The Electric Power Research Institute (EPRI) has published “Utility-Scale Photovoltaic Inverters: Specifications, Standards, Product Options.”
Worldwide grid-connected solar photovoltaic (PV) systems deployment in residential, commercial and utility-scale markets is experiencing significant growth. With the increasing share of distributed, independent power producer and utility-owned generation portfolios, these PV plants’ components, especially the inverters, are commanding more attention to assure availability and performance.
A recent study by one of the major PV fleet operators with 500 PV plants concluded that PV inverters are responsible for 69 percent of the recorded downtime events. There have been several reported incidents in Europe where emissions from PV inverters have interfered with electronic revenue metering. With increased PV inverter deployment, there is an increased need to share selection and qualification and documentation practices that lead to improved plant reliability and uptime.
The work discussed in this report addresses key issues and describes utility practices for selecting, qualifying and accepting PV inverters. No complete performance criteria exist for grid-connected inverters. As penetration levels rise, utilities will increasingly need clear, complete specifications that can be easily referenced and broadly supported. Considering the interconnection resemblance and maturity, electricity metering industry specifications are closely studied to provide insight into the nature and extent of criteria needed for PV inverters.
This report also provides a brief description of existing electric grid interconnection, communication, safety standards and certifications applicable to PV inverters. Commercially available utility-scale — 250 kW or greater — grid-connected inverters are studied and comparisons are made in parameters including DC, AC, environmental and communication.
According to the report:
1. PV is the fastest growing technology in the electricity generation portfolio, and the PV inverter has proven to be the most critical component in determining plant availability and downtime. As penetration levels rise, utilities will increasingly need clear, complete inverter specifications that can be easily referenced and broadly supported.
2. Several opportunities exist to further develop performance and acceptance criteria for PV inverters. In particular, the inverter’s energy conversion performance, grid-support functionality and long-term durability are candidates for more detailed specification in utility procurements. As a future utility plant asset, the inverter will need to be specified at a level of detail similar to revenue meters or transformers.
3. Work by the national labs and adopted by California describes key measures of energy conversion performance including related test protocols. In future work under this program, EPRI recommends development of a sample specification for large-scale, utility-grade inverters that are intended to become part of the utility fleet.