The Solar Power Technologies Engineering Essay

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Our Sun is the largest known energy resource in the solar system. Solar Power technologies have been followed by the media because of the interest in solar power has created in the public and in scientific circles. Solar power should be pursued simply because the Earth receives more energy from the sun in one hour than it uses in one year. Of the 382.7 trillion terawatts(TW) of energy emitted by the Sun in all directions, 120,000 TW reach the Earth's surface. Even with losses of solar energy to the universe, this represents an enormous amount of energy. In the vicinity of Earth, every square meter of space receives 1366 kilowatts of solar radiation, but by the time it reaches the ground, it has been reduced by atmospheric absorption and scattering; weather; and summer, winter and day-night cycles to less than an average of 250 watts per square meter.

Solar energy produced which are transformed from the heat and lights coming from the Sun can generate heat and electricity to supply an increasing number of homes, schools, industries such as factories, refineries, oil-rigs and in the near future be a secondary power source for vehicles. Solar energy can be collected by large utility companies that turn it into electricity for their customers, or single buildings can be equipped with a solar thermal system to turn heat into electricity.

The solar energy business appears to hold the most promise of all alternative energies, yet it must over its unique hurdles to truly compete with oil, coal and natural gas. Like wind and ocean energy, solar energy collection requires method of storing the energy until it is needed. Electricity can be difficult to store; batteries store small amounts but cannot yet store the large amounts needed by electric utility companies. Some companies have explored the idea of trapping solar energy as heat, called solar thermal, rather than electricity because this method is less costly than electrical storage.

In a world where fossil fuels are running out countries choosing solar energy as the next alternative will have to use up large land area to build huge solar panel arrays in order to generate enough energy to meet the increasing demand. These arrays can be installed in three different ways:

Photovoltaic arrangements that focus on the total energy output

A large concave dish of solar panels that uses up less area. (Solar dish Stirling system)

Solar Tower

Long lines of concave arranged solar panels, called troughs.(Parabolic trough)

Photovoltaic (PVs):

Conversion of solar energy to electrical energy depends on a device called photovoltaic cell, also called a solar cell. Photovoltaic cells work by capturing the energy in the Sun's radiation, called photons; the photons then dislodge electrons from material inside the cell and the flow of electrons produce an electric current. Semiconductor materials such as silicon act as the best substance for this conversion of photon energy to electric current. Photovoltaic (PVs) are arrays of cells containing a solar photovoltaic material that converts solar radiation into direct current electricity. Materials presently used for photovoltaic include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide. Due to the growing demand for renewable energy sources, the manufacture of solar cells and photovoltaic arrays has

advanced dramatically in recent years.

Photovoltaic are best known as a method for generating electric power by using solar cells to convert energy from the sun into electricity. The photovoltaic effect refers to photons of light knocking electrons into a higher state of energy to create electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode. Solar cells produce direct current electricity from sun light, which can be used to power equipment or to recharge a battery. Today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC. Cells require protection from the environment and are usually packaged tightly behind a glass sheet. When more power is required than a single cell can deliver, cells are electrically connected together to form photovoltaic modules or solar panels.

Photovoltaic production has been increasing by an average of more than 20 percent each year since 2002, making it the world's fastest-growing energy technology. At the end of 2009, the cumulative global PV installations surpassed 21,000 megawatts. Roughly 90% of this generating capacity consists of grid-tied electrical systems. Such installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building, known as Building Integrated Photovoltaic or BIPV for short Solar PV power stations today have capacities ranging from 10-60 MW although proposed solar PV power stations will have a capacity of 150 MW or more. Building-integrated photovoltaic (BIPV) are increasingly incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power. Typically, an array is incorporated into the roof or walls of a building. Roof tiles with integrated PV cells are also common. The power output of photovoltaic systems for installation in buildings is usually described in kilowatt-peak units (kWp).

Solar dish- Stirling technology:

A solar dish with a Stirling engine uses a solar concentrator to maximize power. The solar concentrator draws the solar energy with the help of concave-shaped solar collectors. The 'dish type' design increases concentration and concomitant reductions in heat loss are achievable. This type of concentrator will focus the solar flux at a point instead of along a line as with trough collector. As a result the achievable concentration ratios are approximately the square of what can be realized with single curvature, trough collectors. This type of design will generate a large energy output.

Solar Tower:

A solar tower uses sunlight-heated air to form an updraft that runs the plant's turbine. A collections of panels arranged around a tall cylindrical tower will be heating the air beneath them with the heat from the sun so as to create the require updraft.

The heliostat field is a field of large, Sun-tracking mirrors called heliostats arranged in rings around a central receiver tower The Heliostat concentrate sunlight on a receiver at the top of the tower. The solar energy heats the air inside the receiver. The heliostats must be able to rotate to optimize the collection of a sun rays directed to the central receiving station. The heliostats orientation will be control by a centum panel in a control room. As the ring of heliostats gets further away from the tower, the separation between the rings and adjacent, concentric rings must increase to avoid shading one ring or mirrors by an adjacent ring.

The first solar power plant based on the solar tower concept was built in the Mojave Desert near Barstow, California in the 1980's. It uses 1900 heliostats to reflect sunlight to the receiver at the top of a 300-foot tall tower. The tower design has the potential to multiply the energy output of the solar panels alone and it requires no energy.

