Nowadays, there is a real need to develop renewable energies and the main reasons are as follows: A first reason is, of course, that they are inexhaustible, contrary to the other energies, notably the fossil energies, whose stocks are limited. For example, in the case of petrol, a recent survey has the tendency to prove that the reserve in years would be in reduction what lets foretell a production decreasing from 2010.
A second reason is the risk that presents the nuclear energy; therefore, many nuclear countries want today to change production of energy to safety methods: United States, Germany, Switzerland, …
A third reason, absolutely vital, and short-term, that imposes us to bet on the renewable energies: it is the notion today unanimous recognized of "lasting development", bound to the pollution in the air. One can expect an increase of the number and the power of the cyclones, desertification of subtropical zones, however flooding of some countries (Low Country, Bangladesh), deterioration of the earths by erosion, deviation of the Gulf Stream allowing the polar air mass to arrive to Europe.
This paper is a contribution to renewable energies study and it concerns the case of Lebanon. More precisely, we consider the convention of photovoltaic and wind power to electrical one. In this work, annual data for Lebanon are discussed, efficiencies of each convention are calculated and the economic costs of each source are compared.
In Lebanon, and according to an investigation done by the ministries of industry and petrol, the hydraulic and electric resources as well as the statistical administration, it takes out again of it that:
-98% of our needs in primary energy have been imported. The renewable energies (solar, wind,…), in spite of a geographical and socioeconomic context auspicious to their development, represent even less of 1% in the global energizing balance of this country.
The yearly consumption in energy per person remained less then the world average and represents 1/5 of the one of the European Community and 1/8 of the one of the United States or Canada.
The invoice of energy increased 20% in 2001 in relation to 2000 and this following the increasing in prices of oil and its derivatives on the international markets.
The analysis of final electricity in relation to the primary resources permits to note that the efficiencies of the thermal power stations don’t pass 33% and that the losses on the networks high voltage and of distribution are estimated to 12%.
The electric consumption rose, but remains even lower to the efficient needs and especially to the level of the seasonal crests and the
reserve powers. The electric production is to 11% hydraulic and 89% thermal.
The combustion of our based energy on the hydrocarbons (4200 tons) and other primary resources, give out in air harmful substances estimated to more then 15 tons of dusts, 80 tons of SO2 and as many of organic compounds. It also produced 3.5 millions of tons of CO2, which is 0,88 ton per person and per year.
It is greater then 25% to the average production of the countries of the region (valued to 0,7 ton of CO2 per person and per year).
Solar energy
Generally speaking, the Earth has two global movements that affect the reception of the solar energy to its surface: the rotation that it makes once on itself per day and the yearly revolution that it makes around the sun. The combination of these movements explains the daily changes in the reception of the solar light in particular places.
The reason for which the energizing flux received to soil does not pass 1000 W.m2 is that the atmosphere modifies in an important way the direct radiance of the sun due to the following mechanisms:
• absorption of light by the various gases constituent,
• diffusion by their molecules,
• absorption and diffusion by the dusts.
In addition, the solar flux received on a surface depends on:
• the orientation and the slant of the surface,
• the latitude of the place and its degree of pollution,
• the period of the year,
• the time considered in the day,
• the nature of the cloudy layers.
Solar panels can be placed on a roof or on the soil if the place is cleared well. The orientation of the panel depends on:
• the impact angle: It is the angle formed by the solar panel and the solar rays. The optimal impact angle is an angle of 90°.
• the slant angle: It is the angle formed by the solar panel and the horizontal.
• the zenith angle: It is the angle formed by the solar rays and the horizontal.
The phenomenon named "photovoltaic effect" consists mainly in converting the solar light in electric energy by means of semiconductors devices named photovoltaic cells. The photovoltaic generator is constituted of a series and parallel association of the number of necessary modules to assure the requisite energy to product.
Wind energy
Wind is simple air in motion. It is caused by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates. During the day, the air above the land heats up more quickly than the air over water.
The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water. In the same way, the large atmospheric winds that circle the earth are created because the land near the earth’s equator is heated more by the sun than the land near the North and South Poles. Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy source because the wind will blow as long as the sun shines.
Like old fashioned windmills, today’s wind turbines use blades to collect the wind’s kinetic energy. Wind turbines work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity.
There are two types of wind turbines used today: horizontal–axis wind machines and vertical-axis wind machines.
Wind farm is clusters of wind turbines used to produce electricity. A wind farm usually has dozens of wind turbines scattered over a large area. Unlike power plants, many wind power plants are not owned by public utility companies. Instead they are owned and operated by business people who sell the electricity produced on the wind farm to electric utilities.
Operating a wind power plant is not as simple as just building a wind turbine in a windy place. Wind farm owners must carefully plan where to locate their wind turbines. One important thing to consider is how fast and how much the wind blows.
As a rule, wind speed increases with altitude and over open areas with no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling. Wind speed varies throughout the country. It also varies from season to season.
New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by tax breaks for renewable energy.
Our study is achieved within the Laboratory of electricity of the Faculty of Engineering in the Lebanese University (Tripoli – Lebanon). The solar experimental part of the system is constituted of a mobile solar panel of 50 W, one battery and one load voltage regulator. The position control of the panel took place so that its surface is always perpendicular to the solar rays. The wind experimental part is constituted of a wind converter of 400 W, one battery, on rectifier and load voltage regulator. In the global experimental system, a microcontroller is used in order to take data about the solar and wind generated energy and that in order to archive them.
Another goal of this microcontroller is to control the functioning of the electric motor moving the solar panel. To make comparison between these two types of renewable energy which should be of the same rated power, we multiplied the data given by the solar panel by eight.
During the year 2006, the energy generated by the wind turbine of 400 W of power is 55.55 kWh. The one produced by a solar panel of 50 W of power is 6.9 kWh. To do a comparison between these two sources of renewable energy, one multiplies the value obtained by the solar panel by eight. Therefore, the energy produced by eight solar panels of total power 400 W is equal to 55.175 kWh.
Thus, for the same rated power of 400 W, the produced wind energy is nearly identical than that delivered by the solar panels. It should be noted that the generated solar energy is maximum, because the sky is cleared around Faculty of Engineering, but, this Faculty is not placed in a windy zone. Consequently, if one places this wind machine in a windy zone, one will be able to note that the wind energy will be more important than that delivered by the solar panels.
Wind and solar energy offer a viable, economical alternative to conventional power plants in many areas of the country. Wind and solar are clean fuel; they produce no air or water pollution because no fuel is burned. This survey consists in creating a data base of the power delivered by the wind machine and the solar panels. It permitted during the year 2006 to determine the monthly and yearly balances of these energies in Lebanon.
The experimental results show that the wind machine can deliver more power than solar panels if it is placed in a windy zone. The calculation of the efficiency and the profitability of these tow types of conversion are also analyzed. We noted that the wind machine’s efficiency is 2.2 times than that of a solar panel and its price is 3 times less expensive than that of the solar panels.
By By A El-Ali et al, www.leonardo-energy.org
