[RE-wrenches] Fwd: Charge control question

[Jeff Irish]

Blue Sky has 15 and 30 amp, 12 and 24 volt charge controllers that are each independently MPPT that can be networked to their controller to communicate and charge a single large battery bank.
Jeff Irish
Hudson Solar

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
Sent: Thursday, October 11, 2012 1:04 PM
To: RE-wrenches
Subject: [RE-wrenches] Fwd: Charge control question

Wrenches,
I'm posting this for Carl Bickford, prof emeritus of the renewable energy training program at San Juan College in Farmington, New Mexico. I'll forward your responses to him.
I have a very interesting and talented friend who is rebuilding a blue-water sailboat for a round-the-world trip. He is well versed in solar and is trying to use a relatively large array to charge a big battery bank that will be used for propulsion as well as general electrical. The propulsion system will be backed up with a propane generator he is building himself out of a Toyota truck engine.
As you can imagine, there is no place on a sailboat where shading isn't a problem. He and I were wondering if there were products out there that could MPPT either individual modules, or small groups of them for 12 V battery charging. I have seen such things for the inputs of grid-tied inverters, but nothing yet for off-grid. The other choice is to go with many small MPPT charge controllers like the ones from Solar Converters.
Any advice you can offer?
Take care,
Carl

Carl Bickford
Professor of Engineering and Renewable Energy
San Juan College
4601 College Blvd.
Farmington, NM 87402
505-566-3503
bickfordc at sanjuancollege.edu<mailto:bickfordc at sanjuancollege.edu>

I offered the suggestion below. Certainly open to other and better ideas.
Allan

I have not encountered this situation, so I have no advice from experience. At 12V, it's hardly an issue as it is with high voltage parallel strings, where a few shaded cells can cause a whole string to drop out of the inverter's MPPT. At most, a shaded cell weakens the output of that module. And since it's charging batteries, there's a greater amount of head room.

I would suggest looking into Blue Sky Energy's "i" series - smaller MPPT controllers that can be networked. We seldom use them, as our residential applications are different. But you could put a controller on a group of modules and network several together. One advantage, I think (you'd want to check this) is that Blue Sky's MPPT algorithm is analog, unlike Outback and others: on the old Solar Boost series, the MPPT boost was set with a trim pot to a particular voltage above battery voltage; the target is to set it to where the boost was greatest. You could set this boost slightly lower than peak, and output just a little below MPP. That way the overall output would be minimally reduced, and a modest amount of shading would not cause the shaded module to drop below collective MPP as readily.

Allan Sindelar
Allan at positiveenergysolar.com<mailto:Allan at positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com<http://www.positiveenergysolar.com/>




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