This article presents a case study of a single-family house, whose current energy source is electricity only. Nine years ago, the heat source for the heating system and domestic hot water was an oil boiler, which was changed to an air–water heat pump. Four years ago, when Poland formed the basis of the prosumer market, the first photovoltaic system was established. It was expanded in the following years. In this work are presented the impact of using a heat accumulator on the coefficient of performance of the heat pump, the self-consumption of energy from the photovoltaic system, and the cost of purchasing energy. Comparative calculations were made, with the demand-side management (DSM) active on work days, and on free days (weekends and public holidays) it was not. Attention was paid to the self-consumption factor depending on the algorithms used in an energy meter. The prosumer market in Poland was also described. The calculations described the house as having an annual energy self-consumption from photovoltaic about 6% higher than average values obtained in buildings with heat pumps. Simultaneously, due to energy storage in heat and the load shifting in the multi-zone tariff, the cost of purchasing energy was 47% lower than in a single-zone tariff (without heat storage and load shifting).

This paper presents the results of analysis of energy and economic efficiency of the hierarchical gas-gas engine, with a note that a trigeneration system was analyzed, in which the production of electricity, heat and cold are combined. This solution significantly increases the energy efficiency of the gas and gas system compared to a system without cold production. The analysis includes a system comprising a compressor chiller which is driven by an electric motor in the system, as well as a system applying the mechanical work that is carried out via a rotating shaft of rotor-based machines, i.e., a gas turbine and a turboexpander. The comfort of the regulation of the refrigerating power rather promotes the use of a solution including an electric motor. Analysis contains also a schematic diagram of the system with a absorption chiller, which is driven by low-temperature enthalpy of exhaust gases extracted from a hierarchical gas-gas engine. Application of turboexpander with heat regeneration in the trigeneration system is also analyzed. Based on the multi-variant economic and thermodynamic calculations, the most favorable system variant was determined using, among others, the specific cost of cold production.

This paper contains the results of a study in which a novel approach using continuous time notation was applied in the search for the optimum capacity of a gas turbine designed for a dual-fuel gas-steam combined heat and power plant in a parallel system. As a result of the application of mathematical models of any functions that account for variations in time of all integrand quantities, for example prices of energy carriers, the model that was developed provides a way to analyze complex dependencies. The results of calculations obtained as a result of using this notation provide a rational selection of technologies and equipment designed for the energy industry. The results are based on an analysis involving a combined heat and power plant with an extraction-condensing steam turbine and extraction backpressure steam turbine for a wide range of the variability in energy prices and environmental charges corresponding to the current prices and environmental charges. All the curves were obtained using innovative methodology and mathematical model in which the total, discounted profit is calculated at the given moment and expressed as NPV achieved from the operation of dual-fuel gas-steam combined heat and power (CHP) plant.

As a result of the development of the up-to-date methods of signal processing it is now possible to obtain spectrum characteristics for any noise for a specific interval in time. Spectrum analysis which applies the combined time and frequency representations of noise can provide additional information regarding the amplitude, power and energy of frequency components found in a particular signal. This pa-per evaluates the possibility of time-frequency analysis application for overvoltage hazard due to lightning discharges in Distribution MV Cable Lines.