With the Current Push to Dramatically Increase the Amount of Renewable Energy Resources — especially wind-generated electricity — two questions must be asked: What transmission would be needed to support the economic use of wind resources to meet the renewable portfolio standards (RPS) that currently exist in the U.S. Eastern Interconnection? What transmission would be needed to support a 20% wind-energy national portfolio scenario?

PLANNING STUDY PARTICIPANTS

The Midwest ISO (Carmel, Indiana, U.S.), PJM Interconnection (Norristown, Pennsylvania, U.S.), Southwest Power Pool (SPP; Little Rock, Arkansas, U.S.) and the Tennessee Valley Authority (TVA; Knoxville, Tennessee, U.S.) have joint operating agreements that call for two-party studies to coordinate transmission planning for reliability purposes. A study done by the Midwest ISO and PJM showed little need for transmission for reliability purposes beyond what was included in the respective regional transmission organization (RTO) plans. However, energy market transmission constraints indicated there was a need for transmission for economic reasons.

The Midwest ISO Transmission Expansion Plan (MTEP) exploratory and economic studies from 2006 and 2008 indicated that a conceptual transmission expansion plan including the Midwest ISO and PJM footprints only, with 20% wind energy in the Midwest ISO footprint only, may produce benefits that exceed the cost of the transmission. The MTEP studies showed that benefits occurred beyond the Midwest ISO and PJM with the conceptual transmission expansion for 20% wind energy in the Midwest ISO. So, rather than producing four reliability plans that did not resolve the issues of the congestion in the energy markets, the Midwest ISO, PJM, TVA and SPP agreed to run economic studies similar to the Midwest ISO process to provide information about possible economic transmission.

To do that, the Joint Coordinated System Planning (JCSP) study was organized in late 2007 with the Midwest ISO, PJM, TVA and SPP. The JCSP group is a voluntary organization; the study results are for information and not binding to be constructed as part of a plan.

Other Eastern Interconnection RTOs and utilities were invited to participate in the JCSP study, which was conducted in an open Federal Energy Regulatory Commission Order 890-compliant process. Twelve meetings were held in various locations to collect information, coordinate studies and present information over a period from November 2007 to December 2008. The JCSP report, issued in February 2009, is available online at www.jcspstudy.org.

One important result of the JCSP study is that it proved it is possible for some of the Eastern Interconnection RTOs and utilities to work together to produce coordinated conceptual transmission plans to provide information concerning the economics of integrating wind into the Eastern Interconnection.

BACKGROUND AND DATA

The Department of Energy's Office of Energy Efficiency and Renewable Energy was interested in determining what would be required to have 20% wind energy nationally by 2030. The National Renewable Energy Laboratory (NREL) produces national wind information, and the American Wind Energy Association (AWEA) is the voice of wind energy in the United States, promoting renewable energy in America.

The NREL-AWEA report “20% Wind by 2030” addressed this issue, but there were no detailed transmission designs produced by this report based on engineering studies. DOE-NREL offered to produce wind data that could be used in the JCSP and Eastern Wind Integration Transmission Studies (EWITS).

JCSP would produce transmission plans for a reference scenario representing existing RPS in the U.S. Eastern Interconnection (which is about 5% wind energy) and a 20% wind-energy scenario. The basic JCSP plans would be modified to analyze three 20% wind-energy scenarios with different generation location assumptions. The generation assumptions cover a range locating wind generation where it has the highest-capacity factors: in the West, heavy offshore locations in the East, and a blend of onshore and offshore.

A 30% wind-energy scenario of heavy onshore and heavy offshore wind-generation scenarios is also be produced by EWITS. Most of the JCSP participants, as well as some additional parties, are participating in EWITS.

One notable additional participant in EWITS that was not in the JCSP is Southern Company (Atlanta, Georgia, U.S.), which serves a sizable portion of the southeast part of the country.

The map in Fig. 1 shows NREL produced a database of wind data for the colored area of the map for the years 2004, 2005 and 2006 in 10-minute periods for 600,000 MW of wind generation at a special resolution of 2 sq km (0.7 sq miles).

The database information is time-synchronized to load so wind-diversity studies can be completed. Prior to the release of this database, the time diversity of wind energy could not be evaluated for more than a one-state area. The database is publicly available on the NREL Web site.

Tremendous progress was made in 2008 and is continuing into 2009 for the analysis of wind scenarios. Information is now available about the potential cost of building transmission for 5% and 20% scenarios.

The DOE's Office of Electricity Delivery and Energy Reliability also participated in the JCSP. The JCSP has the potential of relieving the Eastern National Interest Transmission Corridor by relieving a major portion of the transmission congestion in the U.S. Eastern Interconnection.

GENERATION AND CAPACITY FORECASTS

The JCSP study produced a generation forecast based on assumptions and site constraints provided by stakeholders and commercial databases. Generation expansion was forecast by areas as shown in Fig. 2. Each area is capacity sufficient. For the 20% energy case, the Southeast Reliability Council (SERC; Charlotte, North Carolina, U.S.) and PJM areas required an import of wind energy, which was assigned a 15% capacity credit. The capacity from wind energy was part of the PJM and SERC generation forecast.

The generation forecast for the U.S. Eastern Interconnection is shown in Fig. 3. Announced nuclear plants were inserted into all cases along with generation that has signed interconnection agreements. The column on the left represents this generation and is included in every scenario.

