The installation of wind and solar capacity in the electric grid can influence net load ramp rates and volatility, affecting grid stability and operating costs. In this study, the statistical analysis of load, wind, and solar data from the Electric Reliability Council of Texas (ERCOT) shows how wind and solar capacity impacts these grid flexibility requirements. Growing wind capacity shows only minor correlation with increasing flexibility requirements, and appears to correlate with decreasing flexibility requirements in some instances. Growing solar capacity might initially improve grid flexibility requirements, particularly volatility. However, beyond a certain penetration level (about 1.0 GW in this study), further solar capacity growth develops a direct correlation with increasing flexibility requirements if load patterns do not change. While adding 15.7 GW of wind power had insignificant effects, adding 14.5 GW of solar to the ERCOT grid increases maximum 1-h ramp rates by 135%, 3-h ramp rates by 30%, ramp factors by 140%, 1-h volatility by 100%, and 1-day volatility by 30%. The geographic location and orientation of solar arrays influences these flexibility requirements, with fixed, southeast-facing panels providing a significant reduction. These results can inform strategies for managing the grid flexibility requirements created by growing renewable capacity. (C) 2017 Elsevier Ltd. All rights reserved.