<p>The MPPT will help you the most if your panel is rated at a higher voltage... I am seeing a large savings with the MPPT charge controller on my panel. Even laying flat on the roof (instead of tilted toward the sun), it generates about 190-200+ watts most of the day. Not bad for a panel rated at 235 watts.<br /><br />If you have a smaller panel with the voltage rated in the teens, the MPPT won't give you much extra benefit but it won't hurt, either.</p><p>Like the others, I would go the commercial route for the panel. They have come down a lot in price and, like Bob said, a warranty is nice! I am also concerned about liability. I've had my panel up to 72 miles per hour on the top of the van's ladder rack and feel it is very strong and safe, even sitting well above the roof. Should the worst case scenario happen and it fly off, I would rather explain to State Farm that it was an approved RV style panel...<br /><br />Nonetheless, if you do build a panel, please let us know how it goes! There is a lot of solar interest here.<br /><br />VT</p>