President Obama plans to spend billions building it. General Electric is already running slick ads touting the technology behind it. And Greenpeace declares that it is a great idea. But what exactly is a "smart grid"? According to one big-picture description, it is much of what today's power grid is not, and more of what it must become if the United States is to replace carbon-belching, coal-fired power with renewable energy generated from sun and wind.
Today's power grids are designed for local delivery, linking customers in a given city or region to power plants relatively nearby. But local grids are ill-suited to distributing energy from the alternative sources of tomorrow. North America's strongest winds, most intense sunlight, and hottest geothermal springs are largely concentrated in remote regions hundreds or thousands of miles from the big cities that need electricity most. "Half of the population in the United States lives within 100 miles of the coasts, but most of the wind resources lie between North Dakota and West Texas," says Michael Heyeck, senior vice president for transmission at the utility giant American Electric Power. Worse, those winds constantly ebb and flow, creating a variable supply.
Power engineers are already sketching the outlines of the next-generation electrical grid that will keep our homes and factories humming with clean - but fluctuating - renewable energy. The idea is to expand the grid from the top down by adding thousands of miles of robust new transmission lines, while enhancing communication from the bottom up with electronics enabling millions of homes and businesses to optimize their energy use.
When electricity leaves a power plant today, it is shuttled from place to place over high-voltage lines, those cables on steel pylons that cut across landscapes and run virtually contiguously from coast to coast. Before it reaches your home or office, the voltage is reduced incrementally by passing through one or more intermediate points, called substations. The substations process the power until it can flow to outlets in homes and businesses at the safe level of 110 volts.
The vast network of power lines delivering the juice may be interconnected, but pushing electricity all the way from one coast to the other is unthinkable with the present technology. That is because the network is an agglomeration of local systems patched together to exchange relatively modest quantities of surplus power. In fact, these systems form three distinct grids in the United States: the Eastern, Western, and Texas interconnects. Only a handful of transfer stations can move power between the different grids.
The limitations of these transfer stations are telling. The Eastern, Western, and Texas grids all carry alternating current, or AC, that jiggles back and forth in the wires 60 times a second. But these jiggling currents are out of sync with each other. The transfer stations move power from one grid to another by converting AC to direct current, or DC, and back again. (DC is much like the power supply for a cell phone or laptop. In fact, all electronics ultimately run on DC.) A converter attached to one grid uses some of its AC power to generate DC. A second converter then reverses the process, using the DC to produce a new stream of AC that is in sync with the AC power on the second grid.
The bottleneck that this process creates, along with the grids' patchwork design, makes it impossible to move large amounts of power between regions. Yet that is exactly what is required for distribution of solar energy, wind power, and other renewable sources of electricity. Obama has asked Congress to increase renewable energy to one-fourth of the American power supply by 2025, but only a revamped grid will be able to handle such a load. "It cannot be accomplished without significant new investment in our transmission infrastructure," concluded the U.S. wind and solar industry trade associations in February.
Heyeck says that the existing grid resembles the nation's congested and overloaded road network of the 1950s. President Eisenhower's Interstate Highway System fixed that; now Heyeck is one of a growing number of people calling for the electricity equivalent - a network of power "superhighways" crisscrossing the continent. It would be an overlay on the existing high-voltage grid, just as Eisenhower's blueprint laid a network of modern freeways over the existing patchwork of smaller roads.
Designs for a new interstate power grid exploit two extra-high-voltage technologies. The most efficient over long distances is high-voltage DC (HVDC), which employs converter stations analogous to the transfer stations that mediate power flow among the nation's Eastern, Western, and Texas grids today. The difference is that in HVDC, the converters can be spaced farther apart - hundreds or even a few thousand miles away from each other. Power converted from AC to DC at one station is sent down a cable to be converted back to AC at another station at the end of the line. All that conversion is worth the trouble for long-distance transmission because DC travels with less resistance than AC. As a result, less energy is wasted heating up the cable and more energy reaches its destination.
Using HVDC to move renewable energy is hardly a new idea. Remote dams around the world already deliver hydropower via HVDC lines, including a 1,480-kilometer (920-mile) link that has carried energy from James Bay in northern Quebec to New England since 1990. But the technology is getting better and cheaper, making its use in a transcontinental grid seem more realistic.
One showcase for the new technology is the extra-high-voltage HVDC line that China is building to feed electricity from Xiangjiaba, one of its western hydropower megaprojects, to Shanghai. The 800-kilovolt line will carry three times as much power as Quebec's, enough to satisfy the needs of roughly 31 million people on China's teeming eastern seaboard, according to the company heading the project. (If the 1990-vintage technology had been used, transmission losses would have reduced the population served by about 1 million.) Similar grid upgrades could deliver wind power from America's northern plains and Texas to the Atlantic and Pacific coasts. The downside of this approach involves the converter stations needed to add or remove power from the lines. The industrial-scale electronic switches behind AC-DC conversion are expensive. That cost limits the number of nodes that can be installed in an HVDC network, creating the transmission equivalent of an interstate highway with on- and off-ramps spaced hundreds of miles apart.
