Hawaii is already a real-world test bed for the challenges of bringing high penetrations of rooftop solar onto its island power grids. Now Hawaiian Electric Co., the state’s main utility, is joining forces with SolarCity to try out a tool that could help manage its solar-impacted electricity networks: smart inverters.
Last month, the two announced they’re going to Golden, Colo. to work with the National Renewable Energy Laboratory (NREL) on a combination of smart inverter and smart grid technologies at the lab’s new Energy Systems Integration Facility (ESIF). It’s one of the first real-world tests in the United States of how solar inverters can be programmed and controlled to trip on and off in response to grid voltage fluctuations, inject or absorb reactive power, and perform other critical grid balancing tasks.
“The important thing here is to test the smart inverters in a real-world situation, and show how aggregated control of smart inverters can be a grid asset,” SolarCity CTO Peter Rive said in a recent interview. (This week's Solar Market Insight Conference in San Diego will feature two sessions on the subject of high-penetration PV and advanced inverters, along with more in-depth coverage from GTM Research and the Solar Energy Industries Association's U.S. Solar Market Insight report.)
“You can be a little more nimble when you have a lab environment," Rive noted. For example, SolarCity and HECO want to prove that smart inverters can successfully trip off during a grid fault, a function called "anti-islanding." The idea is to make sure that a group of solar inverters won’t mistake each other’s power for grid power, remaining on to potentially shock utility workers trying to fix the outage. But it’s hard to test repeated grid outages like that on one’s customers, he said.
Beyond that, “we are going to do these tests to prove that high penetrations of solar will not create any grid stability concern, especially in the area of voltage,” he said. One critical condition that HECO wants to test is bidirectional power flow, which happens when a distribution circuit is generating more solar power than its customers are using, pushing electrons back up through the power lines and transformers.
“What we’re trying to show is that bidirectional power flow through certain utility equipment is not a problem at all,” Rive said -- a contention that’s not at all universally accepted in the utility world. “If you have a lot of PV on a circuit that’s going through a substation and serving a different” portion of the grid, “what we’re finding is that they don't know -- well, they don’t always know -- when that’s happening. That’s why it’s interesting that in HECO’s case, they’re assessing these conditions first, because of the amount of solar deployed there.”
Finally, SolarCity will be testing its ability to manage a number of solar inverters as an aggregated grid management tool, he said. “With smart inverters, that there will be a very powerful asset when it comes to reliability services for grid operators -- providing VAR, voltage support, and frequency support. We’re proving that out in low-voltage situations.”
These tests put Hawaii in front of the country’s other test market for smart inverter technology, California, which is set to start its own advanced inverter tests next year. California’s effort is linked with work to create an Underwriters Laboratories certification for smart inverters, a critical first step toward developing the standards and regulations to allow inverter makers to build equipment to meet whatever requirements emerge at the state level.
SolarCity is involved with California’s Smart Inverter Working Group, and “we’re working with a lot of vendors to support those standards, so that aggregated smart inverter control will come in every inverter,” Rive said. SolarCity also installs cellular or broadband-linked servers in the homes and businesses it equips with third-party financed solar systems, and it is working with Tesla Motors on integrating behind-the-meter batteries into that mix.
Hawaiian Electric is arguably the U.S. utility most in need of technology to manage distributed solar as a grid asset. It’s under state regulatory pressure to allow customer-owned solar to keep growing, after it put the brakes on new interconnections last year, citing concerns about solar power backfeeding, two-way power flows and other unusual conditions affecting its most solar-rich distribution circuits. It's also seeking up to 200 megawatts of energy storage projects, and is testing behind-the-meter batteries, grid-integrated water heaters and other distributed, demand-side resources.
As GTM Research analyst MJ Shiao noted, “More than one in every ten HECO customer has solar, with thousands of interconnection applications still waiting for approval. Earlier this year, HECO implemented requirements for residential inverters to comply with transient overvoltage (TOV) concerns, a relatively simple firmware upgrade for most inverters, and it is now looking toward more advanced functionality to ensure that its uniquely high penetration of DG solar doesn't adversely affect grid reliability.”
“Inverter manufacturers, utilities, and other solar stakeholders are eagerly looking to the rules that Hawaii will implement, not just because it continues to be one of the largest U.S. state markets for residential solar,” he said. “New regulations, alongside California's Rule 21 interconnection proceedings, will serve as a precedent for other utilities as they look forward to higher PV penetration.”
HECO may soon have a new owner likely to be more supportive of the utility’s push for green power to reduce its dependence on expensive oil-fired power plants. NextEra Energy, the big renewable power (and nuclear) company, last week announced plans to acquire HECO parent company Hawaiian Electric Industries for $4.3 billion.