Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Renewable Energy shopping experience:

1. Compare - without doubt the biggest advantage that the Renewable Energy offers shoppers today is the ability to compare thousands of Renewable Energy at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Renewable Energy? Wrong! If the Renewable Energy is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Renewable Energy then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Renewable Energy? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Renewable Energy and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Renewable Energy wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Renewable Energy then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Renewable Energy site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Renewable Energy, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Renewable Energy, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

Renewable energy utilizes natural resources such as solar energy, wind energy, tidal energy and geothermal energy, which are naturally replenished. Renewable energy technologies range from solar energy, wind power, and hydroelectricity to biomass and biofuels for transportation. About 13 percent of primary energy comes from renewables, with most of this coming from traditional biomass like Wood fuel. Hydropower is the next largest source, providing 2-3%, and modern technologies like geothermal, wind, solar, and marine energy together produce less than 1% of total world energy demand.International Energy Agency (2007). Renewables in global energy supply: An IEA facts sheet, OECD, p. 3. The technical potential for their use is very large, exceeding all other readily available sources.World Energy Assessment (2001). Renewable energy technologies, chapter 7.

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Renewable energy technologies are sometimes criticised for being unreliable or unsightly, yet the market is growing for many forms of renewable energy. Wind power has a worldwide installed capacity of 74,223 MW and is widely used in several European countries and the USA. The manufacturing output of the ] industry reached more than 2,000 MW per year in 2006, Solar Energy: Scaling Up Manufacturing and Driving Down Costs p. 30. and Photovoltaic power stations are particularly popular in Germany. World's largest photovoltaic power plants Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Solar power plants in the Mojave Desert. Solar Trough Power Plants The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW.{{cite web] from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. America and Brazil Intersect on Ethanol Ethanol fuel is also widely available in the USA.

While there are many large-scale renewable energy projects, renewable technologies are also suited to Remote Area Power Supply, sometimes in rural and remote areas, where energy is often crucial in human development.World Energy Assessment (2001). Renewable energy technologies, p. 221. Kenya has the world's highest household solar ownership rate with roughly 30,000 small (20-100 watt) solar power systems sold per year. What Solar Power Needs Now Renewable Energy Access, 13 August 2007.

Climate change concerns coupled with Oil price increases of 2004-2006 and increasing government support are driving increasing renewable energy legislation, incentives and renewable energy commercialization. EU leaders reached agreement in principle in March that 20 percent of the bloc's 20 percent' energy should be produced from renewable fuels by 2020, as part of its drive to cut emissions of carbon dioxide, blamed in part for global warming. news and Official EP resolution of 25 September 2007 on the Road Map for Renewable Energy in Europe Investment capital flowing into renewable energy climbed from $80 billion in 2005 to a record $100 billion in 2006. United Nations Environment Programme and New Energy Finance Ltd. (2007). Global Trends in Sustainable Energy Investment 2007: Analysis of Trends and Issues in the Financing of Renewable Energy and Energy Efficiency in OECD and Developing Countries p. 3. Some very large corporations such as BP, General Electric, Sharp Corporation, and Royal Dutch Shell are investing in the renewable energy sector. Two oil giants plunge into the wind business: Shell, BP intend to play major role GE Energy

Main renewable energy technologies

The majority of renewable energy technologies are directly or indirectly powered by the sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation, the resulting level of energy within the Earth-Atmosphere system can roughly be described as the Earth's "climate." The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress.Renewable Energy, Sorensen, Elsevier 2004 Solar energy is also responsible for the distribution of precipitation which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels.

Renewable energy flows involve natural phenomena such as sunlight, wind, tides and geothermal heat, as the International Energy Agency explains:"Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources." Renewable energy... into the mainstream p. 9.Each of these sources has unique characteristics which influence how and where they are used.

Wind power

Airflows can be used to run wind turbines. Modern wind turbines range from around 600kW to up to 5 MW of rated power, although turbines with rated output of 1.5-3 MW have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms.

Wind power is the fastest growing of the renewable energy technologies, though it currently provides less than 0.5% of global energy. Over the past decade, global installed maximum capacity increased from 2,500 MW in 1992 to just over 40,000 MW at the end of 2003, at an annual growth rate of near 30%. Due to the Intermittent Power Sources of wind resources, most deployed turbines in the EU produce electricity an average of 25% of the hours in a year (a capacity factor of 25%), Potentials and costs for renewable electricity generation but under favourable wind regimes some reach 35% or higher. Capacity factors are a function of seasonal wind fluctuations and may be higher in winter. It would mean that a typical 5 MW turbine in the EU would have an average output of 1.7 MW.

Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand. This could require large amounts of land to be utilized for wind turbines, particularly in areas of higher wind resources. Offshore resources experience mean wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy."Offshore stations experience mean wind speeds at 80 m that are 90% greater than over land on average. Evaluation of global wind power
"Overall, the researchers calculated winds at 80 meters feet traveled over the ocean at approximately 8.6 meters per second and at nearly 4.5 meters per second over land and 10 miles per hour, respectively." Global Wind Map Shows Best Wind Farm Locations (URL accessed January 30, 2006) This number could also increase with higher altitude ground-based or airborne wind turbines."High-altitude winds could provide a potentially enormous renewable energy source, and scientists like Roberts believe Airborne wind turbine could put an end to dependence on fossil fuels. At 15,000 feet, winds are strong and constant. On the ground, wind is often unreliable — the biggest problem for ground-based wind turbines." Windmills in the Sky (URL accessed January 30, 2006)

Wind strengths near the Earth's surface vary and thus cannot guarantee continuous power unless combined with other energy sources or storage systems. Some estimates suggest that 1,000 MW of conventional wind generation capacity can be relied on for just 333 MW of continuous power. While this might change as technology evolves, advocates have suggested incorporating wind power with other power sources, or the use of energy storage techniques, with this in mind. It is best used in the context of a system that has significant reserve capacity such as hydro, or reserve load, such as a desalination plant, to mitigate the economic effects of resource variability.

Wind power is renewable and produces no greenhouse gases during operation, such as carbon dioxide and methane.

Water power Energy in water (in the form of motive energy or temperature differences) can be harnessed and used. Since water is about 800 times Density of air,{{cite web|url=http://wahiduddin.net/calc/calc_da_m.htm|title=Density Altitude Calculator|accessdate=2007-09-17|author=Richard Shelquist|date=18-Oct-2005-->{{cite web|url=http://www.csgnetwork.com/h2odenscalc.html|title=Water Density Calculator|accessdate=2007-09-17|date=Copyright© 1973 - 2007|publisher=CSG, Computer Support Group, Inc. and CSGNetwork.Com-->even a slow flowing stream of water, or moderate sea Swell (ocean), can yield considerable amounts of energy.

There are many forms of water energy:

Solar energy use In this context, "solar energy" refers to energy that is collected from sunlight. Solar energy can be applied in many ways, including to:

Biofuel Plants use photosynthesis to grow and produce biomass. Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work.

Liquid biofuel Liquid biofuel is usually either a bioalcohol such as ethanol or a bio-oil such as biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40%. In some areas maize, cornstalks, sugarbeets, sugar cane, and switchgrasses are grown specifically to produce ethanol (also known as grain alcohol) a liquid which can be used in internal combustion engines and fuel cells. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers. Biobutanol is being developed as an alternative to bioethanol.

