The fantasy of a U.S. super-grid

October 15, 2009

The United States will need to invest $50-100 billion to upgrade and extend its high-voltage electricity transmission network in the next 15 years, according to industry estimates, to meet growing demand, relieve existing congestion and accommodate a higher share of wind and solar power on the grid.

Legislation before Congress would provide federal loan guarantees and other support. But while visionaries talk about creating a nationwide “super-grid” carrying solar energy from the Mojave and wind power from the plains to load centres on the east coast, most of the investment needed will be in more prosaic projects to strengthen local networks and improve regional transmission over shorter distances.

Generating units connected up to a grid must be synchronised to rotate at the same speed and in the same phase to produce a good quality alternating current (AC) with a smooth waveform. Most advanced economies operate a single nationwide grid, but the U.S. power industry grew up piecemeal and is much more fragmented as a result.

The Lower 48 states are covered by three separate grids with limited transmission capacity between them: the Eastern Interconnection (covering the eastern two-thirds of the country, excluding Texas, with around 710 GW of generating capacity); the Western Interconnection (covering the western third, with 178 GW of capacity); and the Texas Interconnection (covering most of the state, with 80 GW) (http://graphics.thomsonreuters.com/109/US_NERC1009.gif).

The only way to link these unsynchronised AC power grids is via a direct current (DC) line (converting AC from one grid to DC for transmission and then back to AC again in the receiving grid). At present, the United States has just six DC links between the Eastern and Western Interconnections, and two connections between the Eastern Interconnection and Texas.

THE NEED FOR MORE NETWORKING

The power grid’s balkanisation has created a situation where power prices can diverge sharply across the country, with some areas experiencing acute shortages and risk of rolling blackouts (e.g. California) while others have too much power from intermittent sources such as wind and see power prices drop to zero in a bid to force conventional generating capacity offline (e.g. Texas).

Fragmentation threatens to wreck proposals to reduce the power sector’s carbon dioxide emissions by increasing the share of generation from renewable sources, roll out a new generation of nuclear stations, and build zero-carbon integrated gasification and combined cycle (IGCC) power plants with carbon capture and storage (CCS).

Renewables such as wind and solar are intermittent, while nuclear and IGCC plants have to be operated as baseload. The industry is developing more sophisticated demand-side management systems. But in the end the only way to ensure reliable power supplies will be to link renewables, nuclear and IGCC with a new fleet of conventional gas turbines (CT) for fast demand response, and increase the degree of networking in the system so unscheduled changes in generation and power demand can be balanced across a much wider area.

LINKING THE INTERCONNECTIONS

Grid strengthening has become a key priority for both policymakers and the industry. So the announcement on October 13 of a project to build a new three-way system linking the major interconnections using super-conducting high-voltage direct current lines has captured the imagination.

The “Tres Amigas Project”, located at Clovis, New Mexico, near to the common boundary of the three grids, aims to “create the nation’s first renewable energy trading hub”. According to the project’s promoters, it will carry “gigawatts of green power” from region to region and “enhance the capacity, reliability of efficiency of America’s power grids”.

The hub would have 5 GW links between each of the separate interconnections, enabling power to flow from interconnections with surplus low-cost capacity to areas with excess demand or high-cost output (http://www.tresamigasllc.com/pdf/FinalAmigasFactSheet_1253075040.pdf).

But while Tres Amigas is an interesting idea, and might promote slightly greater integration between the three interconnections (especially in the case of Texas) it does not really address the root of the problem — which is the lack of adequate transmission capacity within the interconnections, not between them.

Once Tres Amigas has exported surplus power from (say) Texas to the Western Interconnection, it will still need to be supplied across thousands of miles of existing transmission lines to major load centres on the west coast around Los Angeles and San Diego.

The California power crisis in 2000-2001 was caused, in part, by lack of sufficient capacity on the Path 15 line connecting the northern and southern parts of the state, which was wholly within the state. With Path 15 operating at full capacity, the availability of more power from Texas or the Eastern Interconnection would not have helped.

It is the lack of sufficient transmission capacity within the interconnections that is the real constraint on meeting demand growth, improving reliability and integrating new zero-carbon technology onto the grid.

BOOSTING LOCAL, REGIONAL GRIDS

The 2006 National Electric Transmission Congestion Study, produced by the U.S. Department of Energy, has identified two Critical Congestion Areas (one from New York down the Atlantic Coast to Northern Virginia, and the other in Southern California) as well as a number of lesser Congestion Areas of Concern (http://graphics.thomsonreuters.com/109/US_ENERG1009.gif).

The study also identified a number of Conditional Constraint Areas, where capacity might prove insufficient in future if renewables, coal and nuclear are developed as expected to meeting rising demand and curb emission (http://graphics.thomsonreuters.com/109/US_ENRGY1009.gif).

The real constraint is how to move power from giant wind farms that might be developed in the western half of the Eastern Interconnection around Iowa and Illinois east to the coastal cities of New York, Philadelphia, Baltimore and Washington. Similarly, how to move power generated from the coalfields of the high north and wind farms on the Great Plains south and west to the California coast.

PROJECTED COSTS UP TO $100 BILLION

The Joint Coordinated System Plan (JCSP) for the Eastern Interconnection estimates the eastern grid alone will need around 10,000 miles of new transmission capacity (costing almost $50 billion) as well as 190 GW of extra generating capacity (costing $675 billion) by 2024 simply to meet demand growth under a business-as-usual reference strategy.

But if the share of wind in total generation is increased to 20 percent, as some hope, the amount of new transmission capacity needed would increase 45 percent (14,500 miles, costing almost $80 billion) while extra generating capacity would rise 80 percent (342 GW, costing $1 trillion). Most of the increase results from the need for many more conventional gas turbines to back up the windfarms, as well as longer lines to take the wind energy to the coast.

Under either scenario, new lines will be needed within the Eastern Interconnection to bring power from the wind-rich western states to the power-hungry eastern seaboard (for the most likely transmission corridors see figures 1-2 and 1-3 in the study here http://www.jcspstudy.org/).

The point is that massive new investment will be needed to strengthen existing grids rather than worrying about a nationwide super-grid. The investment cannot be readily financed until the United States makes an irrevocable commitment to developing wind and other power sources by committing to setting a (high) carbon price. Until there is a clear template for the future of the industry, investment will have to proceed piecemeal.

One comment

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Well articulated and supported. A well written commentary. Unfortunately, getting our government to actually implement ANY comprehensive plan is much like herding chickens.

Posted by Eric | Report as abusive