Hybrid Power Plants: Status of Installed and Proposed Projects
Falling battery prices and the growth of variable renewable generation are driving a surge of interest in “hybrid” power plants that combine, for example, wind or solar generating capacity with co-located batteries. While most of the current interest involves pairing photovoltaic (PV) plants with batteries, other types of hybrid or co-located plants with wide-ranging configurations have been part of the U.S. electricity mix for decades. This updated briefing tracks and maps existing hybrid or co-located plants across the United States while also synthesizing data mined from power purchase agreements (PPAs) and generation interconnection queues to shed light on near- and long-term development pipelines. The scope includes co-located hybrid plants that pair two or more generators and/or that pair generation with storage at a single point of interconnection, and also full hybrids that feature co-location and co-control. The focus is on larger, 1 MW+ systems; smaller (often behind-the-meter) projects are also increasingly common, but are not included in this data synthesis. Based in part on Form EIA-860 data, there were at least 226 co-located hybrid plants (>1 MW) operating across the United States at the end of 2020, totaling more than 30 GW of aggregate capacity. Among these operating plants, the most common configuration is PV+storage (with 73 projects totaling 992 MW of PV and 250 MW of storage), followed by several different fossil hybrid categories (fossil+PV, fossil+hydro, and fossil+storage plants—each dominated by the fossil component) and 14 wind+storage plants (with 1,425 MW wind and 198 MW of storage). But there are roughly a dozen other configurations as well, including wind+PV, wind+PV+storage, biomass+hydro, geothermal+PV, and others. Data on projects under development within interconnection queues across the country demonstrate considerable commercial interest in hybrid power plants, and especially in PV+storage. At the close of 2020, there were more than 460 GW of solar plants in the nation’s queues; 159 GW (~35%) of this capacity was proposed as a hybrid, most typically pairing PV with battery storage. For wind, 209 GW of capacity sat in the queues, with 13 GW (~6%) proposed as a hybrid, again most-often pairing wind with storage. While many of these specific projects will not ultimately reach commercial operations, the depth of interest in hybrid projects—especially PV+storage—is notable. To get a better sense for what the near-term hybrid pipeline looks like, we also track data on PV+battery plants that have announced offtake arrangements. A sample of 134 such projects suggests that the near-term development pipeline features longer storage durations and higher battery-to-PV capacity ratios than are seen among existing hybrids. DC-coupled battery configurations will also likely become more common, and a subset of these DC-coupled plants (particularly those in Hawaii) plan to employ very high DC:AC ratios and store the otherwise-clipped power, leading to expected AC capacity factors in excess of 40%. Finally, PPA prices from a subset of these PV+battery plants reveal that the cost of adding storage increases linearly with the battery:PV capacity ratio, and that PPA prices have declined over time despite increasing (on the mainland) or stable (in Hawaii) battery:PV capacity ratios.