3.5 Examples of DER Grid Codes for Advanced Functions
3.5.2 California’s Rule 21 Grid Code Update
California recognized that it was becoming increasingly important to address the challenges posed by higher penetrations of DER systems. California Governor Jerry Brown had called for 12,000 MW of “localized electricity generation”, or DER, to help the State procure 33 percent of its energy from renewable resources by 2020, and has recently increased that goal to 50% by 2030.
The policy driver for most of California’s distributed generation programs to meet these ambitious goals has been to stimulate market development and support emerging technology. However it became increasingly clear that not only market incentives were needed. The policies would also have to address the technical issues of integrating and coordinating DER systems since high penetrations of DER systems that are required to trip-off instantaneously in the event of any distribution system disturbance, can lead to grid stability problems, as experienced in Europe. Specifically, in 2003 Italy experienced a widespread outage due to a frequency glitch that caused all PV systems to trip off.
California’s Independent System Operator (CAISO) also identified another type of problem from high penetrations of PV systems. During afternoons a significant part of the load would be served by these PV systems, but during the evening hours, the PV systems would rapidly decrease their power output, requiring other sources to quickly pick up the load. They showed this in their famous “Duck Curve” diagram, shown in Figure 12.
Figure 13 : California’s Independent System Operator (CAISO) “Duck Curve”
As a result this recognition of pending problems, the CPUC and the CEC jointly formed the Smart Inverter Working Group (SIWG) in January 2013. The purpose of the SIWG is to explore and define the technical steps needed to integrate inverter-based DER functionalities and allow efficient management of the distribution system while maintaining standards of reliable and safe service.
The CPUC noticed the formation of the SIWG to the service list of the interconnection proceeding, R.11-09-011. From its inception, the SIWG has been open to all interested stakeholders, including California’s investor-owned utilities, DER developers and integrators, inverter manufacturers, ratepayer advocates, trade associations, and advocacy groups.
From January through December 2013, the SIWG discussed and assessed the list of autonomous and advanced smart inverter functionalities, communications protocols, and implementation plan contained in this document through biweekly conference calls, a CEC-sponsored web site , an active e-mail list, and an in-person workshop held in June 2013. The result was a document submitted to the SIWG in January 2014, titled “Recommendations for Updating the Technical Requirements for Inverters in Distributed Energy Resources: Smart Inverter Working Group Recommendations”. This document recommended a 3-phased approach to update the CPUC’s Rule 21 Interconnection requirements. These phases cover the following:
- Phase 1: Seven (7) critical autonomous functions. Phase 1 was approved by the CPUC on December 18, 2014 with mandatory implementation of the functions by about mid-2016. These autonomous functions consist of :
- Support anti-islanding to trip off under extended anomalous conditions, coordinated with the following functions.
- Provide ride-through of low/high voltage excursions beyond normal limits.
- Provide ride-through of low/high frequency excursions beyond normal limits.
- Provide volt/var control through dynamic reactive power injection through autonomous responses to local voltage measurements.
- Define default and emergency ramp rates as well as high and low limits.
- Provide reactive power by a fixed power factor.
- Reconnect by “soft-start” methods (e.g. ramping and/or random time within a window).
- Phase 2: Communications capabilities for monitoring, updating settings, and control. These communication requirements include the capability of all DER systems to include communications, as well as specific communication protocol, performance, and cyber security requirements for interacting with utilities.
- Phase 3: Additional DER functions, many requiring communications. This list is essentially the same as shown in Appendix B, Section 4.2
The SIWG is also working with Underwriters Laboratory (UL), Sandia National Laboratory, and other testing experts to establish UL 1741 testing and certification requirements for the advanced DER functionalities to ensure that they operate according to California safety and reliability requirements.
The central challenge of the SIWG has been to understand the entire range of possible functions for smart inverters, and to define a phased approach for recommending how California regulators can make policy changes to realize the benefits of smart inverters.