As the share of wind in power systems increases, it is important to assess the impact on the grid. This paper combines analysis of load and generation characteristics, generation adequacy and base and peak load variations to assess the future role of wind generation. A simulation of Tamil Nadu in India, with a high penetration of wind power (27% by installed capacity), shows a capacity credit of 22% of the installed wind capacity. For seasonal wind regimes like India, neither the capacity factor, nor the capacity credit reflects the monthly variation in the wind generation. A new approach based on the annual load duration curve has been proposed for generation expansion planning with higher penetration of wind. The potential savings in base and peak capacity required with increasing wind power have been quantified. A future scenario for Tamil Nadu for 2021 has been illustrated. It was found that 5500 MW of wind power can save 3200 MU of peak energy required or an average peak capacity of 2400 and 1100 MW of base capacity. This analysis would be useful to assess the future impacts of increasing wind capacity in grids. (C) 2009 Elsevier Ltd. All rights reserved.