Document Type


Publication Date

January 1984


In Utah during the 1960s, the cost of producing electrical energy was as much, or in some cases more, by hydroelectric generation than by plants using steam from coal fired boilers. The relatively high hydropower cost was generally attributed to maintenance and replacement costs associated with plants that had been build in the 1920s. Utah Power & Light Company during the 1960 period decided not to renew power licenses and to abandon many small hdyroplants. Since 1973, rising coal and related fossil fuel costs have caused steam generation costs to accelerate and have made hydroelectric generation relatively more attractive. However, the capital cost of replacing deteriorated pipelines and restoring plants to production capability is high, and the prospect of large capital investment during periods of high interest rates creates a hesitancy to renovate existing or to construct new small hydro units. The cost analysis to replace abandoned plants or to construct new plants has been generally based on restoring an existing configuration or building to design standards in use at the time of the original structure. The traditional design method was to design a pipeline on a flat slope with a relatively large pipe diameter. This method maximized head, but minimized the flow. The resultant energy was therefore less than the potential, but constant. This method also confined the variations in flow to a range that could be handled by a single, or the most two, variable geometry turbines. The flow point on the typical flow duration curve for western mountain streams where the ratio of maximum to minimum flow variation is 4 to 1 or less is at is at or near the 25 percent exceedance level. It is shown in this report that the same diameter pipeline as used in traditional design can by sloped to maximize the power output of the plant (powermax slope) and thus increase the annual energy production by 149 to 186 percent, the difference being dependent upon the amount of energy recovered by the static regain in pressure pipelines when flows are reduced below the maximum. This optimized flow and head without changing the cost of the pipeline. The effect is to reduce the unit cost of energy produced. The higher flow at the powermax slope has a greater variability and will therefore require turbines with greater variability. It is demonstrated that multiple fixed geometry turbines sized in binary steps can effectively span flow variability ratios from 10 to 1 or greater and be installed at less cost than custom designed variable geometry units. Thus, designing at the points on the flow duration curve corresponding to the 10 percent or lower exceedance level is economically feasible. Combining the powermax concept for pipelines with the concept of using binary sized turbines and a pressure system to use the static regain concept can result in hydro plant designs that utilize a greater portion of the potential energy at a given site and reduce the unit cost of energy.