There are two downside to the higher voltage consideration. Do you want the increased electrical safety hazard of having 111V DC running around in a marine environment and you lose some of your partial shading diversity. Not sure if the controller doesn't have to do a little more work in the stepdown or not either. I could not find any eff. data on the FM80 as a function of voltages. But intuatively I would think keeping your input voltage closer to your output would be more eff.
Well, this goes against my usual way of doing things, but I am feeling kinda good about the Outback FlexMax 80 controller, and I am leaning toward getting it. The max input voltage is listed as 150v and startup 145v. I see that wiring more panels in series extends the productive hours for solar generation, so I am rethinking my original idea of pairs in series. Most of these full size panels have a VOC of 37v and so two in series gives a voltage of 74v. Doubling this, with 4 in series, would be 148v, too high. But a series of 3 panels would be 111VOC, which seems like a pretty good compromise.
Since the panels will be mounted on an unobstructed canopy, I am not overly concerned with shading. In my current slip, in the morning there is shade because we have covered piers, but I will probably move out to the head of the pier where there is never any shade, once the entire system is in place. Nothing on the boat will extend above the level of the canopy except a very small masthead light, a VHF antenna, and a MF/HF antenna, and I might just use a wire for that. So I feel pretty good about having a single charge controller. If I still had mast and sails, I would most certainly go with separate controllers. The plan is to go with large panels in the 300w range, and initially buy just the first series of three, unless I win the lottery or something. Then later, purchase the rest. A whole pallet is just totally out of my reach, like forever. I really need that first series, though, before hurricane season next year.
So, does three in series sound like a better plan than two in series? And your opinions, please, regarding maybe initially going with three 100w panels? I know, real engineers don't worry about what the startup cost of anything, right? But I cant just poop money and there are no rich spinster aunts just waiting to bequeath a fortune to me. Saving money is well and good but only if you make enough to save in a lifetime. I have no choice but to buy as I can afford.
I will point out that I have not even constructed the canopy, yet, so don't think that this is all going to happen this week or anything. My goal is to have some solar charging capability before next July and that it is capable of expansion into a 2kw system.
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Posted by: Carter Quillen <twowheelinguy@yahoo.com>
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