In the future, there might be bio-synthetic liquid fuel available. It can be produced by the Fischer-Tropsch process, also called Biomass-To-Liquids (BTL). Status And Perspectives of Biomass-To-Liquid Fuels in the European Union

Solid biomass residue can be used as a biofuelDirect use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines.

Sugar cane residue, wheat chaff, maize and other Biomass can be, and are, burned quite successfully. The net carbon dioxide emissions that are added to the atmosphere by this process are only from the fossil fuel that is often currently consumed to plant, fertilize, harvest and transport the biomass.

Processes to harvest biomass from short-rotation poplars and willows, and perennial grasses such as switchgrass, phalaris, and miscanthus, require less frequent cultivation and less nitrogen than from typical annual crops. Pelletizing miscanthus and co-firing it with coal for generating electricity is being studied and may be economically viable. Biomass Crops as a Source of Renewable Energy: European Experience with Miscanthus and Projections for Illinois The higher heating value of cellulose is about 17.4 MJ/kg . The estimated yield of ethanol from dry cellulose is about 0.2 kg of ethanol per kg of cellulose (60 gal/ton). Since the heating value is 29.7 MJ/kg of ethanol it would be 5.94 MJ/kg of the cellulose that it is made from. Thus the ethanol contains only about 1/3 as much energy as the cellulose that it was made from. Co-firing cellulose with coal would replace about three times as much fossil fuel as using the cellulose to make ethanol. The replaced coal would produce 0.0946 kg CO₂/MJ while the replaced liquid fuel would produce only about 0.0733 kg CO₂/MJ so co-firing the cellulose with coal is about 3.8 times more effective at reducing CO₂ emissions than using it to make ethanol.

Solid biomass can also be gasification, and used as described in the next section.

Biogas Biogas can easily be produced from current waste streams, such as: paper production, sugar production, sewage, animal waste and so forth. These various waste streams have to be slurried together and allowed to naturally ferment, producing methane gas. This can be done by converting current sewage plants into biogas plants. When a biogas plant has extracted all the methane it can, the remains are sometimes better suitable as fertilizer than the original biomass.

Alternatively biogas can be produced via advanced waste processing systems such as mechanical biological treatment. These systems recover the recyclable elements of household waste and process the biodegradable fraction in anaerobic digesters.

Renewable natural gas is a biogas which has been upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to the mass market via gas grid.

Geothermal energy Geothermal Station in northeast IcelandGeothermal energy is energy obtained by tapping the heat of the earth itself, usually from kilometers deep into the Earth's crust. It is expensive to build a power station but operating costs are low resulting in low energy costs for suitable sites. Ultimately, this energy derives from heat in the Earth's core. The government of Iceland states: "It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource." It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW. RESPONSE OF WAIRAKEI GEOTHERMAL RESERVOIR TO 40 YEARS OF PRODUCTION, 2006 (pdf) Allan Clotworthy, Proceedings World Geothermal Congress 2000. (accessed 30 March) The International Energy Agency classifies geothermal power as renewable. Geodynamics says it has the "hottest rocks on earth"

Three types of power plants are used to generate power from geothermal energy: dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200 °C, out of the ground, and allows it to boil as it rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine. In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat.

The geothermal energy from the core of the Earth is closer to the surface in some areas than in others. Where hot underground steam or water can be tapped and brought to the surface it may be used to generate electricity. Such geothermal power sources exist in certain geologically unstable parts of the world such as Iceland, New Zealand, United States, Philippines and Italy. The two most prominent areas for this in the United States are in the Yellowstone National Park basin and in northern California. Iceland produced 170 MW geothermal power and heated 86% of all houses in the year 2000 through geothermal energy. Some 8000 MW of capacity is operational in total.

There is also the potential to generate geothermal energy from Hot dry rock geothermal energy. Holes at least 3 km deep are drilled into the earth. Some of these holes pump water into the earth, while other holes pump hot water out. The heat resource consists of hot underground radiogenic granite rocks, which heat up when there is enough sediment between the rock and the earths surface. Several companies in Australia are exploring this technology.

Renewable energy commercialization 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.{{cite book] levels.

{| class="wikitable"|-|||| 2001 energy costs|| Potential future energy cost|-| align=center colspan=3 | Electricity|-|| Wind power|| 4-8 ¢/kWh|| 3-10 ¢/kWh|-|| Solar photovoltaics|| 25-160 ¢/kWh|| 5-25 ¢/kWh|-|| Solar thermal energy|| 12-34 ¢/kWh|| 4-20 ¢/kWh|-|| Large hydropower]|| 2-10 ¢/kWh|| 1-8 ¢/kWh|-|| Biomass energy|| 3-12 ¢/kWh|| 4-10 ¢/kWh|-|| Fossil fuel power plant (comparison)|| 4¢/kWh|||-| align=center colspan=3 | Heat|-|| Geothermal heating|| 0.5-5 ¢/kWh|| 0.5-5 ¢/kWh|-|| Biomass - heat|| 1-6 ¢/kWh|| 1-5 ¢/kWh|-|| Solar hot water|| 2-25 ¢/kWh|| 2-10 ¢/kWh|-| colspan=3 | All costs are in 2001 $-cent per kilowatt-hour.|-| colspan=3 | Source: World Energy Assessment, 2004 updateWorld Energy Assessment 2004 Update, (energy costs from Table 7). Available for download at its UNDP site.|}

Wind power market grows ]

Figures from the Global Wind Energy Council (GWEC) show that 2006 recorded an increase in installed wind power capacity of 15,197 megawatts (MW), taking the total installed capacity to 74,223 MW, up from 59,091 MW in 2005. Global wind energy markets continue to boom – 2006 another record year Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at the rate of 32% following the 2005 record year, in which the market grew by 41%. 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 2006 reaching €18 billion, or US$23 billion.

The countries with the highest total installed capacity are Wind power in Germany (20,621 MW), Wind power in Spain (11,615 MW), the Wind power in the United States (11,603 MW), Wind power in India (6,270 MW) and Wind power in Denmark (3,136 MW). In terms of new installed capacity in 2006, the USA lead with 2,454 MW, followed by Germany (2,233 MW), India (1,840 MW), Spain (1,587 MW), China (1,347 MW) and France (810 MW).

In the UK, a licence to build the world's largest offshore windfarm, in the Thames estuary, has been granted. The London Array windfarm, 12 miles off Kent and Essex, should eventually consist of 341 turbines, occupying an area of 90 square miles. This is a £1.5 billion, 1,000 megawatt project, which will power one-third of London homes. The windfarm will produce an amount of energy that, if generated by conventional means, would result in 1.9 million tonnes of carbon dioxide emissions every year. It could also make up to 10% of the Government's 2010 renewables target. Windfarms to power a third of London homes

New generation of solar thermal plants in Spain produces electricity from the sun using 624 large movable mirrors called heliostats.

