# Determining Signatures for Energy Mix Produced by Photovoltaic Systems and Wind Turbines
## 1 Introduction
A city bus already needs about 100 kWh/100 km but is able to carry more than 50 people on board [40]. Electric vehicles demand electrical receivers because they need not only large amounts of energy but also high charging power to ensure a short charging time for the vehicle's traction batteries [41]. Currently, electric passenger cars are charged with power reaching 350 kW [42]. They allow the battery to be charged from zero to full in a period of several minutes [43]. This means that photovoltaic systems capable of producing very large amounts of energy with high power must occupy areas of even more than 1 ha. In the case of charging vehicles with energy from photovoltaic systems, we struggle with the same problem of energy availability only when the sun is shining. In the case of using energy storage facilities, their size and therefore their cost will be very high. Therefore, scientists and engineers have proposed the use of renewable energy sources to produce a medium that will be both a good energy carrier in the long term and a good fuel for vehicles. Hydrogen was chosen as the fuel of the future [44; 45], because of its physical and chemical properties [46; 47]. Hydrogen produced by electrolysis [48; 49] from commonly available water can be stored in pressure tanks (up to 700 bar) or in cryogenic tanks and safely transported even over long distances [50; 51]. Electricity and heat can be obtained from hydrogen in hydrogen fuel cells, which are available in both stationary and mobile forms and intended for powering vehicles [52; 53]. Hydrogen produced from surplus energy produced from photovoltaic systems can be used on the same day or at any time [54]. There are low-power hydrogen fuel cell systems (up to 10 kW) capable of supplying electricity and heat to small single-family homes and high-power systems (over 100 kW) capable of supplying larger buildings, passenger cars, and buses [55]. The production of electricity by photovoltaic systems requires balancing the power grid in order to stably supply electricity to all receivers connected to it [56; 57]. This is achieved through appropriate management of energy produced from various renewable energy sources and energy produced in combined heat and power plants from coal and natural gas [58]. Currently, balancing energy produced from photovoltaics with energy produced from water or wind is of great importance [59; 60]. Hydroelectric power plants are usually built in large dams accumulating water from rivers, as is the case, for example, in Aswan in Egypt or on the Solina reservoir in Poland [61; 62]. The energy produced by wind turbines is of great importance in balancing energy from photovoltaic systems [63; 64; 65]. The authors have already repeatedly proven in an analytical manner that effective energy balancing is possible in the case of using a photovoltaic-wind energy mix supported by a small energy storage [17]. In many European countries, including Poland, you can see views such as the one shown in Figure 1. Photovoltaic-wind systems are used to supply entire cities and/or manufacturing companies with electricity both during the day and at night [66; 67]. In Poland, in the Lublin region, preparations are currently underway for the production of low-emission hydrogen at the place of its future use and the implementation of  
* infrastructure for the evacuation of power from renewable energy sources located in the region to future locations for the production of green hydrogen, and
* creation of infrastructure for the production of green hydrogen on an industrial and municipal scale, and importantly, located near future hydrogen recipients. The infrastructure for the evacuation of power, referred to above, is internally called the half-ring of the Lublin Hydrogen Valley and according to the currently implemented project, has a length of up to 100 km [68]. The half-ring of the Lublin Hydrogen Valley will be open to the connection of renewable energy sources, energy storage facilities, and the supply of electrolyzers belonging to external entities.