The paper presents results of a parametric analysis of a hightemperature nuclear-reactor cogeneration system. The aim was to investigate the power efficiency of the system generating heat for a high-temperature technological process and electricity in a Brayton cycle and additionally in organic Rankine cycles using R236ea and R1234ze as working fluids. The results of the analyses indicate that it is possible to combine a 100 MW high-temperature gas-cooled nuclear reactor with a technological process with the demand for heat ranging from 5 to 25 MW, where the required temperature of the process heat carrier is at the level of 650°C. Calculations were performed for various pressures of R236ea at the turbine inlet. The cogeneration system maximum power efficiency in the analysed cases ranges from ~35.5% to ~45.7% and the maximum share of the organic Rankine cycle systems in electric power totals from ~26.9% to ~30.8%. If such a system is used to produce electricity instead of conventional plants, carbon dioxide emissions can be reduced by about 216.03–147.42 kt/year depending on the demand for process heat, including the reduction achieved in the organic Rankine cycle systems by about 58.01–45.39 kt/year (in Poland).

A domestic hot water (DHW) system has been modernized in a multi-family house, located in the southeastern part of Poland, inhabited by 105 people. The existing heating system (2 gas boilers) was extended by a solar system consisting of 32 evacuated tube collectors with a heat pipe (the absorber area: 38.72 m2). On the basis of the system performance data, the ecological effect of the modernization, expressed in avoided CO2 emission, was estimated. The use of the solar thermal system allows CO2 emissions to be reduced up to 4.4 Mg annually. When analyzing the environmental effects of the application of the solar system, the production cycle of the most material-consuming components, namely: DHW storage tank and solar collectors, was taken into account. To further reduce CO2 emission, a photovoltaic installation (PV), supplying electric power to the pump-control system of the solar thermal system has been proposed. In the Matlab computing environment, based on the solar installation measurement data and the data of the total radiation intensity measurement, the area of photovoltaic panels and battery capacity has been optimized. It has been shown that the photovoltaic panel of approx. 1.8 m2 and 12 V battery capacity of approx. 21 Ah gives the greatest ecological effects in the form of the lowest CO2 emission. If a photovoltaic system was added it could reduce emissions by up to an additional 160 kg per year. The above calculations take also emissions resulting from the production of PV panels and batteries into account.