Construction of the largest solar thermal power plant to be built in 15 years, in Boulder City, Nevada, is nearly complete. The 64MW Nevada Solar One power plant will generate enough power to meet the electricity needs of about 40,000 households and follows in the steps of the 354MW SEGS solar thermal power plants located in California’s Mojave Desert. While California’s solar plants have generated billions of kilowatt hours of electricity for the past two decades, the Nevada Solar One plant will use new technologies to capture even more energy from the sun. Largest solar power plant in a generation to be built in Nevada

The California Solar Initiative As part of Governor Arnold Schwarzenegger's Million Solar Roofs Program, California has set a goal to create 3,000 megawatts of new, solar-produced electricity by 2017 - moving the state toward a cleaner energy future and helping lower the cost of solar systems for consumers. This is a comprehensive $2.8 billion program. The California Solar Initiative

The California Solar Initiative offers cash incentives on solar PV systems of up to $2.50 a watt. These incentives, combined with federal tax incentives, can cover up to 50% of the total cost of a solar panel system. There are many financial incentives to support the use of renewable energy in other US states. Financial Incentives in the USA

World's largest photovoltaic power plants Construction of a 40 MW solar generation power plant is underway in the Saxon region of Germany. The Waldpolenz Solar Park will consist of some 550,000 thin-film solar modules. The direct current produced in the modules will be converted into alternating current and fed completely into the power grid. Once completed in 2009, the project will be one of the largest photovoltaic projects ever constructed. Currently the biggest PV plant in the world has an output capacity of around 12 megawatts. Phase One of 40 MW German Solar Park Begun



A large photovoltaic power project has been completed in Portugal, the Serpa solar power plant is at one of the Europe's sunniest areas. Major solar power plant opens in Portugal The 11 megawatt plant covers 150 acres and is comprised of 52,000 PV panels. The panels are raised 2 metres off the ground and the area will remain productive grazing land. The project will provide enough energy for 8,000 homes and will save an estimated 30,000 tonnes of carbon dioxide emissions per year. Portugal starts huge solar plant World's largest solar photovoltaic power plant to be built

A $420 million large-scale Solar power station in Victoria is to be the biggest and most efficient solar photovoltaic power station in the world. Australian company Solar Systems will demonstrate its unique, design incorporating space technology in a 154MW solar power station connected to the national grid. The power station will have the capability to concentrate the sun by 500 times onto the solar cells for ultra high power output. The Victorian power station will generate clean electricity directly from the sun to meet the annual needs of over 45,000 homes with zero greenhouse gas emissions. Solar Systems -- 154MW Victorian Project

However, when it comes to renewable energy systems and PV, it is not just large systems that matter. Building-integrated photovoltaics or "onsite" PV systems have the advantage of being matched to end use energy needs in terms of scale. So the energy is supplied close to where it is needed. Solar Integrated in New Jersey

Use of ethanol for transportation Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a partial result, Brazil, which years ago had to import a large share of the petroleum needed for domestic consumption, recently reached complete self-sufficiency in oil. America and Brazil Intersect on Ethanol

Most cars on the road today in the U.S. can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford Motor Company, DaimlerChrysler, and General Motors Corporation are among the automobile companies that sell “flexible-fuel” cars, trucks, and minivans that can use gasoline and ethanol blends ranging from pure gasoline up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on U.S. roads. The challenge is to expand the market for biofuels beyond the farm states where they have been most popular to date. Flex-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, will also help to expand the market.

Wave farms expand Portugal now has the world's first commercial wave farm, the Aguçadora Wave Park, established in 2006. The farm will initially use three Pelamis Wave Energy Converter machines generating 2.25 MW. Sea machine makes waves in Europe Wave energy contract goes abroad Initial costs are put at euro8.5 million. Subject to successful operation, a further €70 million is likely to be invested before 2009 on a further 28 machines to generate 525 MW. Primeiro parque mundial de ondas na Póvoa de Varzim

Funding for a wave farm in Scotland was announced in February, 2007 by the Scottish Executive, at a cost of over 4 million pound sterling, as part of a £13 million funding packages for Renewable energy in Scotland#Wave power. The farm will be the world's largest with a capacity of 3MW generated by four Pelamis machines. Orkney to get 'biggest' wave farm

Geothermal energy prospects By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 watts, with an additional 28 GW used directly for heating. If heat recovered by Geothermal exchange heat pump is included, the non-electric use of geothermal energy is estimated at more than 100 GWt (gigawatts of thermal power) and is used commercially in over 70 countries.( sec 1.2) During 2005 contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.

Future potential While currently renewable energy sources only supply a fraction of current energy use (ca. 14% of primary energy use, World Energy Assessment 2001, Chapter 5: Energy Resources (table 5.26), coordinating lead author Hans-Holger Rogner. Available for download at its UNDP site., mostly from traditional biomass), 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.

in California with flat-plate solar water heating collectors on its roof.{]s a year)|-|||| Current use (2001)|| Technical potential|| Theoretical potential|- valign="bottom"|| Hydropower|| 9|| 50|| 147|-|| Biomass energy|| 50|| >276|| 2,900|-|| Solar energy|| 0.1|| >1,575|| 3,900,000|-|| Wind energy|| 0.12|| 640|| 6,000|-|| Geothermal energy|| 0.6|| 5,000|| 140,000,000|-|| Ocean energy|| not estimated|| not estimated|| 7,400|-|| Total|| 60|| >7,600|| >144,000,000|-| colspan=4 | Current use is in primary energy equivalent.
For comparison, the current global primary energy use (2001) is 402 Exajoules a year.
Source: World Energy Assessment 2001], the amount of incoming radiation at the earth's surface. The technical potential is a more practical estimate of how much could be put to human use by considering energy conversion efficiency of the available technology and available land area. To give an idea of the constraints, the estimate for solar energy assumes that 1% of the world's unused land surface is used for solar power.

The technical potentials generally do not include economic or other environmental constraints, and the potentials that could be realized at an economically competitive level under current conditions and in a short time-frame is lower still.

Trends favouring Renewables The renewable market will boom when cost efficiency attains parity with other competing energy sources. The following trends are a few examples by which the renewables market is being helped to attain critical mass so that it becomes competitive enough vs fossil fuels:

Other than market forces, renewable industry often needs government sponsorship to help generate enough momentum in the market. Many countries and states have implemented incentives - like government tax subsidies, partial copayment schemes and various rebates over purchase of renewables - to encourage consumers to shift to renewable energy sources. Solar incentives example - California Government grants fund for research in renewable technology to make the production cheaper and generation more efficient. Solar nanotech research

Development of loan programs that stimulate renewable favoring market forces with attractive return rates, buffer intial deployment costs and entice consumers to consider and purchase renewable technology. A famous example is the Indian Solar Loan Programme sponsored by UNEP helping 100000 people finance solar power systems in Solar power in India. Solar loan program in India Success in Solar power in India solar program has led to similar projects in other parts of developing world like Tunisia, Morocco, Indonesia and Mexico.

Imposition of high fossil fuel consumption / carbon taxes, and channel the revenue earned towards renewable energy development. Is It Time for a New Tax on Energy

Many think-tanks are warning that the world needs an urgency driven concerted effort to create a competitive renewable energy infrastructure and market. The developed world can make more research investments to find better cost efficient technologies, and manufacturing could be transferred to developing countries in order to use low labor costs. The renewable energy market could increase fast enough to replace and initiate the decline of fossil fuel dominance and the world could then avert the looming climate and peak oil crises. Power of green

Most importantly, renewables is gaining credence among private investors as having the potential to grow into the next big industry. Many companies and venture capitalists are investing in photovoltaic development and manufacturing. This trend is particularly visible in Silicon valley, California, Europe, Japan. Solar power shines bright in Silicon Valley Betting on Solar Power World events spark interest in solar cell energy start-ups

Constraints and opportunities Critics suggest that some renewable energy applications may create pollution, be dangerous, take up large amounts of land, or be incapable of generating a large net amount of energy. Proponents advocate the use of "appropriate renewables", also known as soft energy technologies, as these have many advantages.

