The term Solar Energy refers to the rays of the sun emitted through radiation that reach the earth in a usable form (Solar Energy Administration, 2007). The sun has produced radiation for billions of years. This radiation is convertible into other forms of energy including heat and electricity, for human use. In fact, it is not only humans that use this energy. Other animals also use the same energy for movement and basic body functions, only that they derive it directly from the plants which they eat, which in turn convert the sun’s rays into energy through the process of photosynthesis.

However, as stated above, Solar Energy is mainly limited to refer to the harnessing of the sun’s energy by human beings for the purposes of generating heat and electricity. The radiant light and heat from the Sun has been harnessed for generations through ever evolving technologies. It is referred to as a renewable energy resource, along with wind, ocean wave power, hydroelectricity and biomass which are themselves derivatives of solar energy. Even though humans cannot possibly renew these types of energy, the term renewable is used to show that they are inexhaustible in the foreseeable future, compared to oil, coal, natural gas and uranium.

Solar energy reaches the earth in plenty and only a fraction of it is used by humans. It is converted into usable forms by heat engine or photovoltaic means. Its applications include room heating and cooling through solar architecture, lighting, and water heating and cooking. Solar technologies are classified as either passive or active solar. This depends on whether they convert sunlight before use, or simply apply it directly. Active solar techniques employ photovoltaic panels, solar thermal collectors, with electrical or mechanical equipment, to convert sunlight.

Passive solar techniques refer to the use of physical means to directly tap the sun rays, for instance orienting buildings towards the sun for daylighting and heat, as well as, use of insulated black materials to directly absorb heat from it. Whatever the method of harnessing used, solar energy is an important and integral aspect of human existence. It is therefore quite useful to understand it fully. History Of and Development of Solar Energy Since the beginning of architectural history, buildings have been oriented according to the position of the sun, Schittich, (1981).

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Early Greeks and Chinese used solar architecture and urban planning to ensure daylighting in buildings. Windows were oriented towards the sun and spaces were left to ensure that there was adequate light and warmth in buildings. A good example of this lighting was the one used in the Pantheon in Ancient Rome. The Early Romans even recognized a right to light as early as the 6th century. English law echoed the same in 1832. Indeed, natural light has always human lighting systems since the antiquity. The history of cooking using thermal solar energy can be traced back to Horace de Saussure who in 1767 built a box cooker.

There are three types of solar cookers: box, panel and reflector cookers. The box cooker is the simplest. In the 1830s British astronomer John Herschel used a similar thermal collector box to cook food during an expedition to Africa. A box cooker consists of a container that is insulated with a transparent lid that allows in sunlight. It can be used in clear or slightly overcast skies, attaining temperatures of up to 150°C. Panel cookers use a panel of reflective material to reflect sunlight onto an insulated container attaining the same temperature.

Reflector cookers use parabolic shaped reflectors to concentrate light on the container and attain higher temperatures than the other two. The Fresnel and Scheffler parabolic reflectors for instance can be used to produce sufficient heat for industrial purposes. The first commercial reflector heater system was the Solar Total Energy Project (STEP) in Shenandoah, Georgia, USA where 114 parabolic dishes were used to provide 50% of the processing heat, air conditioning and electricity for a clothing company. Solar cookers are generally used for cooking, drying and pasteurization.

Electricity production using solar energy dates back to the discovery of the first solar cell by Charles Fritts in the 1880s. He came up with prototype selenium cells that could only convert 1% of incident light into electricity. His work was later developed by scientists Earnst Warner von Siemens, James Clerk Maxwell and Russel Ohl in the 1940s. Further work by Gerald Pearson, Calvin Fuhler and Daryl Chapin created the modern day silicon solar cell in 1954. The three were researchers of the Bell Telephone Company when they came up with the photovoltaic (PV) cell.

