Hello, and welcome to this course on grid integration of solar and wind energy. Over the next two hours, you will learn about the key ingredients and actors of the electrical grid, the challenges arising from large penetration of solar and wind power sources, and the main ideas to overcome them. But before we get started, a simple question has to be addressed. What is the electrical grid and why should we care about it? While a lot of emphasis is usually put on electrical sources, producing power is by no means the end of the story. The electrical grid includes what comes between power production and power consumption. This means much more than just a simple transmission line. Let's say that you've installed some power sources and you want to use them to power your household. Why can't you just connect the former to the latter? The key idea which will be repeated throughout this course, is that production must match demand at all times. It's not just an average energy balance must be maintained where production over the year should meet demand over the year, it's an actual power balance which has to be met at every second. This balance requires constant regulation, because both demand and supply can vary. Demand varies with human activities as appliances are turned on and off, but supply varies as well, especially with renewable sources which are sensitive to weather conditions. In the circumstance where supply exceeds demand, devices will be overloaded, and have to be disconnected to avoid heavy damage. If demand exceeds supply, there is of course not enough electricity to power all connected appliances. This would be inconvenient to watch this video, and it would have much deeper consequences for a hospital, for instance. But an electrical grid is not just a highway for electricity. It's a network that manages the permanent equilibrium between production and demand. It can be as small as a mini-grid connecting a single power source to a single household, or as big as a continent. As a matter of fact, the European grid is the largest industrial system on Earth. When everything goes smoothly, we don't even notice it, we don't even think about it. If you switch on an appliance, a power source somewhere is slightly increased to cover your needs. If you switch it off, a power source somewhere is slightly decreased. But when the balance between production and consumption is broken in either direction, the consequences can be dramatic. In the most extreme case, two large demand leads to such a strong stress on power generators. The turbines have to be disconnected to avoid permanent damage. As power sources are removed from the grid, the imbalance worsens, inducing a cascade of failures. The collapse of the electrical system is called, a blackout. A blackout can plunge the whole countries into darkness, and several dozens of hours can be necessary to restart the network. This graph shows, for instance, that the recovery of the national energy supply after major failures can take more than 20 hours. The repercussions on economics, infrastructure, and even public health can be severe. Such a catastrophe has impacted countries on every continent, and remains a threat for any electrical grid. Balancing demand and supply is not only a question of comfort but of national security. This critical issue has to be addressed in the context of increasing penetration rates of intermittent sources, such as solar and wind. Historically, most variations were due to consumption and supply had to be adjusted to follow the load. This plot shows a typical demand profile which varies throughout the day, with a consumption peak at 07:00 PM when people go back home, and throughout the year with a larger consumption in the cold, short days of winter than in the long, hot days of summer. In addition to these variations of consumption, solar and wind bring variations to the balance on the supply side and thus raise specific challenges. In most grids, solar and wind produce today only a small fraction of electricity and the challenges they raise or not critical yet. In France, the installed capacity of wind and solar is currently around 25 gigawatts and could be easily doubled without major adjustment of the infrastructure. But there shares intended to grow by a factor of five in the next 15 years. This leaves no doubt that integration challenges, must be addressed immediately if we want to achieve a vast deployment of renewable sources, without compromising the electrical grid. How to ensure a constant balance between production and consumption with an increasing share of intermittent sources is a difficult question. To contribute efficiently to the energy transition, renewable sources should not be treated only from the supply side, they have to be considered as part of an electrical grid. The purpose of this course is to introduce you to this perspective. To do so, we will first present electrical grids in more detail, including the main physical, economical, and political actors of this plate. We will then discuss grid stability, why is it so important, and how is it currently insured? This will allow us to highlight the specific challenges raised by solar and wind electricity, before we give an overview of current trends considered to face these challenges.