There
are four main divisions of hydroelectric power plants: 1) micro-scale, 2)
small-scale, 3) large-scale, 4) run-of-the-river, and 5) pumped storage.
Micro-scale plants are capable of producing one kilowatt to one megawatt of
power. They are typically used for small, isolated villages in developing
countries.
Small-scale plants are capable of producing up to twenty megawatts of power.
These systems are relatively inexpensive to implement. They can be
used in developing countries to provide electricity to rural areas.
Large-scale plants are the most efficient type of hydroelectric power plant.
They are typically constructed by damning a river to form a lake.
The largest hydroelectric power plant in the world[1]
produces 12.6 GW of electricity, with an annual rate of 90 million MW hours.
Large-scale plants take advantage of the potential energy of flowing
water due to gravity to extrapolate energy.
Run-of-the-river hydroelectric plants work on the principle that the flow rate
and elevation drops of the water are consistent enough that hydroelectric
plants can be built directly in the river. The water passes through the plant
without greatly changing the flow rate of the river. In many instances a dam is
not required, and therefore the hydroelectric plant causes minimal
environmental impact on its surroundings.
Pumped storage plants are used to provide peak power production during peak
power usage times. During non-peak times, water is pumped back into an upper
reservoir for peak time usage.
Power
production at given time is related to two factors: 1) flow volume, and 2)
head. Head is a measure of the pressure of falling water. Rivers
can be roughly divided into having either high or low[2]
head. Hydroelectric production on rivers with less than two feet of
vertical drop is unfeasible. The higher the head, the more efficient
hydroelectric power production will be. Although high volume can
compensate for low head, a more costly turbine to produce convert the energy to
electricity will be necessary.
A simple formula for power is outlined below.
It shows power dependent on gross head (H) and flow (F), as well as
system efficiency (E), which typically ranges from 40-70%, and a constant (C)
that is dependent on the particular unit system being used (U.S. Department of
Energy, 2001).
Hydroelectric
Dams affect the river in the following ways:
- Create water reservoirs/stagnant pools
- Become breeding groups for
malaria and other diseases
- Higher water temperatures with
little or no monthly variation
- Increased flooding
- Decreased residence time (fill with sediment)
- Increased Eutrophication
- Increased formation of methane gas
- Corrosion of equipment
- Decreased water quality downstream
- Increased water temperature
- Decreased water oxygen content
- Increased siltation
- Increased phosphorous and nitrogen content
- Impact on fish populations
- Energy transmission systems also have a negative
impact on the environment
Damned rivers
can be divided into four main segments: 1) an upstream segment, 2) the segment
immediately behind the damn, 3) the segment immediately downstream of the damn,
and 4) the segment downstream of the dam.
The upstream segment of the river is largely unaffected by the dam. The segment of the river most affected by
the dam is the portion directly downstream of the dam. In this section native fish population are
the most severely affected, to the point that the population may be dominated
by non-native species. With increasing
distance from the dam, and with the influx of other rivers and streams, the
affect of the dam becomes less severe.
Correspondingly, native fish populations are more successful with this
increasing distance (Brown et al, 2002).
Fish populations which migrate each year upstream to spawn are
particularly affected by damning. One
simple solution for this is the construction of fish ladders, which provide
pathways for fish to navigate past damns (Energy Matters, 1998).
Reservoirs have
both positive and negative effects on the upstream and downstream environments
due to the modification of the natural flow conditions. These effects include
higher temperatures, with little to no variation in temperature throughout the
course of a year; increased forest flooding, critical situation in reservoir
filling (from the sediment dropped when the water slows in the reservoir),
decreased residence time, increased eutrophication,
increased gas formation, corrosion of equipment and a decline in the water
quality downstream. One possible
solution that would negate these negative effects is hydraulic equipment to reaerate reservoirs ("Water Quality Simulation in
Reservoirs in the
Table 12: Comparison of means of power generation
in
|
Hydropower and
Electricity |
·
Installed electric capacity of 68.8 million kilowatts, 87%
hydropower (2000) ·
342.3 billion kilowatt-hours generated in 2000, in 2000:
89% hydropower; in 1999: 91% hydropower ·
One of world's top hydropower producers · |
·
See effects above (Part C) |
|
Oil |
·
Second largest oil reserves in ·
Production 1.6 million barrels per day in 2001 ·
Oil consumption almost 2.2 million barrels per day in 2001 ·
Imports from mostly |
·
Combustion results in sulfur and nitrogen impurities,
pollution and green house effect. |
|
Natural Gas |
·
Production and consumption rose steadily throughout the
1990's ·
Imports beginning in 1999 ·
Natural gas reserves as of January 2002 at 7.8 trillion
cubic feet ·
Fifth largest in |
·
More efficient and more economical than some coal and
nuclear plants ·
“20% of total CO2 emissions from fossil fuels
in 1996 came from consuming and flaring natural gas. Natural gas emissions
increased 26.9% from 1987 to 1996, the U.S. and Russia accounting for a
whopping 42% of the world total” (International Energy Annual) |
|
Coal |
·
Brazil's recoverable coal reserves are estimated
approximately 13.2 billion short tons of lignite and sub-bituminous coal,
giving it the largest coal reserves in Latin America ·
Due to high ash and sulfur content and low caloric value
of domestic coal, Brazil imports a significant amount of cal ·
~6.8 million short tons produced in 2000 ·
Consumption about 23.5 million short tons |
·
Emissions include sulfur oxides, nitrogen oxides, organic
compounds, heavy metals, radioactive elements, and ash |
|
Nuclear Energy |
·
Electronuclear ·
2 operational nuclear plants, Angra-1 and Angra-2 ·
1 under construction, Angra-3 ·
On hold, however electricity crisis may restart it, estimated
5 years to become operational ·
Nuclear Program came under Ministry of Defense rather than
Ministry of Mines and Energy ·
Decrease in military funding meant delays in nuclear power
plant construction ·
Government company, to assume responsibility for the
plants |
·
Non-renewable energy ·
Final disposal of radioactive waste ·
In Angra-1: ·
-High levels of shutdowns ·
-Radiation spills |
|
Ethanol and other
biomass |
·
Sugar Cane Industry ·
Came as result of oil shock of 1973 ·
Generates more than 4,000 gigawatt
hours annually to run its own refineries and distilleries ·
Has excess capacity of 200 MW ·
Produces between 3.4 and 3.7 billion gallons of ethanol
for automobiles per year |
·
Could contribute to global warming ·
1975: Brazilian National Alcohol Program created to
regulate ethanol market and encourage production and use of fuel ethanol |
|
Wind turbines (Energy
Matters, 1998). |
·
Current total capacity of only 20MW ·
Further 25MW are to come on line in the north-eastern Ceara state, where trade winds are strong ·
Large numbers of turbines required to produce significant
amounts of electricity ·
Larger impact on environment ·
Minimum wind speed ·
Small: 8 mi/hr ·
Large: 13 mi/hr ·
Large areas of land needed ·
Land can also be used for agriculture ·
High cost relative to production of energy ·
Only generate energy 25% of time |
·
Completely renewable source of energy ·
Safe |
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