Complementarity of Renewable Energy-Based Hybrid Systems

Abstract

Increased attention has focused on scenarios of rapid and deep decarbonization of the U.S. electricity supply, with least-cost solutions typically involving significant expansion of renewable energy, energy storage, and transmission assets. Strategies that enable the integration of renewable energy projects while minimizing transmission expansion could be especially valuable in the future. It is within this context that the concept of hybrid power plants (or hybrid energy systems) has gained prominence. One specific example is the FlexPower concept, which seeks to demonstrate how coupling variable renewable energy (VRE) and energy storage technologies can result in renewable-based hybrid power plants that provide full dispatchability and a full range of reliability and resiliency services, similar to or better than fuel-based power plants. To help inform and evaluate the FlexPower concept, this report quantifies the temporal complementarity of pairs of colocated VRE (wind, solar, and hydropower) resources, based on their native generation profiles. The combined output from complementary resources - i.e., resources whose generation profiles are anticorrelated or out of phase with one another - will be spread more evenly across time, resulting in reduced variability. In turn, hybrid power plants comprising complementary resources can have increased capacity factors, reduced curtailment, and cost synergies due to smaller interconnection and energy storage requirements for smooth and dispatchable generation. Through the evaluation of two complementarity metrics over annual and seasonal timescales, we find evidence that combining multiple VRE resources can reduce the variability in daily plant output across many regions of the United States. In general, complementarity signals are strongest for resource pairs that involve solar photovoltaics (PV), including wind-PV and hydropower-PV combinations. Complementarity varies on a seasonal and regional basis, both in terms of the strength of potential synergies and the resource pairs for which synergies are observed. In the western United States, colocated wind and PV resources are complementary in the Central Valley of California, and output from hydropower dams complements that of colocated PV along the Colorado River, near Tahoe, California, and in northern Utah. In the wind belt and surrounding regions, colocated wind and PV are highly complementary, and generation from hydropower dams in the northern latitudes complements colocated PV (although these dams tend to have small capacities, = 20 megawatts). In the Northeast, both wind and hydropower resources are moderately-to-strongly complementary with colocated PV, while the synergies between wind and hydropower are more muted. In the Southeast, complementarity among all evaluated resource pairs is moderate. This report focuses on the temporal complementarity of pairs of wind, solar, and hydropower resources , but complementarity on its own cannot predict the competitiveness of hybrid energy systems. The economics of a power plant ultimately depend on its ability to deliver power during periods of greatest need and value, and high complementarity may not be optimal from a net economic perspective, accounting for all cost and value categories. In addition, complementarity provides initial insights into where the FlexPower concept could generate transmission and/or interconnection benefits, but the goals of FlexPower are much broader. Insights derived from this complementarity analysis can help with scenario design in operational models to provide a more complete picture of the value proposition of the FlexPower concept, including the addition of energy storage.