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ELEKTROENERGEETIKA INSTITUUT
Referaat
Taastvad Energiaallikad
Esitamise tähtaeg
14.04.2009
Õppejõud: Hannes Agabus
Tudeng: Sergei Belosapko
Nikita Naumov
Tallinn
2009
Contents:
1. Renewable energy
1.1. Costs …………………………………………………………………………………………………….2
1.2. Potential future utilization……………………………………………………………………4
1.3. Why Don’t We Use More Renewable Energy? …………………………………….5
2. Energy Types
2.1. Wind Energy………………………………………………………………………………………….6
2.1.1. Annual Generation…………………………………………………………………………….7
2.1.2. Growth and cost trends ……………………………………………………………………..8
2.1.3. Theoretical potential………………………………………………………………………….9
2.1.4. Benefits of wind energy……………………………………………………………………..10
2.2. Solar Energy…………………………………………………………………………………………..11
2.2.1 Development , deployment and economics …………………………………………12
2.3. Hydroenergy………………………………………………………………………………………….13
2.4. Geothermal Energy………………………………………………………………………………..14
2.5. Biomass Energy……………………………………………………………………………………….16
3. Conclusion ………………………………………………………………………………………………….18
4. Sources …………………………………………………………………………………………………….…19
Renewable energy
Renewable energy is energy generated from natural resources— such as , wind, rain, tides and geothermal heat —which are renewable (naturally replenished). In 2006, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood -burning. Hydroelectricity was the next largest renewable source, providing 3% (15% of global electricity generation),followed by solar hot water/heating, which contributed 1.3%. Modern technologies, such as geothermal energy, wind power , solar power, and ocean energy together provided some 0.8% of final energy consumption.
While there are many large- scale renewable energy projects and production , renewable technologies are also suited to small off- grid applications, sometimes in rural and remote areas , where energy is often crucial in human development. Kenya has the world's highest household solar ownership rate with roughly 30,000 small (20–100 watt ) solar power systems sold per year .
Some renewable energy technologies are criticised for being intermittent or unsightly, yet the market is growing for many forms of renewable energy. Climate change concerns coupled with high oil prices, peak oil and increasing government support are driving increasing renewable energy legislation , incentives and commercialization. New government spending, regulation , and policies should help the industry weather the 2009 economic crisis better than many other sectors.
Costs
Renewable energy systems encompass a broad, diverse array of technologies, and the current status of these can vary considerably. Some technologies are already mature and economically competitive (e.g. geothermal and hydropower ), others need additional development to become competitive without subsidies. This can be helped by improvements to sub- components , such as electric generators.
The table shows an overview of costs of various renewable energy technologies. For comparison with the prices in the table, electricity production from a conventional coal - fired plant costs about 4¢/kWh. Though in some G8 nations the cost can be significantly higher at 7.88p (~15¢/kWh).Achieving further cost reductions as indicated in the table below requires further technology development, market deployment, an increase in production capacities to mass production levels,and of the establishment of an emissions trading scheme and/or carbon tax which would attribute a cost to each unit of carbon emitted; thus reflecting the true cost of energy production by fossil fuels which then could be used to lower the cost/kWh of these renewable energies.
Type
2001 energy costs
Potential future energy cost
Wind
4–8 ¢/kWh
3–10 ¢/kWh
Solar photovoltaic
25–160 ¢/kWh
5–25 ¢/kWh
Solar thermal
12–34 ¢/kWh
4–20 ¢/kWh
Large hydropower
2–10 ¢/kWh
2–10 ¢/kWh
Small hydropower
2–12 ¢/kWh
2–10 ¢/kWh
Geothermal
2–10 ¢/kWh
1–8 ¢/kWh
Biomass
3–12 ¢/kWh
4–10 ¢/kWh
Coal (comparison)
4 ¢/kWh
Geothermal heat
0.5–5 ¢/kWh
0.5–5 ¢/kWh
Biomass — heat
1–6 ¢/kWh
1–5 ¢/kWh
Low temp solar heat
2–25 ¢/kWh
2–10 ¢/kWh
All costs are in 2001 US$-cent per kilowatt -hour.
Source: World Energy Assessment , 2004 update [28]
Potential future utilization
