Wind and solar power are being developed rapidly in the U.S. However, wind speeds and irradiance vary with weather and the time of day, so care must be taken to preserve the reliability of the electric power system when using these resources. Previous studies have investigated the reliability of wind power from one or a few locations, but this study will be the first to assess the reliability of the combination of wind and solar power, when collected from all possible locations in a large electric grid. Renewable power is likely to be more reliable when collected from widely dispersed locations, because some locations will have high winds or clear skies when others do not. In addition, in some regions, winds are stronger at night or in winter, when less sunlight is available, so the combination of wind and solar power may be more reliable than either resource alone. This study will use new datasets of historical weather conditions from the National Centers for Environmental Prediction and NASA to drive a simulation of wind and solar power output at all promising locations throughout the state of California, every 3 hours over a 12-year period. The time-varying, statewide renewable power output will then be analyzed using an electric grid adequacy model, to calculate the amount of conventional electric power and generators that could be displaced by renewable sources, while keeping the electric grid at its current level of reliability. This analysis will be repeated with renewable sources dispersed across large and small geographic areas, and with different ratios of wind and solar power, to measure how the reliability of renewable power changes as the collection area is expanded, and as wind and solar power are combined. This research can later be extended to other regions of the U.S.
Policymakers are increasingly promoting the use of wind and solar energy in the electric power system, in order to reduce our society's emissions of greenhouse gases and air pollutants. An optimal renewable energy policy would be based on a clear understanding of the variability of wind and solar power when they are collected from all locations in the electric power system. However, no study has yet assessed the simultaneous output of wind and solar power at widely dispersed locations, which may be less variable than either resource at any individual location. Without this information, policymakers may set conservatively low targets for the use of renewable energy; indeed, concerns about power system reliability are already slowing wind power development in the U.S. This research project will help fill this information gap, yielding a new and more complete understanding of the contribution that wind and solar resources can make to the electric power system. This will allow policymakers to set more-informed long-term targets for the use of these clean energy sources. The research may also show that it is possible to use solar and wind power to reliably meet more of our energy needs than is currently recognized.