Heyeck sees another way to make the power highways more flexible while sticking with good old AC, albeit at an extra-high 765 kilovolts. Such lines would operate at more than twice the voltage at which most U.S. and European lines max out and carry up to six times as much power, since the capacity of a line is roughly proportional to the square of the voltage. (China just set up ultra-high-voltage 1,000-kilovolt AC lines that push this advantage even further.) This technology minimizes the need for converting back and forth between AC and DC. Moreover, a new network of extra-high-voltage AC lines with plenty of on-ramps would enable long-haul power flows to ride alongside the energy traveling over the existing AC grid.
The higher-voltage AC concept is so attractive that engineers at American Electric Power (AEP) and the American Wind Energy Association have sketched out a model hefty enough to supply 20 percent of U.S. power via wind energy alone (see map below). Their plan employs 19,000 miles of 765-kilovolt lines that would crisscross the country. At $60 billion the price looks high, but nationwide it would add just a few dollars per month to the average power bill.
Ultimately, Heyeck says, the interstate power networks are likely to blend the two technologies, favoring HVDC for the trunk lines that push power the longest distances and 765-kilovolt AC where flexibility counts most.
Interstate transmission could bring renewable power to consumers, but that solves just half the problem. Once the power arrives onsite, it must be used efficiently for the grid to thrive. On the local end, the difference between renewable energy and more conventional forms is variability: Clouds darken the skies above solar panels, and winds fluctuate even from minute to minute. The smart grid must allow customers to make the most of the energy when it arrives while taking back excess and saving for a rainy day. (We may also need to augment renewables with a steady source; see "New Tech Could Make Nuclear the Best Weapon Against Climate Change.")
It all comes down to balancing supply and demand, says mechanical engineer Rob Pratt, who runs the smart grid program at the U.S. Department of Energy's Pacific Northwest National Laboratory in Richland, Washington. "The grid has almost no storage, so it has to generate the power that's being consumed almost instantaneously, inside of a minute," he explains. Get too far behind and the grid goes black. "It's just like your car stalling on a hill. The grid slows down fast, and if it slows down too much, it falls apart."
The present mode of operation - essentially unchanged since the invention of power grids in the late 19th century - keeps blackouts at bay by measuring total consumer demand and throttling up and down on the supply of electricity from power stations as needed. It works, but it is a bad fit for renewable energy. Solar panels and wind turbines can stop supplying electricity at any time if the weather shifts. So even when the renewables are going strong, conventional power plants must always be at the ready to step in and carry the load.
Smart grids will do better by inverting the power system's most basic rule of operation. Instead of adjusting power output in accordance with shifting demand, they will help consumers control their use of electricity, timing it to coincide with availability of the grid's cleanest and cheapest power sources. "With a smart grid we can adjust the load to follow dips in the wind and the sun," Pratt says.
This tail-wagging-the-dog scheme is approaching a critical test in Boulder, Colorado, where Minneapolis-based utility Xcel Energy is rolling out one of the first systemwide installations of a smart grid. The key goal: managing wind and solar resources not just through storage but also through technology-assisted consumer participation.
"Our customers don't change their consumption when the wind quits blowing," explains Mike Carlson, in charge of the smart grid strategy at Xcel. "So we need to build or procure backup resources to keep power level when the wind quits." Getting Xcel's customers engaged is what the smart grid experiment is all about, he notes. The key is giving customers cues when renewable energy is available and making it easy for them to change their consumption patterns accordingly. "Anecdotally, our customers are saying, 'If you give me the tools, I'll help you out when the wind quits blowing so you don't have to keep the fossil fuels burning in the background,'" Carlson says.
By this summer, 25,000 families and businesses in Boulder should have the key tool they will need: a 21st-century upgrade to the humble electromagnetic meters measuring power consumption in basements across the country. Those old meters epitomize today's power grids, where a steady but essentially blind flow of electricity and the occasional visit by a meter reader is all that links power plants and distribution systems to consumers. Xcel's new smart meter, in contrast, belongs to the Twitter generation.
The smart meter will check in with the Xcel central office every few seconds via signals sent over the power line itself, creating a two-way digital conversation. Instantly the utility will know how much power a given customer is using, and perhaps even how much she plans to consume later.
