Annual renewable energy investment has increased from $63 billion in 2006 to $104 billion in 2007 and $120 billion in 2008. In the four years from end-2004 to end-2008, solar photovoltaic (PV) capacity increased sixfold to more than 16 gigawatts (GW), wind power capacity increased 250 percent to 121 GW, and total power capacity from new renewables increased 75 percent to 280 GW, including significant gains in small hydro, geothermal, and biomass power generation. During the same period, solar heating capacity doubled to 145 gigawatts-thermal (GWth), while biodiesel production increased sixfold to 12 billion litres per year and ethanol production doubled to 67 billion litres per year.
Annual percentage gains for 2008 were even more dramatic and wind power grew by 29 percent and grid-tied solar PV by 70 percent. The capacity of utility-scale solar PV plants (larger than 200 kilowatts) tripled during 2008, to 3 GW. Solar hot water grew by 15 percent, and annual ethanol and biodiesel production both grew by 34 percent. Heat and power from biomass and geothermal sources continued to grow, and small hydro increased by about 8 percent.
During 2008, the United States became the leader in new capacity investment with $24 billion invested, or 20 percent of global total investment. The United States also led in added and total wind power capacity, surpassing long-time wind power leader Germany. Spain added 2.6 GW of solar PV, representing a full half of global grid-tied installations and a fivefold increase over Spain’s 2007 additions. China doubled its wind power capacity for the fifth year in a row, moving into fourth place worldwide. Another significant milestone was that for the first time, both the United States and the European Union added more power capacity from renewables than from conventional sources (including gas, coal, oil, and nuclear).
It’s impossible to separate the ‘technical’ and ‘financial’ aspects of the subject of renewable energy from the ‘politics’ which surround it. This is because the technical/financial/political aspects are intertwined; an available energy supply is the cornerstone of any economy and politicians are extremely interested in how economies perform. Politicians like short-term solutions and are reluctant to introduce measures which will make them unpopular.
Power generation using fossil fuels creates many economic externalities that are not taxed or banned by governments to control their use. For example, coal-fired power generation creates the negative externalities of emissions of mercury, NOx, SOx and COx. Many governments don’t limit these negative externalities, created by the power producers, for fear of impact upon the cost of electricity. Consequently, power generation using fossil fuels will always cost less than renewable energy until governments protect their citizens and the planet from the adverse effects of the emissions of mercury, NOx, SOx and COx.
Obviously, people do prefer renewable technologies. It is up to governments to use legislation and fiscal measures to create a level playing field where renewable energy cleanliness is rewarded and fossil fuel negative externalities like emissions of mercury, NOx, SOx and COx are penalized at the correct scale. By this method, renewable energy costs from sources like; solar, wind, tidal and hydro would be equal to those costs achieved with ‘clean’ fossil fuel power generation.
Wednesday, 22 July 2009
Tuesday, 21 July 2009
Wind power production
The success of wind power production depends on wind speed and the actual energy of the wind varies with a multiple power of the wind speed. Double the wind speed, and the wind energy increases more than eightfold.
A 2 kW wind turbine at a site with a wind speed of 12 mph may generate around 1300 kWh/year for a constant wind location, i.e. 150 watts for 8760 hours. At a wind speed of 19 mph, the output could rise to 6000 kWh/year and, at 23 mph, the annual output could be 15,000 kWh. Other factors limit turbine output at very high wind speeds. However, these figures show that good site selection is important for wind power project economics. If the wind only blows for part of the day or week then the number of kWh per year are reduced.
A windy site is starting point for any wind turbine project, but there are other factors too. Wind speed varies with height; the higher a turbine is raised above the ground, the better the wind regime. This benefits larger wind turbines that are placed on higher towers, but larger turbines tend to be more efficient anyway, so additional advantages accrue.
