 Welcome to this learning unit in which you'll get an overview of the outside and the inside of the most common types of wind turbines. On the whole, these wind turbines look very much the same. However, you'll see that there are also some important variations. First, I'll give you some terminology of the components that can be seen from the outside. As you all know, these moving parts are the blades. The blades connect to the hub and together they form the rotor. The rotor connects to the nacelle which houses the machinery. The combination of rotor and nacelle is aptly called the rotor nacelle assembly, which is often abbreviated to RNA. The rotor nacelle assembly is supported by the tower and this rests on the foundation. The tower and foundation together are called the support structure. Sometimes you can recognize the housing of the transformer at the tower base. For an offshore wind turbine, this can be on the platform above the boat landing. Some offshore turbines have the transformer at the rear below the nacelle. If we open up the nacelle, we can see the drivetrain. The drivetrain is the assembly of all rotating components that are involved in the energy conversion. What you see here is traditionally the most common type of drivetrain, the drivetrain with a gearbox. On the left hand side, you see the hub that is connected to a low-speed shaft. The generator that is used in this drivetrain is a more or less off-the-shelf product and needs to rotate at a much higher speed than the rotor. Therefore, it is connected to the low-speed shaft through a gearbox. For multi-megawatt turbines, the gearbox increases the rotational speed by a factor of about 100. The nacelle connects to the tower top through the yaw system, which enables the turbine to align itself with the wind. You will recognize the outside of this type of turbine as many turbines of this type have been built on land. It has the shape of a camper van, but be aware it's usually much bigger. The drivetrain is an elongated assembly of several medium-sized components and therefore the nacelle is relatively long but not so high and wide. The next drivetrain has been a minority for a long time but is growing in popularity. The hub connects directly to the generator and there is no gearbox. This configuration is therefore called a direct drive. The direct drive is particularly gaining popularity for the offshore market. It is expected to have a higher reliability due to its lack of a gearbox and that should lead to less downtime and lower maintenance costs. The generator needs to be much bigger because of its low rotational speed and it is therefore much more integrated into the structure. As a consequence, this type of turbine doesn't have an identifiable low-speed shaft, with instead a large bearing to carry the rotor. As mentioned on the previous slide, the direct drive generator is very large. This can be seen on the outside because it invariably leads to nacelles with rounded forms. The large diameter of the generator is clearly visible while the nacelle is shorter for the lack of a low-speed shaft and gearbox. The third configuration for the drivetrain is a hybrid of the previous two. It does have a gearbox but a much smaller one. The rotational speed of the rotor is only increased by a factor of about 10, so 10 times less than in a traditional drivetrain. Therefore, the generator speed is higher than in the direct drive but lower than in the fully geared system. This leads to an intermediate size for the generator. At first glance, this system seems to inherit the disadvantages of both previous concepts. It still has a gearbox that can fail and the generator is not an off-the-shelf product. However, this type of drivetrain can be easily scaled to larger powers without excessive increase in the drivetrain mass. For the two previous configurations, the mass of either the gearbox or the generator would increase very much with such scaling. The hybrid drivetrain has a more equal distribution of its volume over width, height and length and is therefore very compact. Although it does have potential for large of your wind turbines, there aren't many around at the moment. So you won't commonly spot them in the field. The last drivetrain configuration that I show here is the exception to the rule that all components are aligned sequentially. Here you see four generators that are connected in parallel to the four outgoing shafts of the gearbox. Each generator has a quarter of the power rating of the turbine. In case one of the generators fails, the turbine can continue operation but with a slightly reduced performance. I show this drivetrain to you to make you aware that still new IDs keep popping up and old IDs are dusted off. These IDs especially deal with particular demands for offshore turbines. Every once in a while, such an ID gets taken a step further than just the drawing board and we may therefore see more changes in the future. In this video, you've seen several configurations of drivetrains. As you have seen, these drivetrains have many components in common but in a different configuration. When we are treating the individual components in the next learning unit, you'll be able to visualize how they fit in these configurations. I hope you enjoyed this topic. Thank you very much for your attention.