Availability There is no shortage of solar-derived energy on Earth. Indeed the storages and flows of energy on the planet are very large relative to human needs.



A criticism of some renewable sources is their Intermittent Power Sources nature. But a variety of renewable sources in combination can overcome this problem. As Amory Lovins explains:

"Stormy weather, bad for direct solar collection, is generally good for windmills and small hydropower plants; dry, sunny weather, bad for hydropower, is ideal for photovoltaics." The fragility of domestic energy

The challenge of variable power supply may be further alleviated by energy storage. Available storage options include hydroelectricitys, batteries, hydrogen fuel cells, and thermal mass. Initial investments in such energy storage systems can be high, although the costs can be recovered over the life of the system.

Wave energy is continuously available, although wave intensity varies by season. A wave energy scheme installed in Australia generates electricity with an 80% availability factor.

Aesthetics Both solar and wind generating stations have been criticized from an aesthetic point of view.{{cite web|url=http://www.tvenergy.org/sources-windturbine.htm|title=Small Scale Wind Energy Factsheet|accessdate=2007-09-19|date=Last Updated: 14-02-2007|publisher=Thames Valley Energy--> However, methods and opportunities exist to deploy these renewable technologies efficiently and unobtrusively: fixed solar collectors can double as noise barriers along highways, and extensive roadway, parking lot, and roof-top area is currently available; photovoltaic cell can also be used to tint windows and produce energy.{{cite web|url=http://energypriorities.com/entries/2006/05/xsunx_power_glass_bipv.php|title=Thin Film Could Soon Make Solar Glass and Facades a Practical Power Source|accessdate=2007-09-19|author=Denis Du Bois|date=May 22, 2006|publisher=Energy Priorities--> Advocates of renewable energy also argue that current infrastructure is less aethetically pleasing than alternatives, but sited further from the view of most critics.{{cite web|url=http://news.bbc.co.uk/1/hi/talking_point/3266673.stm|title=What is the worst eyesore in the UK?|accessdate=2007-09-19|quote=I really wish people wouldn't criticise wind farms. I would much rather have 12 hills full of wind turbines than 1 single nuclear power station. |publisher=BBC News-->

Environmental and social considerations While most renewable energy sources do not produce pollution directly, the materials, industrial processes, and construction equipment used to create them may generate waste and pollution. Some renewable energy systems actually create environmental problems. For instance, older wind turbines can be hazardous to flying birds.{{cite web|url=http://www.rspb.org.uk/ourwork/policy/windfarms/index.asp|title=Policy: Wind farms|accessdate=2007-09-19|date=Last modified: 14 September 2005|publisher=Royal Society for the Protection of Birds (RSPB)-->

Land area required Another environmental issue, particularly with biomass and biofuels, is the large amount of land required to harvest energy, which otherwise could be used for other purposes or left as undeveloped land. However, it should be pointed out that these fuels may reduce the need for harvesting non-renewable energy sources, such as vast strip-mined areas and slag mountains for coal, safety zones around nuclear plants, and hundreds of square miles being strip-mined for oil sands. These responses, however, do not account for the extremely high biodiversity and endemism of land used for ethanol crops, particularly sugar cane.

In the U.S., crops grown for biofuels are the most land- and water-intensive of the renewable energy sources. In 2005, about 12% of the nation’s corn crop (covering 11 million acres (45,000 km²) of farmland) was used to produce four billion gallons of ethanol—which equates to about 2% of annual U.S. gasoline consumption. For biofuels to make a muchlarger contribution to the energy economy, the industry will have to accelerate the development of new feedstocks, agricultural practices,and technologies that are more land and water efficient. Already, the efficiency of biofuels production has increased significantlyand there are new methods to boost biofuel production. Hyrogen injection could boost biofuel production

Hydroelectric Dams The major advantage of hydroelectric systems is the elimination of the cost of fuel. Other advantages include longer life than fuel-fired generation, low operating costs, and the provision of facilities for water sports. Operation of pumped-storage plants improves the daily load factor of the generation system. Overall, hydroelectric power can be far less expensive than electricity generated from fossil fuels or nuclear energy, and areas with abundant hydroelectric power attract industry.

However, there are several major disadvantages of hydroelectric systems. These include: dislocation of people living where the reservoirs are planned, release of significant amounts of carbon dioxide at construction and flooding of the reservoir, disruption of aquatic ecosystems and birdlife, adverse impacts on the river environment, potential risks of sabotage and terrorism, and in rare cases catastrophic failure of the dam wall. (See Hydroelectricity article for details.)

Hydroelectric power is now more difficult to site in developed nations because most major sites within these nations are either already being exploited or may be unavailable for other reasons such as environmental considerations.

Wind farms is one of the most environmentally friendly sources of renewable energyA wind farm, when installed on agricultural land, has one of the lowest environmental impacts of all energy sources: Why Australia needs wind power

Studies of birds and offshore wind farms in Europe have found that there are very few bird collisions.newscientist.com June 2005 Wind turbines a breeze for migrating birds Several offshore wind sites in Europe have been in areas heavily used by seabirds. Improvements in wind turbine design, including a much slower rate of rotation of the blades and a smooth tower base instead of perchable lattice towers, have helped reduce bird mortality at wind farms around the world. However older smaller wind turbines may be hazardous to flying birds.{{cite web|url=http://www.countryguardian.net/Chapman.htm|title=Renewable energy industry environmental impacts|accessdate=2007-09-19|author=Andrew Chapman|date=2003-11-15|publisher=Country Guardian|quote=Evaluations of the bird kills at Altamont suggested that the small, 18 metre diameter rotor, turbines rotating a high speed, 60 revolutions per minute, were a major contributor.--> Birds are severely impacted by fossil fuel energy; examples include birds dying from exposure to oil spills, habitat loss from acid rain and mountaintop removal coal mining, and mercury poisoning. What about offshore wind farms and birds?

Longevity issues Though a source of renewable energy may last for billions of years, renewable energy infrastructure, like hydroelectric dams, will not last forever, and must be removed and replaced at some point. Events like the shifting of riverbeds, or changing weather patterns could potentially alter or even halt the function of hydroelectric dams, lowering the amount of time they are available to generate electricity.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion.

Biofuels production All biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented and burned. All of these steps require resources and an infrastructure.

Some studies contend that ethanol is "energy negative", meaning that it takes more energy to produce than is contained in the final product. Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower However, a large number of recent studies, including a 2006 article Ethanol Can Contribute to Energy and Environmental Goals in the journal Science offer the opinion that fuels like ethanol are energy positive. Furthermore, fossil fuels also require significant energy inputs which have seldom been accounted for in the past.

Additionally, ethanol is not the only product created during production, and the energy content of the by-products must also be considered. Corn is typically 66% starch and the remaining 33% is not fermented. This unfermented component is called distillers grain, which is high in fats and proteins, and makes good animal feed. University of Minnesota In Brazil, where sugar cane is used, the yield is higher, and conversion to ethanol is somewhat more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further. Biofuels look to the next generation

According to the International Energy Agency, new biofuels technologies being developed today, notably cellulosic ethanol, could allow biofuels to play a much bigger role in the future than previously thought. International Energy Agency, World Energy Outlook 2006, page 8 Cellulosic ethanol can be made from plant matter composed primarily of inedible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw and rice straw),wood waste, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be sustainably produced in manyregions of the United States. Industrial Biotechnology Is Revolutionizing the Production of Ethanol Transportation Fuel, pages 3-4.

