Funny, I should know how to work the raw math but I "thought"you needed a large voltage difference to achieve MPPT? Time to quit thinking I guess.
No. MPPT controllers are actually more efficient (from what I have measured) if you
don't have to make a large voltage differential. It's not a lot. But with the Classic 150 I experimented with running my panels at ~141 Voc vs ~70 Voc. The amp input the controller is double at 70 Voc. But I got big wire buried from the panels so that's no big deal. The controller puts out a few extra watts running the panels at lower voltage. I assume because the electronics in it are more efficient when it doesn't have to make such a big "step down" in voltage from 100+ down to 24 nominal.
The important thing with solar, from what I found, is to run the panels at Vmp instead of "clamp" voltage from the bank. If you take s single 12 volt panel charging a 12 volt battery, the panel is probably designed for 17 point something Vmpp. And it won't put out its full power running at 12 volts nominal.
When the bank is low is when you want the most power for bulk charging. And that's where the panels perform the worst when they're direct hooked because they're further off from their Vmpp. As the battery charges up, the panels' operating voltage gets closer to the Vmpp and they start to perform better, when you actually don't need them to perform better (with the battery almost charged up).
The MPPT controller "fixes" that allowing the panels to run at full blast at their peak power they can make, regardless of bank voltage. Typically this will require wiring panels in series for higher voltage systems (24 or 48 volt). But when you wire 12 volt panels in series the difference between bank and Vmpp gets even more dramatic, making the MPPT controller even more important than it is with a single panel on a 12 volt battery.
I got along fine with my old 12 volt system with the panels hooked direct. And even got full rated power from them sometimes. When I went to 24 volt the performance of the solar was pretty dismal compared to what the same panels had done on 12 volt before. That's when I started playing with MPPT. The MPPT woke them panels right up
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Chris