In a couple of months, customers in Boulder with smart meters should be able to check their energy usage in real time. By early next year they should be able to check grid conditions and control usage over the Internet—for instance, reducing consumption while away from home by activating a vacation mode.
In this first implementation, the smart grid's feedback mechanism is manual: Consumers must go online for an update on current grid conditions and then actively alter their use of power. For example, winds predicted to energize the nearly 1,100 megawatts of wind turbines on Xcel's grid in eastern Colorado could be a cue to hold off on running the dishwasher until bedtime. "I don't care when my dishes get washed," Carlson says. "I just want them washed by tomorrow morning."
Ultimately, Carlson says, the process will be automated so that computers make many of the power calls, controlling everything from pool pumps and refrigerators to air filtration systems according to changing grid conditions and the consumer's preprogrammed preferences. All of these loads, connected to the system by wires or wireless gateways, can be turned off for a matter of minutes or hours without most customers' ever even noticing.
The impact on the grid could be considerable. In 2007 Pratt's team collaborated with IBM to equip 112 homes on Washington State's Olympic Peninsula with a smart meter and wireless switches to control their thermostats and water heaters. The switches could be programmed to shut off when power demands on the grid (and hence electricity prices) peaked. The average homeowner shifted enough consumption to shrink his peak electricity use by 15 percent.
The effects could be even more dramatic for those Boulder-area residents who will be plugging cars into the smart grid conversation. Xcel hopes to convert up to 500 hybrid cars owned by the county, the city of Boulder, and the University of Colorado to plug-in hybrids by adding larger batteries that can be charged from the grid. Several, including the university chancellor's Ford Escape, are already on the road. Like Carlson's dishwasher, the hybrid vehicles will recharge when electricity is in low demand or when wind power is abundant.
The Boulder plug-ins can also intervene to help the grid. When a blistering summer afternoon has power lines straining to support a city's worth of air conditioners, for example, a signal from the utility could ask the vehicles to give back some of their stored charge. "They can act as storage batteries for the grid, soaking up excess capacity," Pratt says. "That will really help us out with the intermittency of renewables." The chairman of the Federal Energy Regulatory Commission in Washington, Jon Wellinghoff, thinks plug-ins will be so beneficial to the grid that he has taken to calling them "cash-back hybrids." Wellinghoff's bet is that in short order utilities will be paying drivers to keep their mobile batteries plugged in to the grid rather than billing them for the power they consume.
Energy experts expect Obama's stimulus money to crystallize political support for, and industry investment in, the next-generation grid. "The kick start to manufacturers of smart grid gear is going to be huge," Pratt says. "We're going to see a 20-year-plus transition turn into 10 years or less." Carlson says Xcel will await hard numbers on the value of the smart grid, due in late 2010, before it expands beyond Boulder. But if the benefits match Xcel's expectations, he says, look for smart grids to roll out nationwide within five years.
|Images Courtesy NREL|
When it comes to the interstate expansion of power lines, the president's stimulus and his renewable energy tax credits will accelerate a process already under way. The real challenge, according to Heyeck, is the hodgepodge of state and regional agencies whose overlapping authority and conflicting interests make interstate transmission planning a bureaucratic quagmire. State regulators call most of the shots as far as what gets built and who picks up the bill. Most are bound by state laws directing them to consider only the in-state benefits of new lines, so the broader benefits of the interstate grid could be ignored.
Lawsuits inevitably gum up the planning process further, since nobody wants a transmission tower in his backyard - even when it carries renewable energy. The Sierra Club, for example, is fighting a new line designed to bring solar, wind, and geothermal energy to San Diego. The line would bisect a national forest and (like any grid expansion) could also facilitate new deliveries of coal-fired electricity. Such hang-ups make even President Obama's modest goal of adding 3,000 miles of new transmission lines look wishful.
What power companies really need, Heyeck says, is federal law creating a national process for designing an interstate grid, choosing a path for each leg, and allocating the construction and maintenance costs - preferably by billing consumers nationwide. With this kind of mandate, Heyeck vows that companies like AEP will get the job done. "Implement this support and tell us what projects to build," he says, "and the private investment will come."
The upper map shows the best locations for turbines, based on wind conditions, with desirability decreasing from blue to red to purple to pink to gold. The lower map shows existing high-voltage lines capable of transporting wind-generated power in red; lines needed to meet the 2030 goal for renewable energy, according to the American Electric Power/American Wind Energy Association plan, are shown in green. The National Renewable Energy Laboratory of the U. S. Department of Energy (DOE) used information in the maps to project wind energy production and transmission through 2030, when wind could provide 20 percent of the nation’s energy. Called the Wind Deployment System, or WinDS, DOE's predictive model will guide the ramped contribution of wind energy to the American electricity supply over the next 50 years.