The ethan Renewable energy utilizes natural resources such as solar energy, wind energy, tidal energy and geothermal energy, which are naturally replenished. Renewable energy technologies range from solar energy, wind power, and hydroelectricity to biomass and biofuels for transportation. About 13 percent of primary energy comes from renewables, with most of this coming from traditional biomass like Wood fuel. Hydropower is the next largest source, providing 2-3%, and modern technologies like geothermal, wind, solar, and marine energy together produce less than 1% of total world energy demand.International Energy Agency (2007). Renewables in global energy supply: An IEA facts sheet, OECD, p. 3. The technical potential for their use is very large, exceeding all other readily available sources.World Energy Assessment (2001). Renewable energy technologies, chapter 7.

]

Renewable energy technologies are sometimes criticised for being unreliable or unsightly, yet the market is growing for many forms of renewable energy. Wind power has a worldwide installed capacity of 74,223 MW and is widely used in several European countries and the USA. The manufacturing output of the ] industry reached more than 2,000 MW per year in 2006, Solar Energy: Scaling Up Manufacturing and Driving Down Costs p. 30. and Photovoltaic power stations are particularly popular in Germany. World's largest photovoltaic power plants Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Solar power plants in the Mojave Desert. Solar Trough Power Plants The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW.{{cite web] from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. America and Brazil Intersect on Ethanol Ethanol fuel is also widely available in the USA.

While there are many large-scale renewable energy projects, renewable technologies are also suited to Remote Area Power Supply, sometimes in rural and remote areas, where energy is often crucial in human development.World Energy Assessment (2001). Renewable energy technologies, p. 221. Kenya has the world's highest household solar ownership rate with roughly 30,000 small (20-100 watt) solar power systems sold per year. What Solar Power Needs Now Renewable Energy Access, 13 August 2007.

Climate change concerns coupled with Oil price increases of 2004-2006 and increasing government support are driving increasing renewable energy legislation, incentives and renewable energy commercialization. EU leaders reached agreement in principle in March that 20 percent of the bloc's 20 percent' energy should be produced from renewable fuels by 2020, as part of its drive to cut emissions of carbon dioxide, blamed in part for global warming. news and Official EP resolution of 25 September 2007 on the Road Map for Renewable Energy in Europe Investment capital flowing into renewable energy climbed from $80 billion in 2005 to a record $100 billion in 2006. United Nations Environment Programme and New Energy Finance Ltd. (2007). Global Trends in Sustainable Energy Investment 2007: Analysis of Trends and Issues in the Financing of Renewable Energy and Energy Efficiency in OECD and Developing Countries p. 3. Some very large corporations such as BP, General Electric, Sharp Corporation, and Royal Dutch Shell are investing in the renewable energy sector. Two oil giants plunge into the wind business: Shell, BP intend to play major role GE Energy

Main renewable energy technologies

The majority of renewable energy technologies are directly or indirectly powered by the sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation, the resulting level of energy within the Earth-Atmosphere system can roughly be described as the Earth's "climate." The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress.Renewable Energy, Sorensen, Elsevier 2004 Solar energy is also responsible for the distribution of precipitation which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels.

Renewable energy flows involve natural phenomena such as sunlight, wind, tides and geothermal heat, as the International Energy Agency explains:"Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources." Renewable energy... into the mainstream p. 9.Each of these sources has unique characteristics which influence how and where they are used.

Wind power

Airflows can be used to run wind turbines. Modern wind turbines range from around 600kW to up to 5 MW of rated power, although turbines with rated output of 1.5-3 MW have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms.

Wind power is the fastest growing of the renewable energy technologies, though it currently provides less than 0.5% of global energy. Over the past decade, global installed maximum capacity increased from 2,500 MW in 1992 to just over 40,000 MW at the end of 2003, at an annual growth rate of near 30%. Due to the Intermittent Power Sources of wind resources, most deployed turbines in the EU produce electricity an average of 25% of the hours in a year (a capacity factor of 25%), Potentials and costs for renewable electricity generation but under favourable wind regimes some reach 35% or higher. Capacity factors are a function of seasonal wind fluctuations and may be higher in winter. It would mean that a typical 5 MW turbine in the EU would have an average output of 1.7 MW.

Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand. This could require large amounts of land to be utilized for wind turbines, particularly in areas of higher wind resources. Offshore resources experience mean wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy."Offshore stations experience mean wind speeds at 80 m that are 90% greater than over land on average. Evaluation of global wind power
"Overall, the researchers calculated winds at 80 meters feet traveled over the ocean at approximately 8.6 meters per second and at nearly 4.5 meters per second over land and 10 miles per hour, respectively." Global Wind Map Shows Best Wind Farm Locations (URL accessed January 30, 2006) This number could also increase with higher altitude ground-based or airborne wind turbines."High-altitude winds could provide a potentially enormous renewable energy source, and scientists like Roberts believe Airborne wind turbine could put an end to dependence on fossil fuels. At 15,000 feet, winds are strong and constant. On the ground, wind is often unreliable — the biggest problem for ground-based wind turbines." Windmills in the Sky (URL accessed January 30, 2006)

Wind strengths near the Earth's surface vary and thus cannot guarantee continuous power unless combined with other energy sources or storage systems. Some estimates suggest that 1,000 MW of conventional wind generation capacity can be relied on for just 333 MW of continuous power. While this might change as technology evolves, advocates have suggested incorporating wind power with other power sources, or the use of energy storage techniques, with this in mind. It is best used in the context of a system that has significant reserve capacity such as hydro, or reserve load, such as a desalination plant, to mitigate the economic effects of resource variability.

Wind power is renewable and produces no greenhouse gases during operation, such as carbon dioxide and methane.

Water power Energy in water (in the form of motive energy or temperature differences) can be harnessed and used. Since water is about 800 times Density of air,{{cite web|url=http://wahiduddin.net/calc/calc_da_m.htm|title=Density Altitude Calculator|accessdate=2007-09-17|author=Richard Shelquist|date=18-Oct-2005-->{{cite web|url=http://www.csgnetwork.com/h2odenscalc.html|title=Water Density Calculator|accessdate=2007-09-17|date=Copyright© 1973 - 2007|publisher=CSG, Computer Support Group, Inc. and CSGNetwork.Com-->even a slow flowing stream of water, or moderate sea Swell (ocean), can yield considerable amounts of energy.

There are many forms of water energy:

Solar energy use In this context, "solar energy" refers to energy that is collected from sunlight. Solar energy can be applied in many ways, including to:

Biofuel Plants use photosynthesis to grow and produce biomass. Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work.

Liquid biofuel Liquid biofuel is usually either a bioalcohol such as ethanol or a bio-oil such as biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40%. In some areas maize, cornstalks, sugarbeets, sugar cane, and switchgrasses are grown specifically to produce ethanol (also known as grain alcohol) a liquid which can be used in internal combustion engines and fuel cells. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers. Biobutanol is being developed as an alternative to bioethanol.

In the future, there might be bio-synthetic liquid fuel available. It can be produced by the Fischer-Tropsch process, also called Biomass-To-Liquids (BTL). Status And Perspectives of Biomass-To-Liquid Fuels in the European Union

Solid biomass residue can be used as a biofuelDirect use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines.

