Nice find Glort. That does look like it will take a 24V panel input to a 12V battery as Veggie desires, though I couldn't find specs or manual that specifically elaborates that.
The only concern with a fixed voltage converter of either PWM or MPPT is that never going to float or never going to bulk charge voltages in some cases can limit lead acid battery life. You can deal with it by lowering the fixed voltage if it's mostly in float, or raising it if it's going to be discharged more over night. I do it myself on my PV linear regulator for the car, even though it does shave a year off the battery life for overcharging and drying out the AGM battery. I didn't have room for more circuitry, was trying to squeeze it on a nice surplus heat sink I could slip in next to the battery. So I just do a seasonal fixed voltage adjustment, lowering it for summer, raising for winter.
I think PWM vs MPPT is irrelevant. MPPT is mostly hype and I certainly don't give a hoot about the last 15% of PV power under certain low light situations. PV is so cheap now that it's nuts not to design for plenty of extra PV for winter/cloudy days.
While I was sitting here, my 1 hp air compressor is topping off my 500 gallon tank. I know it's still pumping as there's a bug in my battery charge controller which causes it to go to bulk charge voltage when there's a big load on the inverter. It's a handy bug- I can tell when the well pump or air pump is finished when it goes back to float, but I'm trying to fix it anyway. I just added a resistor and capacitor on one critical signal that had some ripple, but alas, it apparently wasn't the one that was causing it to trip out of float. The other is a stinker, the trace that must be cut is completely under the IC. Grrr. I'm trying to get it finalized so I can have new clean PCBs made; it's my original prototype and it's got lots of rework on it.
