Dams and energy production
What is a dam?
A dam is a man made structure built across a river. Most dams are built to control river flow, improve navigation, and regulate flooding. However, some dams are built to produce hydroelectric power.
How do dams make hydroelectric power?
Hydroelectric power is produced as water passes through dams; the more energy is produced. Once a dam is built, an artificial man made lake is created behind the dam. Electricity is produced by a device called a turbine containing metal coils surrounded by magnets. When the magnet spins over the metal coils, electricity is produced.
Turbines are located inside dams. The falling water spins the magnets. Dams provide clean, pollution free energy, but they can also harm the environment.
Location of the highest dam
The highest dam in the world is nurek dam on the vakhsh river in tajikistan, a country in central Asia. This dam is 984 feet (300metres) tall.
Conventional (dams): most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. The power extracted from the water depends on the volume and on the difference in height between the source and the water’s outflow. This height difference is called the head. A large pipe (the “penstock”) delivers water from the reservoir to the turbine.
Pumped storage: it helps at times when it comes to low electrical demand, the excess generation capacity is used to pump water into the highest reservoir when the demand becomes greater, water is released back into the lower reservoir through a turbine. Pumped storage can prove to be commercially important but it is not an energy source, and appears as a negative number in listings.
Run-of-the-river: it consists of small or no reservoir capacity, it depends or relies on what coming from upstream to generate electricity at that moment, and any over supply must pass unused. It is important because of its constant supply of water from a lake or existing natural reservoir upstream.
Tide: a tidal power station makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods.
Large facilities: large-scale hydroelectric power stations are more commonly seen as the largest power producing facilities in the world, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations.
Small hydro: as to do with the development of hydroelectric power on a scale serving small communities or industrial plants.
Micro hydro: it is a term used for hydroelectric power installations that typically produce up to 1000kw of power.
Pico: it is useful in small remote communities that requires only a small amount of electricity. E.g to power one or two fluorescent light bulbs and a T.v or radio for a few homes.
Underground: it is generally used at large facilities and makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake.
Calculating available power
A simple formula for approximating electric power production at a hydroelectric station is: P= -n(mg∆h)= -n(pv)g∆h)
Where P is power (in watts), n (eta) is the coefficient of efficiency, p (rho) is the density of water (~ 1000kg/m3), v is the volumetric flow rate (in kg/s), ∆h (Delta h) is the charge in height (in meters), g is accelerated due to gravity (9.8m/s2)
Advantages of hydroelectric
- Low cost/ high value power, suitability for industrial applications
- Reduced Co2 emissions
- Allows for other uses of the reservoir like water sports
Disadvantages of hydroelectric
- Ecosystem damage and loss of land
- Water loss by evaporation
- Siltation and flow shortage
- Methane emissions (from reservoir s)
- Failure risks
Comparison and interactions with other methods of power generation
Nuclear power: it does not require altering of large areas of the environment but it has a footprint, and hydro power station failures have caused more deaths than nuclear station failures.
Wind power: occasionally weather’s patterns can result in low winds for days or weeks so a hydroelectric reservoir could be needed to balance generation on the grid.
1. A dam is able to hold a large quantity of water because its wall is? (Wassce 2018)
A. Thickest at the top
B. Thickest at the middle
C. Thickest at the bottom
2. Define a dam?
Answer: A dam is a man made structure built across a river.
3.list four (4) generating methods
Answer: (I) conventional dams (ii) run-of-the-river (III) Pico
(III) small hydro (IV) tidal power station
4.list three (3) advantage of hydroelectric power.
Answer: (I) reduced Co2 (ii) flexibility (III) suitability for industrial applications
5. List three (3) disadvantage of hydroelectric power
Answer: (I) ecosystem damage and loss of land (ii) siltation and flow shortage (III) failure risks.