This discovery came about as a result of their examination of sensitivity of silicon wafers to sunlight. The earliest PVs had an efficiency of 6% electricity conversion. These cells were developed in the late 1950s to power U. S. space satellites such as providing back-up power for the Vanguard I satellite launched in 1958 (Solar Energy Administration, 2007). Following their success in space, the PVs were later used to generate electricity in remote locations around the world, powering telecommunication stations, off-shore oil rigs, navigational buoys and railroad crossings in which they are still used to date.

These installations proved very successful accounting for over half of worldwide usage to date. The use of PV was further stimulated by the oil crisis in 1973. The main impediment to PV use was the high price of installation of 100 USD/watt in 1971. By 1985, this had been reduced to 7 USD further improving its performance. However, steady fall in oil prices during the early 1980s further affected the growth of PV.

Currently industrialized countries such as the US, Japan, Germany and Britain have come up with policies to increase the use of PV both to save dwindling sources of non-renewable sources of energy and reduce the impact of energy use on the environment. PV is one of the most environmentally friendly sources of energy. Germany for example, has become the leading PV market worldwide with installations generating approximately 4,150 MW at the end of 2007. Another widespread use of solar energy is the greenhouse. They were first built in Europe in the 16th century to keep imported exotic plants.

Today they are an important part of horticulture worldwide. They employ the use of transparent material that allows in sunlight but retains the heat from it thus keeping the interior warm. To reduce energy consumption, many modern buildings use hybrid solar lighting solutions that combine natural sunlight by day and artificial light by night, Jeff Muhs (2007). Advantages of Solar Energy The main advantage of solar energy that is rather obvious is that it is a renewable source of energy (Solar Energy Administration, 2007). No matter how much it is used, human beings cannot exhaust it in the foreseeable future.

In any case, if the sun were to fail to rise one morning, it would definitely not be because someone used a parabolic reflector dish to tap its rays. This makes it possible to plan for as a long-term inexhaustible source of energy unlike oil or coal that is only to be found in limited storage below the surface of the earth. It is actually, in recognition of this fact that the governments of leading industrialized nations such as Germany, which is the leading user, the US, Japan and Britain, have come up with policies favorable for the development of solar energy.

This will not only help in conserving strategic reserves of oil, but also come in handy in case oil runs out. The amount of solar energy reaching the earths surface in just one year is more than all the energy that will ever be tapped from uranium, oil, natural gas and uranium combined. The Earth receives 174 pet watts (PW) of incoming solar radiation (insulation) at the upper atmosphere . 70% of this energy is absorbed by clouds, oceans and land masses. It is therefore important that this energy is put to use rather than most of it being simply left to go to waste. Secondly, solar energy is widespread.

The rays of the sun reach every square inch of our planet on a regular basis. The remotest areas of the earth therefore, stand to gain from the maximum utilization of this resource. One for instance, needs to live close to a regular, all-season and fairly large river to be able to tap hydro-electricity. Geothermal energy can only be found in specific places. But solar energy can provide as much electricity in the Congo forest and Kalahari Desert as in Washington DC. This makes solar energy advantageous especially in the developing world where the sun coincidentally happens to shine plentifully.

Another point is that the solar energy supports Agriculture and Horticulture, Jeffrey C. Silver tooth, (2003). Apart from the fact that without the sun there would be no photosynthesis that supports plant and animal natural energy needs, solar energy is useful in enhancing production of crops and livestock. From the days of the Little Ice Age, French and English farmers invented the first greenhouses that accelerated ripening by keeping plants warm and thus increasing yields. The use of Greenhouses like those in the Netherlands’ Westland municipality still enhances high yields in vegetables, fruits and flowers.

Since they convert light into heat energy, greenhouses ensure all year round production in an enclosed environment of crops not suited to the prevailing climatic conditions in an area. Some of the oldest forms of this technology were used to produce cucumbers all year round for Emperor Tiberius of ancient Rome. Also, optimizing the capture of solar energy through timed planting cycles, spacing and arrangement of rows of plants as well as mixing of plant varieties improves yields. Other applications of solar energy in agriculture include pumping water, drying crops and brooding chicks

Another advantage of solar energy is that it is versatile and can therefore be used to serve in a wide variety of ways, Philibert (2008). Satellites in space are reached by the suns rays and can therefore run on solar energy. The development of solar powered boats, automobiles and even planes is an on going process. In 1996, Kenichi Horie made the first crossing of the Pacific Ocean using a solar powered aircraft. This follows earlier experiments which include the first unmanned Helios Unmanned Aerial Vehicle (UAV) solar flight in 1974 and the solar powered, man carrying Solar Riser flight which reached an altitude of 40 feet.

