By Tamim Younos
Younos is founder and president, Green Water-Infrastructure Academy, Washington, D.C. and former research professor of water resources at Virginia Tech. He lives in Blacksburg.
At present, solar and wind energy are highly promoted as renewable energy technologies — clean technologies in terms of their carbon footprint. However, the most prominent renewable energy source for generating electricity is hydropower. The history of hydropower for generating electricity in the U.S. goes back to late 19th century. In 1893, the first commercial installation of a hydropower plant at the Redlands Power Plant in California allowed electricity to be transmitted long distances for consumer use. At present, hydropower accounts for nearly 9% of the U.S. electric generating capacity.
The traditional hydropower plant depends on a dam and reservoir built on a river. The water released from the reservoir is supplied to a turbine — a rotary engine that uses an electricity generator to convert water energy into electricity. A large hydropower plant can generate electricity greater than 30 megawatts (MW). For example, the power generation capacity of the Hoover Dam built in 1939 and one of the largest in the U.S. is 2,080 MW. In comparison, the power generation capacity of the Claytor Dam (also built in 1939) on the New River in Pulaski County, Virginia is 75 MW. Most reservoirs are designed for multi-purpose uses that include drinking water supply and irrigation water source. In recent decades, two issues have impeded the construction of dams and reservoirs: (1) restrictions attributed to historic value of land and/or high cost to acquire land; and (2) known ecologic impacts of dams such as hindering fish passage. At present, research and technological development is focused on increasing the efficiency of existing hydropower generation plants. However, there is significant hydropower potential in building small and decentralized (distributed) hydropower plants. The electricity generation capacity of small hydropower plant is 100kW- 30 MW. A micro-hydro power plant can generate electricity up to 100 kW. At present, the significant potential of small hydropower generation is untapped.
The most common type of small hydropower plants are built on small streams. As a matter of fact, before rural electrification, micro-hydropower plants were common in small U.S. communities. For example, in the 1940s, Mr. Lucas (a Giles County, Virginia property owner) constructed a small dam and diversion channel on the North Fork Creek that ran through his property at Glen Alton. The channel supplied water to a small turbine that generated electricity. This original power plant was abandoned when the property was connected to the electric grid. The historic site located within the Jefferson National Forest was later donated to the Federal government. In 2013, Virginia Tech research team (Professor Eugene Brown and students) and I in collaboration with the U.S. Forest Service field manager restored the Glen Alton plant for citizen education purposes using a grant from the Appalachian Regional Commission and in-kind support from the USFS.
A small stream hydropower generation plant has fixed and/or limited power generation capacity due to its physical location. However, other emerging technologies can take advantage of the water and energy nexus to generate electricity. For example, electricity can be generated from pressurized pipe flow that can turn a turbine. Portland, Oregon generates electricity from turbines installed in city water pipes – an average of 1,100 megawatt-hours of electricity per year, enough energy to power about 150 homes. High-pressure flows in the pipelines managed by the San Diego Water County Authority allow the generation of electricity through a 4.5 MW turbine generator. These emerging and decentralized hydropower technologies can be expanded to meet electricity demand in both rural and populated urban areas.
To meet electricity demand using renewable energy technologies, there is a need for a holistic approach that integrates several small and decentralized renewable energy resources, for example solar and small hydropower within the same region. Developing small-scale renewable energy resources at the local level will enhance the reliability of energy availability, reduce electricity transmission cost and the dependency on centralized fossil-fuel based energy resources. Regulatory and permitting requirements for renewable energy systems including small hydropower vary in the U.S. according to state and local regulations. In Virginia, the regulatory requirement for small-scale renewable energy development is tied to large electric power (grid) providers. Along with holistic approach, changes in permitting requirements are needed to facilitate efficient development of integrated small-scale and decentralized renewable energy technologies.