Energy Freek

HISTORY OF SOLAR ENERGY: 

Solar energy has been used for thousands of years in various cultures around the world, including ancient Greece. The Greeks were particularly interested in the use of solar energy for heating water and buildings. Probably the first most early application of the sun light was done the Greek mathematician and philosopher Archimedes (287-212 BC). He magnified the sunlight by using mirrors and burning the Roman fleet in the Bay of Syracuse. This is also known as “Death Ray” From 100 BC to 1100 AD authors made references of this event, but after sometimes it was criticized that at that time these types of magnified mirrors are not available and did Archimedes know about the science of optics to diverse the rays of sun to burn the ship?  

After the passage of time people start thinking about this Archimedes principle.  In his book, Optics, Vitelio, a Polish mathematician, described the burning of the Roman fleet in detail “The burning glass of Archimedes composed of 24 mirrors, which conveyed the rays of the sun into a common focus and produced an extra degree of heat.” Proclus also repeated Archimedes' principle and used this burning method to burn the war of his enemies in Byzantine period. 

SOLAR FURNACE: 

One of the first large-scale applications was the solar furnace built by the well-known French chemist Lavoisier, who, around 1774, constructed powerful lenses to concentrate solar radiation (see Figure 1.4). This attained the remarkable temperature of 1750 C. The furnace used a 1.32 m lens plus a secondary 0.2 m lens to obtain such temperature, which turned out to be the maximum achieved for 100 years. 

SOLAR STEAM ENGINE 

During the nineteenth century, attempts were made to convert solar energy into other forms based upon the generation of low-pressure steam to operate steam engines. August Mouchot pioneered this field by constructing and operating several solar-powered steam engines between the years 1864 and 1878 in Europe and North Africa. One of them was presented at the 1878 International Exhibition in Paris. The solar energy gained was used to produce steam to drive a printing machine. 

In 1875, Mouchot made a notable advance in solar collector design by making one in the form of a truncated cone reflector. Mouchot’s collector consisted of silver-plated metal plates and had a diameter of 5.4 m and a collecting area of 18.6 m2. The moving parts weighed 1400 kg (about 3086.47 lb). 

The efforts were continued in the United States, where John Ericsson, an American engineer, developed the first steam engine driven directly by solar energy. Ericsson built eight systems that had parabolic troughs by using either water or air as the working medium 

In 1901 A.G. Eneas installed a 10 m diameter focusing collector that powered a water-pumping apparatus at a California farm. The device consisted of a large umbrella-like structure opened and inverted at an angle to receive the full effect of the sun’s rays on the 1788 mirrors that lined the inside surface. The sun’s rays were concentrated at a focal point where the boiler was located. Water within the boiler was heated to produce steam, which in turn powered a conventional compound engine and centrifugal pump (Kreith and Kreider, 1978). 

In 1904, a Portuguese priest, Father Himalaya, constructed a large solar furnace. This was exhibited at the St. Louis World’s Fair. This furnace appeared quite modern in structure, being a large, off-axis, parabolic horn collector (Meinel and Meinel, 1976). 

 In 1912, Frank Shuman, in collaboration with C.V. Boys, undertook to build the world’s largest pumping plant in Meadi, Egypt. The system was placed in operation in 1913, using long parabolic cylinders to focus sunlight onto a long absorbing tube. Each cylinder was 62 m long, and the total area of the several banks of cylinders was 1200 m2 . The solar engine developed as much as 37–45 kW continuously for a 5-h period (Kreith and Kreider, 1978). Despite the plant’s success, it was completely shut down in 1915 due to the onset of World War I and cheaper fuel prices. 

SOLAR WATER HEATER: 

In more recent history, the first patent for a solar water heater was issued in 1891 to Clarence Kemp, who is often credited with inventing the modern solar water heater. Kemp's design consisted of a tank of water that was mounted on a roof and covered with glass. The sun's energy was used to heat the water in the tank, which was then circulated through a system of pipes to provide hot water for the home. 

Since then, many other designs for solar water heaters have been developed, and they are now used in a variety of applications, including residential and commercial buildings, as well as in industrial and agricultural settings. 

Photovoltaics 

In the late 1800s, the working and the concept of solar cells started. A number of different scientists have started research on solar photovoltaic cells. Becquerel discovered the PV effect in selenium in 1839. The first successful demonstration of a photovoltaic cell was in 1883, when Charles Fritts created a solar cell using selenium. However, these early cells were not efficient enough to be practical for power generation. In 1958, researchers at Bell Labs developed the first silicon-based solar cell, which had an efficiency of around 11%, although the cost was prohibitively high ($1000/W). The first practical application of solar cells was in space, where cost was not a barrier, since no other source of power is available. Researchers in the 1960s developed PV materials like gallium arsenide (GaAs), compounds of cadmium sulfide (CdS) and cuprous sulfide (Cu2S). They could operate at higher temperature than silicon, but they are much more expensive. 

