The central United States is home to some of the world’s most bountiful energy resources. Strong winds across the Great Plains coupled with high quality solar PV and CSP resources are located in close proximity to new natural gas resources and growing electricity demand. Despite the regional abundance of diverse natural resources, there are three major seams in the U.S. power system that limit the nation’s ability to maximize resource value and facilitate a more reliable, resilient, sustainable, and affordable U.S. electricity system.
Existing financial and operational practices already facilitate large scale coordinated power system activities within the three U.S. interconnections. For instance, resources as far away as Colorado can participate in California energy markets, and differences in the time of peak load between Chicago and the Mid-Atlantic States allow considerable resource sharing across the Eastern Interconnection. However, despite the presence of transmission technologies that can facilitate very long distance energy transmission at low losses, and existing HVDC facilities located along current borders, almost no energy is transferred between the interconnections. This fact stymies the efficient development of diverse generation resources in regions with rich natural gas, wind, and solar resources. Furthermore, a lack of transmission capacity across these seams inhibits the nation from balancing load patterns and managing weather events across the contiguous 48 states. The existing load diversity (the difference in the timing of peak and low load conditions) across the seams (estimated to be about 30,000 MW) and reserve pooling opportunities appear to be able to economically justify significant transmission that could also be used to meet Clean Power Plan, carbon and other goals. The delivery cost of significant amounts of renewable energy over a large footprint can be significantly reduced, when accounting for the load diversity and exchanges via expanded network capacity that could reduce the need for peaking generation, storage facilities, etc.
The Interconnection Seams Study will analyze a range of transmission scenarios that aim to decrease the cost of serving U.S. electricity demand by facilitating efficient transfers of electricity across the interconnections. The study will identify least cost options for increasing the robustness of the U.S. electricity system and decreasing the cost of serving load. In particular, the study will analyze three core scenarios: baseline, transmission upgrade, and national HVDC network; each of which will be described later in this section. The objective of the project is to study and quantify the value of enhancing the U.S. interconnection seams through the two transmission enhancement scenarios with respect to the baseline scenario. This will be achieved by the laboratories and an academic partner, Iowa State University (ISU), by conducting multi-scale economic and reliability analysis of these three core scenarios. ISU was chosen as a partner for this study because of Dr. James McCalley's exceptional relationships with industry and leading optimization tools. Former students of Dr. McCalley's at both NREL and MISO will be active participants in the study, further contributing to the work. The results of the study will inform industry decision makers at utilities, RTOs, state governments, and public utility commissions of options for addressing national and regional grid development needs. It will identify cost effective options for replacing aging grid infrastructure that has a national impact.
While Baseline and Transmission Upgrade Scenarios will focus on the central U.S. essentially comprised of the western part of the Eastern Interconnection and the eastern part of the Western Interconnection, these analyses should be based on equivalized models for both the Eastern and Western Interconnections. This central region of the country has some of the nation's best wind and solar resources. It is also located close proximity to rich natural gas resources. By accessing these remote resources, and providing them with access to transmission capacity and diverse loads, the nation could invest in a wide array of high quality resources.
Modeling Framework and Metrics
Three classes of power system modeling and analysis techniques, namely long-term capacity expansion, yearlong production costing, and power flow- each of which investigating phenomena of interest at different time scales, will be used in a coordinated fashion to identify the economic, environmental, reliability and resiliency benefits of three core scenarios. Long-term generation and transmission capacity expansion for the study will be determined using tools developed at ISU and the laboratories. Specifically to begin with, ISU’s Cooptimized Generation and Transmission Planning (CGT-PLAN) and NREL’s Regional Energy Deployment System (ReEDS) models will be used to develop the overall transmission system topology and capacity of the three core scenarios through the study year of interest determined by the TRC. Then, NREL will use the results of the expansion study as inputs to the power system operations modeling study that will be conducted using the PLEXOS production cost model. In this task, the operations of the enhanced system will be analyzed. Methods and lessons learned from previous integration studies (such as the Western Wind and Solar Integration Study and Eastern Renewable Generation Integration Study) will be applied to maximize the usefulness of this study. This production cost model will be used to simulate the economic commitment and dispatch of resources throughout the nation and consider important elements of renewable integration. The benefits of resource diversity, energy interchange and reserve sharing will be considered, as measured by decreases in operating costs and avoided emissions. Finally, results of the system dispatch from the operational analysis study will be imported to the Siemens Power System Simulation for Engineering (PSS/E) model in order to perform an AC powerflow analysis, which will be conducted by PNNL.