By Martin Gross, ABB | 31 January 2011
POWERGRID International
It’s an interesting time to be involved with electricity. The power industry is on the verge of the biggest changes since the days of Thomas Edison and George Westinghouse. Recent breakthroughs around the world in power transmission systems have made it imperative for the U.S. to develop a more intelligent, flexible, long-haul transmission network that can carry renewable energy from remote locations to major population centers.
RPS Driving Build Out
Today in the U.S., 33 out of 50 states have some kind of renewable standard. These renewable portfolio standards (RPS), and their corresponding deadlines for compliance, have significantly impacted generation spending.
Proposed goals for a national renewable portfolio standard vary from 12 to 25 percent. If the government enacts a national standard, experts estimate that incremental capacity additions of more than 300 GW will be needed. Transmission capacity for this new and mostly remote generation, however, does not exist. With an average construction schedule of 60 months to 72 months for a 500 MW, 345 kV transmission line, it could take well beyond 2025 to build the needed transmission lines.
The North American Electric Reliability Corp.’s (NERC’s) October 2009 publication, “2009 Long Term Reliability Assessment 2009 – 2018,” notes that although existing reserve margins are adequate across the U.S. for the next few years, the first priority must be to expand the grid and increase transmission capacity to handle expected renewable generation growth.
The report concludes by saying: “More than 11,000 miles (or 35 percent) of transmission above 200 kV proposed and projected in this report must be developed on time to ensure reliability over the next five years.” NERC strongly believes that construction siting is the most urgent issue for the electric power industry, now and well into the future.
Bulk Transmission Capacity: A Prerequisite
If utilities are to harvest the vast renewable power potential in remote locations in the U.S., or anywhere in the world, they must be able to move it efficiently from its production point to cities and load centers where people live and work.
Bulk transmission capacity is a prerequisite for large-scale renewable generation. While many renewable power sources’ intermittent nature creates challenges for grid reliability, proven, readily-available and cost-effective transmission technologies exist to mitigate their impact. They are available now and include high voltage direct current (HVDC) and flexible AC transmission systems (FACTS).
Several key transmission projects in the U.S. focus on transmitting renewable generation:
- Southern California Edison continues to add transmission to support wind generation in the Tehachapi region.
- FPL’s NextEra Energy has completed much of its merchant transmission associated with its Horse Hollow Wind Energy Center project in Texas.
- LS Power’s Southwest Intertie will move renewable power from Wyoming and Montana to substations near Las Vegas, using AC and possibly high voltage DC transmission.
- Another LS Power project, Overland Transmission, will apply either high voltage AC or DC circuits across 560 miles to move renewables-fueled generation between eastern Wyoming and southern Idaho.
- San Diego Gas & Electric’s Sunrise PowerLink will play a major role in bringing renewable generation from the Imperial Valley into southern California, even though it was built primarily to ensure system reliability and support load growth. According to the Renewable Energy Transmission Initiative, the Imperial Valley region has potential for 6,870 MW of solar, 3,495 MW of wind and 2,000 MW of geothermal power generation.
Although multiple major transmission projects are underway or nearing construction in the U.S., they are not enough to support RPS requirements. The two key renewable power transmission capacity expansion impediments are:
- The fragmented and time consuming regulatory approval process, and
- The absence of an integrated renewable generation and transmission strategy.
A look at a couple of examples of recent transmission successes in Europe and China provide an idea of what U.S. transmission could look like.
Europe: Visionary Governments Prepare for Offshore Wind
In the North Sea, 81 miles off Germany’s coast, the world’s largest offshore wind farm is connected to the grid using advanced HVDC technology. With HVDC cables lying both underwater and underground, the project’s environmental impact is minimized and the regulatory and siting procedures have been swift. The project connects wind generators and transmits power to a new substation on Germany’s coast. The power is then connected to the existing transmission grid.
The BORWIN 1 offshore wind farm demonstrates how HVDC can effectively accumulate power generated in remote locations and transmit it to load centers. Through the use of HVDC and wind generation, Transpower, the transmission grid operator, expects to avoid 1.5 million tons of CO2 emissions per year by replacing fossil fuel generation.
This summer, an even larger project was launched off Europe’s coast. ABB is working with Transpower to supply an 800 MW power link. This project will use HVDC Light technology to transmit power from the 400 MW Borkum West II wind farm (see Figure 1) and other wind farms to be developed nearby. The wind farms will be connected to an offshore HVDC converter station that will transmit electricity to the onshore HVDC station at Dörpen, on Germany’s northwest coast, via 165 kilometers of underwater and underground DC cables. The Dörpen/West converter station will in turn feed AC power to the mainland grid. At 320 kV, this will be the highest voltage level of extruded cable ever used for HVDC. State-of-the-art transmission technologies like these are integrating renewable energy sources efficiently, ensuring grid reliability and stability and lowering environmental impact.
