Secondary generating resources are commercially available with limited, or small-scale, developmental potential in the Pacific Northwest. While secondary resources are currently in-service or available for development in the region, they generally have limited potential in terms of resource availability or typical plant size. While secondary resources are not usually explicitly modeled (with the exception of conventional geothermal), they are still considered viable resource options for future power planning needs. In the 2021 Power Plan, secondary resources include biomass, biogas, hydropower upgrades to existing projects, small hydropower, combined heat and power, and distributed generation. See the existing system resources for information on recent installations of these technologies in the region.