There are two types of silicon cells discovered. The amorphous silicon and the crystalline silicon. Amorphous silicon cells consist of a thin layer of silicon than crystalline silicon cells whose thickness is between 1 to 100 micrometers. On the other hand, the crystalline silicon cell consists of a bulk of silicon crystals. That is why amorphous silicon is also known as thin-film solar cells. Amorphous silicon has very low efficiency of only 6% but they are very cheaper, and the energy produced by them is very cheap. They are very useful in small-scale production where cost matters. Amorphous silicon can be deposited on a wide range of substrates, both rigid and flexible, which makes it ideal for curved surfaces and “foldaway” modules. But crystalline silicon cells are much more efficient than amorphous silicon cells and have the efficiency of about 20 to 30%. But they are much more expensive the amorphous silicon. They are mostly used in large scale production in commercial as well as residential. Scientists still work harder to increase the efficiency of both cells. 

The two basic types of PV applications are stand-alone and grid-connected systems. Stand-alone PV systems are used in areas that are not easily accessible or have no access to mains electricity grids. A stand-alone system is independent of the electricity grid, with the energy produced normally being stored in batteries. A typical stand-alone system would consist of PV module or modules, batteries, and a charge controller. An inverter may also be included in the system to convert the direct current (DC) generated by the PV modules to the alternating current (AC) form required by normal appliances. 

In the grid-connected applications, the PV system is connected to the local electricity network. This means that during the day, the electricity generated by the PV system can either be used immediately or sold to an electricity supply company. In the evening, when the solar system is unable to provide the electricity required, power can be bought back from the network. In effect, the grid acts as an energy storage system, which means the PV system does not need to include battery storage. 

When PVs started to be used for large-scale commercial applications about 20 years ago, their efficiency was well below 10%. Nowadays, their efficiency has increased to about 15%. Laboratory or experimental units can give efficiencies of more than 30%, but these have not been commercialized yet. Although 20 years ago PVs were considered a very expensive solar system, the present cost is around $2500–5000/kW (depending on the size of the installation), and there are good prospects for further reduction in the coming years. 

SOLAR DESALINATION: 

Water problem now becomes the huge problem around the world. Lack of pure water causes serious water shortage in the world. As in many areas of the world there is no supply of pure water. It also becomes the most important problem in the world. In this situation to overcome this problem, one of the most effective way is by using sun energy. As the sun’s energy can be used and becomes nessecary in every fields and The sun has extremely important influences on our planet. 

Solar desalination is nothing but the concept of converting salt water into fresh water by using solar energy. Early dates back in forth century the concept of solar energy was given by Aristotle. He explain to evaporate impure water and then condense it to obtain potable water. The first application of sea water distillation by solar desalination was shown in figure. The drawing illustrates an account by Alexander of Aphrodisias in 200 AD, who said that sailors at sea boiled seawater and suspended large sponges from the mouth of a brass vessel to absorb what evaporated. In drawing this liquid off the sponges, they found that it was sweet water. 

Solar desalination has been practised for a long time. Many Arab Alchemist working on research ofsolar desalination. The earliest documented work is that of an Arab alchemist in the fifteenth century, reported by Mouchot in 1869in which he used the polished Damascus mirrors for solar desalination. During this period, solar energy was used to fire alembics to concentrate dilute alcoholic solutions or herbal extracts for medical applications and to produce wine and various perfume oils. The stills, or alembics were discovered in Alexandria, Egypt, during the Hellenistic period. A greek alchemist “Cleopatra the Wise” developed many distillers of this type. 

 One of them is shown in Figure. The head of the pot was called the ambix, which in Greek means the “head of the still”. The Arabs, who overtook science and especially alchemy about the seventh century, named the distillers Al-Ambiq, from which came the name alembic. 

Mouchot (1879), the well-known French scientist who experimented with solar energy, in one of his numerous books mentions that, in the fifteenth century, Arab alchemists used polished Damascus concave mirrors to focus solar radiation onto glass vessels containing saltwater to produce freshwater. He also reports on his own solar energy experiments to distill alcohol and an apparatus he developed with a metal mirror having a linear focus in which a boiler was located along its focal line. 

