Hydroelectric Power

Hydroelectric power is the creation of electrical power using the force of moving water. Once in operation these power plants produce much less greenhouse gases as compared to the traditional coal-fired power plants.

There is a rich history of hydropower with some uses going back to the ancient times. Currently around 20% of the world's electricity and close to 90% of the electricity generated from renewable sources is provided by hydropower. In the United States, 7% of all electricity comes from hydropower.

Main Uses

The majority of hydroelectric power comes from potential energy of dammed water driving a water turbine and generator. The power from the water depends on the volume and difference in height between the source and the water's outflow. The amount of potential energy is proportional to this difference. A large pipe then sends the water to the turbine.

Some other hydro methods include: pumped storage, river-flow, tide, and underground. Some of the largest hydroelectric dams produce a few hundred MW to more than 10 GW. The largest in the world is the Three Gorges Dam at 22.5 GW.

Small hydro (up to 10 MW) is for the scale of small communities. Small-scale hydro plants can supplement conventional electrical grids. Micro hydro is usually meant for production up to 100 KW of power. These typically power isolated homes or a small community. Pico-hydro is used for under 5 KW of power. They can be useful for remote communities that require only a small amount of electricity. An example would be to power a couple light bulbs or a TV or radio for a few houses. Even smaller water turbines of a 200 W can power a single home and would require a difference of a meter (between inflow and outflow). For those interested, calculating power generated from water can be accomplished by the following formula:

P=ρhrgk

where,

• P is Power in watts
• ρ is density of water (1000 Kg/m^3 )
• h is height in meters
• r is flow rate in cubic meters per second
• g is gravitational acceleration (9.8 m/s2)
• k is coefficient of efficiency (0-1; closer to 1 with larger, modern turbines)

Keep in mind that hydroelectricity production can vary by a factor of 10 during the course in a typical year with variations in water supply responding to changing weather conditions.

Some Pros And Cons

Some main points to consider for using hydroelectric power:

Starting with the positives...

• Eliminate the cost of fossil fuels to power the electric grid

• Results in a cleaner environment with no direct production of carbon dioxide, since there is not burning of fossil fuels. Minimal pollution.

• Water to run the power plant is free from nature

• Once built, relatively low operation and maintenance costs

• This is truly a renewable source of energy that has been proven over time.

• Reservoirs behind a dam can allow for recreation, such as water sports, fishing, etc.

  Some negatives...

• High investment costs

• There can be ecological damage when land is submerged for creating the reservoirs required for hydroelectrical power. Spawing fish can be harmed with pathways are blocked by the dams. "Fish ladders" can have mixed results. Downstream there can be extra silt, along with other changes.

• Siltation from upstream can literally fill some reservoirs if they aren't maintained, reducing the effectiveness.

Flow shortages will lower power output. These can result from drought, climate change, upstream dams and/or water diversion, etc.

Relocation of people when construction of the hydroelectric plant is planned

Possible dam failure can cause death like in a natural flood

Despite having some downfalls, hydroelectric power eliminates the need for fossil fuel combustion, which is great news for the environment. Avoided are the risks of mining coal also. No nuclear waste is generated. Hydroelectricity is more reliable than wind.

The top producers of world-wide hydroelectricity are found here.

Hydroelectric power shows promise in some locations as an alternative energy source and can be important in our fight against climate change.