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Old 23-09-2014, 17:34   #1
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Options for adding extra solar to my system

I'm currently set up with two 80 watt solar panels and really need to add another 40-60 watts to my system (the 160W normally keeps up with my needs, but doesn't generate enough extra to top up the batteries after a couple of cloudy days). I'm trying to decide the best (most cost efficient) way to do this. Right now the 2 12V panels are mounted on a stern arch of my 27' boat, running through an MPPT charge controller, so I have the option of wiring them in series or parallel. It seems like my options are:

1) replace the current panels wither either one 200-240 watt panel or two 100-120 watt panels. I don't like the idea of a single panel (single point of failure). Cost of the new panels would be under $250 and I could probably get $125 for the current panels so the cost is reasonable, but I'd have to rework the mounts to hold the larger panels.

2) add another 40-60 watt panel to the mix. Probably the cheapest option, but it would mean running the panels in parallel instead of in series. Because of the geometry of my mounting arch it would be easist to use a long narrow panel, but most of the ones this shape that I'm finding are thin film, not chrystalline, with a Voc around 16V, vs. the 20 Voc of my current panels. I'm not sure if this is an issue or not.

Any suggestions?
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Old 23-09-2014, 18:01   #2
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Re: Options for adding extra solar to my system

Add some panels until you run out of your MPPT Amps limit?

Seems best bang to me.

See if angling the panels might work in your case. That's easily extra 25 to 50% daily.

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Old 25-09-2014, 18:47   #3
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Re: Options for adding extra solar to my system

I guess I wasn't clear. I don't have enough room on my arch to add another 80 watt panel, nor do I have the money to upgrade the arch to make the panels tiltable. I'm a member of the cheapass cruising club, so hundreds of dollars to upgrade my arch isn't an option. I'm looking for a solution that will cost me $100 at most (less is better). So the question remains: Will adding a 40 watt thin film panel (with a Voc of 16V) actually add 40 watts to my system? Will replacing one of the 80 watt panels with a 120W panel (and then having to wire the panels in parallel instead of searies to the mppt) actually add 40 watts? Other creative solutions?
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Old 25-09-2014, 19:47   #4
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Re: Options for adding extra solar to my system

Quote:
Originally Posted by susswein View Post
I guess I wasn't clear. I don't have enough room on my arch to add another 80 watt panel, nor do I have the money to upgrade the arch to make the panels tiltable. I'm a member of the cheapass cruising club, so hundreds of dollars to upgrade my arch isn't an option. I'm looking for a solution that will cost me $100 at most (less is better). So the question remains: Will adding a 40 watt thin film panel (with a Voc of 16V) actually add 40 watts to my system? Will replacing one of the 80 watt panels with a 120W panel (and then having to wire the panels in parallel instead of searies to the mppt) actually add 40 watts? Other creative solutions?
If you are using the MPPT technology, you would be better off replacing one of the 80W panels than trying to patch in a panel with lower VOC.
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Old 25-09-2014, 19:53   #5
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Re: Options for adding extra solar to my system

Why not buy a portable/foldable panel normally used by campers? That way you can put it out when needed and where needed.
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Old 25-09-2014, 22:19   #6
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Re: Options for adding extra solar to my system

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If you are using the MPPT technology, you would be better off replacing one of the 80W panels than trying to patch in a panel with lower VOC.
I guess I don't understand (electrically) what the result is if I wire a 12V (nominal) 80 watt panel and a 12V 120 watt panel in series. The 80W panel supplies 4 amps at 20 Voc, while the 120 watt panel supplies 6 amps at 20 Voc. Is the result 4 amps at 40 Voc, or do I get some additional power from the single higher wattage panel?
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