Solar energy generated from the sun as a source of a clean, free, efficient, and sustainable form of energy. This type of energy is an alternative to the fossil fuels that are known to pollute the air and water, harmful to public health, and contribute to global warming. Neglect to make use of the solar energy and apply this in various industries will introduce to a great loss to the present and future generations (26).
The amount of energy derived from the sun on the surface of the earth is enormous. All the eaths energy reserves: coal, oil, and natural gas is equivalent to the solar energy only within a total of 20 days sunshine. Over the earth's atmosphere, the sun's energy (sunlight) is estimated to contain about 1,300W/m2. About 30% of this light is reflected back into space, with some absorbed by the atmosphere. As the sunlight reaches the earth's surface, the energy drops to about 1,000 watts per square meter at noontime on a day without clouds. When an average is performed for the whole surface of the earth, every square meter in a day collects an equivalent energy of 4.2kWh per day or a barrel of oil per year (3).
In the desert, in which there is a very dry air and less cloud formation the most sunlight is received. This is estimated to be more than six kilowatt-hours per day per square meter. The Kingdom of Saudi Arabia in where most of the land area is a desert is a primary area for utilizing solar energy. Sunlight varies at many places due to the season and thus, sunlight the solar energy application can be done in different ways.
Passive Solar Energy Usage
One simple and practical use of solar energy is to light our buildings using the daylight year-round. Capturing the sun's heat at a maximum during winter and minimum during summer in a building is achieved through the building design. Residential as well as commercial buildings contribute more than one-third of the electric energy demand of a certain area. Buildings designed with due consideration to the varying seasons in a year are utilizing passive solar energy without mechanical means to help heat, cool, or light a building. Buildings constructed with the sun in mind can be comfortable and beautiful places to live and work. Adoption of better insulation, solar design, and more efficient appliances could reduce this demand by 60 to 80%.
Simple building design features such as properly orienting a house toward the north and west, putting most windows on the west side of the building, and taking advantage of cooling breezes in the summer are inexpensive yet providing improvements to the comfort and efficiency of a home.
Figure 1 Passive solar home plans
Figure 2 Another passive solar home plans
Solar heat Collectors
Apart from using design features to maximize the use of the sunlight, some buildings are built with systems that actively collects and store energy from the sun. Solar collectors, for example, mounted on the rooftops of buildings to collect solar energy for space cooling, water heating, and space heating. Majority of the solar collectors are large and flat boxes painted black on the inside and covered with glass. In the most basic design, pipes in the box carry liquids that transfer the heat from the box into the building. Hot liquid (usually a mixture of water and alcohol to prevent freezing) is used for heating water in a tank or is passed via radiators that heat the air.
Figure 3 flat-plate collectors
Solar heat can be also used for powering a cooling system. In desiccant evaporators, heat from a solar collector is used to extract moisture out of the air. When the air becomes dry, it also becomes cooler. The hot moist air is separated from the cooler air and vented to the outside. Another method is an absorption chiller. A refrigerant is heated by solar energy. Under pressure; the pressure expands when it is released, it expands, and threby cooling the air surrounding it. This is how air conditioners and conventional refrigerators work, and it's a particularly efficient method for cooling homes or office since buildings need cooling during the hottest part of the day. These systems are currently being used in the USA at humid southeastern climates.
Solar Thermal Concentrating Systems (STCS)
When mirrors and lenses are arranged in such a way as to focus suns rays, solar thermal systems can produce very high temperatures as high as 3,000 degrees Celsius. This powerful heat can be utilized in industrial applications or to produce electricity. There are three nain configurations of solar designs: parabolic troughs, parabolic dishes, and central receivers. The most common is the parabolic receiver in which curved mirrors concentrate the sunlight on a tube carrying a liquid and runs alongside the mirror. The liquid, usualy around 300 degrees Celsius, flows to a central collector, where it is used to generate steam that powers an electric turbine.
Dishes can achieve much higher temperatures, and so, in principle, they are capable of producing electricity more efficiently. But owing to their complexity, they have not succeeded outside of demonstration projects.
Figure 4 Parabolic trough concentrators
Figure 5 parabolic dish collectors with a mirror-like reflectors and an absorber at the focal point
A more hopeful variation uses a Stirling engine to produce power. Unlike a car's internal combustion engine, in which gasoline is exploded inside the engine cylider it produces heat that make the air inside the engine to expand and which subsequently push out on the pistons. Unlike a diesel engine, aStirling engine produces heat by using mirrors that reflect sunlight on the outside of the engine. These Dish-Stirling generators produce about 30 kilowatts of power, and can be used to replace diesel generators in remote locations.
