After these three chapters devoted to The Physics of Semiconductors, we'll implement the concepts of physics that we have described in these previous chapters to treat the entire operation of solar cells. As seen in this animation, we'll thus discuss first, opticalization losses then, thermalization losses. Then we will look to losses is electron hot spot on metal semi-conduct contacts thus, describing the overall operation of the Solar cell. Before discussing the Physics of Solar cell, first, let's look at solar radiation which is available source of energy. Then, it will be seen as a principle of operation of the solar cell is the ideal case. The real case will first focus on the limits of the conversion efficiency and then to the solar cell optics and finally introduce the concept of photovoltaic module. Solar radiation is defined from two quantities which are first, irradiance in watts per square meter, which is a power density delivered by the Solar flux. This is an instantaneous quantity of power. The other is irradiation which is therefore the time integer of irradiance energy. These quantities depend on the time of day, day of the season on latitude of the location considered. The sun is refill from two different angles. Zenith and azimuth as shown in the figure. First, zenith which account for the height of the sun which is in fact the complimentary angle of elevation. When the sun is vertical the zenith is zero. And then the azimuth varies from east to west during the day. We will now focus on seasonal variations in solar irradiance which is illustrated in this animation, where we see the rotation of the earth around the sun during the 12 months of the year. The earth is tilted with respect to its plane of rotation, this is the origin of the various seasons. So for six months of the year, the Northern Hemisphere is oriented towards the sun and during the six months, it is the case of the Southern Hemisphere. We will look now at a few particular days which has the equinox on solstice as shown in the animation. Let's start with the autumn equinox. The autumn equinox as the particular idea that the sun x axis is located in the equatorial plane. So, as the length of the day is 12 hours, the Northern and Southern Hemispheres being equivalent. This equinox there at noon the zenith is equal to the latitude. For the winter solstice Nawfal Nemi sphere. So the celebration is minimum, it corresponds to the shortest day of the year. We take years example of the latitude of the complete eclipse, then we bust to the spring equinox which is exactly equivalent to the autumnal equinox the next 12 hours, then we arrive at the summer solstice the longest day of the year. Sanjayan is a Christian world which is illustrated in the mission. I summarize the previous data year. Data is zenith complementary of elevation on fine latitude. Again, taking the example of the location of polytechnique that is to say latitude 48.7 degrees. At polytechnique at summer solstice, the zenith is 23 degrees, that is to say the sun is high, is 67 degree at noon in contrast to the winter solstice, the sun elevation is only 18 degree at noon which is very low. An important element to describe solar radiation is called air mass that measures the amount of atmosphere caused by the sunlight. More specifically as illustrated in the figure. The air mass is the inverse of the cosine of the zenith. It is zero outside the atmosphere and then increases as a function of the inclination of the sun. If we consider a culprit technique as summer solstice at noon, which is the most favorable case, the air mass value is little more than one. As the winter solstice soars end of December, it is more than three. At the equinox the air mass is 1.5, this air mass ratio varies with the latitude obviously. This figure shows the evaluation of air mass in the Bruxelles region in Belgium on northern. Depending on the time of the day for all months of the year. The winter air mass is very large especially early on late in the day. It is larger than three even at noon. However, the closer you are to the summer solstice the more air mass is more. In June, July, even August, the air mass is smaller than two for most of the day. Let's consider now changes in azimuth of the sun from east to west. Here we present the border coordinates. The red arrow indicates the zenith year. We always consider the case of the Paris region. Contrary to what we often think, the sun does not rise in the East and sets in the West. This behavior is strictly to two days a year, so does with equinox. However, in winter, the sun rises in the southeast and sets in the southwest. Summer on the contrary, the sun rises at the northeast and sets in the northwest. Such data are affected by latitude. We investigated the Earth trajectory around the Sun. We will look thereafter to the solar spectrum on its variation, depending on the wavelengths of the light. Thank you.
