# Possibilities of Powering Military Equipment Based on Renewable Energy Sources
## 2 Literature Review
### The Use of Photovoltaic Cells
The exposition of a PV panel to solar radiation causes its temperature to rise significantly above the ambient temperature. Figure 1 shows a PV panel exposed to solar radiation at the ambient temperature of about 15 \({}^{\circ}\)C with variable cloud cover. The thermographic image taken after 2 h of exposure to solar radiation indicates that the temperature of the PV panel differed from the ambient temperature by 12 \({}^{\circ}\)C, leaving a clear thermal trace. Intelligent power supply systems in military applications are becoming a feasible reality [21]. The supply of fuels intended for feeding diesel-electric units in subunits' operation areas may be difficult or even impossible. Therefore, the use of energy-saving power receivers and a hybrid power supply reduces the demand for diesel and gasoline, which translates into lower operating costs and reduction in the number of possible convoy losses [2; 21]. As part of the NATO Smart Energy program, in countries such as Greece, Germany, United Kingdom, the United States and the Netherlands, intensive research is being carried out and projects for field energy systems are being developed [21; 22; 23; 24; 25; 26; 27; 28]. Poland also wants to join the group of users of similar energy systems on a daily basis. This has resulted in an urge to present selected solutions based on solar panels, which are currently used in other NATO countries. For several years, the German Bundeswer has been equipped with Multicontanier MC66 mobile solar containers [2; 29; 30]. The MC66 PV system includes 66 PV panels, each with a capacity of 300 Wp, which allows for a maximum power of 19.8 kWp. Electricity is stored in a 30 kWh LiFePo4 battery. The PV MC66 system can work independently as well in cooperation with the generator. Everything is stored in a standard container. The set is intended for supplying command posts and military bases [2; 29; 30]. British troops were equipped with a compact photovoltaic power plant by Renovagen Roll-Array of the RAPID Roll system, which is produced in three power options (3.6 kWp, 7.2 kWp and 11 kWp) [22]. The manufacturer has used the flexible PV cells technology. The RAPID Roll 11/120 system consists of a foldable PV panel with a power of 11 kWp, occupying an area of approximately 100 m\({}^{2}\), and an energy storage with 124 kWh, using lithium-ion batteries [22]. Everything is located in the RAPID ROLL \"T\" trailer-towed by a 4 \(\times\) 4 vehicle. The system can cooperate with field power systems powered from mobile sources of energy [2; 22] and is intended to power small military bases [22]. The authors of this study had two basic questions:  
1. If the lithium-ion battery is used, and the battery capacity is particularly large, how to solve the irreversible problem of overcharge and over-discharge? (There is still no clear answer since testing is still going on). 2. How to solve the possible fire and even explosion risk of battery overheating? (Fire protection measures are used at command posts). Figure 1: PV panel-thermographic image (source, prepared by the authors). The described systems are intended for supplying command posts and military bases. For small sub-divisions carrying out missions and long duration, Thales Defense & Security Inc. has designed the Expeditionary Modular Universal Battery Charger (EMUBC). This device combines the functions and capabilities of many battery chargers used by the US Army in one product [18; 19]. The EMUBC charges electricity from the grid, from batteries, and from flexible PV panels. The charger weighs less than 3 kg and can be carried or installed in military vehicles. In the United States, research is being conducted on the Soldier Worn Integrated Power Equipment System (S.W.I.P.E.S.). As part of this program, the US Army is using over 7500 sets [18; 19]. All elements of the SWIPES system are mounted into a tactical vest.