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question</title></head><body>
<div>Hey Bill and All,</div>
<div><br></div>
<div>Scratch that last question. I do know that MPPT controllers
are just going to reference battery voltage which will be pretty rock
solid and the MPPTs act fast - and so no hysteresis - I do wonder
though if there is a slight interaction or any chance of cycling.
I've been doing grid-tie too long - I'm losing my feel for
off-grid!</div>
<div><br></div>
<div>One question though - do manufacturer's release efficiency curves
for controllers? Let's say you have two Sanyo HIT 200s
(55.8 Vmp, 68.7 Voc) modules feeding a TriStar MPPT 45Amp into a 12 or
24 Volt Battery. The Tristar can handle 150 Voc - so is it
better to wire the modules in parallel or series? In other
words, is the controller more efficient converting 112 Vmp into 12 or
24 volts nominal or converting 56 Vmp at twice the amperage?</div>
<div><br></div>
<div>Best,</div>
<div><br></div>
<div>Jeff Clearwater</div>
<div>Village Power Design</div>
<div><br></div>
<div><br></div>
<div><br></div>
<div><br></div>
<blockquote type="cite" cite>Hey Bill,</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Two MPPT charge controls from different
modules in parallel to one battery pack - do they settle into one
voltage or do they sweep each other and constantly search? Do
they need to be identical controllers - what if they have different
algorithms?</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Jeff C.</blockquote>
<blockquote type="cite" cite>Village Power Design</blockquote>
<blockquote type="cite" cite><br></blockquote>
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<blockquote type="cite" cite><br>
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<blockquote type="cite" cite>Allan,</blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite>My beard is pretty gray these days, so
I'll bite. Without getting deep into exactly where these modules have
degraded to, I think your idea of adding the extra MSX77s is a good
one, although it might be a little overkill. Since the customer has
them, I would use them.</blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite>The other issue is that newer modules may
have a better temperature coefficient of voltage than the old Solarex
modules. The SolarWorld 175 will not lose as much voltage at the same
temperature. If you can split like modules on their own MPP charge
controllers, that would solve your problem-Not sure that is an option
for you.</blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite>Bill.</blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite><b>From:</b>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org]<b> On Behalf Of</b>
Allan Sindelar<br>
<b>Sent:</b> Wednesday, April 28, 2010 12:20 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Solarex module match
question</blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite>Calling the old-timer off-grid 12V
graybeard Wrenches...<br>
I am reposting this to the list in hopes of shakin' up a response, as
nobody tried to answer my request for help.<br>
<br>
In short: in theory, if you force an array to operate at a voltage
above its MPP, current drops off significantly on the string I/V
curve. In this case, if I add a fixed array of substantially larger
current and<i> slightly</i> higher Vmp (due to both what's currently
available having a slightly higher module Vmp, and 14 years of module
degradation), will the new array force the old array to operate at too
high a Vmp and thus substantially reduce its contribution to overall
PV input?<br>
<br>
And a related question: the customer reminded me that he still had two
additional matching Solarex MSX77 modules stored away.<i> If</i> I
could mount them on the existing 12-module Wattsun tracker, and<i>
if</i> I wired them as two strings of seven modules (84Vnom), would
that solve this issue, by boosting string voltage enough to maintain
current closer to Isc?<br>
<br>
I'd appreciate any good advice.<br>
Allan<br>
<br>
Original post:<br>
<br>
Wrenches,<br>
We have an off-grid customer with a system that has been growing since
1996; we have cared for it intermittently since 2000.<br>
<br>
The customer has two tracked arrays currently. One has ten Astropower
AP120s for 1200 nominal watts, but that's not the topic today; it'll
come up in 5 years or so. The other older array is 12 Solarex MSX77s,
polycrystalline with 16.9Vmp, 21Voc (when new). The rest of the system
is a SW4024, two Solar Boost 50s (one is currently failing) and two
strings of 800 a/hr Rolls cells.<br>
<br>
The client wants to add 1,200 to 2,000 watts of additional PV. The
problem is that we have two sets of existing buried conductors between
arrays and BOS and don't want to dig up for more. Also, he wants to
upgrade charge controllers, and has had past failures of the SW
inverter - in fact, he keeps a spare put away for the next
failure.</blockquote>
<blockquote type="cite" cite><br>
I have suggested that by upgrading the inverter to a modern pure-sine
48V unit, we can accomplish the array upgrade using the existing input
conductors. I can rewire the Solarexes from 6 24Vnom strings to two
72V strings and have plenty of copper to add more array without
voltage drop issues. (The AP120s can be brought in as 2 60V strings to
a separate FM60 or T80 or similar). This also lets me work with
existing 60 or 80A charge controllers, which I can't do at 24V.<br>
<br>
The customer likes this approach, so here's my question: What modules
would you suggest as having good compatibility with the existing
Solarexes? I would assume that any polycrystalline 72-cell module
would be fairly close but not ideal. I would especially expect the
lower-rated ones within a particular size category to be better
choices, as they would have lower Vmp to more closely match the
existing. But would similar monocrystalline be close enough? Too high
a voltage in the dominant (new) array drags the voltage above MPP,
which reduces output considerably on the Solarexes. Also, I can't find
the temperature coefficient for the old modules, and I suspect that
degradation over 14 years has lowered the MPP of them
anyway.</blockquote>
<blockquote type="cite" cite><br>
I think of using 12 Kyocera KD135s Mitsubishi 125s or 130s;
Solarworld's discontinued SW175 (mono), Sharp 123s, or possibly some
Suntech monos. But I'm certainly open to advice and suggestions
here.<br>
<br>
Also, while the existing arrays are on Wattsun DA trackers (customer's
choice), the new array will be pole-top. I'm not too worried about
tracking/fixed mismatch, as voltage quickly matches even with
non-optimal orientation. But I'll take advice here too.<br>
<br>
<br>
Thanks.<br>
Allan</blockquote>
<blockquote type="cite" cite>--<br>
</blockquote>
<blockquote type="cite" cite><b>Allan Sindelar</b><br>
<a
href="mailto:Allan@positiveenergysolar.com"><u
>Allan@positiveenergysolar.com</u></a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a
href="http://www.positiveenergysolar.com/"><u
>www.positiveenergysolar.com</u></a></blockquote>
<blockquote type="cite" cite><br>
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<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><tt>--</tt></blockquote>
<blockquote type="cite" cite>~~~~~~~~~~~~~~~~~~~<br>
Jeff Clearwater Lernould<br>
Village Power Design<br>
<br>
Solar Design Consultation for the Commercial Sector<br>
http://www.villagepower.com<br>
gosolar@villagepower.com<br>
<br>
NABCEP Certified Solar PV Installer <br>
http://www.nabcep.org/<br>
<br>
Voice: 831-427-2799<br>
Fax: 413-825-0703<br>
245 Dufour St<br>
Santa Cruz, CA 95060<br>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~</blockquote>
<blockquote type="cite" cite><br>
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<div><br></div>
<div><br></div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div>~~~~~~~~~~~~~~~~~~~<br>
Jeff Clearwater Lernould<br>
Village Power Design<br>
<br>
Solar Design Consultation for the Commercial Sector<br>
http://www.villagepower.com<br>
gosolar@villagepower.com<br>
<br>
NABCEP Certified Solar PV Installer <br>
http://www.nabcep.org/<br>
<br>
Voice: 831-427-2799<br>
Fax: 413-825-0703<br>
245 Dufour St<br>
Santa Cruz, CA 95060<br>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~</div>
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