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<br />Slide 11-6 <br /> <br />Available Capacity - Lower Quartile Water Supply <br /> <br />A third alternative is to select awatet supply that would be exceeded only <br />75% of the time. This assumption recognizes the existence of the proposed <br />uprates and the abil ity to make the associated increased river releases. <br />The water supply selected was the 13 year period beginning in the year 1928 <br />and produced minimum dependable capacity of 1607 MW for the winter season <br />and 1570 MW for the surrrner season. This is an increase of 203 MW during the <br />winter and 166 MW during the summer season over the dependable capacity <br />available under the adverse water supply assumption. <br /> <br />Present marketing philosophy is to take .little or no risk in making required <br />capacity purchases to meet contract obllgations. The reason for expressing <br />different probabilities of water supply in determining available capacity <br />is to evaluate the benefits that might be received from the additional risk <br />in purchasing firming capacity. The consequences of purchasing firming <br />capacity in sea~ons where hydro capacity is short is much greater than the <br />consequences of having excess capacity in those seasons when the system may <br />be capacity long. Excess capacity may be marketed from season to season or <br />from year to year, but to purchase capaqity may coincide with times when the <br />costs are excessive or even in times when the capacity is not available at <br />any price. <br /> <br />An a lternat i ve that wi 11 be cons idered; i nc 1 udes market i ng an increment of <br />capacity in addition to that describ~das dependable. That increment would <br />be without reserve or reimbursable by the customer in those years when the <br />purchase of firming capacity is required. <br /> <br />Slide 1I-7 <br /> <br />Available Energy - Average Water Supply, <br /> <br />In contrast to the consequences of purchasing capacity in capacity short <br />years, the consequences of purchasing energy in energy short years is not <br />nearly so great. Therefore, this analysis of available energy has been <br />based upon an average water supply over our study period 1990-1999. Nearly <br />6,000 GWh of energy can be expected to be available annually under this <br />assumpt ion. The imbalance between wi nter and summer energy is not a fi rm <br />proposal. Seasonal energy could be equally balanced. <br /> <br />"Available" capacity and energy, means !'available at plant." <br /> <br />Sl ide II-8 <br /> <br />Available Energy - Median Water Supply <br /> <br />This case evaluates the available energy under median water supply. The <br />difference between median and average being that average is the arithmetic <br /> <br />4 <br />