Present renewable energy sources supply about 18% of current energy use and there is much potential that could be exploited in the future. As the table below illustrates, the technical potential of renewable energy sources is more than 18 times current global primary energy use and furthermore several times higher than projected energy use in 2100.
The Renewable Energy Resource Base (Exajoules per year)
Current use (2001)
Technical potential
Theoretical
potential
Hydropower
9
50
147
Biomass energy
50
>276
2,900
Wind energy
0.12
640
6,000
Solar energy
0.1
>1,575
3,900,000
Geothermal energy
0.6
--
Ocean energy
not estimated
not estimated
7,400
Total
60
>1,800
>4,000,000
Current use is in primary energy equivalent .
For comparison, the global primary energy use was 402 EJ per year in 2001.
Source: World Energy Assessment 2001[53]
Current use is in primary energy equivalent.
For comparison, the global primary energy use was 402 EJ per year in 2001.
Source: World Energy Assessment 2001[53]
Why Don’t We Use More Renewable Energy?
In the past, renewable energy has generally been more expensive to use than fossil fuels. Plus, renewable resources are often located remote areas and it is expensive to build powerlines to the cities where they are needed. The use of renewable sources is also limited by the fact that they are not always available (for example, cloudy days reduce solar energy, calm days mean no wind blows to drive wind turbines , droughts reduce water availability to produce hydroelectricity).
The production and use of renewable fuels has grown more quickly in recent years due to higher prices for oil and natural gas, and a number of State and Federal Government incentives, including the Energy Policy Acts of 2002 and 2005. The use of renewable fuels is expected to continue to grow over the next 30 years, although we will still rely on non-renewable fuels to meet most of our energy needs.
trends
Consumption
Total renewable energy consumption increased by 478 trillion Btu or 7 percent between 2005 and 2006 to 6,922 trillion Btu . At the same time total US energy consumption decreased 1 percent largely due to decreases across the board in fossil fuel energy consumption. The combination of these trends resulted in moving renewable energy's share of total US energy to nearly 7 percent, up from over 6 percent in 2005
During 2006 renewable energy consumption reached its highest level since 1997, which was a record year for hydropower due to water availability . Hydropower is the second largest source of renewable energy consumption.
Biomass and conventional hydroelectric power had the largest volumetric increases at 220 and 166 trillion Btu respectively, while wind energy consumption had the fastest annual rate of growth at almost 50 percent.
The electric power sector continued to be the largest consumer of renewable energy in 2006 (55 percent of total), primarily due to the very large contribution of conventional hydroelectric power . The industrial sector was second (29 percent of the total), due to that sector's major consumption of wood and derived fuels. Geothermal and conventional hydropower played only minor roles in the industrial sector. The residential sector also consumed wood for space heating and solar energy for water heating and electricity. The commercial sector accounted for just 2 percent of total renewable energy consumption. The transportation sector was the fastest growing sector, consuming 40 percent more renewable fuel between 2005 and 2006. This is mainly due to increased ethanol consumption, by far the larger component of biofuels during those years.
Renewable energy used to produce electricity contributed 4.229 quadrillion Btu or 61 percent of total renewable energy consumption in 2006 . Ninety percent of this energy was consumed in the electric power sector, which includes traditional electric utilities and independent power producers whose primary purpose is to sell electricity, or electricity and heat, to the public. Almost all of the remainder is used by the industrial sector. Nonhydro renewable electricity energy consumption expanded slowly from 1,278 to 1,360 trillion Btu between 2002 and 2006. Increases in wind consumption were partially offset by decreases in biomass.
Nonelectric uses of renewable energy made up the balance (2,693 trillion Btu or 39 percent) of renewable energy consumption. Nonelectric uses include applications such as wood for space heating, noncentral station solar, process heat from biomass for manufacturers, geothermal heat pumps and direct use of geothermal, biofuels for transportation and losses and coproducts from the production of biofuels. Over the last five years the share of renewable energy consumed for nonelectric use expanded from 33 to 39 percent.
