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Allan:<br><br>
Welcome to the world of PV design. This is why customers need
experienced designers and installers. The out-of-work electrician
with new magnetic door signs that say "and Solar" will most
likely be unable to finesse this design. A good portion of my work
is following these types around and repairing their designs and
installations.<br><br>
It's all about compromise and working within the constraints you are
given: If you must have strings of three, you either have to
install 15 or 18 modules. 15 does not divide evenly between two
racks. If you must have 15 modules, then divide the racks into
racks of 6 and 9 (DPW can likely accommodate this).<br><br>
If you can have 18, then two racks of 9. Continue the decision
process until you have a design that works and the client will
approve.<br><br>
Sure we'd all like to be able to purchase one system that does
everything: equipment that communicates between chassis and the
outside world, has umpteen hundreds of volts PV input, accepts a wide
range of generator power and start schemes, has multiple AC inputs, can
grid tie, can AC couple, is efficient, is reliable and is inexpensive,
but we have to work with what is available.<br><br>
Good luck,<br><br>
William<br><br>
<br><br>
At 10:41 AM 12/16/2012, you wrote:<br>
<blockquote type=cite class=cite cite>Wrenches,<br>
Please tell me if I'm overlooking something, in what appears to be a
design weakness:<br><br>
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. <br><br>
The base Midnite Classic 150 will safely operate to 198 VDC in this
application, but it won't communicate with the Mate3.<br><br>
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. <br><br>
Any solutions would be welcome.<br>
Thank you,<br>
Allan</blockquote></body>
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