## 3 Results and Discussion
In the case of L days, there was a larger variation in the average value of the total daily irradiance value from L1 to L2 and L3 days. However, in the case of M days the average total daily irradiance values presented by the three groups were similar to each other, slightly higher on days with smaller fluctuations, and lower when there are more fluctuations; the same behaviour was found for H days. It was observed that the days within the three L-type categories, which are those with the lowest irradiance values, corre  
Figure 4.0 Results of the first classification of the days according to the total daily irradiance value using the k-means algorithm. sponded to days with passing clouds. There were hardly any days with daily irradiance values in the range belonging to L days that corresponded to clear sky days, so that in all three types, including L1, the passage of clouds and, therefore, fluctuations of irradiance values, were the most frequent situation, resulting in these low daily irradiance values. Figure 4.1 Sample of daily irradiance profiles obtained in the clusters L1, L2, L3, M1, M2, M3, H1, H2 and H3. Figure 4.2 Centroids of the daily irradiance profiles obtained in the clusters L1, L2, L3, M1, M2, M3, H1, H2 and H3. Figure 4.3 Total in-plane daily irradiance and number of days obtained in the clusters L1, L2, L3, M1, M2, M3, H1, H2 and H3. With respect to the type M or days with medium values of the total daily irradiance, the days with smaller fluctuations due to the lower cloud passage are within the M1 subgroup. In addition, in this M1 group, some clear sky days were obtained, which corresponded to the irradiance received by the panels in January and December, winter days in this geographical location, with a lower number of hours of sunshine than during the rest of the year, which, despite being clear sky, give rise to values of total daily irradiance in the range of the named medium days. In the M2 and M3 categories, as a result of the classification, the medium days which presented greater fluctuations in the irradiance values throughout the day, due to the passage of clouds, logically obtained the highest fluctuations in the M3 cluster. Within the H clusters, with higher values of total daily irradiance, the days that the algorithm considered to be within the H1 cluster corresponded to clear sky days or days with less cloud passage, with fluctuations increasing on H2 type days, and to a greater extent on H3 type days. The type of day with the highest incidence in this geographical location corresponded to H1 days, which account for 40.2% of the total of 3237 days analysed. Comparing M days with H days, it can be seen in Figure 7 how, in the irradiance profiles of H days, the daily sunshine hours were somewhat higher (with sunset taking place later and sunrise taking place before) than those of M days. Furthermore, it can also be seen that, in the irradiance profiles of M days, the passage of clouds resulted in lower irradiance values than in the fluctuations due to the passage of clouds on H days, with these values being even lower in the profiles of L days. Thus, it can be considered that the _k-means_ algorithm correctly carried out the classification of the daily irradiance profiles according to the total daily irradiance values and the fluctuations of the daily irradiance throughout the day. The applied technique can be considered to be robust and easy to apply [24; 25]. Once the classifications were made, the performance of the PV system elements was determined for each of the days obtained in the nine clusters. The results obtained for the average daily _PR_ value, corresponding to the operation of all modules together with the inverter, are shown in Figure 4.4  
Figure 4.5 Average daily performance ratio (_PR_) of the set of 26 PV modules together with the inverter in the clusters L1, L2, L3, M1, M2, M3, H1, H2 and H3.