Businesses view DG as generation capacity located on site and dedicated to one user. (See related entry.) Utilities view DG as capacity that is geographically distributed, not necessarily for proximity to customers, and sold to multiple customers across the grid.

DG for businesses can be as simple as a small electric generator running on gasoline, diesel, propane or natural gas. It's not unusual for office buildings to have generators for backup power, especially after Y2K, the 2003 blackout, and our increasing dependence on a digital infrastructure.

A 10 kilowatt generator is about the size of a small refrigerator on its side, and can run a small service business or retail store. Much larger generators and multi-megawatt arrays can run whole manufacturing facilities.

Generators typically start automatically whenever the power fails. Like any engine, they need the occasional tune-up and oil change. Otherwise, they're hands-free. Connecting to a natural gas line eliminates the hassles and hazards of storing fuels on site.

Some businesses produce a byproduct that can be used to fuel steam turbines. Examples are sawmills, pulp and paper mills, and petrochemical processors. Other businesses generate heat that can produce energy directly without additional fuels, such as certain metals manufacturing and cement kilns.

The hope of the smart energy industry is that an alternative fuel will emerge that is practical for any business, while more economical and less polluting than fossil fuels. Hydrogen fuel cells are the source most likely to replace petroleum-fuel generators.