Types
Wind Energy
Wind power is the conversion of wind energy into a useful form, such as electricity, using wind turbines. At the end of 2008, worldwide nameplate capacity of wind-powered generators was 121.2 gigawatts.Although wind produces only about 1.5% of worldwide electricity use, it is growing rapidly, having doubled in the three years between 2005 and 2008. In several countries it has achieved relatively high levels of penetration, accounting for approximately 19% of electricity production in Denmark , 11% in Spain and Portugal , and 7% in Germany and the Republic of Ireland in 2008.
Wind energy has historically been used directly to propel sailing ships or converted into mechanical energy for pumping water or grinding grain, but the principal application of wind power today is the generation of electricity. Wind power, along with solar power, is non-dispatchable, meaning that for economic operation all of the available output must be taken when it is available, and other resources, such as hydroelectricity, must be used to match supply with demand .
Large scale wind farms are typically connected to the local electric power transmission network , with smaller turbines being used to provide electricity to isolated locations. Utility companies increasingly buy back surplus electricity produced by small domestic turbines. Wind energy as a power source is favoured by many environmentalists as an alternative to fossil fuels, as it is plentiful, renewable, widely distributed, clean , and produces lower greenhouse gas emissions, although the construction of wind farms is not universally welcomed due to their visual impact and other effects on the environment. The intermittency of wind seldom creates problems when using wind power to supply a low proportion of total demand. Where wind is to be used for a moderate fraction of demand, additional costs for compensation of intermittency are considered to be modest.
Annual generation
Annual Wind Power Generation (TWh) for Top 10 countries and their total electricity consumption(TWh
Rank
Nation
2005
2006
2007
2008
Wind
Power
Total
Power
Wind
Power
Total
Power
Wind
Power
Total
Power
Wind
Power
Total
Power
1
Germany
27.2
5.1%
533.7
30.7
5.4%
569.9
38.5
6.6%
584.9
2
United States
17.8
0.4%
4048.9
26.6
0.7%
4058.1
34.5
0.8%
4149.9
52.0
1.3%
4108.6
3
Spain
20.7
7.9%
260.7
22.9
8.5%
268.8
27.2
9.8%
276.8
31.4
11.1%
282.1
4
India
679.2
726.7
14.7
1.9%
774.7
5
China
2474.7
2.7
0.1%
2834.4
5.6
0.2%
3255.9
12.8
0.4%
3426.8
6
Italy
2.3
0.7%
330.4
3.0
0.9%
337.5
4.0
1.2%
339.9
7
Denmark
6.6
18.5%
35.7
6.1
16.8%
36.4
7.2
19.7%
36.4
6.9
19.1%
36.2
8
France
1.0
0.2%
482.4
2.2
0.5%
478.4
4.0
0.8%
480.3
5.6
1.1%
494.5
9
United Kingdom
1.0
0.2%
407.4
383.9
379.8
10
Portugal
1.7
3.6%
47.9
2.9
5.9%
49.2
4.0
8.0%
50.1
5.7
11.3%
50.6
Growth and cost trends
Wind and hydroelectric power generation have negligible fuel costs and relatively low maintenance costs; in economic terms , wind power has a low marginal cost and a high proportion of capital cost. The estimated average cost per unit incorporates the cost of construction of the turbine and transmission facilities , borrowed funds, return to investors (including cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment , which may be in excess of twenty years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially. A British Wind Energy Association report gives an average generation cost of onshore wind power of around 3.2 cents per kilowatt hour (2005).Cost per unit of energy produced was estimated in 2006 to be comparable to the cost of new generating capacity in the United States for coal and natural gas: wind cost was estimated at $55.80 per MWh, coal at $53.10/MWh and natural gas at $52.50. Other sources in various studies have estimated wind to be more expensive than other sources (see Economics of new nuclear power plants , Clean coal, and Carbon capture and storage ).
