California Requirements - Rule 21

California is one of the first states to have adopted a standard practice for the interconnection of DER devices to the electric grid. In October 1999, the California Public Utilities Commission (CPUC) issued an order instituting a new DER rulemaking (99-10-025) to address interconnection standards. This rulemaking progressed into the rewriting of Rule 21, part of each investor-owned utility's tariff, by a working committee including representatives from the California Energy Commission and the state's electric utilities. The new version of Rule 21 specifies standard interconnection, operating, and metering requirements for DER generators.

In November 1999 after a series of public workshops and meetings, the Energy Commission issued an Order Instituting Investigation (OII) to encourage more development in DER. By identifying barriers and offering solutions to remove those barriers, the Energy Commission was able to present its findings to the California Public Utilities Commission (CPUC) for eventual adoption. The Energy Commission used a technical support contract known as FOCUS (Forging a Consensus on Utility System) Interconnection to formulate fair and uniform interconnection standards.

The rulemaking initiated by the Energy Commission and the CPUC progressed into the rewriting of Rule 21 by a working committee, including representatives from both parties and from the state's electric utilities. The new version of Rule 21 specifies standard interconnection, operating, and metering requirements for DER generators.

On December 21, 2000, a CPUC decision (00-12-037) approved in its entirety the Rule 21 language adopted by the California Energy Commission. Pacific Gas and Electric Company (PG&E), San Diego Gas & Electric Company (SDG&E), and Southern California Edison Company (SCE) have now replaced their former Rule 21 with the approved Model Tariff, Interconnection Application Form, and Interconnection Agreement. Specific information regarding the interconnection of DER technologies is available from each of the utilities.

Interconnected DER devices operating in parallel with the electric grid may allow for the flow of electricity in two directions. In this mode of operation, many DER devices are eligible for net energy metering, in accordance with Section 2827 of the California Public Utilities Code. Net metering is defined as the difference between the electricity supplied through the electric grid and the electricity generated by an interconnected DER device. A single electric meter may be used to register the flow of electricity in both directions. Therefore, electricity supplied by the electric grid forces the meter to spin in a positive direction. However, electricity generated by the DER device may be fed back into the electric grid, causing the electric meter to spin in reverse.

The following are links to the key CPUC interconnection documents: