My controller is a Morningstar Sunsaver MPPT 15 which is supposed to hit up to 97% efficient at getting energy from the panel to the battery. I've never personally measured it, though.
You can find MPPT controllers a little cheaper than this one, especially if you don't use 24V panels. I went with a 24V PV system for a couple of reasons. One is that if in the future I want to expand my system beyond 1 battery to use an inverter 24V makes sense, reduced DC current and allows a wider selection of heavy duty inverters.
Even if I just add more storage and stick with a 12V battery bus, running a 24V panel and MPPT controller you get a higher overall energy recovery since the controller is rarely running near its max duty cycle and current. The max panel power rating for the controller doubles at 24V to 400W over 12V panels. My single panel and 12V battery sits right in the middle of most of the rating curves for this controller, so it's never seriously taxed.
Plus, the Morningstar allows me to jump up to 36V panels if I wish in the event I want to build a true self-contained system independent of the grid.
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Last edited by DaveInDenver; 12-10-2013 at 06:27 AM.