Sugar cane residue, wheat chaff, maize and other Biomass can be, and are, burned quite successfully. The net carbon dioxide emissions that are added to the atmosphere by this process are only from the fossil fuel that is often currently consumed to plant, fertilize, harvest and transport the biomass.

Processes to harvest biomass from short-rotation poplars and willows, and perennial grasses such as switchgrass, phalaris, and miscanthus, require less frequent cultivation and less nitrogen than from typical annual crops. Pelletizing miscanthus and co-firing it with coal for generating electricity is being studied and may be economically viable. Biomass Crops as a Source of Renewable Energy: European Experience with Miscanthus and Projections for Illinois The higher heating value of cellulose is about 17.4 MJ/kg . The estimated yield of ethanol from dry cellulose is about 0.2 kg of ethanol per kg of cellulose (60 gal/ton). Since the heating value is 29.7 MJ/kg of ethanol it would be 5.94 MJ/kg of the cellulose that it is made from. Thus the ethanol contains only about 1/3 as much energy as the cellulose that it was made from. Co-firing cellulose with coal would replace about three times as much fossil fuel as using the cellulose to make ethanol. The replaced coal would produce 0.0946 kg CO₂/MJ while the replaced liquid fuel would produce only about 0.0733 kg CO₂/MJ so co-firing the cellulose with coal is about 3.8 times more effective at reducing CO₂ emissions than using it to make ethanol.

Solid biomass can also be gasification, and used as described in the next section.

Biogas Biogas can easily be produced from current waste streams, such as: paper production, sugar production, sewage, animal waste and so forth. These various waste streams have to be slurried together and allowed to naturally ferment, producing methane gas. This can be done by converting current sewage plants into biogas plants. When a biogas plant has extracted all the methane it can, the remains are sometimes better suitable as fertilizer than the original biomass.

Alternatively biogas can be produced via advanced waste processing systems such as mechanical biological treatment. These systems recover the recyclable elements of household waste and process the biodegradable fraction in anaerobic digesters.

Renewable natural gas is a biogas which has been upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to the mass market via gas grid.

Geothermal energy Geothermal Station in northeast IcelandGeothermal energy is energy obtained by tapping the heat of the earth itself, usually from kilometers deep into the Earth's crust. It is expensive to build a power station but operating costs are low resulting in low energy costs for suitable sites. Ultimately, this energy derives from heat in the Earth's core. The government of Iceland states: "It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource." It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW. RESPONSE OF WAIRAKEI GEOTHERMAL RESERVOIR TO 40 YEARS OF PRODUCTION, 2006 (pdf) Allan Clotworthy, Proceedings World Geothermal Congress 2000. (accessed 30 March) The International Energy Agency classifies geothermal power as renewable. Geodynamics says it has the "hottest rocks on earth"

Three types of power plants are used to generate power from geothermal energy: dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200 °C, out of the ground, and allows it to boil as it rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine. In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat.

The geothermal energy from the core of the Earth is closer to the surface in some areas than in others. Where hot underground steam or water can be tapped and brought to the surface it may be used to generate electricity. Such geothermal power sources exist in certain geologically unstable parts of the world such as Iceland, New Zealand, United States, Philippines and Italy. The two most prominent areas for this in the United States are in the Yellowstone National Park basin and in northern California. Iceland produced 170 MW geothermal power and heated 86% of all houses in the year 2000 through geothermal energy. Some 8000 MW of capacity is operational in total.

There is also the potential to generate geothermal energy from Hot dry rock geothermal energy. Holes at least 3 km deep are drilled into the earth. Some of these holes pump water into the earth, while other holes pump hot water out. The heat resource consists of hot underground radiogenic granite rocks, which heat up when there is enough sediment between the rock and the earths surface. Several companies in Australia are exploring this technology.

Renewable energy commercialization 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.{{cite book] levels.

{| class="wikitable"|-|||| 2001 energy costs|| Potential future energy cost|-| align=center colspan=3 | Electricity|-|| Wind power|| 4-8 ¢/kWh|| 3-10 ¢/kWh|-|| Solar photovoltaics|| 25-160 ¢/kWh|| 5-25 ¢/kWh|-|| Solar thermal energy|| 12-34 ¢/kWh|| 4-20 ¢/kWh|-|| Large hydropower]|| 2-10 ¢/kWh|| 1-8 ¢/kWh|-|| Biomass energy|| 3-12 ¢/kWh|| 4-10 ¢/kWh|-|| Fossil fuel power plant (comparison)|| 4¢/kWh|||-| align=center colspan=3 | Heat|-|| Geothermal heating|| 0.5-5 ¢/kWh|| 0.5-5 ¢/kWh|-|| Biomass - heat|| 1-6 ¢/kWh|| 1-5 ¢/kWh|-|| Solar hot water|| 2-25 ¢/kWh|| 2-10 ¢/kWh|-| colspan=3 | All costs are in 2001 $-cent per kilowatt-hour.|-| colspan=3 | Source: World Energy Assessment, 2004 updateWorld Energy Assessment 2004 Update, (energy costs from Table 7). Available for download at its UNDP site.|}

Wind power market grows ]

Figures from the Global Wind Energy Council (GWEC) show that 2006 recorded an increase in installed wind power capacity of 15,197 megawatts (MW), taking the total installed capacity to 74,223 MW, up from 59,091 MW in 2005. Global wind energy markets continue to boom – 2006 another record year Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at the rate of 32% following the 2005 record year, in which the market grew by 41%. 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 2006 reaching €18 billion, or US$23 billion.

The countries with the highest total installed capacity are Wind power in Germany (20,621 MW), Wind power in Spain (11,615 MW), the Wind power in the United States (11,603 MW), Wind power in India (6,270 MW) and Wind power in Denmark (3,136 MW). In terms of new installed capacity in 2006, the USA lead with 2,454 MW, followed by Germany (2,233 MW), India (1,840 MW), Spain (1,587 MW), China (1,347 MW) and France (810 MW).

In the UK, a licence to build the world's largest offshore windfarm, in the Thames estuary, has been granted. The London Array windfarm, 12 miles off Kent and Essex, should eventually consist of 341 turbines, occupying an area of 90 square miles. This is a £1.5 billion, 1,000 megawatt project, which will power one-third of London homes. The windfarm will produce an amount of energy that, if generated by conventional means, would result in 1.9 million tonnes of carbon dioxide emissions every year. It could also make up to 10% of the Government's 2010 renewables target. Windfarms to power a third of London homes

New generation of solar thermal plants in Spain produces electricity from the sun using 624 large movable mirrors called heliostats.

