By David Wagman, Managing Editor
Next time you quench your thirst in Colorado Springs, Colo., realize the water in your glass probably spun a power turbine somewhere between the top of 14,000-foot Pikes Peak, which rises from the city’s west side, and your water glass.
That’s because the city’s utilities department, which provides water and wastewater services as well as electricity to the Colorado city of 360,000, has more than 35 MW of hydroelectric generating capacity connected to its water distribution system. There’s a lot of force behind that water. At the turbine, water pressure can rise to 1,100 pounds. Compare that with water pressure of around 20 pounds for Columbia River hydro plants in the Pacific Northwest.
Colorado Springs’ total hydro capacity may grow by one-third to one-half in the next several years as the city considers adding more turbines. That effort is driven by two primary factors. First, Colorado voters two years ago passed a ballot initiative calling for increased use of renewable electric generation sources. As a municipal utility, Colorado Springs could have opted out of the renewable standard. Instead, utility managers decided to join the statewide effort. Hydroelectric power is one possible solution.
Second, the city shifted hydro and other “remote” energy source management away from its larger thermal power plant operations to a newly created remote energy plant unit. With that shift came adoption of an economic valuation model that considers the full 100-year-plus life of a hydroelectric facility, instead of the typical 30-to-50-years expected from a thermal plant. The result made hydro an economically more attractive option.
 Detail showing the buckets on a 1997-vintage Pelton turbine installed at Colorado Springs Utilities’ Tesla facility. Photo credit Colorado Springs Utilities |
Small-scale hydro can be expensive to build because it lacks the economy of scale advantages enjoyed by larger power plants. After all, transformers and transmission lines need to be installed even at a small hydro site. Automation expenses can also be high because the plants are remotely operated. “The costs just don’t go down,” says Dan Tadie, Remote Energy Plants Manager for the utility.
He estimates small-scale hydro can cost $2,500 to $3,200 a kilowatt to build. By contrast, coal-fired generation costs closer to $1,600 a kW to build. Even so, four factors can favor hydro: lower long-term maintenance expenses, negligible fuel costs, reduced environmental effects and extended plant life that can exceed 100 years.
“It’s all about maximizing value,” says Tadie. “We’re chasing down opportunities every chance we can.”
Hydro power is nothing new in Colorado Springs. Snowmelt from Pikes Peak’s broad shoulders has spun turbines for 100 years. What is unique here is that the turbines spin using the power of water destined for kitchen sinks and backyard faucets across the city. The city water department constantly manages its array of mountainside reservoirs to ensure a steady supply of water is available year-round. Power turbines, therefore, are assured a continuous water supply even as natural runoff shrinks with the snowcap. However, because the city’s domestic water demand fluctuates during a 24-hour period, several power turbines must operate just like a conventional run-of-river system operates; that is, ramping up and down with available water. Colorado Springs has four generating units that operate on this model. Combined they have a capacity of 8 MW.
A larger 28.6 MW turbine entered service in 1997, easing the electric utility’s dependence on the domestic water demand cycle. Known as the Tesla facility, the turbine was designed to maximize power generation by cycling the plant with electricity demand, not water demand.
The Tesla turbine is a Pelton design, which has seen only a few changes in the 120 years since its introduction. Among the most efficient ways to generate electricity, the seven-ton turbine in Colorado Springs operates at around a 93 percent efficiency rate, Tadie says.
A Pelton turbine consists of a set of specially shaped buckets mounted on the rim of a circular disc. Jets of water discharged from one or more nozzles strike the buckets. The buckets are split in half so the central area does not act as a dead spot unable to deflect water away from the oncoming jet. The Pelton turbine bucket deflects the jet through 165 degrees, which is the maximum angle possible without the return jet interfering with the following bucket for the oncoming jet.
In large-scale hydro installations Pelton turbines are normally considered for heads only above around 500 feet. For micro-hydro applications, they can be used at heads down to 65 feet. Pelton turbines are generally not used at lower heads because their rotational speeds become slow and the runner required grows large and unwieldy.
Colorado Springs’ Tesla facility includes a downstream reservoir. This allows plant managers to draw water from upstream reservoirs, run it through the turbine and then discharge the water downstream for later use by the water distribution side of the business.
“The downstream reservoir allows us to dispatch power to meet demand on the grid,” Tadie says. “During peak hours we can take Tesla to full load and have the reservoir act as a buffer.”
The Tesla facility also is designed for a near-infinite turndown, enabling it to generate electricity from almost nothing to its full 28 MW capacity.
Over the next two years, Colorado Springs will evaluate a dozen sites for potential hydro expansion. And the system is three to four years away from possibly adding hydroelectric capacity to portions of the water distribution system that carry already-treated water. The idea is to take advantage of the roughly 2,000-foot elevation difference across the city to generate still more electricity.