Hydroelectric
Overview
Photo by JJ Janee Watts
Water constantly cycles through a vast global system, evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, then flowing back down to the ocean. The energy of this water cycle, which is driven by the sun, can be tapped to produce electricity or for mechanical tasks like grinding grain. Hydropower uses a fuel, water, that is not reduced or used up in the process. Because the water cycle is an endless, constantly recharging system, hydropower is considered a renewable energy resource.
When flowing water is captured and turned into electricity, it is called hydroelectric power or hydropower. There are several types of hydroelectric facilities, all powered by the kinetic energy of flowing water as it moves downstream. Turbines and generators convert the energy into electricity, which is then fed into the electrical grid to be used in homes, businesses, and by industry. Impoundment hydroelectric facilities use a dam to store river water in a reservoir and control the amount of electricity being produced by regulating the flow of water through the penstock (which carries water to the turbines). Diversion facilities channel a portion of the river’s water through a canal or penstock, often without the use of a dam. The Tazimina project in Alaska is an example of a diversion hydropower plant. Pumped storage plants act like impoundment facilities during high load hours, but use extra energy produced during periods of low demand to pump water from a lower reservoir to an upper reservoir. Hydroelectric facilities range in size from large power plants (capacity of more than 30 MW) that supply many consumers with electricity to small (capacity of 100 kW to 30 MW) and microhydro systems (capacity of up to 100 kW) that individuals operate for their own energy needs, or for sale to utilities.
Hydropower in Alaska
The Tazimina Hydropower Plant. (Department of Energy)
Hydroelectric power is Alaska’s largest source of renewable energy, supplying 21% of the state’s electrical energy. Currently 37 hydro projects provide power to Alaska utility customers, ranging in size from the 105 kW Akutan hydro project in the Aleutians to the 126 MW state-owned Bradley Lake project near Homer, which supplies 8% of the Railbelt’s electrical energy.
The majority of the state’s developed and proposed sites for hydroelectric facilities are located near communities in Southcentral, the Alaska Peninsula, and Southeast. In addition to Railbelt communities, Juneau, Ketchikan, Sitka, Wrangell, Petersburg, Kodiak, Valdez, Cordova, and Glenallen all have benefited from the development of hydroelectric systems. Many of the larger projects such as the 8 MW Blue Lake project near Sitka are impoundment dams. Currently, the dam at Blue Lake is 145 feet high with a spillway 342 feet above sea level. Plans are in the works to raise the height of the dam 83 feet, thus increasing generation capacity to 18 MW.
The 31 MW Crater Lake project, part of the state-owned Snettisham project that provides 80% of Juneau’s power, uses the natural impoundment of an existing lake and uses a “lake tap” 200 feet below the normal level of the lake t0 supply water to a powerhouse at sea level. The natural impoundment of Crater Lake creates kinetic energy potential (“head”) without the use of a dam, which can be costly to construct and have unintended environmental consequences. The 4.5 MW Black Bear Lake project on Prince of Wales Island and the 4 MW Goat Lake hydroelectric project near Skagway use the same method of natural impoundment and have both been certified as low-impact by the Low Impact Hydropower Institute. Certification as low-impact means the project has adhered to the Institute’s strict criteria on maintaining river flows, water quality, fish passage and protection, watershed health, endangered species protection, cultural resources, and recreation use and access.
While impoundment hydroelectric projects are one of the largest producing and cheapest forms of renewable energy, they can sometimes have detrimental environmental impacts that make low-impact hydro projects more desirable. “Run-of-the-river” projects use more modest structures to divert a portion of the natural river flow through turbines to make power before returning the water to the river downstream. Although run-of-the-river projects produce less electricity than impoundment projects, they maintain water levels downstream for salmon runs and avoid inundation of riparian valleys. This makes them ideal for many parts of Alaska, where energy demand is low and healthy rivers are important for the preservation of both the economy and wildlife. The Tazimina project near Iliamna is an example of a run-of-the-river project. A 250-foot diversion near a waterfall creates 824 kW of electricity, more than enough to supply the three communities served by the utility I-N-N Electrical Coop. The Falls Creek hydroelectric project near Gustavus is another example of a run-of-the-river project that, once complete, will provide up to 90% of the electric load to the community of Gustavus.
Photo courtesy of Yukon River Intertribal Watershed Council
Many rural communities located on the Yukon and other large rivers are interested in using river current for generating power with low-impact turbines that would act much like an underwater wind turbine. This technology is referred to as river “hydrokinetic” or “in-stream” power. In summer 2008, the Yukon River town of Ruby installed a 5 kilowatt (kW) experimental river current turbine, the first in the world to be connected into a community’s grid, to test the feasibility of in-stream power generation. At the time of the installation of the in-stream hydrokinetic prototype, the retail cost of electricity in Ruby was $0.98 per kilowatt-hour. For several weeks in the summer of 2008 and two weeks in the summer of 2009, the turbine produced enough power to provide electricity to one home in Ruby, averaging approximately 500 watts over the two periods. Despite its small size, the turbine showed that in-stream electricity generation is a possible renewable resource for riverside communities. Similar technology could also be employed for use in tidal energy generation. A 25 kW turbine is scheduled for installation in the town of Eagle in summer 2010 and will generate enough electricity to provide some of the town’s energy from break-up to freeze. A 30 kW turbine is planned for Nenana, and Ruby may receive an additional 25 kW turbine that would provide power for about half the town in the summer of 2011. As a new technology, in-stream hydroelectric power is still relatively expensive as compared to other renewable alternatives and requires further study concerning potential environmental impacts and maintenance concerns. But it may be a viable alternative to costly diesel for many rural Alaskan villages in the near future.
Sources:
Energy Information Administration
Alaska Energy Authority “Renewable Energy Atlas of Alaska”
EnCurrent “Ruby, Alaska”
Yukon Intertribal Watershed Council
