Hi.
Please, keep talking about this topic.
You might already know that some other people are working on that kind of project but I still give the following link in case :
http://www.freechargecontroller.org/index.php?title=Main_Page
http://thesolarpowerexpert.com/introducing-the-v4-charge-controller/
Unfortunately, I'm a very beginner with ARDUINO and I can't understand all the information given. But I'm very interested and I'm studying this project.
Please keep talking, sharing and giving your advice about it.
About what I know about the ARDUINO community, It would be much more active to share about the topic's link I've just given above on the ARDUINO forum.
I'm personally looking forward a high voltage input (200V-250V) to 12V/24V output MPPT regulator. Not for the MPPT function but mostly to use high voltage and lower the line losses on solar panel and batteries' line and save cost on big and long copper wire. In that case; MPPT would just be a nice side effect !
Something like this would be nice !
http://www.dcsolutionsaustralia.com.au/renewables/solar-controllers-mppt/midnite-classic-200v-mppt-solar-controller.html
Arduino420:
I have some experience with solar. Here is an Maximum Power Point Tracker for $20.
The one I'm talking about is not 20$. And the link doesn't even work in France !