Smart Inverters To Connect Distributed Generation in California

California has become the first US state to adopt advanced inverter standards.
Published: Wed 21 Jan 2015

Following the experience in Europe with the use of solar PV inverters to provide reactive power support, the California Public Utilities Commission (CPUC) has ruled that the use of these devices will become mandatory with the deployment of distributed energy resources.

The ruling – the first in the US – is applicable to California’s three investor-owned utilities, Pacific Gas and Electric Company (PG&E), Southern California Edison Company (SCE) and San Diego Gas & Electric Company (SDG&E).

Benefits of advanced inverters

Credit for pushing for the ruling is claimed by the Clean Coalition, a non-profit organization focused on the transition to cleaner local energy generation.

“Enabling the full suite of advanced inverter functionality is essential to bring high levels of distributed generation online quickly and cost-effectively – in California and every other leading market around the world,” explains Craig Lewis, executive director of the Clean Coalition. “These new standards anticipate the needs and capabilities of the distribution grid as penetration levels of local renewables increase.”

Benefits of advanced inverters include improved reliability and efficiency. They also support easier and lower cost interconnection of distributed generation because of their ability to monitor and respond to grid conditions. Specifically, advanced inverters enhance grid operations by:

  • ● Providing fast-acting local grid support in response to changes in voltage, frequency and power requirements

  • ● Allowing distributed generation facilities to provide local voltage support along feeder lines, mitigating both under and over-voltage

  • ● Providing increased visibility into the operating characteristics of the distribution gridsupporting both autonomous response to grid conditions and controlled response via centralized utility commands

  • ● Offering significant potential for reducing system upgrades required to support higher penetrations of distributed generation, while also simplifying and accelerating interconnection studies.

Advanced inverters in California

Under the ruling, the three IOUs must install advanced inverters the later of December 31, 2015, or 12 months after the date the Underwriters Laboratory approves the applicable standards. These will include default voltage ride-through requirements; anti-islanding protection for new voltage ride-through settings; frequency ride-through settings; dynamic volt/var operations requirements; ramp rate requirements; fixed power factor requirements; and reconnection by soft-start methods.

Back-up power systems and replacement of existing inverters are exempted from the new requirement. California utilities will seek approval from the Federal Energy Regulatory Commission (FERC) as needed to harmonize federal interconnection standards with the revisions to California’s Rule 21 Distribution Interconnection Standards.

The Smart Inverter Working Group – a group formed by the CPUC and California Energy Commission – and CPUC are now developing subsequent communication and control standards to realize the full potential of advanced inverters. Completion of these standards is expected in 2015 for adoption into the Rule 21. Following this, the Working Group is tasked with establishing appropriate compensation to inverter owners for the provisioning of grid services.

Advanced inverters in US

IHS in its ‘PV Inverter World Market Report – 2014’ noted the US inverter market as a growing market during 2013, along with Japan and China. During that year, the US market also became highly competitive, with aggressive targeting by European suppliers, largely as a result of declining demand in their home countries, and there was also interest from low-cost manufacturers from Asia. This also resulted in rapid price erosion, with average prices declining nearly 20% in the US in 2013.

Among utilities in the US that want to install advanced inverters, Georgia Power requires that small solar generators use advanced inverters to provision reactive power. The Western Electric Industry Leaders (WEIL) group, which comprises CEOs of utilities and other energy organizations across western North America, has also endorsed the use of advanced inverters and has urged their installation on all new solar facilities in the region. With a premium of only US$150 over standard inverters – about 1% of an overall solar installation cost – this is a “bargain price,” WEIL said.

Noteworthy for 2015 is that IHS predicts significant growth in demand for three-phase string inverters (defined as a capacity less than 60kW) for both commercial and utility-scale applications. IHS forecasts that these inverters will account for a third of worldwide inverter market revenue in 2015, with estimated shipments exceeding 15GW driven by the growing demand in the US, among other countries.