6.9 - Hydroelectric Energy

Kinetic energy

the energy an object has due to its motion, especially the movement or flow of water, which can spin a turbine

Hydroelectricity

electricity generated by the kinetic energy of moving water, either by the natural current of a river, water being impounded by a dam and falling vertically through a channel, or by the natural tides of the moon's grav. pull

water impoundment systems

the storage of water in a reservoir behind a dam. If it is a hydroelectric dam, flow of water through a channel can turn a turbine to generate electricity, which can be tailored to meet electricity demand by opening or closing the channel

Siltation

The accumulation of sediments, primarily silt, on the bottom of a reservoir. The dam blocks the natural flow of nutrient-rich sediment downstream. Over time, it must be dredged out by a crane

Reservoir

a large natural or artificial lake used as a source of water supply, particularly behind a dam. Can provide recreational uses or water supply, but leads to displacement of human settlements and animal habitats

Run-of-the-river systems

water is retained behind a low dam and runs through a channel, with a turbine, generator, etc. before returning to the river. Less electricity generation than water impoundment, but less impact to seasonal flooding & surrounding ecosystems

Tidal energy system

Energy that comes from the movement of water driven by the gravitational pull of the Moon. Rising and lowering tides spin underwater turbines.

Fish ladders

a stair-like structure that allows migrating fish to get around a dam, especially salmon.

Non hydroelectric dam uses

Only 3% of dams in US are hydroelectric. 37% are for recreation/scenic reservoir creation, and 18% are for control of downstream flooding, enabling human construction & ag in floodplains of the river

Hydroelectric Use

The number one renewable source of electricity in the US, and globally.

Global Hydroelectric Use

1. China (Three Gorges Dam on Yangtze = biggest in the world)

2. Brazil

3. US

Water impoundment (dam) pros

- No GHG emissions when gen. electricity

- cheaper per KWH cost of electricity compare to FF

- limit downstream flooding

- reservoir = tourism, recreation, drinking & ag. water source

Water impoundment (dam) cons

- High upfront cost to construct

- Reservoir = displacement of human settlements, and flooding of large ecosystems & habitats

- Limits downstream water flow & nutrient-rich sediment deposit

- disrupts upstream migration of salmon

- large surface area of reservoir = faster evap. rate (water loss)

- anaerobic decomp. of flooded organic matter underneath reservoir releases methane (GHG)