Department of Energy Reports on New Transmission and Wind Curtailment

Last week, DOE released a report titled Reducing Wind Curtailment through Transmission Expansion in a Wind Vision Future.  This report follows up on a 2015 DOE Wind Vision study, which looked at the potential benefits of a scenario in which wind power provided more than a third of U.S. electricity consumption in 2050.  Last week’s report examined the feasibility of developing significantly more wind generation in the western U.S., emphasizing the impediments transmission constraints pose to such development.

Wind power currently makes up approximately 4.7% of total U.S. electricity production.  While technological advances have reduced the costs of deploying variable renewable resources (e.g., wind and solar), these resources still pose operational challenges for the grid because their generation is weather dependent.  As the DOE report explains, grid operators sometimes are unable to accommodate all of the available variable renewable generation because of transmission congestion or the inability to reduce output from other resources.  In such circumstances, variable renewable resources must be curtailed, even though they could provide additional generation at near-zero marginal cost.  Currently, curtailment of variable renewable energy is about 15.5%, but if there were no transmission constraints, curtailment would be just 0.5%.

In contrast to previous research, which used simplified models of system operations and transmission networks, DOE’s new report focuses on curtailment and ways to minimize it.  The report analyzes three transmission buildout scenarios: one with a small amount of additional transmission, one with a greater amount of new transmission, and one that also adds a hypothetical 3,000 MW line from high wind areas in the Rocky Mountains to highly populated areas in southern California.  The report concludes that a small amount of additional transmission would cut curtailment to about 7.8%, but that there are diminishing returns thereafter.  A line from the Rocky Mountains to southern California would further reduce congestion by 1.8%, although the report does not consider the costs of such a project or provide a cost-benefit analysis.

Ultimately, DOE’s analysis suggests that the power system in the Western U.S. can operate with more than 35% of power coming from wind and 12% from solar, but that high levels of transmission‑induced curtailments will make this difficult.  The solution addressed by DOE is the construction of new transmission facilities.  As the report states, even moderate amounts of additional transmission could reduce wind curtailment by half.  (By contrast, the retirement of coal generation is expected to have only a minimal impact on variable renewable resource curtailment.)

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