Wind power

VOLUME 46

JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY

NOVEMBER 2007

Supplying Baseload Power and Reducing Transmission Requirements by Interconnecting Wind Farms
CRISTINA L. ARCHER
AND

MARK Z. JACOBSON

Department of Civil and Environmental Engineering, Stanford University, Stanford, California (Manuscript received 6 July 2006, in final form 6 February 2007) ABSTRACT Wind isthe world’s fastest growing electric energy source. Because it is intermittent, though, wind is not used to supply baseload electric power today. Interconnecting wind farms through the transmission grid is a simple and effective way of reducing deliverable wind power swings caused by wind intermittency. As more farms are interconnected in an array, wind speed correlation among sites decreases and sodoes the probability that all sites experience the same wind regime at the same time. The array consequently behaves more and more similarly to a single farm with steady wind speed and thus steady deliverable wind power. In this study, benefits of interconnecting wind farms were evaluated for 19 sites, located in the midwestern United States, with annual average wind speeds at 80 m above ground,the hub height of modern wind turbines, greater than 6.9 m s 1 (class 3 or greater). It was found that an average of 33% and a maximum of 47% of yearly averaged wind power from interconnected farms can be used as reliable, baseload electric power. Equally significant, interconnecting multiple wind farms to a common point and then connecting that point to a far-away city can allow the long-distanceportion of transmission capacity to be reduced, for example, by 20% with only a 1.6% loss of energy. Although most parameters, such as intermittency, improved less than linearly as the number of interconnected sites increased, no saturation of the benefits was found. Thus, the benefits of interconnection continue to increase with more and more interconnected sites.

1. Introduction
Stabilizingglobal climate, reducing air pollution, and addressing energy shortages will require a change in the current energy infrastructure. One method to address these problems is to initiate a large-scale wind energy program. The world’s electric power demand of 1.6–1.8 TW (International Energy Agency 2003; Energy Information Administration 2004) could, for example, theoretically be satisfied withapproximately 890 000 currently manufactured 5-MW turbines with 126-m diameter blades placed in yearly averaged wind speeds at hub height of 8.5 m s 1 or faster, assuming a 10% loss from energy conversions and transmission (derived from Jacobson and Masters 2001; Masters 2004). This number is only 7–8 times the total number of much smaller turbines currently installed worldwide. The off-Corresponding author address: Cristina L. Archer, Department of Global Ecology, Carnegie Institute of Washington, 260 Panama St., Stanford, CA 94305. E-mail: lozej@stanford.edu DOI: 10.1175/2007JAMC1538.1 © 2007 American Meteorological Society

shore average wind speed at 80 m is 8.6 m s 1, and sufficient winds 6.9 m s 1 at 80 m may be available over land and near shores to supply all electric power needs35 times over and all energy needs 5 times over (Archer and Jacobson 2005). However, a well known barrier to large-scale implementation of wind power is the intermittency of winds. Over a time frame of a few minutes, it is possible to experience sudden changes in wind speed, such as gusts or lulls. The predictability of wind in the short-term is still low, and, even with elaborate forecastingtools, it is often difficult to beat persistency (Giebel 2003; Ahlstrom et al. 2005). The intermittency of wind is directly transmitted into wind power, which dramatically reduces the marketing value of wind (Milligan and Porter 2005). On the other hand, because coal combustion can be controlled, coal energy is not considered intermittent and is often used as “baseload” energy. Nevertheless, because...