Combining Three Regional Grids into One US-Wide Grid
- Written by Shirley Siluk
Right now, the US grid is actually three separate regional grids: the Eastern Interconnection, the Western Interconnection and the Texas Interconnection—or ERCOT (for the Electric Reliability Council of Texas). A convergence of new technologies and developments in the US energy infrastructure is making it possible, for the first time, to seek to link the nation's three major electricity grids into a single, more resilient grid that can support more renewable power.
Currently, there are few links among the three grids, meaning a total of only 2 gigawatts of energy can be transferred from one interconnection to any other. While integrating these grids into a single system has been a goal for many years, it is only recently that the necessary pieces have fallen into place.
The Tres Amigas SuperStation project ("tres amigas" means "three female friends" in Spanish) was launched in early 2008 when it became apparent that linking the three interconnections had at last become feasible. The developments that have made the project possible are:
- • Voltage Source Converters (VSCs) that can efficiently convert alternating current (AC) power from one grid into direct current (DC) power and then back into AC power. This makes it possible to connect two or more asynchronous grids, which cannot be connected directly via AC power. Tres Amigas, LLC, compares the technology to a "power roundabout" in which VSCs act as on- and off-ramps for electricity traveling from one energy highway to another. These types of VSCs for high-voltage direct connections (HVDC) have become available only recently.
- • Advanced software capable of tracking frequent price fluctuations across multiple wholesale energy markets. Transferring power from one grid to another will require not only the ability to keep track of energy prices that change every 15 minutes but the ability to apply advanced analytics to price, demand and supply data. That makes it possible to forecast loads, generation and prices, optimize resources, generate reports and manage energy flows back and forth between asynchronous grids. Again, this level of software capability is a relatively new development.
- • The proximity of the three regional grids. With the planned addition of new transmission lines, the three grids will soon be the closest they've ever been. Tres Amigas has obtained the rights to lease 22.5 square miles of land in Clovis, New Mexico, which falls right in the midst of that three-way near-intersection. And that's where it plans to build the SuperStation that will finally link the Western, Eastern and Texas interconnections on a large scale.
Other cutting-edge technologies contributing to the SuperStation's capabilities will include underground and power-dense superconductor cables between the facility's three converter stations and on-site, dry cell, battery-based energy storage that can respond to demand and output fluctuations or provide backup power to the grid when needed.
Groundbreaking on the Tres Amigas project is set for July 2011, with the first connection—a 750-megawatt VSC linking PNM and Xcel Energy—expected to be energized and operating by mid-2014. Two additional connections of 750 megawatts each—between PNM and ERCOT and between Xcel and ERCOT—will complete phase one of the project.
From there, the SuperStation will remain a work-in-progress, with more and more connections coming online over time. Initially, the project is aimed at providing a total power transfer capacity of around 5 gigawatts. Eventually, however, that capacity could rise to up to 30 gigawatts.
The ability to rapidly transfer such large amounts of energy from one grid to another should help all three regional grids better manage demand fluctuations and infrastructure stresses. For example, making it easier to shift power between grids as needed could help reduce the risk of rolling blackouts like the ones imposed by ERCOT in February 2011 in the wake of exceptionally cold weather and severe winter storms.
Better grid integration should also help to smooth price variations for energy customers. Because the three regional grids are essentially independent of one another at present, energy prices among them can differ by more than $50 per megawatt-hour over 800 to 2000 hours per year. Linking the systems can enable the most efficient and affordable electricity producers to reach customers across all three grids, rather than just one.
Beyond improving resilience by letting the three regional grids share power more effectively, the Tres Amigas project is also designed to enable renewable energy generated in one location to more easily meet the demands of electricity consumers in distant markets. In fact, the organization claims the SuperStation will function as "the nation's first renewable energy market hub."
By uniting a grid that is now "balkanized," Tres Amigas aims to at least partly remove one of the obstacles holding back development of renewable energy: the lack of adequate transmission between areas where sun or wind power is greatest and areas where demand for energy is largest. Agencies such as the Western Electricity Coordinating Council, for example, have called limited transmission resources in the West the biggest limiting factor in developing the region's renewable energy resources.
All the advanced technology alone that is going into the SuperStation certainly qualifies the project as a smart-grid development; however, possibly the smartest thing of all is that it promises to finally provide both generators and customers with a truly national—rather than a segmented—energy grid.