Stock averaged

The stock-averaged value accounts for the fact that appliances in current use are models that have been produced and purchased in previous years. Over these years the energy consumed by an appliance will have varied due to advances in technology.

Some appliances become more energy-efficient as technology advances, but other appliances - notably computers - now consume more energy than before.

The following example illustrates a stock average for desktop computers (without monitors) between the years 2004 and 2006.

Year Stock in use Energy usage kWh/year Product
X Y X*Y
2004 20738755 211.16 4379196271
2005 21657463 229.68 4974293424
2006 22505860 235.18 5292973359
A Sum of X*Y 14646463054
B Sum of X 64902078
Stock-average A/B 225.67

So, the typical desktop computer in use in 2007 will consume 226 kWh of energy in one year.