All,
I bought a charge controller over the weekend - works with both 12v and 24v systems, mppt, and is rated to 400w in a 12v nominal voltage system.
I was told the MPPT controller works best above 36 volts panel voltage. I am getting mixed info on the top end - I think it is 100v open panel voltage and 75v under load, but I am not 100% sure on that. As it was described - the MPPT aspect works all the way through the range on the upper end, but on the low end it does not work well below 36 volts. The controller is said to work with down to 17 volts panel voltage for a 12v system.
I would like to maximize the power production with the controller. It was a bit of an impromptu purchase - I didn't go in to it with specs in mind, I just looked at the opportunity to get it and it fit a lot of ideas I've had in the past. So I am sort of going about the backasswards I think, but none the less I'd like to maximize what I have.
That is where I have my questions.
With the 400 watt limit and the voltage in mind of "no less than 36 volts" the direction I am pointed towards is linking panels in series to get the voltage up.
This is the panel I am looking at - Bioenno BSP-100.
Another source for that one shows the voltage at 18v. I'd think the 18v is more realistic - only in ideal peak conditions would it get any higher, if that.
If I ran 2 of those in series, or 2 in parallel then those pairs in series, that would get me 36-42 volts in peak sun. Or, if I ran 4 in series that would be 72-84 volts (again, not sure how realistic it is to get above 18v or so per panel).
In low light conditions the option of running more panels in series to get the voltage up seems to make a lot of sense. With 4 panels in the realm of possibilities here - is that enough? Or would I have more options if I had smaller panels - like 50w panels instead of 100w? Would 2x 200 watt panels be worth a consideration - especially if the open panel voltage is a lot higher like in the 30-40v range?
One of the other benefits to running higher voltage is lower amperage at the same wattage. Lower amps = less line loss to the charge controller. So what makes sense to "get there"? Wherever "there" is - panel count vs system input voltage?
For what it is worth, this is the controller I got Bioenno sc-122430ne.
I think they have changed their model around a little bit. Mine has different specs than the manual you can download (400w panel capacity at 12v, 800w panel capacity at 24v).