[MUSIC] Imagine for the time of this session that you are an industry. You want to estimate what energy can be produced with the particular wind turbine on a particular site. This is what we will do in the next quiz. So performing such an evaluation, you need two things. First, the characteristics of the wind turbine. If you take the catalog of a large company that produces wind turbines, you find turbines whose height varies between 50 meters and 200 meters with rated power between 300 kilowatts and 8 megawatts for the largest ones. We are going to consider an intermediate wind turbine with a rated power of 2 MW and a hub height 140m above the ground. The important characteristics you need to estimate the power production, is the power curve of the wind turbine. Here is a typical power curve of a real 2 megawatt wind turbine. It gives the power that can be collected by the turbine as a function of the wind speed. Let's see in more details the characteristics of that curve. To be able to perform computations, we have used a piecewise-defined function to model very well, the empirical power curve of a real wind turbine. First, for wind velocities lower than 11 meters per second, the power curve follows a cubic law. Note that we have made the approximation that there is no cut in speed since with this model the energy that corresponds the velocities lower than 2 meter per second is less than 10 kilowatt, the error that we make is negligible. For velocities between 11 and 25 meters per second, the power curve reaches a plateau where the energy produced corresponds to the weighted power, that is to say, 2 megawatt. 25 meters per second is the cut out velocity for wind faster than the speed, the wind turbine is stopped and produces no energy. This is all what you need to know on the characteristics of wind turbine. The second data needed to estimate the energy production of a wind turbine are the characteristics of the wind on the site. The second data needed to estimate the energy production of a wind turbine are the characteristics of the wind on the site. We consider again the site of Sirta where you have studied in the previous session the wind distribution probability. Remember, previously you have obtained at the altitude of 140 meters, three kinds of data, first the histogram of the wind velocities measured directly at 140 meters. Second, a fit of this data to a Weibull distribution, this is a curve in red. And third, we imagine the case where it was not possible to measure directly the wind speed at 140 meters. This is a very usually case for industries. In that case, you have extrapolated the Weibull distribution at 140 metres from the wind velocity's measures they're formed at 40 meters which is the curve in green. What you're going to do in the next quiz is to use the three different data along with the power curve to compute the energy that can be produced over one year by the wind turbine. With the histogram of wind distribution, you can compute that energy E, by summing over the bin of the histogram the number of times Ni where the velocity Vi was observed times the power of P( Vi) associated to that velocity. Multiplying the result with the averaging time delta t which is 10 minutes, you deduce the energy produced in one year. With the probability density function, you compute the energy by first integrating the power P(V) times the probability f(V) of offsetting the velocity over all possible velocities. Multiplying that power by the total time T, which is here, 1 year, gives the energy produced. You will use this method for the direct Weibull fit and for the the extrapolated Weibull low. The interest in doing the free methods is that you can have an ID of the error made by indirect method. First, when you compute the energy that you can produce directly from the experimental measures, this is the more accurate estimate. Second, when you used Weibull fit, the accuracy of the energy production estimate depends on the quality of the Weibull fit. Finally, when you use a Weibull distribution function extrapolated from a different height you expect to make a small error. But this is not a problem as long as you quantify it. Keep in mind that in particular cases, industrial often used indirect method with energy production before starting the wind turbine. Now, you can move to the quiz to compute yourself what is the precision of the different methods. By doing so, if one day you work in the field of wind energy, you will be aware of the confidence one may have in the energy production estimates.