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Old 06-03-2010, 08:34   #1
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Mixing Different Brand and/or Size Panels

I currently have 2 Shell PowerMax Ultra 85-P 85 watt solar panels with a SunKeeper-12 Controller. I'm going to be replacing my 120/propane fridge with a 12V or a 12V/120, so I'm going to need to add a few more panels. I was thinking the simpliest thing to do is just get 2 more of the Shells, which could go on my bimini, upping me to 340 watts, and just connect them to the old panels.

Well, turns out Shell Solar has been sold and the panels I have are discontinued. If I go with a different brand, size, etc. are they going to need their own controller? If so, can I at least make a splice after the controller on both sets of panels, to have a single line going to the batteries, making the wiring and especially the run a little easier? Or do I have to have 2 completely separate lines running in?

When responding please pretend I'm an electronics idiot and a previous owner installed the panels I have.

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Old 06-03-2010, 10:48   #2
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Matching panel's voltage specs, or getting close to a match, is the key...

Grunzster,
1) Your current charge controller (a Morningstar SK-12), is only capable of handling a maximum panel current of 12 amps, and you're just about there now (two Shell 85-P panels should have a max current of 11 amps)....(and it is not spec'd to handle them in series either)
So, you must get a new (bigger) charge controller.....

So, since you'll need a new controller, I'd recommend an MPPT controller.....
The simple explanation of an MPPT controller is that it allows the panels to operate at their maximum power output (Max Power Point = MPP), and provide the maximum charge current to your batteries at their best charge voltage.....
Typically this can mean a 20% increase of actual battey charge current, vs. a standard charge controller (such as your current SK-12)......

My favorite is Blue Sky Energy Blue Sky Energy Inc. - Industry Leaders In Solar Boost Charge Controllers and Maximum Power Point Tracking (MPPT) .....but others have reported good results from others as well....



2) If you're adding more panels to your array, and wish to use a MPPT charge controller (a VERY good idea, in my opinion), then you should try to match the new panel's voltage specs (particularly their Max Power voltage spec) to your existing panel's specs...
(Which would be about 17.2 vdc, for their MPP)

Here's a link (with your Shell 85-P specs) that might be helpful....
Shell Solar 85-P, 85 Watt Solar Panel


Many current "12-volt" panels have MPP voltages of 17.2 to 17.9 volts, and should be close enough to work fairly well, if you cannot fit / find an exact match....


3) There's a lot more info on solar out there.....but I think this answers your question, so I'll not bother to add more that might confuse you....
However, if you wish to see my set-up, have a look here....
Solar Panels


Fair winds and sunny skies...

John
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Old 06-03-2010, 11:40   #3
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Originally Posted by ka4wja View Post
However, if you wish to see my set-up, have a look here....

Solar Panels
A nicely pitched article for those of us slightly electrickery challenged - thanks
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Old 19-03-2010, 10:10   #4
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Forget 85watts! Check this out. 2 of those will get me up to almost 400 watts, and they're 17.1 volts, pretty damn close to the Shells. Even better, Defender's warehouse sale is next week. I can order the panels and the fridge at the same time and save tons of $$$. Just need to find a controller now, I doubt the Go Power one is an MPPT, although it would handle all 4 panels.
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Old 19-03-2010, 10:53   #5
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I recently purchased a 120 watt panel on ebay. The company's name is Solar Cynergy.
The panel is good quality, puts out to spec. and it only cost $299.00 + $30.00 shipping.
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Old 21-03-2010, 13:57   #6
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WOW! Thanks!

Couldn't find them on ebay, but did find them here for the same price. 17.6V, so they should work, but at that price, for that size panel, I'm almost considering buying 4 of them and just selling the Shells with the Sunkeeper.
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Old 21-03-2010, 14:40   #7
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That's the one.
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Old 21-03-2010, 18:22   #8
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I have heard two pieces of advise here, and I like both:

1) go for similar voltage and stay with 12 V,
2) use any, connect in series, get a 24 > 12 Volt controller.

I like both attitudes.

Right, wrong?

barnie
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Old 26-03-2010, 23:39   #9
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Barnie;

I just spoke with a woman on the phone with this exact question today; I called over to altenergy.com (they were extremely helpful by the way; they have a lady dedicated just to boats). She said that a controller really needs to have the same types of panels behind it, but that going with PWM controllers (the less expensive kind) is fine. She said the MPPT controllers are better but really only if you have a lot of wattage and the same panels. When you start having less numbers of panels per controller and multiple controllers, you might as well save your money and use the PWM variety.

The setup I'm getting ready to order are 2x135's and 4x65's. I don't have my sheet of paper in front of me but I think I'm going with 2x20amp PWM controllers.
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Old 26-03-2010, 23:40   #10
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Originally Posted by grunzster View Post
WOW! Thanks!

Couldn't find them on ebay, but did find them here for the same price. 17.6V, so they should work, but at that price, for that size panel, I'm almost considering buying 4 of them and just selling the Shells with the Sunkeeper.
Great link; may have just saved me a bundle!
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