Designing transmission with a long-term vision

Federal, regional and state entities have long recognized both the need and the benefits of investing in new regional and inter-regional transmission systems – and of designing those systems "smart from the start." These entities have encouraged the development of transmission systems through adoption of various laws, policies and planning initiatives.

Since its inception in 2005, the TWE Project has been carefully planned in alignment and collaboration with leading transmission/electrical infrastructure planning groups. This work assures that the multibillion-dollar TWE Project:

  • Connects cost-effective renewable resources to the grid.
  • Coordinates with other projects and with sub-regional planning groups.
  • Adds system reliability, stability and capacity for the Western Interconnection, which is the power grid that connects all of the western states.

The TWE Project represents the type of right-sized, renewable and regional transmission envisioned in multiple federal and regional policies and studies to connect the West's most productive onshore renewable resources with the markets that need them.

Capacity expansion map

A pipe diagram of the Western Interconnection shows that the bulk of the existing transmission capacity, shown in gray, is built along the coast in a "C." It also shows there is limited capacity between the California/Desert Southwest and Intermountain regions. Limited capacity means there is limited access to both diverse renewable resources and to diverse load areas. However, adding the 3,000 MW DC line system and 1,500 MW AC line system of the TWE Project vastly expands the ability to directly and efficiently exchange renewable resources between regions.


The Western Electricity Coordinating Council (WECC) is the primary entity responsible for coordinating and promoting bulk electric system reliability in the Western Interconnection. In 2010, WECC initiated a Regional Transmission Expansion Planning process that was funded in part by the U.S. Department of Energy. The first report was WECC's 10-Year Regional Transmission Plan, issued in 2011.

The planning process analyzed the economics of developing renewable energy resources in different regions and then connecting them by various regional transmission projects to serve the renewable energy needs of California. The 10-Year Plan showed that, with Wyoming's exceptionally high-quality wind, the TWE Project will provide the most cost-effective remote renewable energy resource alternative to satisfy a portion of California's needs – saving ratepayers on the order of $600 million every year.

The 10-Year Plan's economic results were consistent with previous studies by Western Electric Industry Leaders and National Grid that underscored the economic benefits of tapping Wyoming's high-capacity wind energy to meet a portion of California's renewable energy demand.

In 2014, the economic benefits of investing in new direct current transmission between California and Wyoming were confirmed in a study conducted by the DOE's National Renewable Energy Lab. The study found that the economic benefit of such a transmission line is likely to outweigh the costs, with benefit-to-cost ratios ranging from 1.6 to 3.6. Utilities typically consider a new transmission line project as a worthwhile economic investment if the benefit-to-cost ratio is 1.1 to 1.2.

"California-Wyoming Grid Integration Study, Phase 1- Economic Analysis" compared two basic options for providing California with 12,000 GWh per year of new renewable resources between 2017 and 2020. One option would draw on the California in-state renewable energy resources likely to remain undeveloped by that time. The other option would deliver Wyoming wind power to the California marketplace via a 3,000 MW direct current transmission line. Both basic scenarios were tested in consideration of a range of crucial variables, such as technology cost, capacity factors and federal incentives.

According to NREL, the scenarios show economic benefits exceed costs in the range of $2.3 billion to $9.5 billion over 50 years on a net present value basis. The benefits were primarily due to the difference in generation cost for the various renewable technologies studied, strongly influenced by the fact that Wyoming has some of the highest wind capacity factors in the United States. NREL analysts worked with a technical review committee of transmission experts from California and across the West who provided review and input.

Similarly, in 2016, a PA Consulting study reviewed the economics of accessing Wyoming wind to help California achieve a 50% Renewable Portfolio Standard. The study compared a portfolio containing all California renewable resources to a portfolio combining California renewable resources with Wyoming wind resources. The study found that the combined portfolio could reduce California RPS compliance costs by $5 billion to $11 billion in net benefits. The study also examined a variety of transmission configurations to deliver Wyoming wind to the California grid. The study compared a range of proposed transmission solutions to access Wyoming wind resources and found the TWE Project to be the most viable and cost-effective solution.

Planning coordination

In addition to WECC, there are sub-regional planning groups that exist throughout the western U.S. As an interstate transmission system proposed to cross Wyoming, Colorado, Utah and Nevada, the TWE Project will interconnect with four of the five sub-regions. Therefore, in alignment with the importance of coordinating with these groups, TransWest has participated within the planning efforts of these sub-regions for several years as well.

System reliability

The TWE Project will be one of the largest transmission elements within the WECC system. It will up to quadruple the transmission capacity that currently exists between the California ISO and the PacifiCorp balancing areas.

The WECC Rating Process is designed to ensure that transmission projects are properly integrated into the existing transmission grid to enhance the overall reliability of the grid. This process for the TWE Project as a DC-only configuration was initiated in 2008, and this process for the TWE Project with a DC and AC configuration was initiated in 2018. TransWest is a WECC member.

The TWE Project has been the subject of a Regional Planning Project Review conducted in accordance with Western Electricity Coordinating Council planning procedures. Initiated in mid-2007, the review was conducted jointly with PacifiCorp's Energy Gateway South Transmission Project, a proposed 500kV alternating-current transmission line.

  • A Conceptual Technical Report performed as part of the Regional Planning Project Review determined that both transmission projects will cost-effectively serve the Desert Southwest region while minimizing environmental impact.
  • The Regional Planning Project Review also included extensive stakeholder consultation to ensure the efficient development of an overall regional transmission plan. Four public meetings were held in 2007 and 2008 in Wyoming, Utah, Nevada and Arizona.

In addition, the TWE Project was included in work performed by:

  • The Northern Tier Transmission Group, which coordinates planning in the Northwest and Mountain states, included the TWE Project within the study work performed as part of its Fast Track Project Process and 2007 Annual Planning Report.
  • WestConnect, which coordinates planning in Nevada, Arizona, New Mexico and Colorado, included the TWE Project in its 2008-2017 Transmission Plan.


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In the news

"We need to get aggressive on building the electron superhighway. If we are not able to move forward with availability of transmission, we can study the potential of solar and wind and geothermal until the cows come home and it's not going to get done."

- Interior Secretary Ken Salazar, March 2009, in response to questions at a hearing before the Senate Committee on Energy and Natural Resources