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Thanks for the reply. I agree, splitting the power could potentially be problematic. The cheapest I've found a 72v charge controller is $270, which would be about triple the cost of the panel itself. If the panels were mounted at the optimal angle due south on my house they would receive 5.05 sun hours, a little less than 10% more. The problem with mounting them on my house is that they're frameless non UL certified panels. I'd have to buy a frame to mount them along with fasteners and racking to attach them to my roof. I couldn't use them in a grid tie system because they're not UL certified, only an off grid system. To use them for my house I'd have to at a minimum buy an inverter, which will cost another $0.20/W and lose 5-10% of the energy. If I wanted to power my car off of this energy I'd have to invert it again through a charger, which would lose another 10% or so. All in all, mounting it on my roof would cost at least double what mounting on my car would cost and with system losses it would produce about 80%-95% of the energy that mounting them flat on the car without an inverter would. For most instances I think placing them on your house is the best route to go, but sometimes it might be better to put them where you want to use the power. Like you said, splitting the power to different charge controllers could be very problematic, so unless I can solve that I don't think I'll be able to implement a system like this. One possible solution might be to use a single 24V charge controller and charge three groups of 4 batteries each in parallel. Implementing the wiring could get very complex and possibly problematic though. I'm not sure if charging three 24v strings in parallel would interfere with my 72v wiring or not.
I might just bite the bullet and get a new charger. I'd have to spend more on the charger than my motor and controller combined though, but I don't want to ruin my batteries with a charger that is substandard.
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