The greater part of the energy consumed currently comes from the use of fossil fuels like oil, coal, natural gas or nuclear power. These resources become increasingly rare while the energy demands of the world amounted continuously. Since this form of energy covers a large part of the current energy production, it is necessary to find an alternative solution to take the relay. The constraint is to use a source of economic power and low emission as the protection of the environment has become an important point. Photovoltaic solar energy is the direct conversion of part of the solar radiation into electrical energy. This energy conversion is affected throughout photovoltaic cell based on a physical phenomenon called the photovoltaic effect, which is to produce a current when the surface of the cell is exposed to light. Science is naturally interested in the “renewable” resources. Photovoltaic solar energy is increasingly used in various terrestrial applications such as lighting and telecommunications [1] . The use of solar energy will provide electricity to isolated sites of electrical networks and avoid the creation of new electrical lines which generally requires a heavy investment.

The PV cell, also called solar cell, constitutes the basic element of the photovoltaic conversion. This is a semiconductor device that converts electric energy into light energy provided by an inexhaustible source of energy and the Sun. It exploits the properties of semiconductor materials used in the electronics industry: diodes, transistors and integrated circuits. Figure 1 illustrates a typical PV cell where its formation is detailed. The performance of energy efficiency achieved industrially are 13% to 14% for the cells based on monocrystalline silicon, with 11% to 12% of poly crystalline silicon and finally 7% - 8% for the amorphous silicon by thin films [2] . The photopile or solar cell is the basic element of a photovoltaic generator, and the equivalent circuit of a PV cell is shown in Figure 2. It includes a current source, a diode, a series resistance and a shunt resistance.

The photovoltaic effect is manifested when a photon is absorbed in a semiconductor material composed of doped p (positive) and n (negative), referred to as p-n junction (or n-p). Under the effect of doping, an electric field is present in the material permanently (like a magnet which has a permanent magnetic field) [3] . When an incident photon (grain of light) interacts with the electrons in the material, it transfers its energy to the electron hv which finds herself liberated from its valence band and therefore suffers the intrinsic electric field. Under the influence of this field, electron migrates toward the top surface leaving a hole that migrates in the reverse direction. Electrodes placed on the upper and lower surfaces allow the electrons to collect them and to make electrical work to join the anterior surface of the hole. A cell is often modeled by the electrical equivalent diagram it is he that is shown in Figure 2, the photovoltaic generator is modeled by the following equations [4] :

with is currently produced by the cells; is the saturation current; load electron; Boltzmann constant; T (˚C) is the operating temperature of the cell; A is a quality factor of the diode, normally between 1 and 2; and are series and parallel resistors. After the determination of the various parameters of the equivalent circuit, it is possible to solve the equation of characteristic, and also to determine these characteristics (current, power) by numerical method.

The characteristic curve of a PV cell represents the variation of the current which it produces as a function of the voltage at its terminals, since the short circuit (zero voltage corresponding to the maximum current product) till the open circuit (no current to a maximum voltage across the cell) [5] . In this case, we chose a simple model, requiring only the parameters given by the manufacturer to evoke the influence of meteorological parameters on the maximum power point, the I-V characteristic of this model is shown in Figure 3, and for influences of the conditions meteorological illustrated in Figure 4 and Figure 5: The electrical characteristics of the photovoltaic module that we used were obtained by numerical simulation of the model by Matlab-Simulink software.

The maximum power suitable for MPP is very susceptible to light as illustrated in Figure 4: when the illumination decreases from 100 W/m², power decreases by 10%. With cons, the maximum power decreases little with temperature particularly strong illumination. When the temperature increases from 10˚C to about the ambient temperature and illumination of 1000 W/m² power decreased by 4%.

The optimum voltage suitable for MPP varies very little with the illumination and decreases slightly with temperature as illustrated in Figure 5. For illumination of 1000 W/m² and around ambient temperature (25˚C): when the temperature varies from 10˚C, the voltage ranges from 4.2%. These results show that the voltage varies relatively little in the course of the day. Also, it is considered as a first approximation that the optimal operation of PV generator substantially corresponds to operation at constant optimum voltage.

The coefficient of maximum power point MPP and the optimal voltage linking the measured quantities and optimal variables is not always accurately fixed and little vary with time as a function of aging. It depends in particular on temperature and sunlight as illustrated in Figure 4 and Figure 5.

The chopper is a DC-DC converter for converting a DC power to a given level of voltage (or current) in a continuous energy to another level of voltage (or current). Use turns out necessary to store solar energy in batteries or to feed a continuous load equivalent circuit of the chopper is represented by Figure 6 and Figure 7 below. Two topologies of bass conversion circuit (DC/DC), choppers are DC-DC static converters for generating a variable DC voltage source from a source of fixed voltage. The chopper consists of capacitors, inductors and switches. All of these devices in the ideal case do not consume power, this is the reason why the choppers have good yields. Usually the switch is a MOSFET transistor is a semiconductor device mode (block-saturate), for our work we throw a glance on Boost and Buck converters.

The performance of the PV generator is evaluated according to the standard conditions (STC): irradiance 1000 W/m², and Temperature 25˚C. The performance of a PV solar system highly depends on the weather conditions, such as solar radiation, temperature and light, so does the performance of the PV generator degrade with increasing temperature, the decrease in intensity and the illumination load variations. To provide energy continuously throughout the year, a PV system must be properly sized and led by intelligent command to monitor MPPT for extracting the maximum energy. And for the simulation of DC-DC converters, we have shown by simulation that the average value of the output voltage can be adjusted by varying the duty cycle value. In perspective, this work will be continued with a practical realization of MPPT command based microcontroller and a follower by an Arduino board for increasing the efficiency of a solar system to extract the maximum energy.