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Topic: More solar from my wandering mind... (Read 3 times) previous topic - next topic
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More solar from my wandering mind...
Yahoo Message Number: 112308
For any interested, I have more 'musings' I have posted to the files, so in 'Improvements' I started a new folder called 'Solar Power Musings'. I moved my previous post there, and added a couple more. Comments appreciated.

Steve
2004 FL
2013 Honda Fit
Re: More solar from my wandering mind...
Reply #1 –
Yahoo Message Number: 112312
Steve,
 I belive your "Why more solar cells...doc" is right on and said in an easily understood way.  When I installed my 2 panels, I wired them separately to the controller so that I could experiment with running them in series as well as parallel.  Heck if 44 cells are better than 36, 88 must be a heck of a lot better than 44.  It made some sense to me, living in the Pacific NW with lots of overcast/drizzly days and more angle of sun rays, that 88 cells would get me to the needed voltage threshold more often or at least earlier in the day.  Truth is I haven't seen much difference between the two methods yet, but I must say I haven't really stressed the system yet either.  One reason for that result is that solar cell voltage output dosn't vary as much as one might expect based on amount of light.  Current output is the big change factor with more light.
 The only real advantage that I see for more cells (Voltage) for a given power rating of a panel is less loss in the cabling to the controller due to less current. (Not a Big deal for our 15 ft cable runs).
 Rich Gort - 2000 MB - Birch Bay, WA (About as far North as you can get in the contiguous U.S. so angle of the sun is pretty low)
Former 2000 MB- Now Bullet Crossfire 1800RB trailer pulled by a Chevy 2500HD
Re: More solar from my wandering mind...
Reply #2 –
Yahoo Message Number: 112314
Quote

Steve,
 I belive your "Why more solar cells...doc" is right on and said in an easily understood way.  When I installed my 2 panels, I wired them separately to the controller so that I could experiment with running them in series as well as parallel.
The one snag of running the panels in series is that if ANY PART of EITHER panel becomes shaded, the output current from both panels will fall to a very low value.  On the MB, at least, LD's placement of the panels often causes a shadow from the air conditioner to fall on the back panel during part of the day (this depends on what direction the coach faces.
 And yes, the panel's open circuit voltage rises very rapidly with just a little light.  A quick calculation says that the open circuit voltage of a 36 cell panel rated at 22V (open circuit) and 5A(short circuit)will rise to about 16V if there is sufficient light so that the panel will creates 0.01A of current. (For you tekies out there, the panel consists of 36 silicon diodes in series, each with a current source across it.)

Linley
Re: More solar from my wandering mind...
Reply #3 –
Yahoo Message Number: 112315
Quote
The only real advantage that I see for more cells (Voltage) for a given power rating of a panel is less loss in the cabling to the controller due to less current. (Not a Big deal for our 15 ft cable runs).
Thanks for the comments, Rich. One thing to consider is the effects of shading, even more of a problem when the sun angle is low. A shadow on one panel can nearly neutralize the series current. If the panels are in parallel, at least the other panel can supply full power. We do mostly off-season and winter camping, so that is an issue for us as well.

Steve
2004 FL
2013 Honda Fit
Re: More solar from my wandering mind...
Reply #4 –
Yahoo Message Number: 112316
On Sun, 2 May 2010, Linley wrote:

Quote
The one snag of running the panels in series is that if ANY PART of
EITHER panel becomes shaded, the output current from both panels will fall to a very low value.  On the MB, at least, LD's placement of the panels often causes a shadow from the air conditioner to fall on the back panel during part of the day (this depends on what direction the coach faces.

 Very true, Linley, which is why I wired a switch between the panels and the controller.  Up is Parallel, Center is Off and Down is Series.  That way I can have it whichever way I want, whenever I want it.  But like I said, so far I haven't seen much improvement in current to the battery (bottom line) either way, and you do need a controller that can handle the open circuit voltage of the arrays in series, so don't try this at home without the proper controller. For example, AM Solar says thier HPV-22B can only handle 30 V, much less than even two 36 cell panels in series.

Rich
Former 2000 MB- Now Bullet Crossfire 1800RB trailer pulled by a Chevy 2500HD