History of Solar Energy

The star which, by the gravitational pull of its mass, dominates the planetary system that includes Earth. By the radiation of electromagnetic energy, directly or indirectly providing all the energy that sustains life on Earth, because all the food and ultimately fuel comes from plants that use energy from sunlight

Radiant energy is produced in the sun as a result of nuclear fusion reactions. Reaches the Earth through space quanta of energy called photons, which interact with the atmosphere and land surface. The intensity of solar radiation at the outer edge of the atmosphere, considering that the Earth is at its average distance from the sun, called solar constant and its average value is 1.37 × 106 erg/s/cm2, or about 2 cal/min/cm2. However, this amount is not constant, since it seems that varies by 0.2% over a period of 30 years. The real energy intensity available in the earth’s surface is less than the solar constant due to absorption and dispersion of radiation that causes the interaction of photons with the atmosphere.

The intensity of solar energy available at a given point on Earth depends on a complicated but predictable, the day of the year, the time and latitude. Furthermore, the amount of solar energy can be collected depends on the orientation of the receiving device.

The first uses of solar energy are lost in the distance of time. However, for some clay tablets found in Mesopotamia, we know that by the year 2000 before JC priestess lit the sacred fire of the altar by curved mirrors of polished gold.

In Egypt, around the year 1450 BC, there were sound statues of Pharaoh Amenhotep III. The sound produced by these statues was a consequence of the heated air on his huge pedestals, which were hollow and communicated with the outside by a very small hole.

Archimedes used concave mirrors with which the Roman ships caught fire during the Renaissance.

Kicher (1601-1680) ignited a pile of wood at a distance using mirrors a similar procedure to that used by Archimedes.

Tschirnhaus Ehrenfried von (1651-1700), a member of the National Academy of Science, ceramics melt achieved using a lens of 76 cm. in diameter.

George Louis Leclerc (1707-1788) built a solar oven made of 360 mirrors with a common focus and demonstrated in the gardens of Versailles Palace, igniting a pile of wood to 60 m.

The first flat-plate solar collector was manufactured by the Swiss Nicholas de Saussure (1740-1799), and consisted of a glass cover and a black metal plate enclosed in a box with the appropriate thermal insulation. This solar collector was used for cooking food Itís were introduced inside.

Antoine Lavoisier (1743-1794), famous French chemist who discovered oxygen, I experimented with lenses of 130 cm. diameter and melted platinum, whose melting point is 17600C.

In 1874 he settled in Las Salinas (Chile) a passive solar still consisting of 4700 m2 of surface producing 23,000 liters of fresh water a day. This distiller worked for 40 years until it was brought water through a pipeline from Antofagasta.

In 1875, French Mouchont conducted a conical collector area of 18.6 m2 of aperture, for the production of steam and was presented in Paris. This collector had an accident as a result of being left without water.

Abel Pifre used in the Paris Exhibition in 1878 double parabolic collector to produce steam, which is operated with a small press.

The first cylindrical collector. Parabolic was devised by the American John Ericsson in 1883.

Towards the end of last century there was already some interest in solar energy, as evidenced by the various journals of the time.

Early last century the use of solar energy was of special interest in the United States, primarily in California ¬ you, where did some work and studies in collaboration with astronomers, building prototypes of large dimensions.

After World War II such systems in Israel also extended, but due to the low price of conventional fuels, the use of solar energy was relegated to the background.

The resurgence of solar energy as a scientific discipline takes place in 1953 when Daniels Farrington organized at the University of Wisconsin International Symposium on the Use of Solar Energy, sponsored by the National Science Foundation in the United States. Two years later, in Tucson (Arizona), another symposium was held and formed the Association for Application of Solar Energy.

Because of these symposia was established journal “Solar Energy”, very high scientific level, which publishes the International Society of Solar Energy based in Australia, an agency that succeeded the partnership for the implementation of solar energy.

