Report On Wind Mill (2).doc

Report On Wind Mill A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important application was to pump water. Windmills used for generating electricity are commonly known as wind turbines.

Windmills in antiquity The windwheel of the Greek engineer Heron of Alexandria in the 1st century AD is the earliest known instance of using a wind-driven wheel to power a machine. Another early example of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China since the 4th century. It has been claimed that the Babylonian emperor Hammurabi planned to use wind power for his ambitious irrigation project in the 17th century BC. Vertical windmills There is an ongoing debate among historians on whether and how the windmill from the middle East influenced the development of the early European windmill. In northwestern Europe, the horizontal-axis or vertical windmill (so called due to the plane of the movement of its sails) is believed to date from the last quarter of the 12th century in the triangle of northern France, eastern England and Flanders. The earliest certain reference to a windmill in Europe (assumed to have been of the vertical type) dates from 1185, in Weedley, Yorkshire, although a number of earlier but less certainly dated twelfth century European sources referring to windmills have also been found. These earliest mills were used to grind cereals. Post mill The evidence at present is that the earliest type of European windmill was the post mill, so named because of the large upright post on which the mill's main structure (the "body" or "buck") is balanced. By mounting the body this way,

the mill is able to rotate to face the wind direction; an essential requirement for windmills to operate economically in North-Western Europe, where wind directions are variable. The body contains all the milling machinery. The first post mills were of the sunken type where the post was buried in an earth mound to support it. Later a wooden support was developed called the trestle. This was often covered over or surrounded by a roundhouse to protected the trestle from the weather and to provide storage space. This type of windmill was the most common in Europe until the 19th century when more powerful tower and smock mills replaced them. Hollow-post mill In a hollow-post mill the post on which the body is mounted is hollowed out, to accommodate the drive shaft. In this way it is possible to drive machinery below or outside the body while still being able to rotate the body into the wind. Hollowpost mills driving scoop wheels were used in the Netherlands to drain wetlands from the 14th century onwards. Tower mill By the end of the thirteenth century the masonry tower mill, on which only the cap is rotated rather than the whole body of the mill, had been introduced. The spread of tower mills came with a growing economy that called for larger and more stable sources of power though they were more expensive to build. In contrast to the post mill, only the cap of the tower mill needs to be turned into the wind, so the main structure can be made much taller, allowing the sails to be made longer, which enables them to provide useful work even in low winds. The cap can be turned into the wind either by winches or gearing inside the cap or from a winch on the tail pole outside the mill. A method of keeping the cap and sails into the wind automatically is by using a fantail, a small windmill mounted at right angles to the sails, at the rear of the windmill. These are also fitted to tail poles of post mills and are common in Great Britain and English-speaking countries of the former British Empire, Denmark and Germany but rare in other places. Tower mills with a fixed cap are found around the Mediterranean Sea. They are built with the sails facing the prevailing wind direction.

Report on solar panel A solar panel (photovoltaic module or photovoltaic panel) is a packaged, interconnected assembly of solar cells, also known as photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Because a single solar panel can produce only a limited amount of power, many installations contain several panels. A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and interconnection wiring. Theory and construction Solar panels use light energy (photons) from the sun to generate electricity through the photovoltaic effect. The structural (load carrying) member of a module can either be the top layer or the back layer. The majority of modules use waferbased crystalline silicon cells or thin-film cells based on cadmium telluride or silicon. The conducting wires that take the current off the panels may contain silver, copper or other conductive (but generally not magnetic) transition metals. The cells must be connected electrically to one another and to the rest of the system. Cells must also be protected from mechanical damage and moisture. Most solar panels are rigid, but semi-flexible ones are available, based on thin-film cells. Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired current capability. Separate diodes may be needed to avoid reverse currents, in case of partial or total shading, and at night. The p-n junctions of mono-crystalline silicon cells may have adequate reverse current characteristics that these are not necessary. Reverse currents waste power and can also lead to overheating of shaded cells.

Solar cells become less efficient at higher temperatures and installers try to provide good ventilation behind solar panels. Some recent solar panel designs include concentrators in which light is focused by lenses or mirrors onto an array of smaller cells. This enables the use of cells with a high cost per unit area (such as gallium arsenide) in a cost-effective way. Depending on construction, photovoltaic panels can produce electricity from a range of frequencies of light, but usually cannot cover the entire solar range (specifically, ultraviolet, infrared and low or diffused light). Hence much of the incident sunlight energy is wasted by solar panels, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore another design concept is to split the light into different wavelength ranges and direct the beams onto different cells tuned to those ranges. This has been projected to be capable of raising efficiency by 50%. The use of infrared photovoltaic cells has also been proposed to increase efficiencies, and perhaps produce power at night. Rigid thin-film modules

In rigid thin film modules, the cell and the module are manufactured in the same production line. The cell is created on a glass substrate or superstrate, and the electrical connections are created in situ, a so called "monolithic integration". The substrate or superstrate is laminated with an encapsulant to a front or back sheet, usually another sheet of glass.