You have to check the manuacturer's specs for whatever panel you buy. The "max" open ciurcuit voltage should be specified or it could be listed for a specific test condition along with a graph for the output as a function of temperature. The thing to be weary of is that the "nominal" rated output is going to be less than "maximum" output under ideal conditions and your threshold voltages have to be sized accordingly. Fortunately, because the sun is alway moving, you are seldom in the sweet spot for long and the FM 80 can take it for a while. Before my reconfiguration I was routinely hitting the mid to upper 80s for brief periods, (less than an hour), in cold weather and nothing ever blew up.
If you're OK with working with higher voltages then I think the deciding factor for your working voltage should be the controller efficiency. There must be some information on where the sweet spots are. I don't know for sure but I would think the smaller the change in voltage, the better, ie: converting 67V to 48V would be more eff. than going from 111V to 48V. But maybe not, I guess it's a question for controller supplier. The differences are probably small anyway.
On Monday, August 29, 2016 4:45 PM, king_of_neworleans <no_reply@yahoogroups.com> wrote:
Yeah I am okay with having 111v between the array and the controller, I think. I am not concerned about resale and I would probably just strip the boat of useful bits and scrap the hull for the lead and bronze and stuff if I was moving up to a bigger hull. I was actually thinking recently of going with 96v on the propulsion bank. Changed my mind on that, but am okay with higher voltages in general. One hand rule and all that.
So lets say the temp got down to 40, or even 30. If you are a celsius kinda guy, that means a hair below the freezing point of fresh water. How high do you think the voltage could go, on a panel rated at 37VOC? I only have to keep them slightly below 50V. OTOH, I do think that 37vx2 for 74VOC would be acceptable, too. So I can only produce electricity from say 10:00 to say 4:00... that wouldn't be so bad. Don't get much charging with the sun that low, anyway. A temperature controlled relay on the 111v array would maybe be another option, though. A NO relay that closes at say 40°f or higher, maybe, or even 50°f. That way unless the temperature is above the safety temp, the controller would not get any input from the array. Or I could even automatically dump the power into a water heater or something.
A quick look around didn't show me any controllers rated for higher input voltages, so it looks like I will have to work with a limit of 150v.
I hear and appreciate your warning! I just want to consider it all carefully, because the voltage question is one that I want to decide once and for all, and not change my mind on, later. I dont want any regrets on down the line after spending hundreds of $ or even thousands, for my solar energy system.
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Posted by: Carter Quillen <twowheelinguy@yahoo.com>
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