# Determining Signatures for Energy Mix Produced by Photovoltaic Systems and Wind Turbines
## 4 Discussion
The fifth cluster is the brown cluster (cluster_2), which corresponds to medium photovoltaic power, and very low and low wind power. The power generation process classified into it takes place during the day, from early morning to evening. The blue cluster (cluster_4), which corresponds to very low and low photovoltaic power, and high wind power, has a slightly smaller share. It occurs at night  
Figure 15: Clustering results in half-hour periods. and sometimes in the early afternoon. The seventh cluster is the orange cluster (cluster_5), which corresponds to very low and low photovoltaic power, and very high wind power. It occurs almost exclusively at night during very windy weather when the wind turbine is operating at its highest power. We have three more clusters left, which occur during daylight hours. The eighth cluster is the pink cluster (cluster_8), which corresponds to high and very high photovoltaic power, and medium wind power. It occurs during the afternoon hours when the generation of power from the photovoltaic system is the greatest, and, in addition, it occurs with quite a strong wind. It must be remembered that the wind cools the photovoltaic panels, which contributes to work with greater efficiency and with greater power. The ninth cluster is the purple cluster (cluster_3), which corresponds to medium photovoltaic power, and medium wind power. It also occurs only during the day, but in a wider hourly range than the pink cluster. The last largest cluster is the mauve cluster (cluster_9), which corresponds to high and very high photovoltaic power, and high and very high wind power. It means the largest capacities generated by both RES. The heat map showing the number of records in individual clusters and in individual half-hour time intervals is shown in Figure 18. The numbers of records belonging to individual clusters presented on it additionally enrich our knowledge about the course of the process of generating power from photovoltaic and wind mix sources. The data presented in the form of a heat map in Figure 18 clearly show that the process of generating power from the photovoltaic-wind mix is very often present in cluster_7 in the morning hours. It is responsible for generating very low and low photovoltaic power, and very low wind power. This means that it is necessary to balance energy during the period of its highest price when purchased from the power grid. A large number of records in the morning hours in cluster_7 requires the use of an energy storage system. Occurring more than 10 times in half-hour periods of presence can also be seen in cluster_2 in the later morning hours (8:00-9:00) and in the afternoon hours. It is responsible for medium photovoltaic power, and very low and low wind power. These states also require additional energy from the power grid or ESS. But where to obtain the energy for charging the energy storage? The answer can also be found on the heat map. During the day, the  
Figure 16: Sum of measurement points in individual clusters. most frequent occurrence of the process is in cluster_0. It is responsible for high and very high photovoltaic power, and very low and low wind power. Surplus energy produced at noon by the mix will be used to charge the energy storage. The signatures related to the presence of the power generation process in individual clusters can be assigned appropriate energy management strategies. The mauve and pink clusters will require storage of the excess energy produced by the energy mix, which can be returned to the process during its arrival in the yellow and light green clusters. The analysis of the signatures of energy production from the photovoltaic-wind mix can be supplemented with a transition diagram between individual states (clusters). But this will  
Figure 17: Relative frequency of a process’s presence in individual clusters. Figure 18: Heat map showing the number of records occurring in individual clusters and in individual half-hour time intervals. be dealt with by the authors in the next article.