Renewable energy is energy generated from natural resources—such as sunlight, 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%, 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.
Some renewable energy technologies are criticised for being intermittent or unsightly, yet the market is growing for many forms of renewable energy. Wind power is growing at the rate of 30 percent annually, with a worldwide installed capacity of over 100 GW, and is widely used in several European countries and the United States. The manufacturing output of the photovoltaics industry reached more than 2,000 MW in 2006, and photovoltaic (PV) power stations are particularly popular in Germany. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert.The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. 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. Ethanol fuel is also widely available in the USA.
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.
IMPORTANCE OF RENEWABLE ENERGY
Most of the energy sources on Earth originate from the Sun, with the exceptions of the energy in the tides, caused by the gravitational pull of the Moon and Sun, and geothermal energy, which results from the heat escaping from hot rocks 2 km (1.2 mi) below the Earth's surface and from the effects of radioactive decay. The Sun's radiation is equivalent to 1.4 kW/sq mi in space before any attenuation due to travelling through the Earth's atmosphere. This solar radiation is converted naturally into various energy streams. Wave energy results from the interaction between the convection-driven winds and the surface of the sea; hydro-energy is produced by the hydrological cycle; and biological energy (biomass energy) is that which is stored in living organisms by the process of photosynthesis. All these forms of energy are available as renewable resources because of the continual replacement of the energy on a daily, or even hourly, basis.
By way of contrast, fossil fuels such as coal, oil, and gas, although originally laid down effectively as biomass, take millions of years to form and need to be regarded as finite, non-renewable resources.
Interest in renewable energy came to the fore during the worldwide energy crises of the 1970s, when high oil prices highlighted the world's dependence on fossil fuels. Secure and affordable energy provision is vital for nations' development, as all industrialization, manufacturing, and building programmes consume vast amounts of energy. Since the oil crises of the 1970s, and largely as a result of the increased exploration and exploitation of fossil fuel reserves, the abundant supply of oil and coal across the world enabled market forces to drive down the price of fuel, and consequently electricity, to low levels. However, estimates suggest that approximately half of the world's oil reserves, and a smaller fraction of coal reserves, have been used in little over 200 years. As demand outpaces supply, however, renewables can play a major role in bridging the gap.
As well as future supply problems, the environmental impact of sources of energy based on fossil fuel is rapidly generating great concern as the impact of increasing levels of “greenhouse gases” like carbon dioxide (CO2) on the global weather patterns is becoming more apparent. In addition, unburnt hydrocarbons (fuel) and the products of combustion, such as oxides of nitrogen and sulphur, cause far-reaching damage to health and the environment. Renewable energy is largely available without chemical processes and hence production of CO2 and other gaseous emissions involved in renewable energy is negligible as they are only generated during the manufacturing and installation of the necessary devices. The burning of biomass, such as wood, does, however, directly produce CO2 as a result of combustion but the gas is absorbed by new wood as it grows and hence the net emission is zero, as long as the fuel crop is completely replenished.
Some renewable sources of energy are :
(1) Biogas : Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Biogas originates from biogenic material and is a type of biofuel.
One type of biogas is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure or sewage, municipal waste, green waste and energy crops. This type of biogas comprises primarily methane and carbon dioxide. The other principal type of biogas is wood gas which is created by gasification of wood or other biomass. This type of biogas is comprised primarily of nitrogen, hydrogen, and carbon monoxide, with trace amounts of methane.
The gases methane, hydrogen and carbon monoxide can be combusted or oxidized with oxygen. Air contains 21% oxygen. This energy release allows biogas to be used as a fuel. Biogas can be used as a low-cost fuel in any country for any heating purpose, such as cooking. It can also be used in modern waste management facilities where it can be used to run any type of heat engine, to generate either mechanical or electrical power. Biogas can be compressed, much like natural gas, and used to power motor vehicles. Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some parts of the world.
(2) Solar Energy : Solar energy is the light and radiant heat from the Sun that influences Earth's climate and weather and sustains life. Solar power is the rate of solar energy at a point in time; it is sometimes used as a synonym for solar energy or more specifically to refer to electricity generated from solar radiation. Since ancient times solar energy has been harnessed for human use through a range of technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available flow of renewable energy on Earth.
Solar energy technologies can provide electrical generation by heat engine or photovoltaic means, daylighting and space heating in passive solar and active solar buildings, potable water via distillation and disinfection, hot water, space cooling by absorption or vapor-compression refrigeration, thermal energy for cooking, and high temperature process heat for industrial purposes.
