Microgrids: Electricity Goes Local

When Hurricane Sandy hit New York in 2012, most of lower Manhattan went dark, and it was almost two weeks before most of the power was restored. But in one building in Greenwich Village, the lights stayed on and the heat kept working (and the building’s population doubled). That’s because, as University of Wisconsin engineering professor Thomas Jahns explained, that building had “its own miniature version of a utility grid”: a microgrid.

Big Old Power Grid

The trillions of watts of electricity used every year in the United States are delivered by just three huge power grids. The grids’ size and interconnectivity make electricity cheap and accommodate differences in supply and demand between different regions, but it also leaves the whole network vulnerable -- like the time a glitch in an Ohio control room caused a $10 billion blackout in the Northeast and parts of Canada. Or when a worker in Arizona accidentally tripped a power line, and a power outage swept from Southern California to Mexico. The number of major outages like these is rising, and because climate change is expected to increase the frequency of extreme Sandy-like storms, the problem is only going to get worse.

Meanwhile, the demands on the grid are climbing as its aging infrastructure is getting more and more fragile. The average U.S. power plant is 30 years old, and the average power line is 25 years old. Transformers that were only designed to last 40 years have been in service much longer. And even if all those elements were replaced, the grid in its current form was mostly designed in the first half of the twentieth century, when electricity was first a novelty, then a luxury. It was never intended to support a country dependent on air conditioning, computers, and millions of personal electronic devices.

A “Smarter” Option

Planning is underway to replace the aging U.S. power network with a new, “smart” grid, one that’s energy efficient and flexible enough to handle variability in both supply and demand -- and one that can isolate electrical crises before they spread. Incorporating the communication and automation technologies that already facilitate so many other aspects of our lives should make the currently clunky grid much more responsive and efficient enough to save tens of billions of dollars every year.

Microgrids: A New Old Idea

One of the elements of this reimagined grid is actually a recycled old idea: small, independent grids serving neighborhoods, hospitals, and even individual buildings. The key to a modern microgrid is the “smart” switch linking it to the main grid. These switches can respond automatically to the grid’s needs, opening or closing in less than a thirtieth of a second. When it’s connected to the main grid, the microgrid can draw extra power from the communal pool or return any extra energy back to it so that watts on either side of the switch don’t go to waste. But if the power goes out, the switch can open, severing the connection and keeping the outage from spreading. This gives microgrids flexibility that neither a single large grid nor isolated independent grids have on their own.

Juggling Renewables

 “Really, it's a game-changer in a lot of different ways,” Jahns explained. One of the benefits of a microgrid is that its flexibility makes it easier to incorporate renewable energy sources, something that’s perennially tricky. “Renewables are great,” said Jahns, “but unfortunately, the sun goes up; the sun goes down. The wind blows; the wind doesn't blow. But we want to turn on a light switch and expect the light to come on all the time.” For a microgrid, there’s no problem. If it’s cloudy or windless, connecting to the main grid can make up the difference.

Capturing Wasted Heat

 Another major advantage of a microgrid is that it allows you to get much more out of the energy sources you’re using. “I don't think people realize just how much of the energy of a lump of coal -- or even from a nuclear power plant -- how much heat is wasted.” In fact, he said, if you’re turning 50 percent of the source energy into usable electricity, you’re doing well. The rest is lost as heat. In a compact microgrid, combined heat and power generators can recover some of that lost energy and put it to work, boosting energy efficiency from 50 to 80 percent. There’s not much else you can do to make efficiency skyrocket like that, Jahns said.

Adapting to Changing Needs

The microgrid Jahn oversees at the university’s Wisconsin Energy Institute is a cousin of the one that kept the Greenwich Village co-op out of trouble during Hurricane Sandy. This type of microgrid is particularly flexible because it seamlessly adjusts to new loads and new sources without needing a lot of expensive engineering on the front end. “Plug-and-play functionality and autonomous control, that’s the absolutely key part of it,” explained Bob Lasseter, an emeritus professor at UW who developed the technology.

That easy adaptability could make microgrids even more appealing. If a business or a school knew that it wouldn’t have to rework its grid when it needed to add a new building or wanted to put in a solar panel, that might lower the entrance barrier to embracing new technology. These simple but endlessly modifiable microgrids could also be ideal for developing countries without energy infrastructure but with access to energy resources.

The Road Ahead

Getting utilities and governments on board with individual consumers supplying their own electricity -- at least part of the time -- won’t necessarily be easy everywhere. Even though microgrids are designed to interact with the main grid, the ability to produce and consume energy locally constitutes a fundamental change in the way we approach and pay for an integral and ubiquitous service.

“I mean, look out there. What do you see?” Jahns asked, gesturing out the window. “You see power lines and lights. That's a lot of the infrastructure that we just kind of take for granted around us. And now we're talking about changing it in a significant way that is unlike anything that we've seen before. So that's kind of mind-boggling to imagine.”