When you buy "green" appliances, how do you really know you're really saving energy (and money)? One way to figure this out would be to use your monthly energy bill as an indicator. But from month to month, your energy usage patterns change, the weather most certainly changes, you may have gone on vacation one month, etc etc etc...so many variables you can't control.
Fear not young scientist, the Tennessee Valley Authority (TVA) has you covered. From 2009 to 2012, the TVA built 3 identical homes to test this very idea. One home was built to local building requirements and served as a control. The second was retrofitted to have some energy efficient improvements that an average consumer would easily be able to buy, e.g. Energy Star applicances. The third was a "High Performance Home" with solar panels, solar water heating, Energy Star appliances, properly insulated windows, etc.
The TVA didn't stop there. To mimic human activity in each house, every appliance or utility was used at a regular schedule over the course of the experiment. Refrigerator doors opened and closed at preset times (see image right). The TVs turned on to no one watching. The showers sprayed empty tubs. Going one step further, the TVA included "Human Body Emulation Systems" (see image left) which generated ambient heat and humidity similar to what an average human family would output. Containers of water filled the fridges to simulate the humidity and thermal properties of food.
Left: "Human Body Emulation System." Right: Robot refrigerator door openers.
Results showed, unsurprisingly, that the High Performance Home consumed less energy than the Retrofitted home. And both beat the average home built to local laws. More importantly, we see a prime example of how to use controls in a large-scale experiment (I'M LOOKING AT YOU MYTHBUSTERS). via Gizmodo, Popular Science, and the TVA.