SunDevil above included a fantastic link to Handy Bobīs Solar Puzzle. It also really opened my eyes. As an engineer
I thought I had my system worked out so I sat down and checked it all again using Bobīs advice.
And then promptly spent a full day re-wiring it and tweaking the charge controller.
The two major points I got out of his link was:
1) often our wiring
is undersized because this is what the suppliers push on us
2) the bulk and float settings are often too low.
I had bought 630W of panels from Sun Elec in Florida
in late 2010 and connected it up with the 340 W already onboard. They sold me 10AWG for 20ī runs between the panels and controller. The funny
thing is that at West Marine
the current and wire sizing table in the electrical
aisle clearly shows that I should be using 4 and 6 AWG wires which I luckily bought at the time and had onboard. Unluckily I followed Sun Elecīs advice and used their 10 AWG wires in 2010.
Anyway I ripped it all out yesterday and replaced the 10AWG from Sun Elec with 6 and 4 AWG from West Marine
. Immediate jump in results with over 50 A pumping into the batteries today at 11 am. While I was at it, I calculated that the 4 AWG was heavy enough to handle all the panels in parallel and so changed them all to parallel. The losses are insignificant.
With a total of 970 W of panels and 880 Ah of batteries, I can justify an MPPT
controller and will consider it if we need more energy. For now we are fine with a Xantrex 3-stage charge controller. For anyone with less than 500 W, it seems cheaper to just buy another panel rather than an MPPT controller.
So the lesson is to check out what Handy Bob has to say and then recheck your own system.
Thank you to SunDevil for the link!