Learn how a refrigeration system works

To all you people who are popping off about "It is just cheaper, not more efficient!", you might want to learn a bit about how a refrigeration system works before you open your mouth. It makes you look ignorant (or possibly just exposes what you are...)

The concept you are missing is called "Delta T". Heat flows from from hot to cold (that delta T or DT going forward) and it is pretty linear: the greater the DT, the greater the rate of heat flow.

Your standard refrigeration system (car AC, refrigerator, freezer, refrigerated air home cooling, etc) uses this principle twice: the first time, it heats the refrigerate significantly by compressing it, then it dumps the excess energy by allowing it to flow to the outside air (normally). The refrigerant is then cooled significantly by expanding it back to a gas. This cold refrigerant is now much cooler than air it is cooling, so the heat flows from the air (inside your car, your refrigerator or house) to the refrigerant which heats the refrigerant back up while cooling off what you are cooling.

Here is the rub: it takes ENERGY to compress that gas to make it hotter than the outside outside sink. The hotter your sink is, the MORE energy it takes to make the refrigeration system work. When your sink is actually COOLER than your target temperature for what you are conditioning, you can move that energy with much less energy consumption.

One way to do this is to find a cooler heat sink. Geotherm systems do this by dumping the excess energy to the ground (via buried tubes) or to water sources like rivers or lakes. Trying to keep a house at 21C when it is 38C outside is MUCH easier if you are trying to dump the excess heat to a sink that is 13C. Running the AC system at night when it is only 18C (for example) is WAY better than trying to dump the heat to a 38C outside air even if it isn't quite as effective as dumping it to 13C ground.

So yes, there ARE real ENERGY savings by doing the heat dumping at night. The fact that you can also do it using CHEAPER electricity is also a very nice bonus.