Can smart solar inverters help keep grid voltages in balance? Sunnova, SolarEdge and National Grid team up to find out

One of the largest tests of its kind will tap thousands of rooftop solar inverters in Massachusetts and Rhode Island — and examine what it’s worth to both utilities and customers.

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Smart inverters can do a lot to help utilities, from mitigating the disruptions that can arise from increasing rooftop solar penetration to taking a more active role as grid-balancing agents. But before utilities can start to rely on them for these purposes, they’ve got to test them at scales that can really make a difference on the grid.

That’s what utility National Grid is planning to do with Sunnova and SolarEdge in Massachusetts and Rhode Island. On Tuesday, the companies announced a plan to enlist several thousand of Sunnova’s residential solar customers, all of them equipped with SolarEdge inverters, in a program that will offer each a $25 upfront incentive plus $20 per year in exchange for allowing their inverters to be programmed to serve grid needs.

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We’re bringing a portion of our fleet forward and working with our partners to turn on certain settings in the inverter that will allow a voltage regulation service to be provided when the systems are not at their maximum capacity,” explained McCrea Dunton, Sunnova’s director of energy services.

That’s something that smart inverters have shown they can do in pilot projects in California, Hawaii, Arizona, Texas, New York, Illinois and other states, as well as in similar tests around the world. But there’s a big difference between proving this capability in a lab setting or on a handful of distribution circuits, and expanding it across a wide swath of the grid.

In that sense, National Grid’s new project is really a pilot at scale that will allow [the utility] to build out a program for the future,” Dunton said. National Grid has been working on smart inverter pilots for years, ranging from tests of how active control of distributed solar inverters can support transmission grids, to which configurations of inverter settings can best balance local grid circuits under different conditions — the same use case that Sunnova and SolarEdge will help test, Dunton said.

The long road to enabling smart inverters in the field

Getting smart inverter capabilities turned on to serve real-world grid needs has been a slow process. It started with years of work to set the standards for how their inherent capabilities — injecting and absorbing reactive power to alter grid voltages, curtailing solar output to prevent potential overloads and communicating with wider control systems that can tap their data and adjust their operations on the fly — can be put to use.

In the past few years, key solar markets including California have required all new inverters to come equipped with key advanced capabilities enabled by the latest standards. They’ve also begun requiring that inverters turn on some of these smart functions, starting with relatively simple, autonomous grid-stabilizing features.

But moving from these passive, autonomous functions to more active capabilities opens a can of worms for utilities. One of the first challenges has been to get enough customers to enlist in pilot projects to test how large-scale inverter control schemes will affect the grid, as a 2018 report from California’s big three investor-owned utilities pointed out.

National Grid’s Connected Solutions program, which offers lucrative utility incentives to companies that can enlist customers to offer their behind-the-meter batteries, smart thermostats and electric vehicle chargers for grid services, is also hosting the new smart inverter pilot. SolarEdge is a partner in that program and has also built a back-end platform that can manage inverters in the field to control solar systems and batteries for grid needs.

National Grid has been seeking out customers to join up on its own, but turned to Sunnova and SolarEdge to gather the large number of customers needed to meet the scope of the testing it wants to do, Dunton said.

Another barrier to getting customers, or aggregators like Sunnova and SolarEdge, to take part in smart inverter programs is the concern that the grid-stabilizing actions their inverters are asked to undertake could reduce the real power output that forms the basis of rooftop solar systems’ revenue.

That’s why National Grid’s program will only target shoulder periods” when solar systems aren’t at their maximum output, he said — and why National Grid has pledged to repay customers for any lost revenue or credits they may accrue when they participate.

Nor is National Grid going to be telling us to change inverter settings multiple times per day,” Dunton said, since that could present operational challenges. We’re making one passive inverter setting change and monitoring what the fleet can do.”

That doesn’t mean that SolarEdge and Sunnova couldn’t support those kinds of active controls at some point in the future, said Michael Grasso, Sunnova’s chief marketing and growth officer. SolarEdge inverters are connected via cellular backhaul networks to central control platforms, giving it and Sunnova visibility over its fleet of systems.

We share it on a cloud-to-cloud basis [and] share it back with SolarEdge. [We] can commission and provision those systems back to them, and then share it back to National Grid — with customers’ permission,” he said.

Adding smart inverters to the distributed-energy-grid playbook

This networked control capability is being tapped by a wide array of solar and battery vendors like Sunrun, Tesla and sonnen, and smart thermostat and device control vendors such as Google’s Nest and OhmConnect, to create virtual power plants that can reduce grid stress under peak load conditions.

Sunnova itself has pledged to supply 85 megawatts of capacity to grid operator ISO New England by 2024. It will do this by aggregating the value of solar systems it intends to deploy in the region to reduce peak grid demands. It’s pursuing similar opportunities in California and Texas.

But the same kind of control systems used to manage behind-the-meter loads to ease grid stress can be used to tap smart inverters’ unique capabilities to manage grid voltages. These include solving problems caused by solar itself, such as smoothing out the voltage sags and surges that can occur on distribution circuits with heavy solar penetration without expensive grid upgrades, as this National Grid simulation illustrates. 

Image credit: National Grid, EPRI

Smart inverters could also play a broader role in conservation voltage reduction and volt/​VAR optimization schemes, which make the grid more efficient at delivering power by keeping voltages within lower but still safe operating boundaries.

Massachusetts has roughly 840 megawatts of residential solar and Rhode Island nearly 60 megawatts, according to data from research firm Wood Mackenzie. Those aren’t the same levels of solar penetration that have been seen in sunnier states like California, Hawaii and Arizona. But Massachusetts is seeing fast growth of solar, and it is looking to use those resources to optimize power quality, which will reduce costs for all customers,” John Isberg, the National Grid’s vice president of customer sales and solutions, said in a prepared statement.

Eventually, that kind of service could become a standard part of a utility’s toolbox of solutions for managing its grid — one worth rewarding with incentives or payments for services rendered, if regulators, utilities, aggregators and customers can agree on that value.

If we don’t have a real power impact, and therefore we don’t have any customer generation loss, we’re in a situation where we can look to further monetize” those inverter capabilities, Grasso said. While it’s likely that being able to store, shift and shed power consumption across thousands of homes will remain the most lucrative option for aggregators like Sunnova, adding inverters’ voltage regulation capabilities could help boost the business case.

It really hasn’t been done at this scale,” he said. We’re hoping we can learn from it but also to influence how that capability is built for the future.”

(Article image courtesy of Sunnova) 

Jeff St. John is the editor-in-chief of Canary Media. He covers the technology, economic and regulatory issues influencing the global transition to low-carbon energy. He served as managing editor and senior grid edge editor of Greentech Media.