In 2004, wind energy cost one-fifth of what it did in the 1980s, and some expected that downward trend to continue as larger multi-megawatt turbines were mass-produced. However , installed cost averaged €1,300 per kilowatt in 2007,compared to €1,100 per kilowatt in 2005. Not as many facilities can produce large modern turbines and their towers and foundations, so constraints develop in the supply of turbines resulting in higher costs. Research from a wide variety of sources in various countries shows that support for wind power is consistently between 70 and 80 percent amongst the general public.
Global Wind Energy Council (GWEC) figures show that 2007 recorded an increase of installed capacity of 20 GW, taking the total installed wind energy capacity to 94 GW, up from 74 GW in 2006. Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at an estimated rate of 31% following 32% growth in 2006. In terms of economic value , the wind energy sector has become one of the important players in the energy markets, with the total value of new generating equipment installed in 2007 reaching €25 billion , or US$36 billion.
Although the wind power industry will be impacted by the global financial crisis in 2009 and 2010, a BTM Consult five year forecast up to 2013 projects substantial growth. Over the past five years the average growth in new installations has been 27.6 percent each year. In the forecast to 2013 the expected average annual growth rate is 15.7 percent
More than 200 GW of new wind power capacity could come on line before the end of 2013. Wind power market penetration is expected to reach 3.35 percent by 2013 and 8 percent by 2018
Existing generation capacity represents sunk costs, and the decision to continue production will depend on marginal costs going forward , not estimated average costs at project inception. For example, the estimated cost of new wind power capacity may be lower than that for "new coal" (estimated average costs for new generation capacity) but higher than for "old coal" (marginal cost of production for existing capacity). Therefore , the choice to increase wind capacity will depend on factors including the profile of existing generation capacity.
Theoretical potential
Wind power available in the atmosphere is much greater than current world energy consumption. The most comprehensive study to date found the potential of wind power on land and near -shore to be 72 TW, equivalent to 54,000 MToE (million tons of oil equivalent) per year, or over five times the world's current energy use in all forms. The potential takes into account only locations with mean annual wind speeds ≥ 6.9 m/s at 80 m. It assumes 6 turbines per square kilometer for 77 m diameter , 1.5 MW turbines on roughly 13% of the total global land area (though that land would also be available for other compatible uses such as farming). The authors acknowledge that many practical barriers would need to be overcome to reach this theoretical capacity.
Advantages
Wind energy is fueled by the wind, so it's a clean fuel source. Wind energy doesn't pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural gas. Wind turbines don't produce atmospheric emissions that cause acid rain or greenhouse gasses.
Wind energy is a domestic source of energy, produced in the United States. The nation's wind supply is abundant.
Wind energy relies on the renewable power of the wind, which can't be used up. Wind is actually a form of solar energy; winds are caused by the heating of the atmosphere by the sun, the rotation of the earth, and the earth's surface irregularities.
Wind energy is one of the lowest-priced renewable energy technologies available today, costing between 4 and 6 cents per kilowatt-hour, depending upon the wind resource and project financing of the particular project.
Wind turbines can be built on farms or ranches, thus benefiting the economy in rural areas, where most of the best wind sites are found. Farmers and ranchers can continue to work the land because the wind turbines use only a fraction of the land. Wind power plant owners make rent payments to the farmer or rancher for the use of the land.
Disadvantages
Wind power must compete with conventional generation sources on a cost basis . Depending on how energetic a wind site is, the wind farm may or may not be cost competitive. Even though the cost of wind power has decreased dramatically in the past 10 years, the technology requires a higher initial investment than fossil-fueled generators.
The major challenge to using wind as a source of power is that the wind is intermittent and it does not always blow when electricity is needed. Wind energy cannot be stored (unless batteries are used); and not all winds can be harnessed to meet the timing of electricity demands.
