(changed "Listing of the main elements of an installation" headline to "Parts of a hydroelectric plant")
(moved "Assessment of electricity needs" from hydropower)
Line 36: Line 36:


Other equipment to provide is an sand trap on the feeder canal. The grains of sand that accompany the water on the turbine have an abrasive effect that reduces the life of the machine. The biggest materials (stones, bricks) have an even more destructive effect and gratings should be installed at the entrance to the intake line but also at the penstock to prevent such incidents.
Other equipment to provide is an sand trap on the feeder canal. The grains of sand that accompany the water on the turbine have an abrasive effect that reduces the life of the machine. The biggest materials (stones, bricks) have an even more destructive effect and gratings should be installed at the entrance to the intake line but also at the penstock to prevent such incidents.
==Assessment of electricity needs==
It is difficult at first to estimate the effective electricity output since it depends on the project which is associated with the construction of the hydroelectric powerplant. It is known that the provision of electricity promotes its use. Without any regulation system of the consumption (limiting the amount available to the consumer via electrical switchboard, billing of the consumption).
The lighting of offices is an important element for the development of the electricity grid, as well as the sponsoring of communication facilities such as the telephone network, operation of television channels, computers. The electrical energy is also useful to activate the cooling chain (storage of medicines, vaccines ...). Foremost, we must exclude, in the context of a micro-powerplant, thel use of electricity as a means of heating because consumers will become prohibitive for the small network.
To give a general idea however, an installed capacity of 2kW per family is a correct value to identify the electricity needs in a village community. However, Vietnamese experience transposed to the Philippines cites lower values. Once the provision of electricity for a workshop is also considered, it is sufficient to determine the installed capacity to the whole of the envisaged equipment. In the case of a carpentry, engines consuming more than 1500W are common.
It is also possible to set, among the regular customers of a small network, priority clients such as those that manage a cooling chain for vaccines and drugs, or a surgical hospital. These customers will be supplied as long as possible. These provisions should be exposed to all users as a way to maintain cohesion and avoid conflicts. This regulating system allows to supply electricity to more customers but for a more limited period.


== Rural applications in the developing world ==
== Rural applications in the developing world ==

Revision as of 16:50, 21 March 2013

Hydroelectric power, or hydropower, is an established and reliable form of renewable energy. It uses the natural water cycle, and gravity, to generate electricity.

Determining the powerpotential of a site

The following mathematical formula allow to estimate the hydropower potential:

Knowing that: P expresses the electrical power in kilowatt-hour of the current generator; Q expresses the waterflow in the penstock in m³/sec; H expresses the difference in water level between the entrance to the penstock and the leakage channel of the turbine, expressed in meters; R is the overall efficiency of the facility, including the loss of load in the penstock, the turbine efficiency and alternator efficiency. A total efficiency of 60% is acceptable for the estimated hydroelectric potential.

As an example, with Q being 0,1 m³/sec and H being 10m we get a potential of 6kWh.

The efficiency of the turbine is a charisteristic of the machine given by the manufacturer. This efficiency depends on the waterflow. Indeed, if the inflow is, for example, only half of the expected speed (or nominal waterflow), it is easy to understand that the piece of the waterflow that will run between the rotating parts and the fixed parts without reacting on the blades of the machine does little or nothing. So the effective waterflow drops sharply and leads to an efficiency drop.

The potential of a site can be improved if the hydroelectric equipment is not a hydroelectric facility along the waterstream but equipped with an accumulation pond. In these circumstances it is possible to, for a few hours of the day, provide sufficient waterflow for periods of greater consumption of electricity. When the population of the village sleeps, they generally consume much less electricity. This decrease in electricityrequirements accompanies, through the speedregulator discussed above, a decrease in waterconsumption. The saved amount can be used at times of greater need. This accumulation pond should be considered in the context of a daily regulation. If deals around overcoming the insufficiencies of low water flows, the accumulation intake reaches a size that is outside the context of small power plants.

Parts of a hydroelectric plant

An installation, no matter how small, always includes the following elements (following the flow of water):