Currently, there are plans to circumnavigate the globe by the year 2010. However this is technology that is still in the development stages. The same energy is the one used in solar cookers, water heating systems, daylighting of houses and in miniature electronic appliances such as watches, calculators and radios. Solar energy was also used by 16th century Arab alchemists to desalinate water, Daniels (1964). In addition, the US 30% of Heating, Ventilation and Air Conditioning (HVAC) systems in buildings is already powered by solar energy (United States Department of Energy, 2008).

With such a wide variety of uses, this is truly the preferential energy source of the future. Another advantage of solar energy is that it is the cheapest form of energy in the long run. Appliances such as solar cookers are manufactured cheaply from locally available materials such as aluminum foil and black painted wooden boxes, and can be put to immediate use. The photovoltaic cell may be relatively expensive to manufacture but once put in place, it needs little or no maintenance. Some of its main advantages are as follows. One, conversion of sunlight to electricity is direct and does not require bulky mechanical generator systems.

Two, the PV system can be installed quickly, in any size required for all kinds of appliances from wristwatches to large industrial uses. Three, there is little environmental impact as it generates no by-product. This last point brings us directly to the next advantage of solar energy. It is a clean form of energy that is quite environmentally friendly. When one thinks of emissions of carbon monoxide, sulphur dioxide and lead oxide amongst other dangerous gasses from automobile and industrial petroleum engines, the need for environmentally friendly energy becomes quite urgent.

PV cells and solar heating systems do not produce this kind of harmful by-products or the equally dangerous radiation from uranium. Simple solar thermal heat storage systems use readily available materials such as water, earth, stones, paraffin wax and Glauber’s salt to store heat thus regulating room temperatures. The impact of this technique on the environment is insignificant if present at all. The Dover House in Dover Massachusetts was the first to use a Glauber’s salt heating system in 1948.

Since the low cost salts have been used as an effective storage medium due to their high specific heat capacity and ability to deliver heat at temperatures compatible with conventional power systems. Disadvantages of Solar Energy The main disadvantage of solar energy is just as obvious as its main advantage. It is not applicable at night. People tend to use energy both day and night. To use solar powered equipment when there is no sunlight requires cumbersome storage systems like the use of car batteries. This requirement has significantly slowed down the development of solar energy.

It goes without saying that simpler forms of solar appliances such as box cookers are totally useless when there is no sunlight. In fact the main difficulty in using solar energy is in its storage. With the exception of home and water heating systems where the wall or water itself stores the heat, the other forms of storage exhibit high energy loss. Such is the problem often encountered by enthusiastic solar car manufacturers. The second disadvantage is that whereas solar energy itself is environmentally friendly, materials used in manufacturing PV cells have a direct impact on the environment.

One such material is silicon which is consumed producing some waste products. Large solar thermal farms can also harm desert ecosystems if poorly managed, Energy Information Administration (2006). Lastly, as stated earlier, the initial cost of producing PV cells is prohibitively high. The irony of solar energy is such that the countries which need it most, in the developing world, with plenty of sunshine, cannot afford to manufacture the cells in sufficient quantities, if at all.

Conclusion Daniel Lincott (2008) stated that photovoltaics can cover all the worlds’ energy demand. This is true considering the sheer amount of energy that the sun sheds onto the earth everyday. Despite the few disadvantages that are possible to overcome, and the attendant research difficulties that may be encountered in the development of this crucial sector, the world needs solar energy as a cheaper, greener and more reliable and sustainable source of its energy needs.

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