Sunday, February 15, 2009



Hydraulic turbine and electrical generator.

Hydroelectric dam in cross section

• hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator
• The energy extracted from the water depends on the volume and on the difference in height between the source and the water's outflow.
• height difference is called the head
• The amount of potential energy in water is proportional to the head
• Pumped storage hydroelectricity produces electricity to supply high
• Low electrical demand, excess generation capacity is used to pump water into the higher reservoir
• higher demand, water is released back into the lower reservoir through a turbine
• A simple formula for approximating electric power production at a hydroelectric plant is: P = hrk, where P is Power in watts, h is height in meters, r is flow rate in cubic meters per second, and k is a conversion factor of 7500 watts (assuming an efficiency factor of about 76.5 percent and acceleration due to gravity of 9.81 m/s2, and fresh water with a density of 1000 kg per cubic meters
• Annual electric energy production depends on the available water supply
• installations the water flow rate can vary by a factor of 10:1 over the course of a year

• Elimination of the cost of fuel
• The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil, natural gas or coal
• Economically power
• Dams do not burn fossil fuels, they do not directly produce carbon dioxide (a greenhouse gas)
• Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in themselves

• Environmental damage
• Can be disruptive to surrounding aquatic ecosystems (dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed)
• Generation of hydroelectric power changes the downstream river environment
• Large-scale hydroelectric dams have created environmental problems both upstream and downstream.
• Need to relocate the people living where the reservoirs are planned (Three Gorges Dam project in China, the Clyde Dam in New Zealand and the Ilısu Dam in Southeastern Turkey.)
• Failures of large dams, while rare, are potentially serious (the Banqiao Dam failure in Southern China resulted in the deaths of 171,000 people and left millions homeless)
• The creation of a dam in a geologically inappropriate location may cause disasters (the Vajont Dam in Italy, where almost 2000 people died, in 1963)


The Solar Two 10 MW solar power facility, showing the power tower (left) surrounded by the sun-tracking mirrors.

Available solar energy (left) greatly exceeds both potential wind power (center) and global energy consumption (right).

About half the incoming energy from the sun is absorbed by water and land masses, while the rest is reradiated back into space (values are in PW =1015 W).

A solar cell

• Earth receives 174 petawatts of incoming solar radiation (insulations) at the upper atmosphere at any given time
• When it meets the atmosphere, 6 percent of the insolation is reflected and 16 percent is absorbed
• Average atmospheric conditions (clouds, dust, pollutants) further reduce insulation traveling through the atmosphere by 20 percent due to reflection and 3 percent via absorption
• The absorption of solar energy by atmospheric convection (sensible heat transport) and evaporation and condensation of water vapor (latent heat transport) affects the winds and the water cycle
• The total solar energy available to the earth is approximately 3850 zettajoules (ZJ) per year.
• Oceans absorb approximately 285 ZJ of solar energy per year.
• Biomass captures approximately 1.8 ZJ of solar energy per year.
• A solar cell or photovoltaic cell is a device that converts light into electricity using the photoelectric effect
• A solar cell or photovoltaic cell is a device that converts light into electricity using the photoelectric effect
• Total peak power of installed PV is around 6,000 MW as of the end of 2006. It is projected to reach more than 9,000 MW by the end of 2007
• The deployment of PV power depends largely upon local conditions and requirements, most countries are taking an interest in developing PV as one of their options for renewable energy supply.
• Concentrating Solar Thermal (CST) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. It is then used to generate electricity
• Concentrating Solar Thermal technologies require direct insulations to function and are of limited use in locations with significant cloud cover
• A solar trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line
• A parabolic dish or dish/engine system consists of a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector's focal point
• A solar power tower consists of an array of flat reflectors (heliostats) that concentrate light on a central receiver atop a tower
• Focusing is critical and the reflectors track the sun through the day and the year on two axes
• A working fluid (air, water, molten salt) flows through the receiver where it is heated up to 1500 °C before transferring its heat to a power generation or energy storage system

• Elimination of fuel cost
• Save energy consumption
• No pollution
• Long life time energy supply

• Need wider area to concentrating solar energy
• Certain country where less time received the sunlight will be worse