  1. a main water intake which ensures that as long as there is water in the river, it is directed towards the power plant. This intake is fitted with a valve that can cut the water supply in case of failure of the turbine or in case of repairs of the infrastructure.
  2. an intake channel more or less long will lead water from the main water intake to the head intake or startup room. This channel can also create a greater drop height when choosing a suitable route.
  3. the intake of the startup room ensures filling the pipeline linking the intake to the turbine. The correct creation of the startup room allows to keep the penstock submerged. The intake is foreseen of a emergency release to allow the evacuation of excess water by reducing the water needs of the turbine.
  4. the penstock (pipe between the intake of startup room and turbine) creates the water column which allows the startup of the turbine. This pipeline usually of steel for conventional plants, but can be carried out in polyethylene for pico-power. Its diameter is calculated to avoid loss of charges in the flow of water. A large pipe is expensive in purchase and placement but reduces the loss. When the height of the water column is low, there is no penstock but a concrete construction in which water flows to supports the water column.
  5. the turbine room of the facility, is a kind of wheel that is rotated by the flow of water flowing through it. The type of wheel is to be chosen depending of the given instantaneous waterflow, but also depending of the water pressure. Some of these turbines resemble the old bucketwheels are particularly suitable for plants that need to operate with significant waterflow variations. The turbines may be vertical or horizontal axis.
  6. The speed regulator controls the speed of the turbine. In times of normal operation, speed is a balance between the hydraulic load that turns the turbine and the resistive load of the electricity production. In case of a ruptured electrical circuit, the resistive electrical is canceled and the speed of the turbine will accelerate because the hydraulic load remains unchanged. Too much speed can be fatal to the equipment and the presence of the regulator corrects the beginning of the acceleration also called the runaway.
  7. The electricity generator, is another essential part as it will convert the mechanical energy of the turbine into electrical energy. This conversion into electricity facilitates the provision on places that can be removed from the turbine. Today, the generator is an alternator that provides alternating current, a type of electricity that is more widespread than direct current. To provide an alternating current conforming to the needs of network users, the alternator must turn in a speed range set by the manufacturer. Between the generator and the turbine, which rotates much more slowly, a gearbox is installed to make the operation of the two machines compatible. The generator is set synchronous or asynchronous, as determined or set on the frequency of the cycles of current of the network, being 50 cycles per second except on the American continent where it is 60 cycles. If the plant is the only or main power source of the network, install a synchronous alternator.
  8. Electrical cabinet for control and distribution. For the safety of the facilities and also the people, one should distribute the current on the network via a switchboard where the devices (fuses, disconnectors) allow the controlling of the distribution. At the other end of the network similar equipment should be installed to control the distribution with the client.
  9. The electrical distribution network includes wiring that allows the transport of the power to the users. This network is either low voltage, ie operating voltage of client devices, or high voltage. This is necessary when the transport distance is over 500m. Indeed, to carry 20 kW at a voltage of 220V, one requires a 90 amp electrical cable of at least 10mm2 section. If the voltage is 5000V, a section of 1mm2 is sufficient. The cost of this cable will probably be cheaper than the other one.
  10. The leakage channel is the route of escape of the water that has gone through the turbine. This channel is connected to the stream that resupplies the watervolume that is diverted to the water intake. It is important that this channel is not flooded in case of riverflood. Indeed, the rise of water level can cause flooding of the engine room (generator and turbine) with a risk of damage.

Other equipment to provide is an sand trap on the feeder canal. The grains of sand that accompany the water on the turbine have an abrasive effect that reduces the life of the machine. The biggest materials (stones, bricks) have an even more destructive effect and gratings should be installed at the entrance to the intake line but also at the penstock to prevent such incidents.

Assessment of electricity needs

It is difficult at first to estimate the effective electricity output since it depends on the project which is associated with the construction of the hydroelectric powerplant. It is known that the provision of electricity promotes its use. Without any regulation system of the consumption (limiting the amount available to the consumer via electrical switchboard, billing of the consumption). The lighting of offices is an important element for the development of the electricity grid, as well as the sponsoring of communication facilities such as the telephone network, operation of television channels, computers. The electrical energy is also useful to activate the cooling chain (storage of medicines, vaccines ...). Foremost, we must exclude, in the context of a micro-powerplant, thel use of electricity as a means of heating because consumers will become prohibitive for the small network. To give a general idea however, an installed capacity of 2kW per family is a correct value to identify the electricity needs in a village community. However, Vietnamese experience transposed to the Philippines cites lower values. Once the provision of electricity for a workshop is also considered, it is sufficient to determine the installed capacity to the whole of the envisaged equipment. In the case of a carpentry, engines consuming more than 1500W are common. It is also possible to set, among the regular customers of a small network, priority clients such as those that manage a cooling chain for vaccines and drugs, or a surgical hospital. These customers will be supplied as long as possible. These provisions should be exposed to all users as a way to maintain cohesion and avoid conflicts. This regulating system allows to supply electricity to more customers but for a more limited period.

Rural applications in the developing world

The use of water power in the People's Republic of China has reflected the same pattern, with first water wheels and then turbines being built in great numbers as power demands increased along with technical production capabilities. By 1976 an estimated 60,000 small hydroelectric turbines were in operation in South China alone, contributing a major share of the electricity used by rural communes for lighting, small industrial production, and water pumping.

With the rising cost of energy in the United States today, small hydroelectric units are returning in large numbers. Generating stations along New England rivers are being rehabilitated and put back into operation. The number of companies making small waterpower units has jumped. The U.S. Department of Energy has estimated that 50,000 existing agricultural, recreational, and municipal water supply reservoirs could be economically equipped with hydroelectric generating facilities.