Construction of the largest solar thermal power plant to be built in 15 years, in Boulder City, Nevada, is nearly complete. The 64MW Nevada Solar One power plant will generate enough power to meet the electricity needs of about 40,000 households and follows in the steps of the 354MW SEGS solar thermal power plants located in California’s Mojave Desert. While California’s solar plants have generated billions of kilowatt hours of electricity for the past two decades, the Nevada Solar One plant will use new technologies to capture even more energy from the sun. Largest solar power plant in a generation to be built in Nevada

The California Solar Initiative As part of Governor Arnold Schwarzenegger's Million Solar Roofs Program, California has set a goal to create 3,000 megawatts of new, solar-produced electricity by 2017 - moving the state toward a cleaner energy future and helping lower the cost of solar systems for consumers. This is a comprehensive $2.8 billion program. The California Solar Initiative

The California Solar Initiative offers cash incentives on solar PV systems of up to $2.50 a watt. These incentives, combined with federal tax incentives, can cover up to 50% of the total cost of a solar panel system. There are many financial incentives to support the use of renewable energy in other US states. Financial Incentives in the USA

World's largest photovoltaic power plants Construction of a 40 MW solar generation power plant is underway in the Saxon region of Germany. The Waldpolenz Solar Park will consist of some 550,000 thin-film solar modules. The direct current produced in the modules will be converted into alternating current and fed completely into the power grid. Once completed in 2009, the project will be one of the largest photovoltaic projects ever constructed. Currently the biggest PV plant in the world has an output capacity of around 12 megawatts. Phase One of 40 MW German Solar Park Begun



A large photovoltaic power project has been completed in Portugal, the Serpa solar power plant is at one of the Europe's sunniest areas. Major solar power plant opens in Portugal The 11 megawatt plant covers 150 acres and is comprised of 52,000 PV panels. The panels are raised 2 metres off the ground and the area will remain productive grazing land. The project will provide enough energy for 8,000 homes and will save an estimated 30,000 tonnes of carbon dioxide emissions per year. Portugal starts huge solar plant World's largest solar photovoltaic power plant to be built

A $420 million large-scale Solar power station in Victoria is to be the biggest and most efficient solar photovoltaic power station in the world. Australian company Solar Systems will demonstrate its unique, design incorporating space technology in a 154MW solar power station connected to the national grid. The power station will have the capability to concentrate the sun by 500 times onto the solar cells for ultra high power output. The Victorian power station will generate clean electricity directly from the sun to meet the annual needs of over 45,000 homes with zero greenhouse gas emissions. Solar Systems -- 154MW Victorian Project

However, when it comes to renewable energy systems and PV, it is not just large systems that matter. Building-integrated photovoltaics or "onsite" PV systems have the advantage of being matched to end use energy needs in terms of scale. So the energy is supplied close to where it is needed. Solar Integrated in New Jersey

Use of ethanol for transportation Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a partial result, Brazil, which years ago had to import a large share of the petroleum needed for domestic consumption, recently reached complete self-sufficiency in oil. America and Brazil Intersect on Ethanol

Most cars on the road today in the U.S. can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford Motor Company, DaimlerChrysler, and General Motors Corporation are among the automobile companies that sell “flexible-fuel” cars, trucks, and minivans that can use gasoline and ethanol blends ranging from pure gasoline up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on U.S. roads. The challenge is to expand the market for biofuels beyond the farm states where they have been most popular to date. Flex-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, will also help to expand the market.

Wave farms expand Portugal now has the world's first commercial wave farm, the Aguçadora Wave Park, established in 2006. The farm will initially use three Pelamis Wave Energy Converter machines generating 2.25 MW. Sea machine makes waves in Europe Wave energy contract goes abroad Initial costs are put at euro8.5 million. Subject to successful operation, a further €70 million is likely to be invested before 2009 on a further 28 machines to generate 525 MW. Primeiro parque mundial de ondas na Póvoa de Varzim

Funding for a wave farm in Scotland was announced in February, 2007 by the Scottish Executive, at a cost of over 4 million pound sterling, as part of a £13 million funding packages for Renewable energy in Scotland#Wave power. The farm will be the world's largest with a capacity of 3MW generated by four Pelamis machines. Orkney to get 'biggest' wave farm

Geothermal energy prospects By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 watts, with an additional 28 GW used directly for heating. If heat recovered by Geothermal exchange heat pump is included, the non-electric use of geothermal energy is estimated at more than 100 GWt (gigawatts of thermal power) and is used commercially in over 70 countries.( sec 1.2) During 2005 contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.

Future potential While currently renewable energy sources only supply a fraction of current energy use (ca. 14% of primary energy use, World Energy Assessment 2001, Chapter 5: Energy Resources (table 5.26), coordinating lead author Hans-Holger Rogner. Available for download at its UNDP site., mostly from traditional biomass), 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.

in California with flat-plate solar water heating collectors on its roof.{]s a year)|-|||| Current use (2001)|| Technical potential|| Theoretical potential|- valign="bottom"|| Hydropower|| 9|| 50|| 147|-|| Biomass energy|| 50|| >276|| 2,900|-|| Solar energy|| 0.1|| >1,575|| 3,900,000|-|| Wind energy|| 0.12|| 640|| 6,000|-|| Geothermal energy|| 0.6|| 5,000|| 140,000,000|-|| Ocean energy|| not estimated|| not estimated|| 7,400|-|| Total|| 60|| >7,600|| >144,000,000|-| colspan=4 | Current use is in primary energy equivalent.
For comparison, the current global primary energy use (2001) is 402 Exajoules a year.
Source: World Energy Assessment 2001], the amount of incoming radiation at the earth's surface. The technical potential is a more practical estimate of how much could be put to human use by considering energy conversion efficiency of the available technology and available land area. To give an idea of the constraints, the estimate for solar energy assumes that 1% of the world's unused land surface is used for solar power.

The technical potentials generally do not include economic or other environmental constraints, and the potentials that could be realized at an economically competitive level under current conditions and in a short time-frame is lower still.

Trends favouring Renewables The renewable market will boom when cost efficiency attains parity with other competing energy sources. The following trends are a few examples by which the renewables market is being helped to attain critical mass so that it becomes competitive enough vs fossil fuels:

Other than market forces, renewable industry often needs government sponsorship to help generate enough momentum in the market. Many countries and states have implemented incentives - like government tax subsidies, partial copayment schemes and various rebates over purchase of renewables - to encourage consumers to shift to renewable energy sources. Solar incentives example - California Government grants fund for research in renewable technology to make the production cheaper and generation more efficient. Solar nanotech research

Development of loan programs that stimulate renewable favoring market forces with attractive return rates, buffer intial deployment costs and entice consumers to consider and purchase renewable technology. A famous example is the Indian Solar Loan Programme sponsored by UNEP helping 100000 people finance solar power systems in Solar power in India. Solar loan program in India Success in Solar power in India solar program has led to similar projects in other parts of developing world like Tunisia, Morocco, Indonesia and Mexico.

Imposition of high fossil fuel consumption / carbon taxes, and channel the revenue earned towards renewable energy development. Is It Time for a New Tax on Energy

Many think-tanks are warning that the world needs an urgency driven concerted effort to create a competitive renewable energy infrastructure and market. The developed world can make more research investments to find better cost efficient technologies, and manufacturing could be transferred to developing countries in order to use low labor costs. The renewable energy market could increase fast enough to replace and initiate the decline of fossil fuel dominance and the world could then avert the looming climate and peak oil crises. Power of green

Most importantly, renewables is gaining credence among private investors as having the potential to grow into the next big industry. Many companies and venture capitalists are investing in photovoltaic development and manufacturing. This trend is particularly visible in Silicon valley, California, Europe, Japan. Solar power shines bright in Silicon Valley Betting on Solar Power World events spark interest in solar cell energy start-ups

Constraints and opportunities Critics suggest that some renewable energy applications may create pollution, be dangerous, take up large amounts of land, or be incapable of generating a large net amount of energy. Proponents advocate the use of "appropriate renewables", also known as soft energy technologies, as these have many advantages.

Availability There is no shortage of solar-derived energy on Earth. Indeed the storages and flows of energy on the planet are very large relative to human needs.



