There are many proven technologies available to produce renewable energy, and some new technologies are under development. One of the most promising renewable energy technologies for electricity generation is wind energy that uses airflows to run wind turbines. In good wind regimes, cost-wise, wind power is comparable to fossil alternatives, particularly when economic or environmental concerns are considered. Modern wind turbines range from around 600 KW to 5 MW of rated power. Most common wind turbines for commercial use are of a rated capacity of 1.5-3 MW. Wind energy is the fastest-growing renewable energy in the world. Since 1993, it is growing on average 30 percent a year. Windmills typically run at 2535 percent of their capacity over the course of a year.
A photovoltaic module composed of multiple photovoltaic cells or arrays is used to convert sun light directly into electricity. Photovoltaic power is also widely viewed as cost competitive, like wind power. As energy from the Sun is free and the cost of the photovoltaic cells is dropping, a solar energy boom is likely in the near future. Solar energy is good for many grid-connected and building-integrated uses. They are widely used for off-grid applications ranging from telecommunications, to village power in remote and rural areas. In general, solar energy is of two types: solar thermal and solar electric. Solar thermal technologies provide heat and hot water for residential, commercial, and industrial end uses. Solar electric technologies or concentrating solar power (CSP) creates heat to produce steam and/or electricity. At present, producing a few kilowatts to hundreds of megawatts of electricity is feasible through commercial solar electric technologies, but a hybrid application of the technology with fossil fuel would be more economically competitive.
Hydropower is another clean energy source and is the most mature form of renewable energy. It has a significant share of electricity generation worldwide. Because water is denser than air, water has more energy producing ability than wind. Hydropower units not only provide electricity, but also help in flood control, irrigation, pisciculture, navigation, and recreation. Energy from the ocean in the form of tidal forces, ocean currents, wave power, and thermal gradients can be feasibile to produce electricity. It can be harnessed using technology similar to underwater windmills. It is being deployed in many countries, although it is a new concept. Portugal has the world's first wave farm. It generates 2.25 MW of initial electricity using three Pelamis P-750 machines.
Geothermal technology obtains energy by tapping the heat of the Earth. It is expensive to build a power station, but operating costs are low, resulting in low energy costs for suitable sites. Geothermal electricity generation is a base load technology. It can be a low-cost option if hot water or steam from geysers is at a high temperature near the surface of the Earth. This technology contributes positively towards global warming as its taps some of the greenhouse gases emitted through geysers.
Biofuel is another renewable resource that is produced from biomass. It is not as clean as the other renewable energies. Biomass can be directly burned to produce heat energy or steam to run turbines for electricity generation. Liquid biofuel can be produced indirectly from biomass that is available worldwide in a variety of forms: wood, grasses, crops, and crop residues. These are converted to energy through thermal or biological conversion or as feedstock to produce liquid or gaseous biofuels. Biomass itself is carbon neutral, but when used for biofuel production, the emission of methane is blocked, thus helping the environment. Unsustainable ways of biofuel production are not environmentally friendly. However, the Roundtable on Sustainable Biofuels is working to define criteria, standards, and processes to promote sustainably-produced biofuels to positively impact global warming mitigation.
Biogas is produced through biogas plants. These plants operate using waste from paper and sugar production, sewage, animal waste, and other biodegradable wastes. These wastes are slurried together and allowed to ferment with bacteria to produce methane gas. This methane gas is a renewable natural gas used for cooking, heating, and electricity production. In Asia, many developing countries such as India, Nepal, Bangladesh, Laos, Cambodia, Vietnam, Bhutan, have individual household biogas plants to meet household energy demands. There is immense viability to having commercial biogas plants. Current sewage treatment plants can easily be converted to biogas plants. Once the methane gas is extracted from waste, the remaining sludge can be used as a fertilizer. It is five times higher in nitrogen than compost produced from the same biomass.
Hydrogen can act as a crucial storage medium and carrier of renewable energy. According to the IEA, hydrogen, along with renewable energy technologies, is a major potential contributor to the sustainability of the energy sector. Over the longer term, if costs can be dramatically reduced, hydrogen can act as the crucial storage medium and carrier of energy produced from renewables. Hydrogen is already being used in some vehicles. With proper research and development, hydrogen, battery-powered electricity, and solar energy will fully replace fossil fuels as energy source for vehicles.
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