Understanding how the aggregate output risk of intermittent wind and solar resources scales with the location and magnitude of these generation capacity investments is increasingly important to maintaining a reliable supply of electricity. Using hourly generation unit-level output data from the California ISO control area for a one-year time period, hourly output and hourly revenues mean/standard deviation efficient frontiersfor
wind and solar resource locations in the California ISO control are computed. For both mean/standard deviation efficient frontiers, economically meaningful differences between portfolios on the efficient frontier and the actual wind and solar capacity mix are found. The relative difference is particularly large for the hourly wind and solar output frontier, with more than a 40 percent increase in the expected hourly output of wind and solar energy possible without increasing the standard deviation in hourly output beyond its level with the actual capacity mix. For the hourly revenues efficient frontier, a 30 percent increase in mean hourly revenue is possible without increasing the standard deviation of hourly revenue beyond its current level. Most of the hourly output and hourly revenues risk-reducing benefits are captured by a mix of wind resources, with the addition of solar resources only slightly increasing the set of feasible portfolio mean and variance combinations. The risk-adjusted maximum expected hourly output portfolio and the risk-adjusted maximum expected hourly revenue portfolio are computed and in both cases, the weights for these portfolios are found to focus on a small number of existing wind and solar locations. Measures of non-diversifiable wind and solar energy and revenue risk are computing using the actual market portfolio and the risk-adjusted expected hourly output or hourly revenue maximizing portfolios. In both cases, the results demonstrate significant heterogeneity across wind and solar locations in the non-diversifiable solar and wind output and revenue risk.