Good wind sites are often located in remote locations, far from cities where the electricity is needed.
Wind resource development may compete with other uses for the land and those alternative uses may be more highly valued than electricity generation.
Although wind power plants have relatively little impact on the environment compared to other conventional power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have been killed by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly siting wind plants.
The Benefits of 20% Wind Energy by 2030
According to the American Wind Energy Association, if we increase our nation's wind energy capacity to 20% by 2030, it would…
Reduce Greenhouse Gas Emissions
A cumulative total of 7,600 million tons of CO2 would be avoided by 2030, and more than 15,000 million tons of CO2 would be avoided by 2050 .
Conserve Water
Reduce cumulative water consumption in the electric sector by 8% or 4 trillion gallons from 2007 through 2030.
Lower Natural Gas Prices
Significantly reduce natural gas demand and reduce natural gas prices by 12%, saving consumers approximately $130 billion.
Expand Manufacturing
To produce enough turbines and components for the 20% wind scenario, the industry would require more than 30,000 direct manufacturing jobs across the nation (assuming that 30% – 80% of major turbine components would be manufactured domestically by 2030).
Generate Local Revenues
Lease payments for wind turbines would generate well over $600 million for landowners in rural areas and generate additional local tax revenues exceeding $1.5 billion annually by 2030. From 2007 through 2030, cumulative economic activity would exceed $1 trillion or more than $440 billion in net present value terms.
Solar Energy
Solar energy technologies use the sun's energy and light to provide heat, light, hot water, electricity, and even cooling, for homes , businesses, and industry.
There are a variety of technologies that have been developed to take advantage of solar energy. These include:
Photovoltaic Systems
Producing electricity directly from sunlight. Solar cells convert sunlight directly into electricity. Solar cells are often used to power calculators and watches. They are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect. Solar cells are typically combined into modules that hold about 40 cells; a number of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat -plate PV arrays can be mounted at a fixed angle facing south , or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. Several connected PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single , large PV system.
Solar Hot Water
Heating water with solar energy. The shallow water of a lake is usually warmer than the deep water. That's because the sunlight can heat the lake bottom in the shallow areas, which in turn, heats the water. It's nature's way of solar water heating. The sun can be used in basically the same way to heat water used in buildings and swimming pools. Most solar water heating systems for buildings have two main parts: a solar collector and a storage tank. The most common collector is called a flat-plate collector. Mounted on the roof , it consists of a thin , flat, rectangular box with a transparent cover that faces the sun. Small tubes run through the box and carry the fluid – either water or other fluid, such as an antifreeze solution – to be heated. The tubes are attached to an absorber plate, which is painted black to absorb the heat. As heat builds up in the collector, it heats the fluid passing through the tubes.
Solar Electricity
Using the sun's heat to produce electricity. Many power plants today use fossil fuels as a heat source to boil water. The steam from the boiling water rotates a large turbine, which activates a generator that produces electricity. However, a new generation of power plants, with concentrating solar power systems, uses the sun as a heat source. There are three main types of concentrating solar power systems: parabolic -trough, dish/ engine , and power tower. Parabolic-trough systems concentrate the sun's energy through long rectangular, curved (U-shaped) mirrors . The mirrors are tilted toward the sun, focusing sunlight on a pipe that runs down the center of the trough. This heats the oil flowing through the pipe. The hot oil then is used to boil water in a conventional steam generator to produce electricity.
