Introduction During the last dozen years it has become obvious, that the conventional and unrenewalbe sources of energy will be slowly replaced by new, renewable sources. It results from the fact, that conventional sources of energy like nuclear power plants and coal power plants, pollute the enviroment and with every year become more expensive in maintening. Considering, that nuclear energy meets great resistance of the citizens of alomost every country where it exists and where it is projected, we can assume that this source of energy may not become the only alternative in the future. In many countries the basic source of energy are coal power plants. If we assume that coal mining will keep on the same level what right now, the exhaust of conventional sources will become a fact in about 40 years for an oil, 60 years for a natural gas, 197 years for a hard coal and in 293 years for a brown coal.
The greatest source of unlimited, free and clear energy is the sun energy. Sun is a source of energy with power of 27*1.000.000.000 MW. During 14 days, it sends to the earth the same amount of energy, what the whole energy requirement of all mankind. The energy of sun radiation is a source with a great potential and it's capability is almost unexhausted - it will suffice for about 5 bilion years. The energy of sun has been used for many years thanks to inventing the photowoltaic cells and solar collectors. But common use of these devices took place after starting the production of them on a mass scale and thanks to the technological progress. The advantages of solar energy  The sun is a basic, unexhaustable and clear source of energy. In a form of sun radiation to the outer layer of atmosphere gets the energy of 1.36 kW/m2. It is called the sun constant. While comining through the atmosphere the radiation is weaked by reflection, dispersion and absorption on the molecules of gas and dust. This part of radiation that reaches the earth directly is called "the direct radiation". While this part, which is reflected and absorbed and further emitted by the molecules of gas and dust, coming to the earth surface is called "the dispersed radiation". The sum of the direct radiation and and dispersed radiation, which reaches the earth is defined as the total sun radiation - G [W/m2].  Whereas the sum of direct, dispersed and reflected irradiation that fall in a specific unit of time is called the insolation - H [W/m2]. The following important criterion of the heliocentric conditions is the mean number of hours when the sun rays reaches the earth directly.
In Eastern Europe geographics latitudes, when are the optimal weather conditions (cloudless heaven, the noon), the value of total energy of sun radiation amounts from 900 kWh/m2 year to 1200 kWh/m2 year.
According to the standard it is 1000 kWh/m2 year ± 10%. The value of insolation in Poland, between 9-15 hour, ranges within 600 - 800 [W/m2].
In a year scale, in Poland the number of hours with the direct sun radiation ranges from 1390 to 1900 hours, depending on the country region. Usually the number of 1600 h is accepted. |
