A study out last week suggests that the United States could, at least in theory, use new high-voltage power lines to move renewable power across the nation, and essentially eliminate the need to add new storage capacity.
This improved national grid, based on existing technologies, could enable utilities to cut power-sector carbon dioxide emissions 80% from 1990 levels by 2030 without boosting power prices, researchers report today in Nature Climate Change.
The findings come on the heels of the Paris climate agreement, in which theUnited States pledged to cut its national emissions by up to 28% from 2005 levels by 2025. About 40% of U.S. emissions come from the power sector, and the U.S. Environmental Protection Agency (EPA) recently released rules that task states with reducing power-sector emissions. States can choose from a menu of strategies, EPA says, such as boosting renewable energy use.
But some observers wonder whether the U.S. power grid can rise to the renewables challenge.The grid is divided into several regional grids or “interconnections,” which contain smaller subdivisions. Because regions experience both sunless and windless periods, energy planners and experts have long believed that a wind- and solar-dominated grid would need to store some power for later use. The problem is that large-scale storage technologies haven’t been commercially realistic.
Alex MacDonald, a National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C., researcher, was familiar with that problem. But he realized that researchers hadn’t explored all the potential solutions. For instance, meteorological data suggest that wind is always blowing somewhere in the United States, MacDonald says. So, although renewable energy output might be intermittent on a regional scale, it would have a more constant flow at a national scale. MacDonald wondered whether the U.S. grid might be able to overcome intermittency problems if it added high-voltage, direct-current (HVDC) transmission lines—which suffer less energy loss than do traditional alternating-current transmission lines—to connect regional grids, so that power could be moved to where it was needed.
MacDonald, Christopher Clack of NOAA and the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder, and other colleagues wanted to test this idea. They built a computer model to analyze different configurations of a weblike network of interregional HVDC lines plus renewable energy installations. The model divides the United States into a grid of 152,000 squares that are assigned to regional grids. In order for the program to evaluate the potential for solar and wind power in each square, the researchers inputted data on sunlight and wind speeds between 2006 and 2008 (but the program excluded areas, such as national parks and mountain slopes, that typically can’t host windmills or solar panels). Then, using forecasts for power prices and demand, the program could calculate where it would be economical to build wind and solar projects, and move renewable power from region to region. Finally, the researchers told their program to find the lowest-cost way to achieve certain emissions cuts while still meeting future power demand.
By 2030, with HVDC lines meeting at 32 nodes between regional grids, the United States could add enough wind and solar power to cut power sector emissions by up to 80% from 1990 levels, the researchers concluded. And they calculated that power prices would be lower, on average, than a business-as-usual scenario. And “these results are the minimum of what we could get to,” MacDonald tells ScienceInsider, explaining that the researchers used very cautious assumptions.
Stanford University in Palo Alto, California, energy researcher Jonathan Koomey, who wasn’t involved in the work, agrees that the NOAA team’s assumptions are generally cautious. U.S. power demand may rise less than the team’s projections, for instance, as a result of new energy-efficiency measures. And the team gets its rosy results even though it didn’t add in the health and environmental costs of the pollution created by burning fossil fuels. But Koomey also offers major caveat: The study doesn’t consider the potential for electricity demand to rise more than expected should electric vehicles catch on, he notes. If that happened, the United States would need more renewable projects to achieve the same emissions cuts.
The bigger hurdle to realizing the study’s vision of a national grid, however, may be persuading policymakers, utilities investors, and landowners that it’s a good idea, says Susan Tierney, a former U.S. assistant secretary of energy under President Clinton who’s currently an energy consultant at the Analysis Group in Boston. “The problem is not rooted in technology, but rather in the way that the U.S. power system is organized legally, politically, economically, and culturally,” she says. Utilities and politicians are sometimes loath to depend on distant power producers, for example, and communities often fight the construction of large power lines.
Koomey notes that the researchers aren’t necessarily advocating a totally storage-free, national system or trying to bash storage technology. “They’re just saying, ‘Let’s just explore a system without storage and see if it’s possible.’” The answer, he says, is that it’s more possible than many people might think.