I've been studying and closely following in some cases the work of Tim Nolan (timnolan.com, Michael Pedersen (http://techmind.dk) and Julien Ilett (http://256.co.uk and [https://www.youtube.com/user/julius256]]) as I've been on a mission to build an MPPT Solar Battery charger for off-grid usage based around Arduino. The focus has been on cheap, available components and open-source design.
Whilst I'm not really anywhere near having something working, I've uploaded to GitHub the WIP code based on Tim Nolan's (modified by Michael Pedersen) code and will have more info coming soon around circuit schematics and the modifications I have made once I start to get things working a bit better.
I'm basing my hardware around the ACS712 30A current sensor module, and Arduino Pro Mini, a Freetronics 128x128 OLED module, a pair of voltage dividers for voltage measurement, and a simple buck convertor controlled by the PWM output of the Arduino.
Feel free to get in contact if you've got any questions about the code or what I've been working on. I'd love to hear from people working on similar projects.