Hello. Today we'll start, a series of courses, that are devoted to the physics of solar cells,based on silicon. Silicon is the most widely used semiconductor. To be simple, solar cells based on silicon, are almost all solar cells that you see around you. Before describing the physics of solar cells, we will introduce, the topic by addressing the energy on climate context, on the various forms, of use of solar energy. Photovoltaics being only one of the possible way, of the use of solar energy. At the end of the chapter, we'll discuss the current situation of photovoltaics worldwide, as well as future developments. Here,we present, the evolution, of the global, primary energy consumption. I show you the different forms of energy used on the evolution of consumption, over nearly, two centuries. It appears, very clearly, that these primary energy is mainly due, to fossil sources, coal, oil and gas. It is found out of the Second World War, a very sharp increase in the consumption of primary energy in the world. To understand the sudden increase in energy consumption, we present the evolution of the world population. The breakings of global energy consumption, corresponds, roughly, to described in the evolution, of the world population. It also presents, possible scenarios, of evolution, in the 21st century. The red curve, correspond to the extrapolation of the current trend, doubling, of the population at the end of the century. On the other two curves, more proactive scenarios in terms of birth control. So,remember, basic order of magnitude. In 2011, we passed the stage, seven billion people on the globe. And in 2050, we will be 10 billions, representing a growth of about, 50 percent. Energy consumption depends ofcos, of living level. It is higher per capital in developed countries, than in developing countries of Africa and Asia. But as a first order, energy consumption, follows, the evolution of the world population. Firstly, we have to face with a world population increase. The second element of context, is related to the limitation of fossil resources. This is what is shown in this graph, where the red curve, shows the accumulated consumption, of fossil fuels, since 2000. Compare, to global reserves. Overall, global reserves, are difficult to assess, precisely. For example, in the case of conventional oil, they can be evaluated to 40 or 50 years, given the current level of consumption. This number can be doubled if we take into account unconventional sources such as, shale oil. The case of gas, the resources are larger, probably 60 years. Should also take account of shale gas, which is not known with good precision. For coal when gets about two centuries, for the resource evaluation. The cumulative consumption curve seen here, that lies between the two extremes for 2050. So, to keep in mind a rough estimation, the fossil resources, if we continue to consume, energy, as we do now, will be exhausted by a little over, a century, with extraction costs probably increasing. Let us now focus on electricity, which represents a quarter of total energy consumption. This figure shows, the sources of production worldwide. Within a strong domination of fossil sources, coal, gas, oil. The type of power generation is strongly influenced by national policies. The case of China is displayed here. 75 percent of electricity, is generated from coal, without noticeable evolution. This feature explains the effects of pollution well known in China. In France however, 76 percent of the electricity pollution, comes from nuclear, 63 gigawatts installed. In contrast, the US production is better balance. Coal, accounts for nearly half, gas on nuclear roughly, representing the other half. Electricity produced from renewable sources, currently represent less than a quarter of the electricity in the world. As seen here, hydropower, is by far, the largest renewable source, followed by wind power. Currently, is the solar PV, represent a less than one percent, of the global electricity production. Thank you.