In developing countries, the potential for small hydropower installations has never carefully been measured. Past surveys of hydropower potential have focused on possible sites for large dams, as small hydroelectric units were considered uneconomical or ill-suited to the goal of providing large blocks of electric power for cities, industrial estates, or aluminum production. With the rapidly increasing costs of energy, however, the economics are now much more favorable for small hydroelectric units, which are also well-suited to the needs of small rural communities, and do not bring the degree of environmental disruption associated with large reservoirs. Many small units do not require reservoirs at all, and use small diversion canals instead.

The success of waterpower installations can be greatly affected by forest conservation practices in the watershed above. Rapid deforestation brings high rates of soil erosion and subsequent rapid silt filling of reservoirs behind dams. At the same time, greater rain runoff causes increasingly violent floods that threaten hydropower installations. During the months following the floods, low water flows are likely to reduce generating capacity. A program to protect the watershed and the construction of a diversion canal may be necessary to prevent damage to a small waterpower installation.

Method

A large scale hydroelectric power plant forces water, generally held in a dam, through a hydraulic turbine connected to a generator. After the water exits the turbine it returns to the stream or river below the dam.

Because of the dependence on gravity, hydroelectric power is generally more feasible in mountainous regions than in flat country.

Hydroelectricity has relatively low operations and maintenance costs, especially compared to other forms of renewable energy.

Reliability

Hydroelectricity is a long-established technology, and the process itself is very reliable.

However, hydropower is highly dependent upon precipitation (rain and snow) - droughts can effect generating capacity.

Environmental impact

Hydroelectricity has very little impact on air pollution and climate change, as no fuel is burned. However, vegetation in the flood zone when the dam is built will decay in the lake formed by the dam, releasing methane. The net result is still believed to be a very small amount of greenhouse gases for the electricity produced, but it will vary from dam to dam.

The ecological effects of a dam on the downstream side of the structure, however, can be severe, as the water restriction often dramatically changes the normal flow of the river or stream. The range of anadromous fish (such as salmon) upriver is understandably hampered by the concrete and turbines of dams, beyond which is a habitat that has been deprived of a main predator. The buildup of sediment and silt behind the dam can substantially alter the geology of the downstream reaches.

The problems with dams

The largest impact of hydropower is generally from the dam. To avoid the serious negative impacts of a dam, a "run of the river" design is far preferable.

See Alternatives to hydroelectric energy.

Sizes of hydroelectric plants

Today, to transform hydropower to electrical power, it is possible to construct very large but also small-sized plants. This article lists the parameters to determine small hydroelectric facilities. They have a place in the process of the development of small communities and in the process of sustainable development because of the economy in terms of CO²-emissions. See http://www.kuleuven.ac.be-ei-public-publications-EIWP900-09_fr.pdf

The technical literature considers small power plants, those plants that generate a power output less than 2000kW or 2 MW. The small power plants are divided into mini power (maximum power output 500kW), micro-power (maximum power output of 100 kW) and pico-power (0.2 kw to 5kW). These powers outputs are to be considered as orders of magnitude because, depending on the country or region, different figures have been cited. The pico-plants have been installed mostly in Asia, Vietnam (120,000) and the Philippines.

Country Micro (kW) Mini (kW) Small (MW) Source
United States <100 100-1000 1-30 Dragu, 2002
China <500 - 0,5-25 Dragu, 2002
Italy - - <3 European Commission, 2000
Portugal,Spain, Ireland, Greece, Belgium - - <10 European Commission, 2000
France 5-5000 - <8 European Commission, 2000
India <100 101-1000 1-1,5 Dragu,2002
ESHA-European Small Hydropower Association <100 101-500 0,5-10 ESHA,1998

[1]

Use

Use of hydroelectric plants depending on size

Template:Hl3 align="center"|Size Template:Hl3 align="center"|Power Output Template:Hl3 align="center"|Typical Use
Large >10MW Usually part of a large grid.
Small 1MW-10MW Usually grid intertied. (up to 50MW in Canada[2])
Mini 100kW-1,000kW (1MW) Community and industry. Often grid intertied.
Micro 1kW-100kW Small low energy consuming community, small industry, rural high energy consuming household. Usually off-grid.
Pico <1kW Radio tower, low energy consuming household, charging station. Almost always off grid.

Please note that these are averages, many different communities classify hydropower somewhat differently.

Big and small

Microhydro is relatively simple and affordable technology used to provide power to a community. However, this is still many thousands of dollars, typically.

Picohydro refers to tiny generators, possibly made from old car alternators, generating power from a stream of water flowing through a large plastic bucket.

The future of hydroelectricity

The ability to build new generating capacity is extremely limited, especially in developed countries, because:

  • Most suitable sites are already being used.
  • Building a dam is extremely controversial, guaranteed to face strong opposition from environmental groups and owners of affected farms and other property. In practice, only an authoritarian government is likely to choose to build a new dam. In other cases, new capacity must be in the form of smaller "run of the river" systems.

See also


Template:Stub

Cookies help us deliver our services. By using our services, you agree to our use of cookies.