Washington Post: The amount of energy that the average American requires at home has changed little since the early 1970s — despite advances in technology that have made many home appliances far more energy efficient. Dishwashers use 45 percent less energy than they did two decades ago, according to industry data. Refrigerators use 51 percent less. But on a per-capita basis, Americans still require about 70 million British thermal units a year to heat, cool and power their homes, just as they …