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The experience of operating solar arrays indicates the need to solve the problem of creating effective and reliable switching elements to block defective and damaged photovoltaic cells. Available methods of solving this problem (for example, the use of transistor switches, electronic systems, etc.) either do not completely solve it, or are expensive. The tasks of increasing the reliability and efficiency of switching elements, preventing the destruction of photovoltaic cells which occurs during heating by dark current ("hot spots" and fire hazardous situations) are relevant. Recently, one of the promising solutions of this problem is the use of additional devices for isolating inactive (shaded or defective) areas of both separate photovoltaic cells and their modules. These devices are PPTC (polymeric positive temperature coefficient) resettable fuses of PolySwitch type, which are polymer composites with nanoscale carbon fillers. The basic functional property of PPTC fuse is an abrupt increase in electrical resistance by several orders of magnitude when a temperature is reached and a return to the initial high conductive state when the temperature drops. The advantages of such structures based on polymer composites with nanocarbon fillers include: – close to the metal resistance to the switching temperature and to the resistance of the insulator above the specified temperature; – possibility of realization in the form of discrete elements and continuous film-tapes (that is important at the decision of problems of realization of isolation of defective local area of the separate photovoltaic cell); – reaction in the form of temporary isolation of separate components of the solar array to increase their temperature. The research results are presented and the concept of overload protection by using resettable fuses based on polymer nanocomposite materials with nanocarbon fillers is substantiated in this paper. In particular, the expediency of series connection of PolySwitch fuses to photovoltaic modules with parallel connection of their strings is shown to prevent an abnormal situation, namely, a complete loss of electrical energy generated by such a string, which can occur when one of its modules is short-circuited. The circuit solutions in the form of combined structure based on layers of a varistor ceramics and a posistor polymer nanocomposite with carbon filler being in thermal contact are investigated. The prospect of its use to protect photovoltaic cells with a high reverse resistance from overvoltage is established. The problem of protection against local overheating in photovoltaic cells (or their parallel connections) by physical and technological methods, in particular, by creating photovoltaic cells with a built-in layer based on a posistor composite being in thermal contact with it, is analyzed. In general, the described results represent a new direction in the field of improving photovoltaic systems, in particular, in terms of increasing their efficiency, operating time and reliability by using solid-state devices based on polymer posistor nanocomposites and varistor ceramics as means of their protection from electrical and thermal overloads. Keywords: SOLAR ARRAY, PHOTOVOLTAIC MODULE, PHOTOVOLTAIC CELL, ELECTRIC OVERLOAD, POLYMER POSISTOR NANOCOMPOSITE, HOT SPOT, VARISTOR CERAMICS

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A relevant scientific-practical issue related to the sustainable development of outer space is the selection of optimal parameters of solar panels for the uninterrupted supply of energy in the power plants of spacecraft. It has been determined that advancing energy-efficient technologies is a prerequisite for ensuring stable space activities. The decision-making process regarding the choice of alternative options for ensuring the electrothermal protection of solar panels in the power plants of spacecraft occurs under the conditions of uncertainty and various risks. A methodical approach to assessing the effectiveness of options for building electrothermal protection systems for solar panels in the power plants of spacecraft has been devised. The hierarchical structure of the problem about approving of the choice of electrothermal protection of solar panels has been constructed on the basis of the method of analytical hierarchical process, which makes it possible to derive a set of optimal options. Five alternative options for electrothermal protection of solar panels have been chosen, which, unlike existing ones, take into consideration the phases of the life cycle, namely, the period of active operation. The selection of criteria for choosing the parameters of electrothermal protection of solar panels in the power installations of spacecraft has been substantiated: ensuring the smooth operation of solar panels; availability of service in emergencies; the life cycle of solar panels; the cost of solar panels; technical safety; mass-size indicators. It is argued that the chosen optimal alternative "Solar panels with protection on the basis of self-resetting fuses" could prolong the active life cycle and, as a result, reduce the number of repairs (current and overhaul) of solar panels in space activities. Owing to the use of this option, positive results could be achieved such an increase in the active life cycle by 20 %, as well as an increase in technical safety by 24 %