An Evaluation of the U.S. Department of Energy's Marine and Hydrokinetic Resource Assessments (2013) / Chapter Skim
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6 In-Stream Hydrokinetic Resource Assessment
6 In-Stream Hydrokinetic Resource Assessment
Pages 67-75
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From page 67... ...
. In general, hydropower generation broadly describes the process of converting potential or kinetic energy of stored or flowing water contained in rivers and streams into electricity.
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From page 68... ...
More recently, the potential for recovery of hydrokinetic energy in streams has attracted increasing attention. In-stream hydrokinetic energy is recovered by deploying a single turbine unit or an array of units in a free-flowing stream (see Figure 6-3 for centerline view of a turbine array along a river reach)
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From page 69... ...
FIGURE 6-3 Centerline view of an array of bed-mounted hydrokinetic turbines deployed in a stream.
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From page 70... ...
Estimates of the maximum extractable energy that minimizes environmental impact range from 10 to 20 percent of the naturally available physical energy flux (Black & Veatch Consulting, 2004; Bryden et al., 2004)
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From page 71... ...
PROJECT DESCRIPTION The in-stream assessment group developed its analysis of the in-stream hydrokinetic energy resource by first examining the river reaches available in the United States. Using the NHD Plus1 suite of data sets, the assessment group identified stream networks in the contiguous United States with mean annual discharge greater than 1,000 cubic feet per second (cfs)
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From page 72... ...
, N is the number of turbines in the river segment, and Ar is the swept area of the turbine. These calculations developed device array configurations for the 5th percentile flow, assumed the average recovery factor across all discharges for a given river reach was equal to the recovery factor for the mean flow, and assumed that device diameter D equaled 80 percent of the average depth with lateral and longitudinal device spacing of 0.5D and 5D, respectively.
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From page 73... ...
Future work could focus on developing an estimate of channel shape for each stream segment and then, using the flow statistics for each segment along with an assumed array deployment, directly calculating the technically recoverable resource based on equation 3 (above) over the range of expected flows.
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From page 74... ...
CONCLUSIONS AND RECOMMENDATIONS After reviewing the in-stream resource assessment report, the online information database, and additional information presented by the assessment group during committee meetings, it is the committee's opinion that the estimate of the theoretical resource is based upon a reasonable approach and provides an upper bound to the available resource; however, the estimate of the technical resource is flawed by the assessment group's recovery factor approach and the omission of other important factors, most importantly the statistical variation of stream discharge. A more thorough assessment of both modified Manning's coefficient and the recovery factor used by the in-stream assessment group is needed to ascertain the usefulness of these approaches.
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From page 75... ...
The five hydrologic regions that comprise the bulk of the identified in-stream resource should be tested further to assure the validity of the assessment methodologies. In addition, a two- or three-dimensional computational model should be used to evaluate the flow resistance effects of the turbine on the flow.
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