Hydropower is the world's most exploited renewable energy source. It provides a substantial, flexible, and reliable source of renewable energy, complementing other renewables like solar and wind power. Besides conventional hydropower potentials and technologies, the development of technologies for the exploitation of hidden hydropower potentials is an ongoing process. This paper presents the current state of hidden hydropower technologies and links them with possible applications in different hydropower potentials. Technologies and potential applications are structured within three main groups (pressurized systems, hydro storage, unpressurized systems), with their mutual interconnections analysed and displayed throughout the paper. The opportunity for the application of hidden hydropower technologies in different roles within the energy system is recognized through the concepts of off- and on-grid roles, the prosumer concept, and on-site measurement powering. This paper shows that hidden hydropower technologies could emerge as significant contributors to a smoother energy transition, especially with the prosumer and off-grid concepts.

Single axis trackers have their application in the efficiency improvement process of photovoltaic systems. In spite of large investment costs, their application is necessary in the areas with a low amount of available solar irradiation. This is applicable only if it is required to exploit all available energy sources at any cost. With optimization and improvement of these systems it is possible to increase their efficiency, reduce energy usage for their movement and improve system reliability. Motion parameters are significant for the optimization of the system. It is necessary to set and monitor the right parameters as a prerequisite for system optimization. The process of calibration of single axis tracker prototype is shown in this paper. It is shown that proper calibration and system adjustment could improve efficiency of the system.

Characteristics of the vibrations of rotational systems with misalignment and rotating looseness are well known and they are used for fault detection in the rotating machinery. For the better understanding and easier decision make in the fault removing process it is necessary to know how severe each fault is. Lack of procedures for quantification of this faults in rotational machinery is evident. In this paper is investigated the possibility for use of multiple regression analysis for determination of quantity of faults in vibration velocity signal. An experimental motor – coupling – rotor system is created and produced. These systems have capability of changing the values of misalignment and rotational looseness. Measurement of vibrational quantities were conducted on these systems by using piezoelectrical accelerometers for different combinations of fault values. All measurements were stored and processed digitally. All measurements have shown the presence of the main characteristics of introduced faults. It is confirmed that it is not possible to use RMS (root mean square) of vibration velocity, since there is a lot of other factors which has significant impact on the vibration quantity.

Knowing all characteristics of rotational system vibrations is most significant for a maintenance technician or engineer. Vibrations are carriers of a machine condition and by analysis of the vibration characteristics, it is possible to find what is the real cause of the vibrations. As a part of the research of rotational machinery vibrations, mathematical modeling of a rotational system is common tool before research is transferred to a real physical model. As an excellent method for this purpose, the best candidate could be a Finite Element Method. In this paper, an analysis of a Finite element model of rotational system motor – flexible coupling – rotor is presented. As a fault analyzed in this paper, misalignment and rotating looseness are modeled as external loads. For this FEM model of a rotational system is shown that it is suitable for the analysis of rotational machinery vibrations.