Parabolic Troughs:

They are a collection panels arrayed in long straight arrangements. This type of design is the most common concentrator design available commercially. Sunlight is focused onto a circular pipe absorber located along the focal line. The trough rotates about the absorber centerline in order to maintain a sharp focus of incident beam radiation on the absorber. Selective surfaces and glass enclosure s are used to minimize heat losses from the absorber tube. This is one of the basic designs which have the capability of producing large amounts of solar power.

Advantages:

The amount of Sun energy reaching the Earth's surface is plentiful - almost 6,000 times more than the 15 terawatts of average electrical power consumed by humans. Additionally, solar electric generation has the highest power density (global mean of 170 W/m²) among renewable energies.

Solar power is pollution-free during usage. Production end-wastes and emissions are manageable using existing pollution controls. End-of-use recycling technologies are under development. It is quiet and causes little disturbance of land.

PV installations are quick to install and can operate for many years with little maintenance or intervention after their initial set-up, so after the initial capital cost of building any solar power plant, operating costs are extremely low compared to existing power technologies. The photovotaic cells can last for several decades.

Solar electric generation is economically superior where grid connection or fuel transport is difficult, costly or impossible. Long-standing examples include satellites, island communities, remote locations like the oil-rig platforms and ocean vessels.

When grid-connected, solar electric generation replaces some or all of the highest-cost electricity used during times of peak demand (in most climatic regions). This can reduce grid loading, and can eliminate the need for local battery power to provide for use in times of darkness. These features are enabled by net metering. Time-of-use net metering can be highly favorable, but requires newer electronic metering, which may still be impractical for some users. Nevertheless, experimental high efficiency solar cells already have efficiencies of over 40% in case of concentrating photovoltaic cells and efficiencies are rapidly rising while mass-production costs are rapidly falling.

Disadvantages:

Solar electricity is seen to be expensive due to the high installation cost. Once a PV system is installed it will produce electricity for no further cost until the inverter needs replacing. Current utility rates have increased every year for the past 20 years and with the increasing pressure on carbon reduction the rate will increase more aggressively. This increase will (in the long run) easily offset the increased cost at installation but the timetable for payback is too long for most. It takes 40-50 years for energy savings to make up for the initial cost.

Solar electricity is not available at night and is less available in cloudy weather conditions from conventional photovoltaic technologies moreover it need access to the sun about 60% of time. Therefore, a storage or complementary power system is required. This is why many buildings with photovoltaic arrays are tied into the power grid; the grid absorbs excess electricity generated throughout the day, and provides electricity in the evening.

Some homeowners do not like the appearance of the solar panels. While the modules are often warranted for upwards of 20 years, much of the investment in a home-mounted system may be lost if the home-owner moves and the buyer puts lesser value on the system than the seller.

The photovoltaic cell used in capturing solar energy receives photons (the Sun's rays), which silicon absorbs. This action releases an electron from a silicon atom each time a photon strikes. Oppositely charged poles on either side of the cell induce the electrons to form a current. There appears to be no major alternative technology to the sawn silicon wafer as the basic starting material in photovoltaic manufacturing process. The sawing process for manufacturing silicon wafers from bulk ingots produces large amounts of waste silicon powder kerf in the form of a slurry, currently estimated at 8,750 metric tonnes of silicon pa.

This bring us to an environmental issue that we must address the prospect of used panels inundating landfills and leaching toxic waste into the environment. An extremely toxic substance, silicon tetrachloride renders crops infertile, causes skin burns and increases the likelihood of lung disease, and transforms into acids and poisonous hydrogen chloride gas when exposed to air.

When a solar module outlives its usefulness 20 to 25 years after installation, its disposal must be carefully handled to avoid contamination from the enclosed chemicals.

Future Development:

The two emerging solar technologies are Solar films and Solar satellites.

Solar Films:

Standard solar panels contain crystalline silicon that must be of a minimum thickness to generate an electric current. These solar panels take up space atop buildings or on land. Though solar power is rapidly gaining ground in total energy production worldwide, some experts in the field believe the technology may soon yield to new, thinner solar collectors called solar films. These flexible solar films can be constructed to roll onto a surface similar to wallpaper and replace bulky solar panels with a lower profile appearance.

The thin solar film contains the following four layers: 1) A transparent conducting material which will be exposed to the sunlight. 2) A buffer layer 3) A layer of chemicals such as copper, cadmium, indium, gallium and diselenide, which produces electric current from the sunlight. 4) The last under lying contact layer.

The interface between the buffer layer and contact layer generates the electric current. Thin solar film manufacturer are now making films containing these four layers that measure no more than 100 nanometers thick, or about one-thousandth the thickness of a human hair. This is a fast growing segment of the solar power market and they hope to soon see solar see solar film rolled out onto roofs, walls and windows.

One important aspect of this solar film technology is that it will eliminate the dependency on hazardous material silicon as its manufacturing materials.

Solar Saterllites:

Satellite solar power may be the best way to collect energy from the sun and beaming the energy back to back to Earth. There will be lesser energy losses as compared to surface mounted solar collectors on the earth surface.

The satellite -mounted photovoltaic cells would capture photons, and then a device would convert the current produced in the solar cells to radio waves or infrared light. These in turn will be beamed back to a receiving antenna on earth connected to an electrical generating utility.

The only set back of the solar satellite technology is its expensive set up cost. Expensive light weight solar panels, are mounted onto the satellite which holds them. Huge sponsorship will be required to prepare a launch vehicle, transmission and collection instruments.

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