE: SPAM: Re: UI w/SB50 controllers , was C40's and SW's
[RE-wrenches]


> Kirk and Graham,
>
> I would have to disagree with Kirk on the flat statement to get rid of the
> C-40. It has proved to be the most reliable PV charge controller to date
and
> the benefits are marginal at best for the SB50. Only in very cold climates
> with high irradiance does the SB50 clearly win. For California and other
> mild climates, I would be willing to bet that the SB50 is the same or
worse.
> Heresy, I know--but show me some good ANNUAL data to prove otherwise.
Until
> I see it I'm going to stay with the C-40.
>
> Max Power Tracking is seldom perfect. I also have no data to say that the
> SB50 does it well. Until I see an official test I will reserve judgement
and
> remain sceptical--no personal vendeta against RV Products--just 15 years
of
> Max Power Tracking experience that says that many don't work very well.
They
> almost always have errors on the high voltage side which is tremendously
> unforgiving in a PV system. My fixed-voltage system consistently operates
> from a worst case of about 8% lower power up to spot on max power point.
It
> makes a lot of difference what kind of array you are running and how high
> the fill factor is. Many modules are running fill factors in the low 60%
> range, so a fixed voltage system can actually outperform a max power
tracker
> that is loosing 5% in conversion efficiency. Temperature compensation is
> absolutely critical to all battery-based systems--particularly with AGM
> batteries.
>
> Moral of the story--don't jump to conclusions--it all depends. MPT
> controllers make sense: (1) if it works!!!, (2)On higher fill factor
arrays,
> and (3) On stand-alone applications (not floated). I can't be dogmatic in
> either direction--several factors must be considered.
>
> Bill.
>
> -----Original Message-----
> From: Kirk Herander, VSE [mailto:kirk at vtsolar.com]
> Sent: Tuesday, February 04, 2003 12:28 PM
> To: RE-wrenches at topica.com
> Subject: SPAM: Re: UI w/SB50 controllers , was C40's and SW's
> [RE-wrenches]
>
>
> I have a dual SW5548 system with 4.8 kw array, divided into 4 sub-arrays,
> each controlled by a Solar Boost 50 MPPT controller, utility-intertied  in
> combo w/ a sealed AGM battery bank. I have set both bulk & (float)
voltages
> on the inverters to the batteries recommended float voltage of roughly
52.5
> vdc. I trust that this voltage is acceptable to keep the batteries well
> maintained, and I want to maximize the delta between panel MPPT voltage
and
> battery voltage, so there is more voltage to convert to current and
> therefore more power to send to the grid.
>
> In the middle of a cool and sunny Vermont day last fall, I measured an
> efficiency of 91% when comparing DC PV power into the Solar Boosts vs. AC
> power sent to the grid. The gains to the grid using MPPT vs. the C40 are
> impressive, so I would suggest getting rid of the C40 altogether. It is
not
> appropriate for a battery-based UI system.
>
> Kirk

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