I read about this a few weeks back, but I stumbled across it again while reading up on disaster preparedness. Man Retrofits Freezer to Make an Ultra-Efficient Fridge:
An off-grid experimenter in Australia, Tom Chalko, has retrofitted a chest freezer to create a fridge that uses only 100 watt-hours (0.1 kWh) per day! Why a chest freezer? Tom points out that vertical door refrigerators are inherently inefficient. As soon as you open a vertical fridge door the cold air escapes, simply because it is heavier than the warmer air in the room. When you open a chest freezer, the cool air stays inside, just because it’s heavy. Any leak or wear in a vertical door seal causes significant loss of efficiency.Tom took a standard chest freezer (a Vestfrost SE255), added a $40 external thermostat, then wired the freezer to turn off when the desired temperature was reached. The thermostat runs on 2 AAA batteries which last for months. The freezer runs for about 90 seconds per hour and then shuts down completely, making it not only very efficient but very quiet.
As one commenter noted, this efficiency boost is much, much more important if you’re trying to live off the grid. On the grid, it saves you about $3 per month — at the expense of having to bend over and dig things out of your fridge.