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Tacoma Power

Mossyrock Upgrade Study
Tacoma Power

Tacoma, Washington

BIS staff worked with Tacoma Power to evaluate upgrade of the Mossyrock hydroelectric project. The three main parts of the study are described below.


The study included a calculation of the revenue from the existing units, the proposed upgrades, and installation of a third unit. This analysis used a dispatch-optimization tool, based on 20 years of historical hydrology and hourly future prices projected by Tacoma Power. In general, this analysis showed that there was significant benefit from efficiency increase.


The optimum program was determined using a risk-based approach. Key components at the plant were evaluated to determine whether there was economic justification for including them in the program. The analysis also considered the effect on risk of installing a third unit, which would act somewhat like a spare for the other two.


The results of the generation and risk analyses along with construction cost estimates were entered into an economic analysis model to evaluate the incremental costs and benefits of each upgrade scenario and to determine the optimal upgrade strategy. The analysis showed that there was significant benefit from an overall upgrade program, however the direct revenue benefit from runner upgrade was not, by itself, sufficient to justify the upgrade program. The benefit streams from avoided risk and O&M costs, brought about from rehabilitation or upgrade of aging equipment, were required to justify the upgrade program. Tacoma Power is now in the process of implementing an upgrade program recommended by this study.

Date Completed: 2002

Optimized number of spare transformers. Defined process to identify projects and optimize them economically. Identification of long-term revenue needs.
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