The pro-hydro plant talking point that the Castle Creek Energy Center would cut back Aspen’s coal consumption by 5 million pounds annually overstates the plant’s reduction of the carbon-based fuel’s use in the early years of operation, but the proposal could offset more depending on how much power it produces.

Opponents of the hydro plant, which is up for a voter referendum in November, have keyed in on the 5 million pounds claim, asking city officials to back it up. Officials from the municipal electric utility presented information this week explaining their calculations.

According to preliminary estimates, the hydro plant is expected to generate 5.5 million kilowatt hours (kWh) of electricity annually, when running at full production. That output, however, would be curtailed for at least the first three years by about one-third, under the “slow start” implementation program, which is designed to take lower amounts of water from the creek, allowing scientists to examine the impacts before more flow is diverted. If a board of experts agrees that the streams aren’t being harmed, then power production — and water diversions — would ramp up, taking at least another three years to reach full production, according to preliminary plans.

The city bases its calculations on 1 kWh of power requiring the burning of 1.2 pounds of coal, a fuel associated with global warming-causing greenhouse gasses, such as CO2. This number also is an estimate, and the actual amount of coal required per kWh depends on the carbon density of the coal and the efficiency of the generator. In general, estimates range from 0.95 to 1.5 pounds of coal required per kWh.

Power produced from the hydro plant would replace energy Aspen purchases from the Municipal Energy Agency (MEAN) of Nebraska, which in 2011 supplied 27 percent of the 70 or so million kWhs Aspen uses each year. The power Aspen gets from MEAN is between 70 and 80 percent coal fired, according to Dave Hornbacher, director of utilities and environmental initiatives for the city of Aspen. Transmitting the power to Aspen also results in an estimated 7 percent loss of power.

The 5.5 million kWh figure, multiplied by 0.8 to represent the amount of displaced power produced by coal on the high end (80 percent), multiplied by 1.2 for the required coal and then 1.07 to account for transmission losses, equals 5.65 million pounds of coal offset annually. If the amount of coal MEAN uses for Aspen’s power is 70 percent, that number shrinks to 4.94 million.

But Aspen’s power plant, if built, may not produce 5.5 million kWh annually for at least six years into its life span, which is between 50 and 75 years. For the first three years, it would run at two-thirds of full capacity, with an output of around 3.63 million kWh. Using the same formula as above, this would result in the avoidance of 3.72 million pounds of coal if 80 percent of MEAN’s power is coal fired, or 3.26 if MEAN’s coal proportion is 70 percent.

In other words, the low-end of the coal-avoidance spectrum, using power production numbers associated with the “slow start” is about 35 percent lower than the 5-million-pounds-of-coal-replaced claim.

Currently, with Aspen getting about 19 million kWh per year of its power from MEAN, that means the city’s utility is responsible for burning between 17 million and 19.5 million pounds of coal annually.

Other sources of Aspen’s power, other than MEAN, according to 2011 data supplied by the city, are: wind energy purchased from Wyoming and Nebraska, 29 percent; hydropower from Ruedi Reservoir, 27 percent; hydropower purchased from the federal Western Area Power Administration, 10 percent; Maroon Creek hydropower, 3 percent; and additional power purchased on the open market, 4 percent.

curtis@aspendailynews.com [1]