Figure 6 Solar Stirling engine
A central receiver is another type of concentrating system. Such a system utilizes a power tower filled with water that is heated using mirrors. The powerful heat boils water and thereby produce steam that can drive a several megawatt generators at the base of the tower.
Residential uses for solar heating include hot water, washers and dryers, furnaces or boilers, floor heating, indoor swimming pools and hot tubs or Jacuzzis. Commercial uses for solar heating include hot water, food processing and manufacturing, commercial laundries, space and floor heating, and industrial process heat.
Voltage Generation Solar Systems (Photovoltaic) (Solar Cells)
In 1839, a French scientist, Edmund Becquerel, found that certain materials would give off a spark of electricity when struck with sunlight. Then a Polish scientist - Jan Czochralski, discovered Silicon material, which is a semi-conductor, consisting of conductors and insulation materials (22). In the 1950s, scientists at Bell Labs went back to the technology and, by using silicon, they produced solar cells that could convert four percent of the energy in sunlight directly into electricity. Within few years, these photovoltaic (PV) cells were powering spaceships and satellites (5).
Solar Cells Functionality
Figure 7 Photovoltaic cell
Majority of the PV systems are made up of individual square cells which on average size are about four inches on each side. Every cell produce a small amount of power (less than two watts). As a result, they are usually grouped together in modules. Modules can also be grouped into larger panels enclosed in plastic or glass material which protect them against weather, and these panels, in turn, are either used as separate units or grouped into even larger arrays (16).
Sunlight is made of particles called photons. As these particles hit the silicon molecules of the solar cell, it is transformed to detached electrons, separating from the other photon particles (22). The photons, which are white ball like particles activate/energized and collide with each other. As this collision rate increases, the solar cells collects or build-up the electrons, converting it into electric current energy. Solar cells silicon molecules are organized together in the process (16). Two separate sorts of silicon are made. First is n-type, which has save electrons, and second p-type, which is missing electrons, leaving "gaps" in the spaces. When these p and n type materials are placed side by side inside a solar cell, the n-type silicon spare electrons jump over from n-type to p-type to fill the gaps in the p-type silicon. Consequently, the n-type silicon becomes positively charged while the p-type silicon is negatively charged, and in the process creating an electric field across the cell (22). Because silicon is a semi- conductor, it can act as insulator, maintaining this imbalance. As the photons crush the electrons of the silicon particles, this field drives them along in a precise way, giving the electric presence, thus electric energy is created (16).
The most common solar panels are for 12V applications. To attain that voltage, 24 cells would be enough. However, for charging batteries and circumstances where there is a need to compensate for voltage drops due to various factors, a PV panel usually contains between 28 and 40 cells for a higher voltage. Solar panels and the elements inside the panel need to be protected from humidity (22).
The three basic types of solar cells produced from silicon cells are amorphous, single-crystal,and polycrystalline (5).
Single-crystal cells are made of long cylinders and sliced into round or hexagonal wafers. While this process is energy-intensive and with wasteful of materials. It produces the highest-efficiency cells (as high as 25% in some lab tests). Because these high-efficiency cells are more expensive, they are sometimes used in combination with concentrators such as mirrors or lenses. Concentrating systems can be used to boost efficiency to approximately 30 percent. Single-crystal comprise 29% of the global market for PV (22).
Polycrystalline cells are manufactured from molten silicon cast that is drawn into sheets, and then subdivided into squares. While production costs are lower, the efficiency of the cells is lower too (around 11-15 percent). Since the cells are square, they can be easily packed more closely together. Polycrystalline cells comprise 62% of the global PV market.
Amorphous silicon (a-Si) is a radically different approach. Silicon is essentially sprayed onto a glass or metal surface in thin films, making the whole module in one step. This approach is by far the least expensive, but it results in very low efficiencies (only about 8-10 percent).
Some raw materials, other than silicon, are under development, such as gallium arsenide (Ga-As), V, and copper-indium-diselenide (CuInSe2). These materials not only offer higher efficiencies but they also exhibit other interesting properties, including the ability to manufacture amorphous cells that are sensitive to different parts of the light spectrum. By stacking cells into multiple layers, they can capture more of the available light. Although a-Si accounts for only five percent of the global market, it appears to be the most promising for future cost reductions and growth potential (22).
Advantages of Generating Electricity via Solar Panel
When the cost of connecting remote locations to the mains electricity is expensive, solar energy becomes a cost-effective alternative. Costs of PV systems have come down 25 fold over the last 20 years and are now often the most cost effective in applications such as remote areas including cabins and resorts. In remote locations, connecting to the grid is prohibitively expensive, making an alternative power system a necessity. A renewable energy system requiring an inverter application is economically viable in most situations, as the cost of extending grid wiring to a remote location can cost anywhere from $20,000 to...
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