(3) Hydropower : Hydropower is the largest source of renewable energy. This renewable source of energy provides 10% of the nation's electricity. As of now, there are 77,000 Megawatts of hydropower, enough to provide 35 million homes with energy. Converting flowing water into usable energy produces hydropower. Most of this water comes from rivers and is released through turbines to produce energy. Although this power source does not release pollution, it can possibly harm fish and wildlife, displace people, and alter the quality of water. Better technology is trying to reduce the loss of aquatic life, but the problem with this technology is that it is highly expensive and takes a long time to build.
(4) Wind Energy : Wind energy produces about 2,500 Megawatts of energy, and generates a mere .1% of our electricity. The wind rotates blades around a hub, which is connected to the main shaft. The main shaft spins a generator. The size of turbines is determined by how much energy is needed. Small wind turbines are usually used for homes, farms and ranches. Other ways to use wind energy include grinding grain and pumping water.
Wind is classed in categories of 1 through 7, with 7 being the highest and 1 being the lowest. A good wind source that has a class of 3 or higher is the east coast and along the Appalachian Mountains. North Dakota is an excellent wind source.
The disadvantages of wind energy are that again, the technology is very expensive, the machinery is known to be noisy, birds have been killed by running into the turbines, and the wind might not be present at certain times throughout the year.
(5) Tidal Energy : Tides are generated through a combination of forces exerted by the gravitational pull of the sun and the moon and the rotation of the earth. The relative motion of the three bodies produces different tidal cycles which affect the range of the tides. In addition, the tidal range is increased substantially by local effects such as shelving, funnelling, reflection and resonance.
Energy can be extracted from tides by creating a reservoir or basin behind a barrage and then passing tidal waters through turbines in the barrage to generate electricity. Tidal energy is extremely site specific requires mean tidal differences greater than 4 metres and also favourable topographical conditions, such as estuaries or certain types of bays in order to bring down costs of dams etc.
(6) Geothermal Energy : Geothermal energy is capable of producing about 2,800 Megawatts of energy per year, or roughly .2% of the energy in the U.S. Geothermal energy is produced from naturally occurring steam and hot water from under the Earth's surface. The steam rotates a turbine, which in turn powers an electric generator. Also, hot water can be used to directly heat buildings. The downside to geothermal energy is that land sites are very hard to find and extremely rare. A positive fact is that geothermal energy is very cost effective and reliable.
EARLY EXPLOITATION OF RENEWABLE ENERGY
Water wheels were used in ancient Greece and Rome and windmills have been operating for hundreds of years. Indeed, in the Domesday Book of 1086 there are reports of 5,600 water mills in England. Before the knowledge and large-scale burning of fossil fuels, energy provision came essentially from renewable resources like wood, vegetable and animal oils, and thousands of small-scale hydro schemes. More recently there have been many dam-based hydro schemes built and wind turbines installed around the world. Initially, such large-scale schemes were seen as quite benign but since the 1990s the true scale of the environmental as well as social impact because of, for example, the displacement of whole villages for hydro schemes, and the highly intrusive nature of wind farms, has been recognized.
WORLD ENERGY DEMAND
According to United Nations (UN) projections the world population will have risen from 6 billion in 2000 to 10 billion by 2040. This fact, coupled with the increasing expectations of a high “quality of life” and the associated increase in per capita energy demand by those living in the developing world, indicates that world energy demand is likely to double by 2050 and quadruple by 2100.
The imbalance between the world energy supply and demand has prompted a rapidly accelerating interest and concern about the impact on energy resources, pollution, and global climate, as a result of supplying this thirst for energy.
Since the Industrial Revolution people have been depleting the world's resources of coal, oil, and more recently gas at an ever-increasing rate, which has been completely unchecked. Early technology for burning these natural resources was extremely wasteful and only made use of 10 per cent, or less, of the energy available in the fuel. This level of efficiency is comparable to the conversion efficiency of solar power, wind, and many of the other renewables. Modern-day machines based on fossil fuels have benefited from 100 years of technological advances and can perform at 80 to 90 per cent energy conversion efficiency for Combined Heat and Power systems (CHP). It is fair to say that many renewable technologies are in their infancy and present a relatively untapped resource. The quest for high efficiency is of much less concern to the technologists developing energy systems based on renewable resources than to those developing machines based on fossil fuel. This is because the energy source, in the case of solar, wind, tidal, or hydro is essentially free and the only pressure for increasing efficiency is to ensure that absolute energy demand is satisfied at an acceptable capital outlay. As efficiency increases the visual and environmental impact is likely to be reduced.
There have been several detailed studies performed to date by oil companies, pressure groups, and government agencies, which suggest that as much as 50 per cent of the world's energy requirements could be satisfied by renewables before the middle of this century but to achieve this would involve enormous political support and investment.
