Smart inverters are going to play a major role in how utilities manage rooftop solar's effect on the edges of their grids. They could also be a key interconnection point for behind-the-meter batteries, smart thermostats and appliances, plug-in electric vehicles, and other distributed energy resources. 

On Tuesday, home energy management provider EnergyHub and inverter maker SMA announced a new step in making this kind of cross-DER aggregation a reality. It will start with an Arizona Public Service pilot project, aimed at taking the utility’s groundbreaking smart inverter work into a broader context. In the coming months, EnergyHub is poised to deliver the same functionality to its more than 40 utility customers, according to Tuesday's press release.

The APS pilot will tap SMA smart inverters at commercial and multifamily housing solar PV systems, combining them with a growing fleet of homes and businesses equipped with rooftop solar, smart thermostats, smart water heaters and behind-the-meter batteries. EnergyHub and APS will then operate these systems in tandem to help shift the state’s surplus of solar energy later in the day, stabilize solar-saturated distribution circuits, and otherwise turn what could be a disruptive set of distributed energy resources (DERs) into a grid-reinforcing asset.

Key markets like Hawaii and California already require that inverters come with key advanced capabilities, ranging from grid-stabilizing automated features to, eventually, more complex aggregated controls. But utilities and solar inverter makers haven’t really started turning on these capabilities, beyond pilot projects.

But APS is ahead of other U.S. utilities in its smart inverter work, helped along by state regulations that allow it to own the solar, inverter and other assets associated with this and other select DER pilots. In fact, its work with the Electric Power Research Institute has informed utility smart inverter pilots across the country. 

Likewise, APS’ work with EnergyHub is one of the first efforts to include smart inverters with other DERs, Matthew Johnson, EnergyHub’s vice president of business development, noted in a Tuesday interview. That’s important, because while smart inverters are an important linchpin in utility-to-DER communications and controls, they’re only one tool in a broader array that it’s working with to meet APS’ broader goals. 

The big-picture problem for APS is its oversupply of solar generation at midday, which matches the “duck curve” supply-demand imbalance of neighboring California’s energy market, he noted. “They’re very interested in how to curtail solar output and match load to solar output,” largely by using batteries, water heaters and thermostat settings to "soak up" excess midday solar generation to use later in the day, when solar production is fading and customer electricity demand is rising. Last year, APS launched new rates that are among the first in the country aimed specifically at encouraging people to use more energy at certain times of the day in this way.

Standardizing the DERMS-smart inverter interface

While these DERs offer energy storage and load-shifting capability, however, it’s the smart inverters that serve as their interconnection to the grid at large, he said. What’s more, inverters can adjust their operations to inject reactive power to boost voltage, ramp output up and down more smoothly to ease sags and surges in local PV output, and otherwise serve as shock absorbers for the solar power they’re feeding to the grid, according to Johnson. 

These capabilities can be very helpful in solving the local distribution circuit problems that can arise with heavy penetration of distributed solar, as projects in Hawaii, California and other vanguard markets have shown.  But “to take inverters shipped with standard settings and dynamically reach in there and respond to specific grid conditions— we’re fairly confident this is a unique project,” he said. 

It’s also a rare instance of a distributed energy resource management system (DERMS) that has operationalized smart inverter capabilities using standards-based technologies, Johnson noted. Its implementation with APS will use the IEEE 2030.5 standard for energy data communications, also known as Smart Energy Profile 2.0. And the EnergyHub-SMA integration is compliant with California's Rule 21, which governs DER interconnection in the state, and the Common Smart Inverter Profile, developed by industry group SunSpec Alliance. 

Brooklyn, New York-based EnergyHub, which was acquired by in 2013, has about 40 utilities using its Mercury DERMS platform, most of them in full-scale deployments, CEO Seth Frader-Thompson said in an interview last year. While its smart inverter work with APS is largely aimed at data-gathering and analysis, the effort also supports the kind of remote reconfiguration that has been standard for solar inverters since early this decade, after Germany’s solar industry was forced to spend hundreds of millions of euros to retrofit inverters to ensure they didn’t all trip offline at once during voltage excursions.  

And as Johnson noted this week, while EnergyHub is working with utility-owned assets in the APS pilot, “there’s no reason for other deployments not to control customer-owned assets,” as long as the customers and solar or inverter vendors involved are signed on. 

SMA, for one, has already integrated its cloud platform for managing its inverter fleet with EnergyHub’s Mercury DERMS, he noted, making integrating existing or new SMA inverters compatible with the same level of monitoring and controls it’s working on with APS — at least for inverters made in the past few years.