# Determining Signatures for Energy Mix Produced by Photovoltaic Systems and Wind Turbines
## 4 Discussion
Figure 14 shows the clustering results for the time history of the power generated by the wind turbine. At night, only five cluster colors are clearly visible, which correspond to the very low and low power of the photovoltaic system (orange, light green, red, blue, and orange cluster). These colors indicate the complete or almost complete replacement of photovoltaic power by the power generated by the wind turbine. The remaining cluster colors indicate the complementation of one source by another. Replacement also occurs in the other direction. Classes with brown and dark green colors are often arranged close to the x-axis, which indicates a wind power value close to 0 or equal to 0, which is then completely replaced by the power generated by the photovoltaic system during the day. The occurrence of individual clusters in half-hour periods is shown in Figure 15. This graph clearly shows that only 5 out of 10 clusters (orange, light green, red, blue, and orange clusters) occur during the night. We can say that they are characteristic of the night. During the day, all clusters occur, although some very rarely. During the day, five clusters occur in almost all half-hour intervals (purple, mauve, pink, dark green, and brown clusters). We can say that these are clusters characteristic of the day. By clustering a selected photovoltaic system operating in an energy mix with a wind turbine, we create their unique signature. It depends on the size of both sources and their individual characteristics related to the design features and geographical context (location). Figure 14: Clustering results for the time history of wind turbine power. The clustering results, and thus the energy mix signature, can be influenced, for example, by changing the location of one or both energy sources. By making structural changes in the direction and angle of the panels, the final shape of the signatures can also be influenced. A popular procedure of this type is to install panels in the northern hemisphere of the earth in the east-west direction and not exactly south. Such a procedure allows an increase in the level of power generated by the photovoltaic system in the morning and evening hours, unfortunately, but at the cost of lower power generated at noon. In terms of balancing the energy system, this has its huge advantages. However, the authors will deal with this issue in the next article. In the analysis related to the complementation of various energy sources in the mix and their replacement, the time of the process in the individual clusters is important. It can be expressed as the sum of measurement points in the individual clusters (Figure 16) or the relative frequency of the process in the individual clusters (Figure 17). Both of these figures clearly show that for the longest time during the entire month, the process of energy production from the photovoltaic-wind mix was in the yellow cluster (cluster_7), which corresponds to very low and low photovoltaic power and very low wind power. This clearly means small amounts of power produced in both RES. The process in this cluster requires energy to be supplied from other sources or from energy storage. If we return to Figure 14, we will immediately see that the yellow cluster occurs only at night. The second largest cluster is the light green cluster (cluster_6), which corresponds to very low and low photovoltaic power, and low wind power. It differs from the previous cluster in the higher power produced by wind. The process in this cluster also usually takes place at night. It occurs very sporadically during the day. The third largest is the dark green cluster (cluster_0), which corresponds to high and very high photovoltaic power, and very low and low wind power. This cluster occurs only during the day and is the result of sunny and windless weather. The fourth cluster is the red cluster (cluster_1), which corresponds to very low and low photovoltaic power, and medium wind power. It occurs at night and also sporadically in the afternoon.