Later on, during the Renaissance, Giovani Batista Della Porta (1535–1615), one of the most important scientists of his time, wrote many books. In one of them, Magiae Naturalis, which appeared in 1558 in which he mentions three types of solar desalination system. In 1589 he issued a second edition in which he mention seven types of solar desalination. The most important of them is a solar distillation apparatus that converted brackish water into freshwater. In which wide earthen pots were used which are heated by solar radiations to evaporate water and then condense the the water intovases placed underneath. In this book he also give the concept to collect water from air which is now known as humidification or dehumidification. 

Around 1774, the great French chemist, Lavoisior uses a large glasses lens which is fixed on a supporting structure, to concentrate solar radiations on solar distillation flask. In 1870, the first American patent on solar desalination was granted by the experimental work of Wheeler and Evans. The inventors described the greenhouse effect, analyzed in detail the cover condensation and re-evaporation, and discussed the dark surface absorption and the possibility of corrosion problems.   

Two years later, in 1872, an engineer from Sweden, Carlos Wilson, designed and built the first large solar distillation plant, in Las Salinas, Chile thus, solar stills were the first to be used on large-scale distilled water production. The plant was constructed to provide freshwater to the workers and their families at a saltpeter mine and a nearby silver mine. They used the saltpeter mine effluents, of very high salinity (140,000 ppm), as feed-water to the stills. The plant was constructed of wood and timber framework covered with one sheet of glass. It consisted of 64 bays having a total surface area of 4450 m2 and a total land surface area of 7896 m2. It produced 22.70 m3 of freshwater per day (about 4.9 l/m2). The still was operated for 40 years and was abandoned only after a freshwater pipe was installed, supplying water to the area from the mountains. 

The use of solar concentrators in solar distillation was reported by Louis Pasteur, in 1928, who used a concentrator to focus solar rays onto a copper boiler containing water. The steam generated from the boiler was piped to a conventional water-cooled condenser in which distilled water accumulated. 

After the First World war the concept of solar distillation was going to its peak due to the shortage of fresh water. At this time different new devices were developed, such as the roof-type, tilted wick, inclined tray, and inflated stills. Before World War Two only a few solar distillation plants existed. In the period of 1930-1940 due to the dryness in California, the concept of solar distillation became stronger but due to the depressed economy few of them were implemented.  

During the World War Two,  when hundreds of allied troops were suffered from drinking when stationed in North Africa. At that time the concept of small solar desalters for rafts and ships were started. Then a team lead by Maria Telkes, starting different experiments on that and finally the team got succeed to design a small individual plastic solar desalter for lifeboats and small ships. 

After the world war Two, there was a huge shortage of drinking water. It becomes the major problem of that time. In July, the US government set up the office of Saline water (OSW) in 1952 for the research of water desalination. Five demonstration plants were built, and among them was a solar distillation plant in Daytona Beach. 

Experimental work on solar distillation was also performed at the National Physical Laboratory, New Delhi, India, and the Central Salt and Marine Chemical Research Institute, Bhavnagar, India. In Australia, the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Melbourne carried out a number of studies on solar distillation. In 1963, a prototype bay-type still was developed, covered with glass and lined with black polyethylene sheet. 

Between 1965 and 1970, water distillation plants were constructed on 4 Greek islands which can give small amount of water, using asymmetric glass-covered greenhouse type with aluminum frames. The stills used seawater as feed and were covered with single glass. Their capacity ranged from 2044 to 8640 m3 /day. The installation on the island of Patmos is the largest solar distillation plant ever built. 

SOLAR DRYING 

Solar drying is a method of drying food and other substances using the heat from the sun. It was invented in the 1950s as an alternative to open sun drying but gained more attention after the oil crisis in 1973. Solar drying systems are used extensively in many countries to improve product quality, minimize waste, and employ renewable energy sources. 

Solar drying works by heating air to a constant temperature with solar energy, which facilitates the extraction of humidity from the material being dried. Solar radiation falling on the collector plate heats up the air inside it. The warm air rises and discharges into the collector. The air, thus, is circulated via natural convection. The drying chamber consists of a vertical stack of trays on which the material to be dried is placed. In more advanced versions of conventional sun drying, such as solar drying, the product is kept in a transparent container exposed to the sun. 

Solar drying can be used to eliminate the moisture content from crops, vegetables, fruits, and meat. Agricultural products can be dried open-air directly in the sun or with dryers powered by biomass or solar energy. The Solar Drying System is a simple, hygienic drier which you can make yourself with local building materials like wood of bamboo. The size of the Solar Drying depends on the amount of material to be dried. Chimney solar dryer designed by UC Davis researchers for the Horticulture Innovation Lab allows farmers and others to use the sun to efficiently dry fruits, vegetables.