Solar PWM vs MPPT
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Topic: Solar PWM vs MPPT
Posted By: CharlieM
Subject: Solar PWM vs MPPT
Date Posted: 01 Aug 2014 at 2:02pm
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Techntrek, Given that real estate and sunshine are limited for us, maybe even more than money for these small systems, what are your thoughts on PWM vs MPPT for 100-200 watt systems. I'm thinking we need to squeeze as much power as we can within those limits. Additional panels are not always practical. Also, has technology fixed the problem of a panel shutting down if one part of it is blocked from sun? ------------- Charlie Northern Colorado OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD |
Replies:
Posted By: techntrek
Date Posted: 01 Aug 2014 at 4:38pm
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I've always recommended MPPT on all systems. On these smaller ones since adding panels isn't possible, and on the larger ones since the additional gains are worth the cost. On small systems adding additional PV is the better choice dollar-wise (and stick with PWM), but again the goal is as many amps as possible which is why I say go with MPPT. Unfortunately PV panels do have shading issues. Even a small corner covered by a leaf can cut the output 50%, and not much more shading can cut it to 10%. ------------- Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ http://www.rpod-owners.com/forum_posts.asp?TID=1723 - Pod instruction manual 
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Posted By: CharlieM
Date Posted: 01 Aug 2014 at 5:02pm
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Doug, Kind of what I thought on MPPT. On the shading my understanding is that a shaded solar cell looks like an open diode, thereby shutting down all other cells in series. This would seem to argue for connecting two panels in parallel, not series. You'd have to increase the wire size to carry more current, but shading of one would not affect the second. However this might eliminate some charging from series connected panels in low morning or evening light. Damned if you do and damned if you don't. Yes? ------------- Charlie Northern Colorado OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD |
Posted By: techntrek
Date Posted: 01 Aug 2014 at 5:57pm
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Correct. You also tend to get better performance from MPPT with a higher input voltage, which requires wiring in series, so you need to balance that with the advantages of wiring two panels in parallel. ------------- Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ http://www.rpod-owners.com/forum_posts.asp?TID=1723 - Pod instruction manual
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