Air compressors are common in auto repair garages and farm shops. What does it cost the customer (dollars per year) if he ignores a modest-size system leak and just lets the compressor cycle on/off as needed all day?
Air compressors are surprisingly inefficient devices. Even if it is not used for shop work and no air is removed from the tank, even a small leak causes the unit to cycle on/off to maintain pressure. If you can hear the leak, it is worth fixing in terms of energy savings.
The size of the leak in this example is approximately the diameter of a thin mechanical pencil lead. The other assumptions are typical for a compressor of this size.
The result? At 9 cents per kilowatt-hour, the customer is wasting about $70 per year. This is just to keep up with the leak, and does not include electricity consumed when the system is used to serve air tools, inflate tires or other tasks.