As inverter manufactures complete preparations for complying with NEC 2014, another rule, and amending standards to fulfill it, are right around the corner. Here’s a brief explanation of what’s coming up.
California Rule 21: Gigawatts of solar have been added to the California grid, but as more and more come online the grid must become smarter to handle the increased capacity. This means instating better communications and automated control to manage voltage fluctuations that could result from distributed-generation resources, such as solar. Utilities are looking to inverters as the “brains” of PV systems to provide this expanded grid functionality.
This type of smart inverter functionality already exists in Europe. The Smart Inverter Working Group (SIWG) was formed by the California Public Utilities Commission and California Energy Commission, and includes over 50 organizations including inverter manufacturers. Its purpose is to provide recommendations to revise California’s Rule 21. The rule concerns the technical requirements for interconnecting solar to the grid. Revising the rule means amending UL and IEEE standards concerning testing and certifying smart inverters.
IEEE 1547 and UL/ANSI 1741: IEEE 1547 states that inverters connected to the grid may change DC power to AC power and turn off when they sense that the voltage or frequency of a circuit moves outside normal parameters. An amendment (known as IEEE 1547 a) is under development to widen the range of grid voltage and frequency conditions under which inverters may remain connected. This would allow inverters to actively contribute to voltage and frequency regulation. For utility-interactive equipment, UL/ANSI 1741 is intended to supplement IEEE 1547, and the standard for conformance test procedures for equipment interconnecting distributed resources with electric power systems IEEE 1547.1.
SIWG has assembled a three-year plan to achieve smart inverter adoption. Recommendations for automated functions will be made in the first year. Then communications capabilities will be addressed and finally implementing smart inverters is slated for 2016.
California PUC www.energy.ca.gov