13)Electricity/ history and development

It is impossible to imagine our civilization without electricity: economic and social progress will be turned to the past and our daily lives completely transformed.

Electrical power has become universal. Thousands of applica­tions of electricity such as lighting, electrochemistry and electro­metallurgy are longstanding and unquestionable.

With the appearance of the electrical motor, power cables re­placed transmission shafts, gear wheels, belts and pulleys in the 19-th century workshops. And in the home a whole range of various time and labour saving appliances have become a part of our ev­eryday lives.

Other devices are based on specific properties of electricity: electrostatics in the case of photocopying machine and electromagnetism in the case of radar and television. These applications have made electricity most widely used.

The first industrial application was in the silver workshops in Paris. The generator — a new compact source of electricity — was also developed there. The generator replaced the batteries and other devices that had been used before.

Electric lighting came into wide use at the end of the last cen­tury with the development of the electric lamp by Thomas Edison. Then the transformer was invented, the first electric lines and net­works were set up, dynamos and induction motors were designed.

Since the beginning of the 20th century the successful develop­ment of electricity has begun throughout the industrial world. The consumption of electricity has doubled every ten years.

Today consumption of electricity per capita is an indicator of the state of development and economic health of a nation. Elec­tricity has replaced other sources of energy as it has been realized that it offers improved service and reduced cost.

One of the greatest advantages of electricity is that it is clean, easily-regulated and generates no by-products. Applications of electricity now cover all fields of human activity from house wash­ing machines to the latest laser devices. Electricity is the efficient source of some of the most recent technological advances such as the laser and electron beams. Truly electricity provides mankind the energy of the future.

14) Solar energy

Solar power is associated with the harnessing of the sun's present emissions of heat or light. Solar energy is typically divided into three categories: passive solar, active solar, and photovoltaic (electrical) solar energy. All of them produce solar energy, but in very different ways. 

In active solar category the solar energy is directly converted in the application form. One of the simplest and economical ways to utilize solar energy is through solar thermal systems. Solar thermal technology is employed for collecting and converting the sun energy to heat energy for application such as water and air heating, cooking and drying, steam generation, distillation, etc. 

Solar thermal technologies include solar heat collectors (flat-plate collectors, evacuated-tube collectors) and solar concentrating collectors.

Solar concentrating collectors (parabolic concentrators) use mirrors and lenses to concentrate and focus sunlight onto a receiver mounted at the system's focal point. The receiver absorbs and converts the sunlight into heat. This heat is then transported by means of a heated fluid through pipes to a steam generator or engine where it is converted into electricity. Solar concentrating systems produce high temperatures that can be used for industrial purposes. 

Photovoltaic (electrical) solar technologies directly convert solar radiation into electricity through the use of photovoltaic cells (PVs), also called solar cells. Photovoltaic or solar electric panels use semiconductor materials such as silicon to convert sunlight to electricity. This electricity can either be used directly as it is or can be stored in the battery. The stored electrical energy then can be used at night. 

Of all the solar energy technologies, photovoltaics show the greatest promise for worldwide acceptance and application. Working photovoltaics are relatively simple in design, have no moving parts, need very little maintenance and are environmentally benign. They simply and silently produce electricity whenever they are exposed to light. In the developing world PVs are seen as a very attractive option. They are especially useful for rural electrification, vaccine refrigeration and water pumping. 

Solar energy demand has grown at about 25% per annum over the past 15 years but it has clearly not reach its full potential. The main reason for the lack of mass exploitation of solar power technologies is economic. In order for widespread generation of electricity using solar panels to be feasible it needs to be economically advantageous. In order for solar panels to be an economically viable choice for the production of electricity, production costs must go down and efficiency of the final product must go up. 

The hidden factor behind the lack of widespread solar power production is the absence of mass consumer demand for solar technologies. If there is a demand for a product, there will be people that will supply that product at a cost that fulfills that demand. As a result, economic and efficient solar power technologies will be developed and exploit more quickly.

15) other nontraditional sources of energy

With the growing concerns over the environmental problems today (air pollution, global climate change, massive flooding in river systems, etc.) and the price of non-renewable energy sources soaring, we have to take a closer look at the alternative energy sources. Alternatives to the fossil fuels and nuclear power are renewable sources of energy and they are considerably more attractive in many ways. Renewable sources are derived and replenish quickly from nature and usually do not pollute our environment when used to generate electricity. The five renewable sources used most often include hydropower (water), solar, wind, biomass, and geothermal. 

Hydropower or water power is power derived from the energy of falling water or running water, which may be harnessed for useful purposes. Since ancient times, hydropower from many kinds of watermills has been used as a renewable energy source for irrigation and the operation of various mechanical devices, such as gristmills, sawmills, textile mills, trip hammers, dock cranes, domestic lifts, and ore mills. A trompe, which produces compressed air from falling water, is sometimes used to power other machinery at a distance.

Since the early 20th century, the term has been used almost exclusively in conjunction with the modern development of hydroelectric power. International institutions such as the World Bank view hydropower as a means for economic development without adding substantial amounts of carbon to the atmosphere,  but in some cases dams cause significant social or environmental issues

Wind power is extracted from air flow using wind turbines or sails to produce mechanical or electrical power. Windmills are used for their mechanical power,  wind pumps for water pumping, and sails to propel ships. Wind power as an alternative to fossil fuels, is plentiful, renewable, widely distributed, clean, produces no greenhouse gas emissions during operation, and uses little land. The net effects on the environment are generally less problematic than those from nonrenewable power sources.

Large wind farms can consist of hundreds of individual wind turbines which are connected to the electric power transmission network

Wind power is very consistent from year to year but has significant variation over shorter time scales. It is therefore used in conjunction with other sources to give a reliable supply. As the proportion of wind power in a region increases, a need to upgrade the grid, and a lowered ability to supplant conventional production can occur. Power management techniques such as having excess capacity, geographically distributed turbines, dispatchable backing sources, sufficient hydroelectric power, exporting and importing power to neighboring areas, using vehicle-to-grid strategies or reducing demand when wind production is low, can in many cases overcome these problems. In addition, weather forecasting permits the electricity network to be readied for the predictable variations in production that occur