Hydropower plants range in size from small systems suitable for a single home or village to large projects producing electricity for utilities. Learn more about the sizes of hydropower plants. The most common type of hydroelectric power plant is an impoundment facility.
An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released to meet changing electricity needs or other needs, such as flood control, recreation, fish passage, and other environmental and water quality needs. A penstock is a closed conduit that channels the flow of water to turbines with water flow regulated by gates, valves, and turbines.
Prolonged droughts may diminish the water level of the river, lowering electricity generation, while melting glaciers, rapid snowpack melt, or changes in precipitation patterns from snow to rain may significantly alter the river flow. Run-of-the-river plants have no water storage facilities but may use low-level dams to increase the difference between the water intake level and the turbine.
In this case, the natural river flow generates electricity and the amount of power generated fluctuates depending on the cycle of the river. Although run-of-the-river technology can be used for large scale power generation, it is commonly applied to supply individual communities with electricity, with capacities of less than 30 MW. This form of power generation is popular in rural areas of China, but has potential application in many places, including in the United States.
Run-of-the-river technology typically disrupts much less of the river flow as compared to large hydropower dams. Current generation works similarly to a wind turbine, but underwater. Because water is denser than air, water moving at a given speed will produce much more power than that generated by a comparable wind speed. However, the turbine itself must be stronger and, therefore, is more expensive.
The environmental impact of current turbines is not clear. It could harm fish populations but fish-safe turbines have been developed.
The United States has many potential sites where current generation could occur, and several projects are underway, including those in the East River in New York and the San Francisco Bay. Ocean tidal power harnesses the predictable cycle of energy produced by the tides. A tidal barrage works similarly to a large hydropower reservoir dam, but it is placed at the entrance to a bay or estuary.
The retained water in the bay is released through turbines in the barrage and generates power. China, Russia, and South Korea all have smaller tidal power plants. Tidal turbines are similar to wind turbines in that they have blades that turn a rotor to power a generator. They can be placed on the sea floor where there is strong tidal flow. Because water is about times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines.
Tidal turbines are more expensive to build than wind turbines but can capture more energy with the same size blades. A tidal fence is a type of tidal power system that has vertical axis turbines mounted in a fence or row placed on the sea bed, similar to tidal turbines.
Water passing through the turbines generates electricity. As of the end of , no tidal fence projects were operating in the United States.
Hydropower explained Tidal power. What is energy? Units and calculators. Use of energy. Energy and the environment. Also in What is energy? Forms of energy Sources of energy Laws of energy. Exploiting the vertical rise and fall of the water level over a tidal cycle. A barrage is constructed with gates that close at high water, to retain the water inside the barrage while the water level outside goes down.
Once a height difference has developed, the water inside is allowed to run out through turbines, operating much like the traditional hydro systems described above, but with a relatively small height difference. There are variations on this approach, but all exploit the cyclic change in water level in a similar way.
Exploiting the speed of a fast tidal flow. Some places in the world have exceptionally fast flows for various reasons, and this approach puts turbines in the water to extract energy from them, analogous to underwater wind farms. Wave power aims to extract energy usually electricity from the periodic motions of swell waves - the large waves that you can see breaking offshore from a beach.
There are a lot of different methods being developed as prototypes, and there is no clear leading approach as yet. This is what is commonly thought of when people refer to solar power. However, the term could also be used to describe Concentrating Solar Power CSP plants, where sunlight is focussed on a large scale to heat steam or another fluid , and that steam is used to drive a turbine to produce electricity.
As noted in the comments, it could also refer to a few less common solar power techniques, such as solar updraught towers, but this is less likely as these technologies are poorly developed at present. Hydro power uses dams or at least a pipe where one end is as much higher as possible than the other to use the pressure of water at the bottom to turn a turbine and generate electricity or occasionally, do some other work such turn a mill.
They are often located on the edge of a large lake in a mountainous area so that even when there hasn't been much rainfall recently there is still a good amount of water to use. For those interested, the power able to be generated is based on a simple formula which is: the flow multiplied multiplied by the "head" the height difference between the surface of the water and the outlet where the turbine generates the power. In general, examples include coiled black hose to warm water for a pool solar thermal , silicon photovoltaic panels on the roof of a building to supply electricity, or even a parabolic mirror which concentrates sunlight into a small spot for providing a much more intense heat.
The graph provided specifically use the unit of dollars per kilowatt, so presumably is considering industrially sized electricity generation techniques. This means it won't be including the use of a black hose to heat your pool for solar thermal, but would include something like a solar tower with many mirrors that concentrate the heat enough to run a steam turbine.
There is some ambiguity in the table. If it's only about electricity generation, that helps a lot. The two types of solar could get split in different ways. Solar thermal could mean the directly supply of hot water from solar thermal panels or other thermal harvesting mechanisms.
OR it could refer to what's also called concentrating solar power, CSP, whereby sunlight is concentrated - either by a huge array of tracking mirros onto a central tower, or by parabolic troughs onto pipes - and that heat is then used to drive a turbine to generate electricity. PV panels are nearing maturity now; CSP is still at the grid-scale commercial prototypes. There's low uncertainty on costs of PV , and on the rate of decline of PV costs - it's called Swanson's Law, and works similarly to Moore's Law for computers.
The IEA have famously been rather inept on predicting how quickly deployment would occur, and how quickly costs would come down. There's high uncertainty on the costs of CSP.
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