For 5%, 20% and 30% wind, the total connected forecasted generation is greater than the capacity need. Because wind energy is available mainly in the evening and at night, only 15% of the wind is credited as able to supply capacity.

Wind generation is an energy resource that provides a choice of obtaining energy from the wind (when it is available) rather than from fossil-fuel-fired generation. Other generation is needed to supply capacity on a reliable basis, and that is the generation represented below the equivalent convention capacity line in Fig. 3.

For the wind scenarios, there is an overabundance of generation capacity compared to if the generation expansion were supplied by conventional generation, as indicated by the light-green line. Off peak, most of the generation capacity is available and produces energy choices from low-cost generation and lower energy prices. On peak, this capacity is not generally available, and the conventional generation supplies the energy. Fig. 4 shows the location of wind generation in the JCSP 20% wind-energy scenario.

Wind generation was sited locally due to political and economic development concerns, as well as concerns about congestion in high production areas. Other forecasted generation was located, as shown by the color code of the dots on the map in Fig. 4.

All existing and new generation is modeled in the JCSP study, as the conceptual transmission system expansion is designed to accommodate all types of generation. For the 20% wind case, there is 229,000 MW of new wind generation and 174,000 MW of other new generation.

Note the reduction in coal generation with increasing wind and the increase in gas generation. Coal generation could be replaced with nuclear or gas generation if other generation scenarios were considered. Replacing coal with gas generation did not change the conceptual transmission expansion significantly when tested in a sensitivity study.

PRICE SENSITIVITIES

Fig. 5 shows the energy price impacts that would occur with the 20% wind-energy scenario but without the transmission system. The large price differences are reduced when the JCSP transmission-expansion overlay (Fig. 6) is added. The reduction in prices produces a benefit for the load on the East Coast by reducing the energy costs and a benefit to the wind generation that is passed to the load in the West by increasing revenue. The price difference produces the benefits that would allow the transmission overlay to pay for the annual costs of the transmission.

The benefit-to-cost ratio for the 20% wind-energy scenario is calculated to be 1.7:1 in the year 2024. There is uncertainly due to the changes of prices of line construction, the price of gas and other fuels for generation, the price of generation, load changes and other factors in this number. The estimated price of the 20% transmission overlay is US$80 billion. The estimated price of the reference transmission overlay is $50 billion. The benefit-to-cost ratio of the reference transmission overlay is 1.4:1. If the assumptions used in the JCSP apply, the necessary conditions may apply to a business case to start construction of the transmission overlay. All the wind needed is in existing state-by-state RPSs. The variability of construction costs and gas prices are the largest risks. Transmission and generation construction prices appear to be dropping with the current economic situation.

The cost of the 20% conceptual transmission overlay is 2% of the expected price for wholesale energy in the year 2024. The reference cost is 1%. Transmission is a small part of the overall energy price. The breakdown is shown in Fig. 7. Note the reduction in the production cost (primarily fuel) component. Wind energy does displace the need to burn as much fuel to produce energy. The carbon-dioxide levels of the 20% case versus the reference case are reduced by 8%.

THE TRANSMISSION OVERLAY

The conceptual transmission overlay for the 20% wind scenario shown in Fig. 8 has both 800-kV HVDC rated at 6400 MW per bipolar line and 765-kV ac combined into one integrated design. HVDC delivers energy at a lower cost than 765 kV for distances over 600 miles (966 km). The length of some of the HVDC lines is 1200 miles (1931 km). HVDC is used in the overlay design where it has advantages, and 765 kV is used where it has advantages and to link the HVDC lines together to transfer power during contingencies.

The overlay is designed to contain outages of the overlay lines within the overlay and to within the present limits of the ac underlying system. The underlying ac system does not have to be rebuilt for the transmission overlay to function well. The HVDC lines and 765-kV ac lines have transmission reserve margin capable of rescheduling the power on a lost line to the remaining HVDC and ac lines of the overlay. HVDC can change schedules in cycles.

A GOOD START

The JCSP provides the most-complete information to date concerning the transmission required to integrate wind in both a 5% and a 20% wind-energy scenario for the U.S. Eastern Interconnection. JCSP provided a transmission system for EWITS. EWITS is continuing to augment the JCSP information with more detailed data about various operating aspects of wind integration for periods of less than an hour. The combined effort provides much-needed information about how to manage a large injection of wind generation into the power grid of the future. JCSP and EWITS have shown that it may be possible to plan and construct a transmission overlay that allows for large amounts of wind generation to be developed with transmission offering a net benefit to the power system as a whole.

Much more needs to be done. There are generation scenarios that include nuclear, gas and other generation-expansion forecasts as well as wind generation. The JCSP just focused on two of the many options that need to be explored. If the entire Eastern Interconnection, including Canada, were involved, the result would be expected to be an even better product with even better conclusions.


Dale Osborn (DOsborn@midwestiso.org) is the technical transmission director for the transmission asset management group of the Midwest ISO. Current projects include evaluation of transmission expansion for possible future wind scenarios. He is the vice chair of the IEEE Wind Power Coordinating Committee. He is a member of the board of directors for the Utility Wind Integration Group.

Carl Dombek (cdombek@midwestiso.org) is manager of external communications for the Midwest ISO. Prior to joining the MISO, he worked for GE, the federal government and a county government.