A criticism of some renewable sources is their Intermittent Power Sources nature. But a variety of renewable sources in combination can overcome this problem. As Amory Lovins explains:

"Stormy weather, bad for direct solar collection, is generally good for windmills and small hydropower plants; dry, sunny weather, bad for hydropower, is ideal for photovoltaics." The fragility of domestic energy

The challenge of variable power supply may be further alleviated by energy storage. Available storage options include hydroelectricitys, batteries, hydrogen fuel cells, and thermal mass. Initial investments in such energy storage systems can be high, although the costs can be recovered over the life of the system.

Wave energy is continuously available, although wave intensity varies by season. A wave energy scheme installed in Australia generates electricity with an 80% availability factor.

Aesthetics Both solar and wind generating stations have been criticized from an aesthetic point of view.{{cite web|url=http://www.tvenergy.org/sources-windturbine.htm|title=Small Scale Wind Energy Factsheet|accessdate=2007-09-19|date=Last Updated: 14-02-2007|publisher=Thames Valley Energy--> However, methods and opportunities exist to deploy these renewable technologies efficiently and unobtrusively: fixed solar collectors can double as noise barriers along highways, and extensive roadway, parking lot, and roof-top area is currently available; photovoltaic cell can also be used to tint windows and produce energy.{{cite web|url=http://energypriorities.com/entries/2006/05/xsunx_power_glass_bipv.php|title=Thin Film Could Soon Make Solar Glass and Facades a Practical Power Source|accessdate=2007-09-19|author=Denis Du Bois|date=May 22, 2006|publisher=Energy Priorities--> Advocates of renewable energy also argue that current infrastructure is less aethetically pleasing than alternatives, but sited further from the view of most critics.{{cite web|url=http://news.bbc.co.uk/1/hi/talking_point/3266673.stm|title=What is the worst eyesore in the UK?|accessdate=2007-09-19|quote=I really wish people wouldn't criticise wind farms. I would much rather have 12 hills full of wind turbines than 1 single nuclear power station. |publisher=BBC News-->

Environmental and social considerations While most renewable energy sources do not produce pollution directly, the materials, industrial processes, and construction equipment used to create them may generate waste and pollution. Some renewable energy systems actually create environmental problems. For instance, older wind turbines can be hazardous to flying birds.{{cite web|url=http://www.rspb.org.uk/ourwork/policy/windfarms/index.asp|title=Policy: Wind farms|accessdate=2007-09-19|date=Last modified: 14 September 2005|publisher=Royal Society for the Protection of Birds (RSPB)-->

Land area required Another environmental issue, particularly with biomass and biofuels, is the large amount of land required to harvest energy, which otherwise could be used for other purposes or left as undeveloped land. However, it should be pointed out that these fuels may reduce the need for harvesting non-renewable energy sources, such as vast strip-mined areas and slag mountains for coal, safety zones around nuclear plants, and hundreds of square miles being strip-mined for oil sands. These responses, however, do not account for the extremely high biodiversity and endemism of land used for ethanol crops, particularly sugar cane.

In the U.S., crops grown for biofuels are the most land- and water-intensive of the renewable energy sources. In 2005, about 12% of the nation’s corn crop (covering 11 million acres (45,000 km²) of farmland) was used to produce four billion gallons of ethanol—which equates to about 2% of annual U.S. gasoline consumption. For biofuels to make a muchlarger contribution to the energy economy, the industry will have to accelerate the development of new feedstocks, agricultural practices,and technologies that are more land and water efficient. Already, the efficiency of biofuels production has increased significantlyand there are new methods to boost biofuel production. Hyrogen injection could boost biofuel production

Hydroelectric Dams The major advantage of hydroelectric systems is the elimination of the cost of fuel. Other advantages include longer life than fuel-fired generation, low operating costs, and the provision of facilities for water sports. Operation of pumped-storage plants improves the daily load factor of the generation system. Overall, hydroelectric power can be far less expensive than electricity generated from fossil fuels or nuclear energy, and areas with abundant hydroelectric power attract industry.

However, there are several major disadvantages of hydroelectric systems. These include: dislocation of people living where the reservoirs are planned, release of significant amounts of carbon dioxide at construction and flooding of the reservoir, disruption of aquatic ecosystems and birdlife, adverse impacts on the river environment, potential risks of sabotage and terrorism, and in rare cases catastrophic failure of the dam wall. (See Hydroelectricity article for details.)

Hydroelectric power is now more difficult to site in developed nations because most major sites within these nations are either already being exploited or may be unavailable for other reasons such as environmental considerations.

Wind farms is one of the most environmentally friendly sources of renewable energyA wind farm, when installed on agricultural land, has one of the lowest environmental impacts of all energy sources: Why Australia needs wind power

Studies of birds and offshore wind farms in Europe have found that there are very few bird collisions.newscientist.com June 2005 Wind turbines a breeze for migrating birds Several offshore wind sites in Europe have been in areas heavily used by seabirds. Improvements in wind turbine design, including a much slower rate of rotation of the blades and a smooth tower base instead of perchable lattice towers, have helped reduce bird mortality at wind farms around the world. However older smaller wind turbines may be hazardous to flying birds.{{cite web|url=http://www.countryguardian.net/Chapman.htm|title=Renewable energy industry environmental impacts|accessdate=2007-09-19|author=Andrew Chapman|date=2003-11-15|publisher=Country Guardian|quote=Evaluations of the bird kills at Altamont suggested that the small, 18 metre diameter rotor, turbines rotating a high speed, 60 revolutions per minute, were a major contributor.--> Birds are severely impacted by fossil fuel energy; examples include birds dying from exposure to oil spills, habitat loss from acid rain and mountaintop removal coal mining, and mercury poisoning. What about offshore wind farms and birds?

Longevity issues Though a source of renewable energy may last for billions of years, renewable energy infrastructure, like hydroelectric dams, will not last forever, and must be removed and replaced at some point. Events like the shifting of riverbeds, or changing weather patterns could potentially alter or even halt the function of hydroelectric dams, lowering the amount of time they are available to generate electricity.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion.

Biofuels production All biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented and burned. All of these steps require resources and an infrastructure.

Some studies contend that ethanol is "energy negative", meaning that it takes more energy to produce than is contained in the final product. Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower However, a large number of recent studies, including a 2006 article Ethanol Can Contribute to Energy and Environmental Goals in the journal Science offer the opinion that fuels like ethanol are energy positive. Furthermore, fossil fuels also require significant energy inputs which have seldom been accounted for in the past.

Additionally, ethanol is not the only product created during production, and the energy content of the by-products must also be considered. Corn is typically 66% starch and the remaining 33% is not fermented. This unfermented component is called distillers grain, which is high in fats and proteins, and makes good animal feed. University of Minnesota In Brazil, where sugar cane is used, the yield is higher, and conversion to ethanol is somewhat more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further. Biofuels look to the next generation

According to the International Energy Agency, new biofuels technologies being developed today, notably cellulosic ethanol, could allow biofuels to play a much bigger role in the future than previously thought. International Energy Agency, World Energy Outlook 2006, page 8 Cellulosic ethanol can be made from plant matter composed primarily of inedible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw and rice straw),wood waste, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be sustainably produced in manyregions of the United States. Industrial Biotechnology Is Revolutionizing the Production of Ethanol Transportation Fuel, pages 3-4.

The ethan

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