Grid Codes for Large-Scale PV Plants
A thorough investigation of existing grid codes around the world shows inadequate sets of rules developed for solar PV generation plants [42]. This is also noticeable from Table 7. The reason behind such deliberate development of PV grid codes is that PV generation has developed in a different way, starting with very small units on rooftops connected to the local secondary distribution system. Therefore instead of TSO, the distribution system operators were the first to adopt standards to welcome inverter-based PV generation. Especially, IEEE Std. 1547–2003 [43], has been the established standard governing the connection of distributed resources including PV plants with aggregate capacity of 10 MVA or less at primary or secondary distribution voltage levels in USA. FERC Order 661-A [11] was the first rule to directly impact the interconnection of large RPPs in the transmission system. However it was primarily developed only for WPP integration. On July 2, 2010, the California Independent System Operator Corporation (CAISO) filed [44] with FERC for revisions of its tariff relating to interconnection requirements related to both WPPs and solar PV plants [45]. The TSOs that have incorporated separate rules for large-scale PV integration include—State Grid Corporation of China (China, 2011), CEI (Italy, 2006) and REE (Spain, 2010). Section 3 of Chapter ‘‘Frequency Control and Inertial Response Schemes for the Future Power Networks’’ of Spanish grid code P.O. 12.2 has provided a few guidelines on operating voltage range and control of PV integrated systems. However, this is still in draft form [46]. Several other joint utility groups have drafted similar codes including power factor, voltage support, LVRT, frequency ride through, real power ramping, and curtailment capabilities for PV plants. It is expected that most of these regulations will ultim