Simple use of biomass fuel (Combustion of wood for heat).
• Biomass is grown from several plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sugarcane and oil palm (palm oil)
• Although fossil fuels have their origin in ancient biomass, they are not considered biomass by the generally accepted definition because they contain carbon that has been "out" of the carbon cycle for a very long time
Low tech processes include
• composting (to make soil conditioners and fertilizers)
• anaerobic digestion (decaying biomass to produce methane gas and sludge as a fertilizer)
• fermentation and distillation (both produce ethyl alcohol)
More high-tech processes are:
• Pyrolysis (heating organic wastes in the absence of air to produce gas and char. Both are combustible.)
• Hydro gasification (produces methane and ethane)
• Hydrogenation (converts biomass to oil using carbon monoxide and steam under high pressures and temperatures)
• Destructive distillation (produces methyl alcohol from high cellulose organic wastes).
• Acid hydrolysis (treatment of wood wastes to produce sugars, which can be distilled)

• Can save environment from pollutions when used the waste material to make the fuel
• Low cost provided

• can contribute to global warming


• Uses dry steam, typically above 235°C (455°F), to directly power its turbines
• Dry steam is steam that contains no water droplets
• Dry steam plants are used where there is plenty of steam available that is not mixed with water
• Dry steam plants are the simplest and most economical of geothermal plants

• Use hot water above 182 °C (360 °F) from geothermal reservoirs
• The high pressure underground keeps the water in the liquid state, although it is well above the boiling point of water at normal sea level atmospheric pressure.
• The water is pumped from the reservoir to the power plant, the drop in pressure causes the water to convert, or "flash", into steam to power the turbine
• Flash steam plants, like dry steam plants, emit small amounts of gases and steam.

• Used in binary-cycle power plants is cooler than that of flash steam plants, from 107 to 182 °C (225-360 °F)
• The hot fluid from geothermal reservoirs is passed through a heat exchanger which transfers heat to a separate pipe containing fluids with a much lower boiling point
• These fluids, usually Iso-butane or Iso-pentane, are vaporized to power the turbine
• These plants also do not emit any excess gas and, because they use fluids with a lower boiling point than water, are able to utilize lower temperature reservoirs, which are much more common

• clean and safe for the surrounding environment
• unaffected by changing weather conditions
• extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability
• a large geothermal plant can power entire cities while smaller power plants can supply more remote sites such as rural villages

• can adversely affect land stability in the surrounding region


An example of a wind turbine. This 3 bladed turbine is the most common design of modern wind turbines because it minimizes forces related

Worldwide installed capacity and prediction 1997-2010

• Wind turbines can be used to generate electricity in areas with strong, steady winds
• With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller, units, which makes them less visually distracting and safer for airborne animals
• Wind is a form of solar energy
• Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth
• The terms wind energy or wind power describe the process by which the wind is used to generate mechanical power or electricity
• Wind turbines convert the kinetic energy in the wind into mechanical power
• The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity

• A clean fuel source
• Doesn't pollute the air like power plants
• Don't produce atmospheric emissions that cause acid rain or greenhouse gasses
• A domestic source of energy
• The lowest price renewable technologies

• The cost of wind power has decreased dramatically in the past 10 years
• The wind is intermittent and it does not always blow when electricity is needed
• The noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have been killed by flying into the rotors


Washington Public Power Supply System Nuclear Power Plants 3 and 5 were never completed.

• Nuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity
• Produced by a controlled nuclear chain reaction and creates heat—which is used to boil water, produce steam, and drive a steam turbine. The turbine can be used for mechanical work and also to generate electricity
• As of 2004, nuclear power provided 6.5% of the world's energy and 15.7% of the world's electricity, with the U.S., France, and Japan together accounting for 57% of nuclear generated electricity
• A nuclear power plant uses the same fuel, uranium-235 or plutonium-239, a nuclear explosive involves an uncontrolled chain reaction, and the rate of fission in a reactor is not capable of reaching sufficient levels to trigger a nuclear explosion because commercial reactor grade nuclear fuel is not enriched to a high enough level
• The chain reaction is controlled through the use of materials that absorb and moderate neutrons
• Light water reactors use ordinary water to moderate and cool the reactors.
• That negative feedback stabilizes the reaction rate.

• Can generate very high rates of energy
• Long time energy supply
• Long cycle life

• Damage through Uranium mining, radioactive effluent emissions, and waste heat
• Disposal of nuclear waste, with high level waste proposed to go in Deep geological repositories and nuclear decommissioning
• Expensive cost to build it
• Built close to large water sources
• Uneconomic
• Accidents (The Chernobyl disaster in 1986 at the Chernobyl Nuclear Power Plant in the Ukrainian Soviet Socialist Republic)

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