A proposed hub for connecting the three independent electricity grids that span the continental United States could make it easier to ramp up production of renewable electricity.
The project, called the Tres Amigas Superstation, would use superconducting “pipelines” and converter stations to connect three grids: the Western, Eastern, and Texas Interconnections. Connections between the grids have been limited because the grids aren’t synchronized–the AC power is out of phase. Special stations that convert AC power into DC power and then back into AC power in the correct phase are needed to move power from one grid to another.
Only a fraction of 1 percent of the electricity generated in the United States can currently be transferred between the grids, and there is no direct connection between Texas and the Western grid. The Tres Amigas station, which will connect all three grids together in one place for the first time, will initially more than double the ability to transfer power between them, providing five gigawatts of capacity. Eventually, the station is expected to transfer as much as 30 gigawatts of power.
The station will “solve a host of problems” related to renewable energy, says Phil Harris, CEO of the Tres Amigas company, based in Santa Fe, NM. Primarily, it will help address a key problem with renewable sources of energy–their intermittency. Because wind comes and goes and clouds block the sun from time to time, wind and solar power can destabilize the electric grid.
One way to compensate is to make sure that no renewable source accounts for too much of the total power mix–so that other sources can easily fill in when there’s a drop in power. In Texas, however, this strategy would quickly limit the size of wind farms, since the grid there is relatively small. By connecting to the rest of the country, Tres Amigas removes the limit on the size of these farms.
Intermittency can also be addressed by gathering renewable energy over a wide area. That way, a drop in solar power due to a cloudy day in one region could be offset by wind or solar elsewhere. Connecting the three grids makes it possible to draw on a wider variety of renewable sources, especially in the Southwest, which is divided by the borders between them. The station will also provide between 50 and 150 megawatts of battery storage to smooth out power fluctuations on the grid to help prevent outages.
The project could also be a valuable testing ground for direct current superconducting transmission lines, which could have significant advantages over conventional power lines for delivering large amounts of power over long distances, says Steven Eckroad, a project manager at the Palo Alto, CA-based Electric Power Research Institute (EPRI), which is studying the potential of superconductors for long-distance transmission. Such transmission lines could collect wind power from the Midwest, where it is abundant, and transmit it to the South, which has fewer renewable resources.
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