Lincoln Electric System (LES) in Nebraska has put a 29-megawatt (MW) microgrid in service at virtually no cost.
The dual-fuel generator at the heart of the microgrid can serve critical loads in downtown Lincoln during an emergency or outage, including city, county and state facilities, as well as the state capitol building, the Pinnacle Bank Arena, gas stations, a grocery store, and local residential buildings.
The microgrid, which entered service in October, uses the existing distribution system and a generator that can be fired either by on-site diesel or piped natural gas.
The generator, which is about 50 years old, has black-start capability and was always capable of islanding and serving critical loads during an outage, but LES had not tested the system for that purpose.
The microgrid concept first emerged in 2016. “We were just talking, and the idea just came up,” Scott Benson, LES’ manager of resource and transmission planning, said.
The idea lost traction for about two years, mostly because “we only wanted to feed critical infrastructure.” In the original conception, the noncritical loads would have had to be disconnected from the generator manually, which would have been time consuming enough to render the operation moot.
Benson said in 2018 they had an epiphany when they realized LES could feed the entire area, residential housing and all. “It made all the difference in the world," said Benson. “We realized we could put the microgrid in place without spending a whole lot of dollars.”
The generator already had islanding capability, so turning it into a microgrid would not require any new equipment or even a microgrid controller. The generator, which mostly runs a handful of times a year as a peaking plant, feeding into the Southwest Power Pool, was already capable of following load. All that was needed was to test the concept.
The generator had never been called on to serve a load as large as downtown Lincoln, and it is not feasible to shut down a portion of the city to test the system, so LES brought in two 5-MW load banks, essentially “two large toaster units” that use a lot of electrical power. They also took an “ultra-conservative” approach, looking at load profiles on feeders from the utility’s peak July-August period to determine the extent of the area the microgrid could serve.
The tests demonstrated that the system was capable of ramping up to full capacity in 5-MW increments. So, if the Lincoln area were hit by a large or persistent outage – a rare occurrence for the region – Benson said LES could put the microgrid in service and dispatch operators, “dropping in load systematically in no more than 5-MW chunks.”
Because the generator is already designed to follow load, it would also be able to handle the distributed energy resources in the downtown area, which include five customer-sited solar facilities totaling about 300 kilowatts (kW) and a 500-kW, six-hour thermal energy storage system that uses chilled water to store energy and defray cooling costs.
“Practically speaking, we could go two decades and not need this system,” Benson said. “At the same time, knowing it's ready and done and in the background ready to work is worth its weight in gold.”
“Part of the beauty of the system,” Benson said, “is that we had all the pieces, and it all fell into place.” Since the peaking generator could already island and follow load, “in essence it becomes your controller.”
“Other utilities might also be sitting on a ready-made microgrid like we were,” or might just need incremental work to get there, Benson said.
Meanwhile, the National Renewable Energy Laboratory (NREL) is helping the Department of Energy draft a publication that would highlight LES’ J Street microgrid and its potential to leverage existing infrastructure to provide new community benefits.
More details about LES’ microgrid project are available on slide 58 of the minutes from the utility’s July administrative board meeting.