These studies set out to predict how the uptake and promotion of renewable energy might be influenced by world economic factors. The International Energy Agency (IEA), World Energy Council (WEC), the UN, the European Union (EU), and oil companies, among others, have performed many forward-looking simulations based on different investment scenarios and environmental policies. The studies all highlight the complex dynamic interactions between different energy sources (that is, fossil fuels and renewables), the markets, security of supply, and the finite nature of fossil fuels. The studies show that environmental controls, if enforced by governments, could profoundly influence the future balance of our energy sources. The various scenarios assume the implementation of various fiscal and environmental measures that governments could enforce to encourage increased energy efficiency, technological developments, and investment in renewable projects. There is broad agreement between these studies that the maximum likely contribution from renewables could reach 50 per cent by 2050, based on current thinking and the state of the art in renewables technologies. A figure of 10 to 20 per cent would seem to be quite achievable, and more likely if the correct fiscal measures and incentives are put in place.
RENEWABLE ENERGY IN FUTURE
The cost of provision of heat and electricity has been subject to considerable fluctuation as a result of political factors, wars, and market anomalies, as well as supply of and demand for coal, oil, and gas. Many of these influences have been dismissed as transients in an otherwise stable and reliable market and have been regarded as largely determined by the natural time lag in any market driven by price. Because world oil production has reached a plateau and gas production is likely to reach a peak by 2015, the only controls left for these markets is price. Oil and gas production is going to decline steadily as the world population and energy demand double by 2050. The obvious advantage of renewables is that their supply is essentially infinite and the resource is replenished each day (except in the case of geothermal energy). It will be possible for coal and nuclear power to compensate for the shortfall, but again there are very considerable environmental factors associated with both of these technologies. There is no transparent way of comparing the risk of a nuclear accident against the risk of sea level rising because of CO2 concentration. Indeed, the current problem of dwindling fossil fuels is a direct result of relying on oil so heavily. A long-term and sustainable solution to energy supply, which can withstand political and environmental upsets and the unknown future impacts of any technology used, may be one that uses a variety of different fuels, as in nature.
Renewable energy will play an increasingly important part in ensuring supply but it cannot take on the whole burden. The future lies with “clean energy” and that means renewable energy together with nuclear power. This combination is unavoidable if we are to meet the pressing need for energy while reducing greenhouse gas emissions. The current “dash for gas” must ultimately falter. Looking to the second half of the 21st century, when demand for energy will have trebled or even quadrupled, energy supply could well be a mix of renewable energy (25 per cent) and nuclear power (25 per cent), with clean-coal technology, gas (some from gas hydrates), and declining oil making up the other 50 per cent. Energy prices will rise, which should encourage people to use energy more efficiently, and sequestration of some of the carbon dioxide produced by burning fossil fuel will be essential if carbon dioxide emissions are to be kept within safe bounds.
There is a natural tension between the long-term requirements for successful energy policy and the short-term nature of national governments. The concern for the environment, coupled with the over-reliance on fossil fuels, is a global problem that begs a global response.
THE WORLD'S REACTION
The initial concern about the ozone layer in the 1970s led to a ban on the use of CFCs as aerosol propellants in several countries, including the U.S. However, production of CFCs and other ozone-depleting substances grew rapidly afterward as new uses were discovered.
Through the 1980s, other uses expanded and the world's nations became increasingly concerned that these chemicals would further harm the ozone layer. In 1985, the Vienna Convention was adopted to formalize international cooperation on this issue. Additional efforts resulted in the signing of the Montreal Protocol in 1987. The original protocol would have reduced the production of CFCs by half by 1998.
After the original Protocol was signed, new measurements showed worse damage to the ozone layer than was originally expected. In 1992, reacting to the latest scientific assessment of the ozone layer, the Parties to the Protocol decided to completely end production of halons by the beginning of 1994 and of CFCs by the beginning of 1996 in developed countries.
Because of measures taken under the Montreal Protocol, emissions of ozone-depleting substances are already falling. Levels of total inorganic chlorine in the stratosphere peaked in 1997 and 1998. The good news is that the natural ozone production process will heal the ozone layer in about 50 years.
To make sure we have plenty of energy in the future, it's up to all of us to use energy wisely. We must all conserve energy and use it efficiently. It's also up to those who will create the new energy technologies of the future.
All energy sources have an impact on the environment. Concerns about the greenhouse effect and global warming, air pollution, and energy security have led to increasing interest and more development in renewable energy sources such as solar, wind, geothermal, wave power and hydrogen.
But we'll need to continue to use fossil fuels and nuclear energy until new, cleaner technologies can replace them. The future is ours, but we need energy to get there.