The U.S. Department of Energy (DOE) said recently that a new report confirms that adding even limited electricity transmission can significantly reduce the costs of expanding wind energy to supply 35% of U.S. electricity by 2050.
DOE added in its Jan. 9 statement that the “Reducing wind curtailment through transmission expansion in a wind vision future” report, authored by the National Renewable Energy Laboratory (NREL), affirms the findings of DOE’s 2015 “Wind Vision” study, which showed that a future in which wind provides 20% of U.S. electricity in 2030, and 35% in 2050, is achievable and would provide significant economic, energy security, and health benefits to the country.
For the study, NREL simulated operation of the electric power grid under a scenario where 35% of electricity comes from wind in the year 2050, using PLEXOS, which is an integrated modeling tool commonly used by utilities and transmission organizations, DOE said. The study focuses on the Western Interconnection grid, which includes 11 states, two Canadian provinces, and parts of northern Mexico where the U.S. grid crosses the border, DOE said.
The study includes a baseline scenario assuming no significant transmission expansion across the western grid, as well as three scenarios with varying levels of transmission buildout, DOE said. In the baseline scenario with no transmission expansion, substantial renewable energy curtailment could become a major issue, DOE said, adding that in that scenario, about 15.5% of wind energy capacity goes unused with consequent increases in system costs as a result of idled wind generation.
The study also found that if just four currently proposed transmission projects are built, wind curtailment can be reduced by about half, cutting lost generating potential to 7.8%, DOE said. If the country deploys additional transmission beyond those four proposed projects, wind curtailment can be reduced even further – allowing full use of wind energy, reducing generation costs, and unleashing additional economic and societal benefits, DOE said.
“We find that wind curtailment could be reduced by approximately 50% under a scenario adding 10.5 GW of new transmission, based on four proposed projects,” the report said. “This avoided wind curtailment could lower annual production costs and reduce carbon dioxide emissions substantially. Greater transmission expansion was found to yield further benefits, although the marginal benefits of these new lines were found to have diminishing returns. … Overall, these results suggest that the power system can be operated with more than 35% wind penetration (and 12% solar penetration), but that transmission expansion is necessary to fully utilize the available renewable energy.”
According to the report, the four lines – which represent proposed projects that have been or are being considered as effective means of transferring renewable energy out of relatively low load areas – are the:
- Zephyr Power Transmission Project (Duke-American Transmission Co.)
- TransWest Express Transmission Project (TransWest Express)
- SunZia Southwest Transmission Project (sponsored by Salt River Project; Shell WindEnergy; SouthWestern Power Group II/MMR Group; Tri-State Generation and Transmission Association; and Tucson Electric Power)
- Mountain States Transmission Intertie, or MSTI (NorthWestern Energy)
The report noted that it uses those four proposed projects to estimate the value of transmission in reducing wind curtailment in the context of the “Reference” scenario, and that the report does not intend to suggest that those projects are likely to succeed based on this analysis, nor is this a comprehensive benefit-to-cost analysis for any of the projects. The report said that the analysis considers only the avoided generation costs from a more efficient commitment and dispatch of the generator fleet enabled by additional transmission, which includes avoided curtailment.
The “Reference” scenario involves adding the high levels of wind (37%) and solar (12%) to a system without major infrastructure changes relative to the grid as modeled in the Western Electricity Coordinating Council Transmission Expansion Planning Policy Committee 2024 Common Case, in order to assess whether increased penetrations of wind and solar require major changes to infrastructure, the report said.
The addition of the specified four lines has a definite impact on the “Reference Wind Vision” scenario, the report said, adding that the annual curtailment is reduced by roughly half (15.5% to 7.8%) through substantial curtailment reductions in the Mountain States. The change is significant despite the relatively small amount of transmission added, the report said.
Among other things, DOE said in its statement that the report quantifies on a regional scale what has happened in Texas in recent years, noting that wind curtailment on Texas’s grid ranged from 8% to 17% between 2009 and 2011, but fell to only 1% after new transmission lines and other upgrades were completed under the state’s Competitive Renewable Energy Zone initiative.