Depending on the efficiency of a wind turbine, there is a cut-off wind speed below which wind power generation is not considered economical. This figure depends on the efficiency of wind turbine design as well as on the turbine cost. With the turbines available at the moment, a wind speed as low as 10 mph is considered economically exploitable at an onshore site. Since offshore costs are higher, an offshore wind speed of 15 mph is needed to make a site economically attractive.
Once a potential site has been identified, it must be studied in more detail to confirm that it is suitable. Long- and short-term wind speed measurements will normally be needed to ascertain the wind regime. Figures for at least one full year will normally be required, longer if possible.
When wind passes over land, the unevenness of the ground and interference to wind flow from trees or undergrowth cause a significant amount of turbulence. Turbulent air creates an additional strain on a wind turbine blade, accelerating the onset of fatigue damage. In order to limit this damage as much as possible, wind turbines are normally placed on a tower, which is tall enough to raise the blades above this turbulent layer of air.
Most wind turbines have blades attached perpendicularly to a horizontal shaft and this arrangement imposes restrictions on the wind turbine design because the turbine must be raised on a tower for the blades to clear the ground and the turbulent layer of air next to it. Additionally, a yawing system is needed so that the rotor and generator enclosure can be rotated as the wind direction changes.
Alternatively, a vertical axis machine has all its weight supported by a ground-level bearing. However, the vertical configuration has not yet achieved significant commercial success.
A 2 kW wind turbine at a site with a wind speed of 12 mph may generate around 1300 kWh/year for a constant wind location, i.e. 150 watts for 8760 hours. At a wind speed of 19 mph, the output could rise to 6000 kWh/year and, at 23 mph, the annual output could be 15,000 kWh. Other factors limit turbine output at very high wind speeds. However, these figures show that good site selection is important for wind power project economics. If the wind only blows for part of the day or week then the number of kWh per year are reduced.
A windy site is starting point for any wind turbine project, but there are other factors too. Wind speed varies with height; the higher a turbine is raised above the ground, the better the wind regime. This benefits larger wind turbines that are placed on higher towers, but larger turbines tend to be more efficient anyway, so additional advantages accrue.
Depending on the efficiency of a wind turbine, there is a cut-off wind speed below which wind power generation is not considered economical. This figure depends on the efficiency of wind turbine design as well as on the turbine cost. With the turbines available at the moment, a wind speed as low as 10 mph is considered economically exploitable at an onshore site. Since offshore costs are higher, an offshore wind speed of 15 mph is needed to make a site economically attractive.
Once a potential site has been identified, it must be studied in more detail to confirm that it is suitable. Long- and short-term wind speed measurements will normally be needed to ascertain the wind regime. Figures for at least one full year will normally be required, longer if possible.
When wind passes over land, the unevenness of the ground and interference to wind flow from trees or undergrowth cause a significant amount of turbulence. Turbulent air creates an additional strain on a wind turbine blade, accelerating the onset of fatigue damage. In order to limit this damage as much as possible, wind turbines are normally placed on a tower, which is tall enough to raise the blades above this turbulent layer of air.
Most wind turbines have blades attached perpendicularly to a horizontal shaft and this arrangement imposes restrictions on the wind turbine design because the turbine must be raised on a tower for the blades to clear the ground and the turbulent layer of air next to it. Additionally, a yawing system is needed so that the rotor and generator enclosure can be rotated as the wind direction changes.
Alternatively, a vertical axis machine has all its weight supported by a ground-level bearing. However, the vertical configuration has not yet achieved significant commercial success.
Turbine working principle
A turbine is a means of extracting work from a fluid as it changes from a high pressure to a low pressure. A turbine consists of a shaft carrying a number of vanes or blades, and there is a transfer of energy between the fluid and the rotor. In a turbine, the fluid does work on the rotor.
