Hydroelectricity

Hydroelectric Facility Classification

Classification of hydroelectric facilities is based on the amount of electricity generated. Hydroelectric facilities could be categorized as large (?500MW), medium (?10MW and <500MW), and small (<0.01MW and <10MW). Small hydroelectric facilities comprise mini/micro (? 0.01MW and <0.5MW) and pico (< 0.01MW). The challenge in utilizing installed capacity to categorize small hydro facilities could be explained, for example, in the case of a 10MW, low-head small hydro facility. Compared to high head facilities, the 10MW small hydro low head requires greater volumes of water and larger turbines for electricity generation.

Hydroelectric power—like that produced by the Grand Coulee Dam on the Columbia River in Washington state—offers cleaner energy than traditional fossil-fuel electricity. Hydroelectricity accounted for 18 percent of the global electricity supply in 2006.

Hydroelectric Project Components

Construction of a large-scale hydroelectric facility is typically achieved through several years of hydrological studies (usually employing more than 50 years of hydrological data) and a robust environmental impact assessment. Small hydroelectric facilities, on the contrary, require fewer years’ data and less stringent environmental assessment.

Techno-economic viability of hydroelectric power projects are very site specific. The economics of an identified hydroelectric project depends on several factors including the power (capacity) to be generated, the existence of feed-in tariffs for generated electricity, and prevailing market price for the generated electricity. Hydroelectric facilities comprise a dam, water passage, and a powerhouse.

The constructed dam helps direct the water into a penstock. The force of the flowing water in the penstock is employed to spin the turbine, resulting in electricity generation. The water exits the powerhouse through the tailrace, back into the river. The water passage consist of the entrance to the penstock; the penstock; the openings and exit of the turbines as well as valves to seal off water flow to the turbine for periodic maintenance work; and the tailrace. Most of mechanical and electrical equipment in a hydroelectric facility are housed in the powerhouse. The mechanical and electrical equipment in the powerhouse include valves for shutting off water to the turbines; river bypass gate to prevent flooding of catchment areas; hydraulic control system for the turbines and valves; electrical switch-gear; electrical protection and control system; transformers utilized internally for station [Page 220]service and also for power transmission and distribution systems; water cooling and lubricating system; ventilation system; telecommunication systems; fire alarm systems and backup power supply.

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