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Grid Interconnection

Photo of transmission towers and lines extending for miles towards a pink sunset in the distance.

Distributed energy technologies can relieve transmission bottlenecks by reducing the amount of electricity that must be sent long distances down high-voltage power lines.

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, creating added costs that may make an installation economically unfeasible.

Typical requirements include equipment that prevents power from being fed to the grid when the grid is de-energized (for power line maintenance, for example), 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.

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.

At the national level, the Institute of Electrical and Electronics Engineers (IEEE) has developed a series of standards that address interconnection. The base standard — IEEE 1547, "Standard for Distributed Resources Interconnected with Electric Power Systems" — provides requirements relating to the performance, operation, testing, safety considerations, and maintenance of the grid interconnection. Additional standards in the series address interconnection system testing, applications, monitoring, information exchange and control, intentional islanding, and network systems. See the IEEE 1547 Series website for more information.

Navigating the many interconnection requirements for distributed generation equipment can be extremely complicated for the uninitiated. The U.S. Department of Energy (DOE) has made this process a little easier by producing the following guide: