[RE-wrenches] Radian design limitation - am I missing something?

[Kent Osterberg]

Allen,

I agree with Kirpal's comments. In fact, because the 300-volt breakers 
take up so much extra space, I'd stay with the three-modules-in-series 
design even if using the Classic charge controller; unless the PV array 
was so far away that you need the extra voltage to reduce wiring losses. 
But, for the example you are talking about with four modules in series 
you would want a Classic 200 not the Classic 150 because the Classic 150 
would goes into non-operational hyper-Voc mode at 28°C (82°F), measured 
at the cell.

The fact that the FM charge controller will talk to the Mate has 
advantages: 1) Only one temperature sensor is needed, 2) Voltage 
adjustment for grid-tie mode, and 3) Synchronization of equalize, 
absorb, and float modes. Not one of these is a significant enough issue 
to merit choosing the FM, and suffering from it's lower efficiency and 
poor MPPT tracking, over the Midnite Classic or Morningstar TriStar MPPT 
charge controllers.

Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com


On 12/16/2012 10:51 AM, Kirpal Khalsa wrote:
> Allan...indeed this is a limitation....and yes i agree with you that a 
> higher voltage charge controller would be a welcome update to Outbacks 
> line up.....Looking at the DPW top of pole list, i would suggest to 
> you a design using 15 255 watt modules with the FM80 charge controller 
> which would both meet your total wattage requirements, would still 
> only  need one charge controller, as well as conform to the 3 module 
> multiplication requirement....additionally it would require less 
> foundation/excavation work, but would in fact be a honker of an 
> array....just an idea! Locally in your area I know Focused Energy has 
> a good price and availability of the US made SolarWorld 255's which we 
> use often...
> Good luck.
> Kirpal
>
> On Sun, Dec 16, 2012 at 10:41 AM, Allan Sindelar 
> <allan at positiveenergysolar.com <mailto:allan at positiveenergysolar.com>> 
> wrote:
>
>     Wrenches,
>     Please tell me if I'm overlooking something, in what appears to be
>     a design weakness:
>
>     I would like to use an Outback Radian system for a standard GTBB
>     system. In order to take full advantage of the system's
>     capabilities, I have to use all of Outback's main components; in
>     this case the FM60 or FM80 charge controller. The problem is that
>     the most common (and lower-cost) modules today are 60-cell,
>     meaning 20 Vnominal. Given the 150V DC hard maximum voltage limit
>     of the FM-series charge controller, in our cold climate I can only
>     use these 20V modules in 60 Vnominal series strings; that is, in
>     multiples of three modules. As the Radian is (wisely) offered in
>     48V only, pairs of modules would provide too low a voltage, and
>     series strings of four modules would exceed 150 Voc in cold weather.
>
>     The base Midnite Classic 150 will safely operate to 198 VDC in
>     this application, but it won't communicate with the Mate3.
>
>     Is this a fundamental design limitation in the Radian system,
>     suggesting that Outback is due for a controller upgrade, or am I
>     missing something obvious? It appears that arrays and racks have
>     to be sized in ~720-watt sets of three-module series strings,
>     which can be problematic in some designs. In the design in
>     question I would like to use 16 240W modules on two 8-module
>     pole-top racks (for seasonal adjustability); nothing in sets of
>     three meets the customer's output and aesthetic needs.
>
>     Any solutions would be welcome.
>     Thank you,
>     Allan
>     -- 
>     *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 <tel:505%20424-1112>*
>     _www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
>
>     *
>     *
>

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