Monday Study – A Model For A National Transmission System

Design Study Requirements for a U.S. Macrogrid; A Path to Achieving the Nation’s Energy System Transformation Goals

February 2022 Energy Systems Integration Group

Executive Summary

Several recent, comprehensive studies of a clean energy future for the United States point to the same conclusion: a clean electricity future for the United States will require massive development of the bulk transmission infrastructure.

States, utilities, and consumers have significant commitments to rapidly decrease carbon emissions in the power sector and to use more electricity to reduce emissions in other sectors. In the autumn of 2020, the Energy Systems Integration Group conducted a series of virtual workshops to consider the implications of and opportunities highlighted by the above referenced studies. These workshops confirmed that our current transmission development approaches and processes would almost certainly be inadequate for the challenge of growing to enable a clean energy future.

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The advanced hybrid grid may be part of the key for the massive transmission expansion required to support very high levels of clean electricity for the United States. Some major features of the macrogrid concept (Figure ES-1, p. 2) are the principle of looped circuits and the interspersed converter stations to either collect clean electricity or deliver it to demand centers.

The macrogrid concept proposed here is more than massive build-out of conventional high-voltage DC (HVDC) lines and converter stations. The macrogrid vision consists of a backbone of long-distance lines composed of networked, multi-terminal HVDC based on voltage source converter (VSC) technology.

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Major Benefits of a Macrogrid

The benefits of a national macrogrid go well beyond simply serving as conduits for moving clean energy from source to load. The general attributes of a macrogrid fall into the following broad categories:

• Reliability. The macrogrid’s capabilities will be extremely valuable for grid management and security with very high levels of renewable resources to support decarbonization goals. Increased interconnectivity between regions of the United States can contribute to significant improvements in reliability. The technologies comprising the macrogrid—extrahigh and ultra-high voltage DC (EHVDC and UHVDC) transmission that can make the bulk transmission network highly controllable—can be leveraged to address long-standing challenges with bulk power system reliability.

The controls associated with HVDC equipment, and wide-area situational awareness enabled by new connectivity and technology, will tie regions together in ways that facilitate better and more efficient overall grid performance. Energy, capacity, and ancillary services would be deliverable from any region of the country to any other region, not just between neighbors. A macrogrid can provide operational tools and capabilities that not only can reduce the bulk power system’s susceptibility to failure, but can enhance outage restoration capabilities and speed, which can be critical during extreme operating scenarios.

• Resilience. Extreme weather events, a growing concern in a changing climate, can affect large regions of the country as experienced in California in August 2020 and Texas in February 2021. The scope and scale of the macrogrid will provide interconnectivity that spans the entire country (and potentially the northern and southern borders as well) and goes well beyond the connections that we have now, between mostly adjacent regions. Such interconnectivity is needed to ensure the resilience of the electricity infrastructure on which the country’s residents and economy depend.

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• Economics. Some recent studies indicate that a macrogrid would substantially reduce the overall cost for a clean energy future, saving as much as one trillion dollars (see, for example, VCE (2020)). Conventional power system planning models under-value transmission, but newer approaches capture the benefits of moving power to balance power systems with dispersed variable resources based on the location and time of output. A macrogrid can facilitate the use of the most economically attractive resources (bulk generation and storage, for energy and ancillary services), which can be dispatched to cover energy demand across four time zones to serve all regions and customers. And HVDC transmission has lower costs when transmitting electricity over hundreds of miles.

• Operability. The macrogrid would add an overarching layer on the existing grid management structure, enabling the coordination of national and regional energy flows. The macrogrid’s capabilities will be extremely valuable for grid management and security with very high levels of renewable resources to support decarbonization goals. The controls associated with HVDC equipment, and wide-area situational awareness enabled by new connectivity and technology, will provide capabilities that would not only reduce the bulk power system’s susceptibility to failure, but also enhance outage restoration capabilities and speed, which can be critical during extreme operating scenarios.

The U.S. Department of Energy, through the National Renewable Energy Laboratory and Pacific Northwest National Laboratory, has launched efforts to explore transmission development for supporting clean electricity futures. We propose that the macrogrid be evaluated in the context of this DOE initiative as an alternate transmission approach for supporting very high levels of clean electricity. Using the clean electricity scenarios developed by the laboratories as the starting point, a quantitative process based on recent transmission expansion planning principles, augmented to accommodate the scale and technologies envisioned for the macrogrid, would be applied. From this initial design, a series of studies would be conducted to elicit the full range of costs and benefits of the macrogrid, along with identification of outstanding questions and recommendations for future research.

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Central Tasks in Working Toward a Viable Macrogrid Design

This report explores the central tasks involved in working toward a viable macrogrid design and presents specific steps for addressing them:

• Technical studies on reliability, resilience, economics, and operations. A series of technical studies is proposed and described here to design and evaluate the macrogrid alternative for grid expansion. An initial design for the macrogrid would be based on clean electricity scenarios already under development in DOE initiatives. It is recommended that the initial macrogrid design be based on the end-point scenario, and not involve a multi-step incremental expansion exercise. The initial macrogrid design would then be subjected to additional technical analysis to elicit further details on the range of ancillary benefits provided by the macrogrid infrastructure.

• Coordination and oversight of the physical infrastructure. Physical operation of the macrogrid raises a number of technical challenges and questions. Currently, there is no operating entity that has the purview and national scope of the macrogrid infrastructure, or has the tightly coupled operating interactions with the number of entities that would be necessary here.

• Cost comparisons. The costs to build the macrogrid are obviously of major importance and would be compared to other alternatives for grid expansion to support the same clean electricity scenario. Against these costs, the full range of benefits—including those related to improved power system reliability and resilience—would be captured and quantified to develop a full picture of the macrogrid economics.

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• Use of rights-of-way. Acquisition of rights-of-way for new transmission is a barrier to any form of grid expansion. Because of the architecture, the HVDC lines comprising the macrogrid would likely be much longer than new lines that are part of a more conventional grid expansion. Further, utilization in terms of power transfer of the rights-of-way would be much higher. As part of this evaluation, opportunities to use existing or more readily available line routes, such as interstate highways or railroads, would be explored in detail.

The convergence of the national push for very high levels of clean electricity and the advances in HVDC transmission technology of the last decade have created a unique opportunity for a detailed exploration of an alternative to the conventional transmission expansion process to address identified challenges for the U.S. electric power system.

It is recommended that the initial macrogrid design be based on the end-point scenario, and not involve a multi-step incremental expansion exercise. The initial macrogrid design would then be subjected to further technical analysis to elicit further details on the range of ancillary benefits provided by the macrogrid infrastructure… click here for more

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