California’s Rule 21 will be going into effect on Sept. 8, at which time, if you are installing solar in California, you will need to install advanced inverters that meet Rule 21 requirements on any new interconnection application. Some background from an in-depth Solar Builder feature on exactly what the point of Rule 21 is:
The experience of Germany was cited as one reason to take action. In Germany, significant grid destabilization problems arose when high penetration levels of solar PV were reached because most of these DER were required to trip off within fairly small frequency tolerances. Not all existing PV inverters had the firmware capability to change the frequency trip setting wide enough to allow stable operation of the grid. Thus, site visits were needed across the region in order to update the firmware and/or change the frequency settings retroactively.
Seeing the need for not only frequency tolerance but grid supportive functions in general, the California Public Utilities Commission and the California Energy Commission convened the Smart Inverter Working Group in early 2013 to start developing recommendations of technical requirements for inverter-based DER in California.
We’ve been posting news on inverters that meet these new requirements as they come our way, but we turned to the California Solar Energy Industries Association for a more complete list of every inverter meeting the specs. Here is that list — which is continually updated and located here. Note that this may not be a comprehensive list and you should also be checking with your distributors and favorite manufacturers for more information.
— Solar Builder magazine