odd values call for odd systems? 8V 190W solar panel issue

lookskijuolker

Hi there,

I got a hold of a 24V 190W monocristaline solar panel.
For reasons not worth stating, I have no use for a 24V panel. I could use it with a wide input voltage range controller, to charge a 12V or less battery bank. This means i'm wasting too much efficiency and there's a more interesting option: Opening up the back box of the panel, I can easily find the panel is built with an arrangement of solar cells in 3 groups of 8V 190W connected in series. It's too tempting to "transform" the panel into two different panels: one 12V 190W and another 8V 190W. I'm happy to take advantage of the impecable build of the panel, with high quality glass, framing and insolation from the elements. The panel is 5 years old and looks/behaves as new. Splitting it into two, means basic wiring work, disconnecting one of the 8V groups from the rest (removing the corresponding connection in the box, and adding two extra output wires through the built in box, which is already prepared to accommodate them. Integrity wise, the panel would be pristine as it has always been.
It would also be perfect to prepare two independent systems, which by experience is the way to go when managing power resources living off-grid. I intend to use the 12V panel for my laptop (with 100 to 200Ah bank), and the 8V panel to provide power for the dim/presence/signaling lighting around the house, access paths and roads.

All this explanatory jargon comes down to: How can I take advantage of this "spare" 8V 190W panel? What kind/size of battery bank should I use with it? What kind of charge controller can I use? 8V 190W has two problems for a low-to-medium knowledge person like me: odd voltage to find equipment, odd-and-very high power output for such a low Voltage rating...

Ideas?

Thanks in advance!

706jim

I suppose you could use it to charge two lithium ion cells which are around 3.7 volts nominal.
But with the present low prices of solar panels I'd be tempted to leave it alone and maybe swap it for a 12 volt panel.

lookskijuolker

Hey Jim,
Thanks for the quick reply and suggestion.
Isn't the power rating of this "leftover" 8V panel fry up the Li ion cells? If not, what kind of charging control would you suggest?

littleharbor2

You need to start at square one. You know nothing about solar panels or electronics in general. If it were possible to magically split a solar panel, (it's not), You aren't going to get a 12 volt 190 watt panel and an 8 volt 190 watt panel. The only thing in common would be the amperage rating of the panel because every cell puts out THAT amperage at about .5 volts.

mcgivor

Splitting a panels output is not the way to go, using a MPPT controller is the best solution, though they are more expensive than PWM, the advantage being it is designed to use a 24V nominal panel with a 12V nominal system. There are some small MPPT controllers available at modest prices, but be aware some which make the claim to be such are not true MPPT, the really cheap Chinese ones commonly found on Amazon, Ebay etc. 

NANOcontrol

I've been buying these 72V 15A converters for about $5 and they work great.  These are my absolute favorite buck converter to modify.  Sure they won't supply exactly that power, but they are cheap.  Voltage is limlted to 12V exactly, a downside that is easily corrected.  They work fine at 30V or more.  For less than a buck they can be modified to operate at power point.  If you have sufficient panel power, they will work like a MPPT.

lookskijuolker

Hey little harbor,
Honest mistake. I don't think square one would be necessary.
Anyway, the point of splitting the panel would be to use the 12V ninety something W and the 8V sixty something W in the context of managing resources through independent systems. I'm looking for interesting ideas to use the odd value 8V side. Anything you would like to share? 
Thanks in advance, Little Oh Be One Harbor. 

littleharbor2

How about a big solar powered whirly-gig? Here's a fun solar powered one for the bathroom window.