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The Alternative Energy Source to Oil

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1.0 "Renewable Energy" is the term used to describe those energy flows that occur naturally and repeatedly in the environment, e.g. from the sun, wind and the oceans, and from plants and the fall of water. It also refers to the energy available from wastes and to the emerging clean technology of fuel cells.

There are wide ranges of renewable energy sources/technologies, varying in technical and commercial viability. These include:

Ð'* Solar Power (Photovoltaic)

Ð'* Hydro Ð'- electric Power

Ð'* Hydrogen Fuel Cells

Ð'* Geothermal

Ð'* Wind Power

Ð'* Nuclear Power

1.1 The modern drive to harness renewable energy began in the 1970's. It was promoted by concerns over the price and availability of fossil fuels Ð'- oil, gas, and coal. Fossil fuels are finite Ð'- only coal is predicted to be available in significant quantities at the end of the 21st century at current rates of consumption. Using fossil fuels to generate electricity also produces pollutants, which can lead to environmental problems (such as acid rain and the "greenhouse effect").

By contrast, renewable energy produces few, if any, harmful emissions. Exploiting renewable, which at present meet over 2% of the UK's electricity needs, also reduces the rate at which other energy resources are used up. With the world's population continuing to grow, renewable energy promises to play an increasingly significant role in the future.

1.2 The estimated oil reserves in the Earth's crust are about 1 trillion barrels. Oil consumption is at 25 billion barrels per year and increasing at 1.5% per year. At current rates of consumption, measured against known reserves, there is only a 30-year supply of oil in the Earth's crust. Even if the reserve estimate were doubled, it is a moral imperative that the population takes immediate action to develop a sustainable energy economy.

Solar Energy

2.0 Solar energy is quite simply the energy produced by the sun and collected elsewhere, normally the Earth. The sun creates its energy through a thermonuclear process that converts about 650,000,000 tons of hydrogen to helium every second. The process creates heat and electromagnetic radiation. The electromagnetic radiation (including visible light, infra-red light, and ultra-violet radiation) streams out into space in all directions.

Only a very small fraction of the total radiation produced reaches the Earth. The radiation that does reach the Earth is the indirect source of nearly every type of energy used today. The exceptions are geothermal energy, and nuclear fission and fusion. Much of the world's required energy can be supplied by solar power.

2.1 The first practical solar cell was developed at Bell Laboratories in 1954. With the advent of the space program, Photovoltaic cells made from semi-conductor grade silicon quickly became the power source of choice for use on satellites. The systems were very reliable, and cost was of little concern. In the early 1970s, the disruption of oil supplies to the industrialized world led to serious consideration of Photovoltaic as a terrestrial power source. This application focused research attention on improving performance, lowering costs and increasing reliability.

Due to the nature of solar energy, two components are required to have a functional solar energy generator. These two components are a collector and a storage unit. The collector simply collects the radiation that falls on it and converts a fraction of it to other forms of energy (either electricity and heat or heat alone). The storage unit is required because of the non-constant nature of solar energy; at certain times only a very small amount of radiation will be received. The storage unit can hold the excess energy produced during the periods of maximum productivity, and release it when the productivity drops. In practice, a backup power supply is added, too, for the situations when the amount of energy required is greater than both what is being produced and what is stored in the container.

2.2 The solar cells that can be seen on calculators and satellites are Photovoltaic cells or modules (modules are simply a group of cells electrically connected and packaged in one frame). Photovoltaic cells, as the word implies (photo=light, voltaic=electricity), convert sunlight directly into electricity.

Diagram of Photovoltaic (PV) cell

Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy dislodges electrons within the material, allowing them to flow freely. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, the current can be drawn off to be used externally. This current, together with the cells voltage (which is a result of its built in electric field or fields), defines the power (or wattage) that the solar cell can produce.

2.3 Most of the PV cells available today operate at an efficiency of less than 15%, that is, of all the radiation that falls upon them, less than 15% of it is converted into electricity. The maximum theoretical efficiency for a PV cell is only 32.3%, but at this efficiency, solar electricity is very economical. Most other forms of electricity generation are at a lower efficiency than this. Unfortunately, reality still lags behind theory and a 15% efficiency is not usually considered economical by most power companies, even if it is fine for toys and pocket calculators. However, hope for bulk solar electricity should not be abandoned, for recent scientific advances have created a solar cell with an efficiency of 28.2% in the laboratory. This type of cell has yet to be field-tested. If it maintains its efficiency in the uncontrolled environment of the outside world, it will be economical for power companies to build solar power facilities.

2.4 Solar power has two major



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