Passive Solar Heating and Daylighting
Using solar energy to heat and light buildings. Step outside on a hot and sunny summer day, and you'll feel the power of solar heat and light. Today, many buildings are designed to take advantage of this natural resource through the use of passive solar heating and daylighting. The south side of a building always receives the most sunlight. Therefore, buildings designed for passive solar heating usually have large, south-facing windows . Materials that absorb and store the sun's heat can be built into the sunlit floors and walls. The floors and walls will then heat up during the day and slowly release heat at night, when the heat is needed most. This passive solar design feature is called direct gain .
Development, deployment and economics
The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan . Other efforts included the formation of research facilities in the US ( SERI , now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).
Commercial concentrating solar power (CSP) plants were first developed in the 1980s. CSP plants such as SEGS project in the United States have a LEC of 12–14 ¢/kWh.[139] The 11 MW PS10 power tower in Spain, completed in late 2005, is Europe's first commercial CSP system, and a total capacity of 300 MW is expected to be installed in the same area by 2013.
Solar installations in recent years have also largely begun to expand into residential areas, with governments offering incentive programs to make "green" energy a more economically viable option . In Canada the government offers the RESOP (Renewable Energy Standard Offer Program). The program allows residential homeowners with solar panel installations to sell the energy they produce back to the grid (i.e., the government) at 41¢/kWh, while drawing power from the grid at an average rate of 20¢/kWh . The program is designed to help promote the government's green agenda and lower the strain often placed on the energy grid at peak hours. With the incentives offered by the program the average payback period for a residential solar installation (sized between 1.3 kW and 5 kW) is estimated at 18 to 23 years, considering such cost factors as parts, installation and maintenance, as well as the average energy production of a system on an annual basis.
Photovoltaics are 85 times as efficient as growing corn for ethanol. On a 300 feet (91 m) by 300 feet (1 hectare) plot of land enough ethanol can be produced to drive a car 30,000 miles (48,000 km) per year or 2,500,000 miles (4,020,000 km) by covering the same land with photo cells. The deserts of the South Western United States could produce sufficient electricity to fulfill all of the electrical needs of the United States, and could use electrolysis to produce Hydrogen from water to power aircraft
Hydroenergy
Hydro energy is simply energy that is taken from water and converted to electricity. Hydro energy can be obtained by using many methods of capture. The most common method of using energy from water is a hydroelectric dam, where water coming down through an area causes turbines to rotate and the energy is captured to run a generator. Power can also be generated from the energy of tidal forces or wave power, which uses the energy created by waves.
Many countries in the world use hydro energy for conversion to electricity. Canada maintains the highest use, while the United States comes in second. One of the main reasons that hydro energy is used is that it is a renewable energy, meaning it will not be depleted over time and it will consistently be replenished. It is also a clean energy source, as it does not emit any toxins.
One downside to using hydro energy is that it can sometimes change the natural flow of the water which can make it possible to harm plants and animals in the water. It can also damage areas and wildlife , as when creating a hydro electric dam, areas must be flooded.
Other reasons that many want to use hydro energy is that it is cheaper than using other methods to convert energy to electricity. It is also reliable and can be used almost immediately when turned on to meet the demand for electricity. Therefore, one must weigh the pros and cons before deciding to use hydro energy to supply their demand for electricity.
There are many forms of water energy:

• Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams. Examples are the Grand Coulee Dam in Washington State and the Akosombo Dam in Ghana .
  
• Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a Remote Area Power Supply (RAPS). There are many of these installations around the world, including several delivering around 50 kW in the Solomon Islands.
  
• Damless hydro systems derive kinetic energy from rivers and oceans without using a dam.
  
• Ocean energy describes all the technologies to harness energy from the ocean and the sea:
  
• Marine current power. Similar to tidal stream power, uses the kinetic energy of marine currents
  
• Ocean thermal energy conversion (OTEC) uses the temperature difference between the warmer surface of the ocean and the colder lower recesses. To this end, it employs a cyclic heat engine. OTEC has not been field-tested on a large scale.
  
• Tidal power captures energy from the tides. Two different principles for generating energy from the tides are used at the moment:
  

Tidal motion in the vertical direction — Tides come in, raise water levels in a basin , and tides roll out. Around low tide, the water in the basin is discharged through a turbine, exploiting the stored potential energy.
Tidal motion in the horizontal direction — Or tidal stream power. Using tidal stream generators, like wind turbines but then in a tidal stream. Due to the high density of water, about eight -hundred times the density of air, tidal currents can have a lot of kinetic energy. Several commercial prototypes have been build, and more are in development.

• Wave power uses the energy in waves. Wave power machines usually take the form of floating or neutrally buoyant structures which move relative to one another or to a fixed point. Wave power has now reached commercialization.
  
• Osmotic power or salinity gradient power, is the energy retrieved from the difference in the salt concentration between seawater and river water. Reverse electrodialysis (PRO) is in the research and testing phase.
  
• Vortex power is generated by placing obstacles in rivers in order to cause the formation of vortices which can then be tapped for energy.
  
• Deep lake water cooling, although not technically an energy generation method, can save a lot of energy in summer. It uses submerged pipes as a heat sink for climate control systems. Lake-bottom water is a year-round local constant of about 4 °C.
  

Geothermal Energy
The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius. In general, the temperature rises one degree Celsius for every 36 metres you go down. In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat.Geothermal energy has been used for thousands of years in some countries for cooking and heating. The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat".
Geothermal power is cost effective, reliable, and environmentally friendly, but has previously been geographically limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for direct applications such as home heating. Geothermal wells tend to release greenhouse gases trapped deep within the earth, but these emissions are much lower than those of conventional fossil fuels. As a result, this technology has the potential to help mitigate global warming if widely deployed.
How it works
Hot rocks underground heat water to produce steam.
We drill holes down to the hot region , steam comes up, is purified and used to drive turbines, which drive electric generators.
There may be natural "groundwater" in the hot rocks anyway, or we may need to drill more holes and pump water down to them.
The first geothermal power station was built at Landrello, in Italy, and the second was at Wairekei in New Zealand . Others are in Iceland , Japan, the Philippines and the United States.
In Iceland, geothermal heat is used to heat houses as well as for generating electricity.
If the rocks aren't hot enough to produce steam we can sometimes still use the energy - the Civic Centre in Southampton, England, is partly heated this way as part of a district heating scheme with thousands of customers..
Advantages

• Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect.
  
• The power stations do not take up much room , so there is not much impact on the environment.
  
• No fuel is needed.
  
• Once you've built a geothermal power station, the energy is almost free.
  It may need a little energy to run a pump, but this can be taken from the energy being generated.
  

Disadvantages

• The big problem is that there are not many places where you can build a geothermal power station.
  You need hot rocks of a suitable type, at a depth where we can drill down to them.
  The type of rock above is also important, it must be of a type that we can easily drill through.
  
• Sometimes a geothermal site may "run out of steam", perhaps for decades.
  
• Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of.
  

Biomass Energy
Biomass is biological material derived from living , or recently living organisms. In the context of biomass for energy this is often used to mean plant based material, but biomass can equally apply to both animal and vegetable derived material.
Biomass is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms, including alkali, alkaline earth and heavy metals. These metals are often found in functional molecules such as the porphyrins which include chlorophyll which contains magnesium .
Fossil fuels
Fossil fuels such as coal, oil and gas are also derived from biological material, however material that absorbed CO2 from the atmosphere many millions of years ago.
As fuels they offer high energy density, but making use of that energy involves burning the fuel, with the oxidation of the carbon to carbon dioxide and the hydrogen to water (vapour). Unless they are captured and stored, these combustion products are usually released to the atmosphere, returning carbon sequestered millions of years ago and thus contributing to increased atmospheric concentrations .
The vital difference between biomass and fossil fuels is one of time scale.
Biomass takes carbon out of the atmosphere while it is growing, and returns it as it is burned. If it is managed on a sustainable basis, biomass is harvested as part of a constantly replenished crop. This is either during woodland or arboricultural management or coppicing or as part of a continuous programme of replanting with the new growth taking up CO2 from the atmosphere at the same time as it is released by combustion of the previous harvest.
This maintains a closed carbon cycle with no net increase in atmospheric CO2 levels.
Within this definition, biomass for energy can include a wide range of materials.
The realities of the economics mean that high value material for which there is an alternative market, such as good quality , large timber , are very unlikely to become available for energy applications. However there are huge resources of residues, co-products and waste that exist in the UK which could potentially become available, in quantity, at relatively low cost, or even negative cost where there is currently a requirement to pay for disposal.
There are five basic categories of material:

• Virgin wood, from forestry, arboricultural activities or from wood processing
  
• Energy crops: high yield crops grown specifically for energy applications
  
• Agricultural residues: residues from agriculture harvesting or processing
  
• Food waste, from food and drink manufacture, preparation and processing, and post-consumer waste
  
• Industrial waste and co-products from manufacturing and industrial processes.
  

