We will now deal with the solar spectrum which is shown in these figures. The yellow curve corresponds to the black body radiation at 5900 degrees k yellow color. So, orange column matches the solar spectrum outside the atmosphere. So, it correspond to 1.3 kilowatts per square meter. The spectrum outside the atmosphere follow very well the Planck's law, so as your first order system the AVs as the black body. Then, the radiation is affected by the interaction with atmosphere. It is revealed by the third spectrum, sea level AM equal 1.5. Ultraviolet part is absorbed by the atmosphere, this is due to absorption by ozone. So, you have violet contributions that correspond to the most energetic photons more than three AV, represents only five percent of the spectrum. The visible range blue to red from 0.4 to 0.75 microns, 40 percent of the radiation. Then, the spectrum hazard tail is inside, which represents more than half of the solar spectrum energy. The infrared portion more than 0.75 micrometer displays absorption bands relative to the absorption of photons by either the CO2 or the water vapor. Solar modules are characterized in normalized conditions given here. This radiation absorption phenomenon by gaseous molecules can be explained quite simply. Consider the case of a CO2 molecule which consists of two double CO bonds. These bonds have vibration modes is inside. The infrared photons at this energy will excite these vibration modes, CO, HO, and so on, and will therefore be absorbed. This is also the case for SIO2 glass, that for the same reason, absorption is infrared. This is the origin of the greenhouse effect. The gas or CO2 is transparent in the visible black body at 5900 K, but absorbs infrared and beyond tradition at 300 K, resulting in over 18. Another node is the course of semiconductors. We often mention energies showing electron volts. However, the solar spectrum is usually describing from wavelength. So, wavelength is the inverse of the energy. To easily switch from one to the other, we must remember that E, electron volt is equal to 1.24 over Lambda, the wavelength in micrometer. For example, the energy of a blue photon 0.4 microns, correspond to three ev, for red light wavelengths around 0.6 micron, so energy is two ev. We present here, is a variation of the solar spectrum as function of the air mass ratio out of atmosphere AM0. So, integrating radiation is 1.3 kilowatts per square meter. At AM1, the sun at its zenith, the power density is slightly less than one kilowatt per square meter. The standard solar module performances at recorded at AM1.5 curve three, and curve four corresponds to AM2. That is to say, at lower son elevation, AM2 corresponds to less than 700 watts per square meter. The comparison of the values curve shows that the high energy part of the spectrum is preferably absorbed by the atmosphere. This is why when the sun at sunset, high-value AM appears red or reddish. So far, we have considered only the direct solar radiation, but the sensor such as a photo dice is sensitive to all components of the radiation. Direct radiation is the one coming directly from the sun, but part of the solar spectrum that is scattered in the upper atmosphere for example by aerosol or water vapor droplets. The so-called Rayleigh's scattering, which varies as Lambda to the minus four. So, Rayleigh's scattering tends to preferentially affect high-energy photons, which explain the blue color of the sky. Also, satellite can be scattered by other elements such as clouds and so on, as shown here. This diffusion can be more or less isotropic. Albedo corresponds to the ground reflection with an angular on spectral dependence strongly affected by the soil. For example, in the case of snow. The optical concentration mirrors, lenses, concerns only direct radiation and only marginally affect the scattered radiation. All the components mentioned above vary considerably depending on the time of the day, on weather conditions. I represent data recorded on the compass of a culprit technique in summer. The blue curve corresponds to direct radiations, diffuse radiation in red and the green one to the irradiance on the horizontal plane, down welling. The first recall August 11th, corresponds to a clear day with some clouds in the afternoon. Direct radiation almost reaches one kilowatt per square meter at noon while the diffuse radiation is low under 10 percent. So, next day is a cloudy day, or probably rainy especially in the afternoon. Direct radiation in blue becomes very small, and diffuse radiation in red becomes dominant close to 500 watts per square meter. Cloudy crossing so greatly affects the impinging solar energy. It's coercion into electricity therefore affect significantly the power grid. We treated during the seconds, the solar spectrum, that is to say, the available energy. We will look subsequently to the operating principle of solar cells. Thank you.
