When the National Renewable Energy Laboratory suffered a surprise power outage, the laboratory had few options for recovery: It had no microgrid controller and no preconfigured setup, just a large battery, solar panels, and wind turbines.
Its response would make MacGyver proud.
NREL recently offered details on the improvised controls that it turned to during its own outage. Its approach could make microgrids easier to operate and at a lower cost in places where they are needed most.
The publication, “Unleashing the Frequency: Multi-Megawatt Demonstration of 100% Renewable Power Systems with Decentralized Communication-less Control Scheme,” describes a microgrid approach that sidesteps the central controller and its reliance on communications.
Instead, the lab’s approach used native controls of battery, solar, and wind systems.
“NREL’s approach makes it possible to assemble devices into a microgrid without arduous configuration, relying on just renewable energy and amateur electrical experience—perfect for recoveries in a pinch,” said Przemyslaw Koralewicz, NREL engineer and co-developer of the communication-less method.
NREL said that microgrids offer one answer for recovery and resilience, but that the costs of a controller often present a barrier to adoption. In 2019, NREL found that microgrid controllers had a mean cost of $155,000/MW, potentially putting resilient microgrids out of reach for vulnerable areas.
In addition to costs, controllers require communications and system settings, which NREL said often are opaque, proprietary, and designed to suit particular scenarios.
As an alternative, NREL prioritized fail-safe startup and favored what it said were “exceedingly basic controls” that still allow more advanced designs to be built on top.
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How it works
NREL’s said its scheme is decentralized, meaning that the devices do not exchange data or issue commands (in other words, they are “communication-less”).
Instead, devices self-regulate using system frequency as the common language. NREL said that a battery or other power source forms the grid by supplying power at a set frequency. Other generators like solar panels and wind turbines follow the grid by watching frequency and changing their power accordingly.
The method mirrors so-called “droop” controls that are familiar in standard fossil fuel generators. The NREL researchers showed that the method works with 100% renewable energy, can be scaled, and is feasible with almost any energy device.
One innovation is that NREL’s method frees the grid frequency from a tight 60Hz. Unbound by mechanical rotation, the microgrid frequency can take a wider range.
This range allows the devices to coordinate without communicating. As frequency rises past 60 Hz, generators reduce power. At even higher frequencies, the generators cut their power further, rebalancing the frequency around 60 Hz. The system self-stabilizes, NREL said, never overcharging the batteries or underserving the loads.
“NREL’s method is the very first step in a design that could become the standard for fail-safe microgrids,” Koralewicz said. This communication-less method could be natively configured in future devices or possibly certified for easy access by operators.
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With standardized adoption, Koralewicz said microgrids of any type “could count on an unfailing foundation to their day-to-day operations.”
Read the NREL report here.
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Author: Renewable Energy World