This report describes the methodology and results of the most rigorous assessment to date of the riverine hydrokinetic energy resource in the contiguous 48 states and Alaska, excluding tidal waters. The assessment provides estimates of the gross, naturally available resource, termed the theoretical resource, as well as estimates, termed the technically recoverable resource, that account for selected technological factors affecting capture and conversion of the theoretical resource. The technically recoverable resource does not account for all technical constraints on energy capture and conversion.
The U.S. Department of Energy (DOE) funded the Electric Power Research Institute and its collaborative partners, University of Alaska – Anchorage, University of Alaska – Fairbanks, and the National Renewable Energy Laboratory, to provide an assessment of the riverine hydrokinetic resource in the continental United States.
The goal of this project was to estimate the riverine hydrokinetic resource in the continental United States.
The project team derived an assessment of the hydrokinetic resource in the 48 contiguous states from spatially explicit data contained in NHDPlus, a geographic information system (GIS)-based database containing river segment-specific information on discharge characteristics and channel slope. The team estimated the segment-specific theoretical resource from these data using the standard hydrological engineering equation that relates theoretical hydraulic power (Pth, Watts) to discharge (Q, m3 s-1) and hydraulic head or change in elevation (ΔH, m) over the length of the segment, where γ is the specific weight of water (9800 N m-3):
For Alaska, which is not encompassed by NHDPlus, the team manually obtained hydraulic head and discharge data from Idaho National Laboratory’s Virtual Hydropower Prospector, Google Earth, and U.S. Geological Survey gages. The team estimated the technically recoverable resource by applying a recovery factor to the segment-specific theoretical resource estimates. This analysis, which included 32 scenarios, led to an empirical function relating recovery factor to slope and discharge. For Alaska, where data on river slope was not readily available, the recovery factor was estimated based on the flow rate alone.
Segment-specific theoretical resource, aggregated by major hydrologic region in the contiguous, lower 48 states, totaled 1,146 TWh/yr. The aggregate estimate of the Alaska theoretical resource is 235 TWh/yr, yielding a total theoretical resource estimate of 1,381 TWh/yr for the continental United States. The technically recoverable resource estimate for the continental United States is 120 TWh/yr.
Results of this study can be geo-spatially visualized, queried, and downloaded from the National Renewable Energy Laboratory’s website at: http://maps.nrel.gov/river_atlas. Currently, results are only available for the 48 contiguous states. Alaska will be added in the future.
Applications, Values, and Use
While the calculation of the technically recoverable hydrokinetic resource takes into account some important constraints, a fuller accounting of additional practical constraints on turbine deployment would further reduce the portion of the theoretical resource that is estimated to be recoverable. The practically recoverable resource remains an unknown – and perhaps small -- portion of the technically recoverable resource. Additional data, assumptions, and highly detailed analysis are required to reliably estimate the practically recoverable hydrokinetic resource.