U.S. Department of Energy - Energy Efficiency and Renewable Energy

Distributed Energy Program

Grid Interconnection

Grid interconnection has been identified by industry groups as the most significant barrier to the installation of distributed generation technologies. Electric utilities have understandably always placed a high priority on the safety of their workers and the reliability of their electrical systems; faced with the interconnection of potentially large numbers of distributed generators owned and operated by nonutilities, some members of the utility industry have perceived distributed generation as a threat to both. This has led some utilities to place overly conservative restrictions on interconnected systems, causing added costs that may make an installation economically unfeasible. These issues can be compounded if the electric utility also perceives distributed generation as a competitor.

Typical requirements include equipment that prevents power from being fed to the grid when the grid is de-energized (for example, for power line maintenance), manual disconnects that are easily accessible to utility personnel, and power quality requirements such as limits on the interconnected system's effects on "flicker" and other types of distortion. Systems may also be required to automatically shut down in the event of electrical failures — to accomplish this, protective schemes at the grid interface may include a synchronizing relay, protection against under- and over-voltage, protection against under- and over-frequency, phase and ground over-current relays, ground over-voltage relays, and more. Even more restrictive (and expensive) requirements can include an isolation transformer for the system and liability insurance against worst-case scenarios of damage to utility equipment and harm to utility personnel.

While local restrictions on grid interconnection place a burden on the individual or company that intends to buy and use the generator, they also cause difficulties for the manufacturers, distributors, and installers of distributed generation technologies:

Manufacturers — face uncertain requirements for their equipment, which could lead to over-design of a system to meet overly conservative requirements, or alternatively, could lead manufacturers to build a system that may not meet utility requirements in some areas.
Distributors — face local restrictions that can drive up costs because of the need to both track the local requirements and stock items appropriate for a variety of requirements. Distributors may also incur additional costs if a system is delivered to a client that does not meet the requirements of that client's electric utility.
Installers — face additional time, labor, and materials in determining the local utility's requirements and meeting those requirements.

To overcome the interconnection barrier, and to lower costs for all parties — most importantly, the buyer of the system — efforts are underway at state, national, and international levels to establish standards for grid interconnection.

Pursue the following links for more information.