The Department of Energy’s 2015 Wind Vision study analyzed an aggressive scenario in which wind power served 35% of U.S. electricity consumption in 2050 and showed the potential for wind energy to provide substantial health, environmental, and economic benefits. Using a higher fidelity modeling framework we build on this research by assessing the operational feasibility of a similar high wind future in the western United States. For this analysis, we use a commercial unit commitment and economic dispatch model to simulate grid operations and transmission flows with high spatial and temporal resolution. Our detailed simulations affirm the Wind Vision conclusions that effective power system operation can be achieved with wind penetrations above 35%.
Although our analysis identifies no reliability issues in any of the high-wind scenarios, we find that transmission expansion is likely to be critical. Absent significant upgrades to the western transmission network, we find that a substantial amount of renewable energy cannot be utilized by the system, and therefore is curtailed. This curtailment results from an inability to transmit power from where it is generated to where it is needed, and could degrade the potential for wind power to reduce fuel costs and emissions. To assess the value of transmission to mitigate wind curtailment, we model a suite of transmission expansion scenarios. 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 (Transmission 1 in Figure E1). 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 (Transmission 2 and 3 in Figure E1). 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.
Results from and implications of our analysis are summarized as follows:
- Effective power system operation can be achieved with annual wind penetrations greater than 35%.
- This finding helps affirm conclusions from the Wind Vision study that variability is manageable and the grid will be operable under a high renewable energy future.
- High fidelity nodal modeling found no hours of unmet load or unserved reserves. Although this confirms some aspects of grid reliability, this is not a full reliability study, which would include analysis of dynamic stability and frequency response. Other analyses have focused on these questions for high renewable penetrations in the western United States.
- Transmission expansion will play a vital role in allowing for efficient usage of renewable resources.
- Renewable curtailment can be mitigated by transmission expansion. Reducing curtailment also effectively reduces generation costs and carbon dioxide emissions.
- If transmission is not built to support new wind generation in the western United States, significant renewable energy curtailment (15.5%) could be an issue.
- Curtailment can be reduced by about half (to 7.8%) based only on proposedtransmission projects.
- Further transmission buildout continues to reduce curtailment and generation costs but with diminishing returns.
- Transmission can provide flexibility for electric power system operation. Inefficient scheduling practices can reduce this flexibility; these practices could include fixed bilateral contracts or the lack of ability to adjust schedules in real-time operations. Inflexibility in transmission scheduling can increase costs and curtailment.
- Grid simulations showed that inflexible transmission utilization could double curtailment levels compared to a scenario with optimal transmission utilization. Generation costs also increased as a result of increased dispatch of fossil-fired units.