Biomass production for human use and consumption
This is a list of estimated biomass for human use and consumption. It does not include biomass which is not harvested or utilised. See Primary Productivity of the Biosphere for details
Location
(million km²)
(gram dryC / m² / year)
(billion tonnes / year)
(kg dryC / m²)
(billion tonnes)
(years)
Tropical rain forest
17.00
2,200.00
37.40
45.00
765.00
20.50
Tropical monsoon forest
7.50
1,600.00
12.00
35.00
262.50
21.88
Temperate evergreen forest
1,320.00
6.60
35.00
175.00
26.52
Temperate deciduous forest
7.00
1,200.00
8.40
30.00
210.00
25.00
Boreal forest
12.00
800.00
9.60
20.00
240.00
25.00
Mediterranean open forest
2.80
750.00
2.10
18.00
50.40
24.00
Desert and semidesert scrub
18.00
90.00
1.62
0.70
12.60
7.78
Extreme desert, rock, sand or ice sheets
24.00
3.00
0.07
0.02
0.48
6.67
Cultivated land
14.00
650.00
9.10
1.00
14.00
1.54
Swamp and marsh
2.00
2,000.00
4.00
15.00
30.00
7.50
Lakes and streams
2.00
250.00
0.50
0.02
0.04
0.08
Total continental
149.00
774.51
115.40
12.57
1,873.42
16.23
Open ocean
332.00
125.00
41.50
0.003
1.00
0.02
Upwelling zones
0.40
500.00
0.20
0.02
0.01
0.04
Continental shelf
26.60
360.00
9.58
0.01
0.27
0.03
Algal beds and reefs
0.60
2,500.00
1.50
2.00
1.20
0.80
Estuaries and mangroves
1.40
1,500.00
2.10
1.00
1.40
0.67
Total marine
361.00
152.01
54.88
0.01
3.87
0.07
Grand total
510.00
333.87
170.28
3.68
1,877.29
11.02
Conclusion
As we can see there are many types of reneable energy. In the past our civilization did not have technologies to use them all. Thats why we used traditional sources of energy. But now progress in science is very huge. And since the previous century we started using alternative energy sources very much. There are a lot of advantages using them . For example they are clean, they will never end because they are renewable, they are not dangerous like nuclear energy. With appropriate technologies they can be even cheaper than traditional energy sources. For many years part of alternative energy sources in our energy system rises, nowadays it is near 7%-8% . It is very tiny part, but undoubtely it will rise even more in future. Between them, alternative energy sources could deliver more than twice as much electricity than the new fleet of nuclear reactors being debated - and the renewables would be built more quickly. Even then, the full potential of these sources would not have been tapped - much more could be harnessed in the future. But we have to start now if we're going to end our dependence on fossil fuels and reduce emissions. Ambitious support for renewables will bring benefits - not just of clean, fuel-free energy, but the jobs and economic growth that come from pioneering new industries and technology.
Sources

• World Energy Assessment, 2004 update[28]
  
• World Energy Assessment 2001[53]
  
• www.wikipedia.org
  
• www.eia.doe.gov
  
• www1.eere.energy.gov
  
• www.renewableenergyworld.com
  
• www.greenenergyhelpfiles.com
  
• www.biomassenergycentre.org.uk
  
• www.therenewableenergycentre.co.uk/
  
• www.sciencedaily.com
  
• http://www.greenpeace.org.uk/climate/solutions/renewable-energy