The efficiency of the photovoltaic energy conversion depends on the temperature significantly. We monitored the behavior of I-V characteristics of the PV cell based on monocrystalline silicon in temperature range with extreme limits from −170°C to +100°C. We have not yet found a similar measurement in this temperature interval. The temperature of PV modules without radiation concentration can reach values of −100°C to +100°C on the Earth's surface. The temperature range may be few wider in space. Changes of I-V characteristics and P-V characteristics are discussed in terms of the theory of solids. The open-circuit voltage dependence is approximately linear over a wide temperature range, but saturation occurs at temperatures around −150°C, which is also explained in accordance with the theory of semiconductors. The decrease in energy conversion efficiency with increasing temperature has a value of about 0.5%/°C throughout the whole temperature range possible on the Earth's surface. If there are large changes in the temperature of the PV modules during operation of the PV system, the electrical voltage of the PV modules will also change considerably. In space applications, these fluctuations may be greater. This must be taken into account when designing PV systems (especially for deep space missions). For example, electronic inverters are sensitive to overvoltage or undervoltage.

This paper shows the influence of grid frequency oscillations on synchronous machines coupled to masses with large moments of inertia and solves the maximum permissible value of a moment of inertia on the shaft of a synchronous machine in respect to the oscillation of grid frequency. Grid frequency variation causes a load angle to swing on the synchronous machines connected to the grid. This effect is particularly significant in microgrids. This article does not consider the effects of other components of the system, such as the effects of frequency, voltage, and power regulators.

Wireless sensor networks (WSN) have found wide applications in many fields (such as agriculture) over last few years, and research interest is constantly increasing. However, power supply to the sensor nodes remains an issue to be resolved. Batteries are usually used to power the sensor nodes, but they have a limited lifetime, so solar energy harvesters are a good alternative solution. This study provides a comparative analysis between battery and solar energy harvesters for sensor nodes used for soil water monitoring. Experimental results show that small-sized solar panels with low-power energy harvester circuits and rechargeable batteries distinctly outperform secondary batteries in outdoor and continuous-operation applications. The power level of the energy storage device of sensor node 1, which was powered by a small PV panel, remained constantly close to 90% for all days. The power of the other three nodes, which were powered by a rechargeable battery, was initially at 100% of the charge and gradually started to reduce. Sensor node 1 performed a total of 1288 activations during the experimental period, while sensor nodes 2 and 4 behaved satisfactorily and performed a total of 781 and 803 activations, respectively. In contrast, sensor node 3 did not exhibit the same behavior throughout the experiments.

In synchronous machines, electromechanical swinging can be damped by parametric control of the excitation current. This is possible only in case the excitation time constant is much smaller than the mechanical constant of the machine. The method described in this paper is effective for damping oscillations caused by oscillations in the grid frequency, grid voltage, and mechanical torque fluctuations. The method is based on the Lyapunov stability theory and demonstrated on a real synchronous machine. This machine operates as a noninterruptible backup power system. The original power fluctuations were up to 50% of the nominal power of the machine. With the described control, a sevenfold increase in the damping of fluctuations caused by grid frequency variations has been achieved.

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