Hilton....there are a couple ways to approach this.....There are some string inverters with multiple MPPT inputs....each different slope of roof would be installed into its own input.....the other way is to use micro inverters or other individual module optimizers....in which case you are completely free from mismatched orientation and slope constraints.....<br>
If you are looking to use a single MPPT channel string inverter you may consider splitting the arrays and having two single string inverters one for each tilt angle....That said the tilt angle difference feeding the same inverter does not have as big of a negative impact as if the sub arrays are facing different directions....<br>
good luck,<br>Kirpal Khalsa<br><br><div class="gmail_quote">On Wed, Apr 4, 2012 at 9:14 AM, Hilton Dier III <span dir="ltr"><<a href="mailto:hiltondier@gmail.com">hiltondier@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<font face="Times New Roman, Times, serif">Wrenches,<br>
<br>
I am talking with a potential client about a roof mounted PV
array. The client has a reasonably large south facing roof, but it
is broken up by a large (18' W x 16' H) shed dormer. The roof is
10:12 and the dormer is </font>6:12. I designed a layout that
gave the dormer some room to avoid shading. The client was
disappointed by how much wattage I could get on his roof. I pointed
out that installing modules in the shade of the dormer was a bad
idea.<br>
<br>
<font face="Times New Roman, Times, serif">He is also talking to
another installer. </font>The other installer proposed installing
part of the array on the 10:12 roof and part on the 6:12 dormer. The
client had already asked me about that and I gave him a rudimentary
explanation of maximum power point tracking and the inefficiency of
such an arrangement. He asked them about that and their guy said "No
big deal." He is still considering the two-angle scenario.<br>
<br>
So, how much efficiency will he lose by going with two angles? It
seems like the ultimate MPPT design error to me, but I don't have a
number for him to make my case. I suppose it all comes down to cents
per delivered kWh in the end, but two different roof angles seems
the the wrong way to go. I'd like to be able to give him a
definitive idea of what he would be sacrificing with that scenario.<br>
<br>
Side note: The other installer is using the new Sunpower E20
modules. They seem to be available only from the manufacturer.
Anybody have a source? Has anybody used them yet? Do they live up to
the hype?<br>
<br>
Many thanks,<br>
<br>
Hilton<span class="HOEnZb"><font color="#888888"><br>
<pre cols="72">--
Hilton Dier III
Renewable Energy Design
Partner, Solar Gain LLC
453 East Hill Rd.
Middlesex, VT 05602
</pre>
</font></span></div>
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