For gas, steam or water turbines, the fluid is accelerated in a set of fixed nozzles, and the resulting high-speed jets of fluid then change their direction as they pass over a row of curved blades attached to a shaft. A force is exerted on the blades equal to the rate of change of momentum of the fluid, and this produces a torque at the rotor shaft. The momentum of the fluid in the tangential direction is changed and so a tangential force on the rotor is produced. The rotor therefore rotates and performs useful work, while the fluid leaves it with reduced energy. The velocity of the fluid is reduced to somewhere near the value it possessed before entering the nozzles.
For any turbine, the energy held by the fluid is initially in the form of pressure. For a turbine in a hydro-electric scheme, water comes from a high-level reservoir: in a mountainous region, several hundred metres head may thus be available, although water turbines are in operation in other situations where the available head is as low as three metres or less. For a steam turbine, the pressure of the working fluid is produced by the addition of heat in a boiler; in a gas turbine, pressure is produced by the chemical reaction of fuel and air in a combustion chamber.
The impulse (or constant pressure) turbine has one or more fixed nozzles, in each of which the pressure is converted to the kinetic energy of an unconfined jet. The jets of fluid then impinge on the moving blades of the rotor, where they lose practically all their kinetic energy and, ideally, the velocity of the fluid at discharge is only just sufficient to enable it to move clear of the rotor.
In a reaction turbine, the change from pressure to kinetic energy takes place gradually as the fluid moves through the rotor and, for this gradual change of pressure to be possible, the rotor must be completely enclosed and the passages in it entirely full of the working fluid.
It was during the oil crisis of the early 1970s that modern interest in wind turbines took form. From this period, the basic wind energy conversion system for power generation has gradually taken shape. Today, the basic system starts with a large rotor comprising two, three or four blades mounted on a horizontal shaft at the top of a tall tower. The blades interest the wind and capture the energy it contains, energy which causes them to rotate in a vertical plane about the shaft axis. The slow rotation of the shaft is normally increased by use of a gearbox, from which the rotational motion is delivered to a generator.
For gas, steam or water turbines, the fluid is accelerated in a set of fixed nozzles, and the resulting high-speed jets of fluid then change their direction as they pass over a row of curved blades attached to a shaft. A force is exerted on the blades equal to the rate of change of momentum of the fluid, and this produces a torque at the rotor shaft. The momentum of the fluid in the tangential direction is changed and so a tangential force on the rotor is produced. The rotor therefore rotates and performs useful work, while the fluid leaves it with reduced energy. The velocity of the fluid is reduced to somewhere near the value it possessed before entering the nozzles.
For any turbine, the energy held by the fluid is initially in the form of pressure. For a turbine in a hydro-electric scheme, water comes from a high-level reservoir: in a mountainous region, several hundred metres head may thus be available, although water turbines are in operation in other situations where the available head is as low as three metres or less. For a steam turbine, the pressure of the working fluid is produced by the addition of heat in a boiler; in a gas turbine, pressure is produced by the chemical reaction of fuel and air in a combustion chamber.
The impulse (or constant pressure) turbine has one or more fixed nozzles, in each of which the pressure is converted to the kinetic energy of an unconfined jet. The jets of fluid then impinge on the moving blades of the rotor, where they lose practically all their kinetic energy and, ideally, the velocity of the fluid at discharge is only just sufficient to enable it to move clear of the rotor.
In a reaction turbine, the change from pressure to kinetic energy takes place gradually as the fluid moves through the rotor and, for this gradual change of pressure to be possible, the rotor must be completely enclosed and the passages in it entirely full of the working fluid.
It was during the oil crisis of the early 1970s that modern interest in wind turbines took form. From this period, the basic wind energy conversion system for power generation has gradually taken shape. Today, the basic system starts with a large rotor comprising two, three or four blades mounted on a horizontal shaft at the top of a tall tower. The blades interest the wind and capture the energy it contains, energy which causes them to rotate in a vertical plane about the shaft axis. The slow rotation of the shaft is normally increased by use of a gearbox, from which the rotational motion is delivered to a generator.
Subscribe to:
Posts (Atom)