Variability in Wind Energy Generation across the Contiguous United States

Abstract

ERA5 provides high-resolution, high quality hourly wind speeds at 100 m and is a unique resource for quantifying temporal variability in likely wind-derived power production across the USA. Gross capacity factors (CF) in seven independent system operators (ISOs) are estimated using the location and rated power of each wind turbine, a simplified power curve and ERA5 output from 1979-2018. Excluding the California ISO, the marginal probability of a calm (zero power production) is less than 0.1 in any ERA5 grid cell. When a calm occurs, the mean co-occurrence across wind turbine containing grid cells ranges from 0.38-0.39 for ISOs in the Midwest and Central Plains (MISO, SPP and ERCOT), increasing to 0.54-0.58 for ISOs in the eastern USA (PJM, NYISO and NEISO). Periods with low gross CF have a median duration of ≤?6 hours except in California, and are most likely during summer. Gross CF exhibit highest variance at periods of one day in ERCOT and SPP, on synoptic scales in MISO, NEISO and NYISO and on inter-annual timescales in PJM. This implies differences in optimal strategies for ensuring resilience of supply. Theoretical scenarios show adding wind energy capacity near existing wind farms is advantageous even in areas with high existing installed capacity (IC), while expanding into areas with lower IC is more beneficial to reducing ramps and the probability of gross CF falling below 20%. These results emphasize the benefits of large balancing areas and aggregation in reducing wind power variability and the likelihood of wind droughts.

Wind power production from very large offshore wind farms

“…Power losses due to transmission, curtailment for grid operation, and operations and maintenance actions for onshore wind farms decrease CFs in the U.S. by an average of 4 percentage points. 40 Assuming that this estimate is also appropriate for offshore wind turbine arrays, the resulting estimated net-CF for these U.S. east coast offshore LAs is $42%. This is comparable with, or better than, values reported for European (38% during 2019 41 and 40.8% cited in a meta-analysis 31 ) and global (40% to 42% 11 ) offshore wind farms.…”

“…The ERA5 reanalysis model ingests an unprecedented suite of assimilated in situ and remote sensing observations. 50 ERA5 exhibits relatively high fidelity for 100-m wind speeds 40,[51][52][53] and has been used as LBC in a range of WRF-based regional simulations including those performed for the New European Wind Atlas. 54 The periods for which WRF simulations are performed are selected based on analyses of WS and direction at 100 m a.g.l.…”

Extreme Wind and Waves in U.S. East Coast Offshore Wind Energy Lease Areas

“…Evaluation of mean wind speeds and gusts indicate ERA5 wind speeds give a better representation than ERA-Interim, except in complex terrain [40]. ERA5 underestimation of wind speeds in complex terrain due to excess orographic drag [48] is also a concern in the western US [44]. However, this is not of concern for this offshore analysis.…”

“…Wind speeds from ERA5 have been subject to extensive evaluation and are generally seen as exhibiting fidelity relative to independent observations [41][42][43][44][45]. ERA5 output have been used to estimate wind resources in the U.S. [44], global extreme wind speeds [22], the Spanish near-shore [46] and over the Indian shelf seas [47]. ERA5 wind speeds have approximately 20% lower errors than MERRA compared with aggregated wind generation in five countries [41].…”

Climate change impacts on wind energy generation in Ireland

“…An increase in wind speed correlations between all locations in a country imply more homogeneous wind conditions, suggesting that more backup energy will be required during future low‐wind power events. To ensure resilience in supply, Leahy and McKeogh 22 show that there are advantages to increasing the installed capacity in areas even with existing high levels of installed capacity. In order to reduce wind power variability and the likelihood of wind droughts, introducing more installed capacity to lower installed capacity regions can reduce ramps and low wind power production.…”