# Determining Signatures for Energy Mix Produced by Photovoltaic Systems and Wind Turbines
## 1 Introduction  
With each decade of the 21 st century, humanity needs more and more electricity and heat [1]. Paradoxically, the increasing energy demand coincides with the need to reduce energy production from fossil fuels [2]. The greenhouse effect forces governments and entrepreneurs to limit carbon dioxide emissions into the atmosphere [3]. International organizations such as the European Union and individual countries have developed and are implementing strategies for decarbonizing the entire industry [4]. These strategies legally enforce the climate and energy transition of entire countries, individual industries, individual companies, and individual households [5, 6]. The question therefore arises: where to obtain large amounts of ecologically produced energy? Such energy can come from so-called Renewable Energy Sources (RES) [7, 8, 9]. These include primary energy produced from the sun by photovoltaic systems [10, 11, 12, 13, 14], wind energy produced by wind turbines [15, 16, 17, 18], and water energy produced by water turbines [19, 20, 21], especially Savonius type [22, 23]. What does humanity need electricity for and can individual RES provide such large amounts of it to meet the actual demand? Will it be possible to completely replace energy produced from coal, natural gas, and crude oil with green energy by 2050? Electricity is needed by individual households [24], institutions [25], and manufacturing companies [26; 27; 28; 29; 30] to provide lighting and power to various types of office equipment and production equipment [31]. The latter can be characterized by a very high demand for electricity depending on the industry. Therefore, supplying energy from renewable energy sources to homes, public institutions, and companies is a big challenge. Usually, distributed production of electricity from photovoltaic systems is used for this purpose. Photovoltaic panels placed on the roofs of houses, companies, warehouses, and shopping centers are able to produce large amounts of electricity. If someone does not have a roof surface, photovoltaic systems can be installed on the ground, water, or on special structures called carports [32]. Carports installed in parking lots produce electricity and generate shade for vehicles parked under them. Distributed systems generating energy from the sun are usually connected to the power grid (on-grid) and provide a large percentage of the required energy. Only where it is not available are off-grid photovoltaic systems used [33]. However, photovoltaic systems have one basic disadvantage--they produce electricity only when the sun shines. Therefore, at night and in some countries at certain times of the year, photovoltaic systems do not produce any energy at all or very little of it. Cyclicity due to day/night and seasonality due to the overlapping seasons means that photovoltaic systems are not sufficient to independently power individual homes, institutional buildings, and, above all, manufacturing companies with a large and continuous demand for energy. Energy storage systems (ESS) are a good solution for storing excess energy produced during the day and releasing it at night [34]. However, they are not able to store large amounts of energy over longer periods of time, such as months [35]. This is economically unjustified. Individual and collective transport of both passengers and goods is also very energy-intensive. Vehicles with internal combustion engines burning fossil fuels [36] are gradually being replaced by ecological electric vehicles [37]. Electric vehicles powered by electricity from renewable sources do not emit any pollutants into the atmosphere such as particulate matter, hydrocarbons, nitrogen oxides, carbon monoxide, and many other unregulated exhaust components [38]. They need an average of 15 to 20 kWh of electricity to cover a distance of 100 km. These are quite large amounts of energy compared to the total daily demand of apartments and single-family houses, which is on average 5 to 20 kWh [39].