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<br /> <br />5 na!(g 2?Jver <br /> <br /> <br />Hells Canyon Dam <br />on the Snake River <br /> <br />heating and cooling) can vary sharply from one part of the grid to another. Instantaneous <br />changes can occur if a key transmission line suddenly drops out of service. Power compa- <br />nies must "wheel" electricity from one region to another. and the entire grid must be able <br />to instantly respond to sudden fluctuations in demand. <br />Throughout the West, a large proportion of electricity is generated by coal.fired and <br />nuclear plants that efficiently supply constant maximum levels of power. These thermal <br />plants become very inefficient. however, when they are run at less than maximum capac- <br />ity. Once shut down. these plants take hours to come up to full steam. Electrical utilities <br />are better off buying additional electrical power from another utility at a premium price to <br />cover brief peak demands, rather than covering peak demands by investing in additional <br />coal.fired plants or natural gas turbines that will be used for only a few hours a day. <br />Hydroelectric power. on the other hand. can be brought on line in a matter of minutes. <br />Turbine efficiency remains high throughout a wide range of dam releases. Consequently. <br />hydroelectric power has long been viewed as an ideal asset with which to respond to <br />perturbations of demand within a power grid. This ability to instantly generate more <br />power is valuable, and "peak power" is sold for considerably more than power generated <br />during "off-peak" or base-load periods. Idaho Power Company operates coal-fired generat. <br />ing stations that supply base.load energy. but the company obtains all of its peak power <br />from dams of the Hells Canyon Complex, The company tries to hold the water of the <br />Snake River behind the dams when electrical demand is low. and releases water when <br />demand (and the price per kilowatt - hour) is high. <br />The Hells Canyon Complex has the capacity to generate 1,400 megawatts (mw) <br />when releasing 30,000 ft3/s from all three dams. Larger discharges must flow through <br />spillways. bypassing both the dams' generators and the company's revenues. More than <br />half of the total generation capacity comes from Brownlee Dam. When possible, the <br />company follows the fluctuations of power demand with its Brownlee units. Water <br /> <br />23 <br />