In the decade of the 60s, the excessive lowering of conventional fuels made little attention is devoted to the topic of solar energy; although this time he built the solar oven from Font Romeu (France).

In this context is expected, after more than 15 years since that date are crucial, a moderate but steady growth of applications of solar and other renewable energy sources worldwide.

The natural collection of solar energy is produced in the atmosphere, oceans and plants on Earth. The interactions of the sun’s energy, oceans and atmosphere, for example, produce winds, used for centuries to turn the mills. Modern systems use propellers wind strong, lightweight, weather resistant and aerodynamic design that, when attached to generators, produce electricity for local and specialist or to feed the power grid of a region or community.

Almost 30% of solar energy reaching the outer edge of the atmosphere is consumed in the water cycle, producing rain and potential energy of mountain streams and rivers. The energy generated by this moving water to pass through modern turbines is called hydropower.

Through the process of photosynthesis, solar energy contributes to the growth of plant life (biomass) which, together with wood and fossil fuels from the geological point of view derived from ancient plants, can be used as fuel. Other fuels such as alcohol and methane can also be extracted from biomass.

The oceans also represent a form of natural collection of solar energy. As a result of its absorption by the oceans and ocean currents, temperature gradients occur. In some places, these vertical variations reach 20 ° C at distances of a few hundred meters. When great masses at different temperatures, thermodynamic principles predict that you can create a cycle power generator that extracts energy from the mass with higher temperature and transfer an amount to the mass with lower temperature. The difference between these energies manifests itself as mechanical energy (to drive a turbine, for example) that can be connected to a generator to produce electricity. These systems, called systems of ocean thermal energy conversion, require huge energy exchangers and other devices into the ocean to produce power on the order of megawatts.

The direct collection of solar energy requires artificial devices called solar collectors designed to collect energy, often after concentrating the rays of the sun’s energy, once collected, is used in thermal processes or photoelectric, or photovoltaic systems. In thermal processes, solar energy is used to heat a gas or liquid which is then stored or distributed. In the photovoltaic process, solar energy is converted into electricity without any intermediate mechanical device. Solar collectors fall into two main types: flat plate and concentrating.

In thermal processes flat plate collectors intercept solar radiation on an absorber plate by passing the so-called carrier fluid. This, in liquid or gaseous form is heated when passing through the channels by heat transfer from the absorber plate. The energy transfer from the carrier fluid, divided by the solar energy striking the collector and expressed as a percentage, is called the collector instantaneous efficiency. Flat plate collectors generally have one or more transparent cover plate to help minimize heat loss from the absorber plate in an effort to maximize efficiency. They are capable of heating carrier fluids up to 82 ° C and get between 40 and 80% efficiency.

Flat plate collectors have been used effectively for heating water and heating. Typical systems used for house-room fixed collectors mounted on the roof. In the northern hemisphere are oriented towards the south and in the southern hemisphere toward the North. The optimum angle for mounting the collector depends on latitude. In general, for systems that are used throughout the year, such as producing hot water collectors are inclined (to the horizontal plane) equal to an angle of 15 ° latitude and are oriented approximately 20 ° S latitude and 20 ° N. latitude

Besides the flat-plate collectors, the typical systems of heating and hot water are formed by circulating pumps, temperature sensors, automatic controllers to activate the pump and a storage device. The fluid can be both air and liquid (water or water mixed with antifreeze), while bedrock or a single tank served as a means of storing energy.

For applications such as air conditioning and central power generation and heat to meet the industrial needs large, flat plate collectors do not provide, in general, fluids with temperatures high enough to be effective. They can be used in a first stage and then the fluid is treated with conventional heating means. Alternatively, you can use concentrating collectors more complex and costly. These are devices that reflect and concentrate solar energy incident on a small receiving area. As a result of this concentration, the intensity of solar energy increases and the temperature of the receiver (called `white ‘) can go to several hundreds or even thousands of degrees Celsius. Concentrators must move to follow the sun if they are to act effectively, the devices used for this are called heliostats.

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