Refrigerators are, despite advances in their design, terribly inefficient. Every time you open the door, the cold air comes cascading right out onto the floor. Chest freezers don't suffer from this draft effect, and can be converted into super-efficient refrigerators.
How super-efficient? Energy usage with a chest-freezer-turned-fridge is barely 0.1kWh a day. Modern stand-up refrigerators use around 1kWh a day.
Tom Chalko, a extremely energy-conscious Australian, modified a chest freezer into a refrigerator to cut down on the pull a standard refrigerator would place on solar/wind system that runs his home. He started off with a simple thermostat to control the on/off cycle of his chest refrigerator, but after becoming dissatisfied with the cheap—and sometimes dangerous—quality of the products he built his own thermostat timer.
For more information about his journey towards an ultra-efficient, off-the-grid refrigerator, check out the full description at the link.