Average annual temperatures across the 48 contiguous United States have risen approximately 1.5 degrees Fahrenheit since the dawn of the 20th century—and with this rise have come increasingly costly and increasingly frequent severe weather events that have taken a toll on people, property, and pocketbooks.
Hurricane Sandy pounded the East Coast in the fall of 2012, leaving devastation that affected 24 states. Utilities reported damage to more than 7,000 transformers and 15,200 power poles; two oil refineries with capacity of 300,000 barrels per day were shut down. The hurricane left 8.2 million people without power for weeks, and caused $71 billion in total loss. New York Governor Andrew Cuomo convened the New York State Commission 2100 in response to not only Hurricane Sandy, but other recent and unprecedented severe weather events such as Hurricane Irene and Tropical Storm Lee. The Commission recommended measures including protecting key transmission and distribution lines, strengthening marine terminals, and building a modern, more resilient grid that can take advantage of renewable energy and that can be a model for improving energy infrastructure nationwide.
NREL Director Dan Arvizu, who was a member of the New York 2100 Commission that issued the recommendations, said: "Given the magnitude of recent climate-related calamities, and the inevitability of more in the coming years, it is imperative that we grasp the opportunity to build a more resilient energy sector."
Priority must be placed on improving grid equipment and operations to better manage the complex, ever-changing load conditions—and to increase reliability and resilience. A more distributed and resilient energy infrastructure can overcome the long delays before power is restored, Arvizu said.
"Renewable energy can do much more than save on greenhouse gas emissions," he said. In the face of more and more extreme weather events, "islanded microgrids that combine renewable energy with backup storage can keep local power going when the grid goes down. And that can save both money and lives."
A key asset of some microgrids is that during a utility grid disturbance they can separate and isolate themselves from the utility seamlessly with little or no disruption to the loads within the microgrid. When the utility grid returns to normal, the microgrid automatically resynchronizes and reconnects itself to the grid in an equally seamless fashion.
Microgrids Scale up from Household Size to Large Networks
One house can have its own microgrid, a combination of, say, rooftop solar and a battery in the basement that stores the excess power generated by the sun and provides backup power to keep the furnace running in the case of a power outage.
Utilities working with homeowners or businesses can create a network of microgrids that help entire neighborhoods or cities to power through outages. In Portland, Oregon, customers with their own diesel generators have agreed to give the utility control of them when needed. The utility, Portland General Electric (PGE), uses a combination of solar power, battery storage, and backup diesel to ride through outages when the main system goes down. Tests at NREL addressed integration and communications issues, and helped PGE install a more robust system with minimal impact to electricity users.
NREL also helped test a microgrid system designed by the Consortium for Electric Reliability Technology Solutions (CERTS) that ties together natural gas co-generation and a microgrid gateway to provide both heat and electricity to customers, uploading and downloading power on and off the grid. This microgrid is currently owned and operated by the Sacramento Municipal Utility District.
This summer, NREL is collaborating at the ESIF with an Australian utility that is using inverters to integrate solar, diesel generators, and batteries. The effort will include development and testing of a microgrid control network that has the job of determining whether and when backup battery power is needed, and ensure consistent electricity is provided to users.
NREL's ESIF is the Place to Validate Integration of Power Sources
"It's a matter of getting stuff to work together," Martin said. And that requires partnerships. GE wants to sell appliances; Toyota wants to sell cars that plug into garage outlets. Sacramento Municipal Utility District needs to be sure that the rooftop solar and a box of backup batteries are working together seamlessly.
As the new generation of microgrids and inverters proves its mettle, there also needs to be an evolution in the standards that define the interface between the utility and the microgrid. "We're trying to make sure that these great new ideas work," Martin said. Solar arrays are becoming very robust, but there is still plenty of work to do to ensure that batteries and other equipment integral to energy integration communicate with each other flawlessly in real situations.
The ESIF has the capacity to test large components and systems, say, 500-kilowatt or 1-megawatt photovoltaic inverters. One of the ESIF's main missions is to be the last stop before the field. "Until we run it at rated power, kick it and bump it with grid fluctuations, and see what it actually does, we can't be sure it's going to function well in the field," Martin said. "That's why we're here. No one has ever been able to lab-test their equipment at a scale that is possible here at the ESIF."