The global need for energy increases with mankind evolution and proliferation. The sharp decrease in fossil fuel sources and pollution increase, triggered research for renewable energy sources. The solar energy, available and sustainable, may be easily converted into both electricity and thermal energy. The photovoltaic paradox (need solar energy to function, but the electricity output decreases if temperature rises under the Sun's heat) was controlled by using various cooling techniques for panels. A large number of papers published to date in literature on solar energy conversion applications are reviewed and classified. The emphasis is placed on methods employed to increase the solar-to-electricity energy conversion efficiency, i.e. thermal management of photovoltaic panels. The use of thermoelectric modules (in PV-T-TE devices, photovoltaic-thermal-thermoelectric) is highlighted.

The progress of solar energy conversion technologies during the last few decades triggered the development of various types of collectors, thermal, photovoltaic (PV), or hybrid. In this paper, authors present the basic elements of thermal (energy and exergy) analysis solar collectors and their efficiency. The review of thermal analyses covers basic types of collectors and is extended to some constructive variations, e.g. with supplemental thermal elements (TEG). Thermal radiation proves to be the most important energy loss factor, due to the large temperature difference between the collector surface and the sky. To determine the total efficiency of solar collector operation, as a more complex analysis method of solar collector systems is proposed, to include economic, environmental and life-cycle analysis elements.

Implementation of the Energy Related Products directive in September 2015 had focused attention on the condensing boilers more than ever before since they are the unique boiler technology complying with the requirements of this new regulation. The main benefit of condensing boilers comes from the latent heat recovery by condensing the water vapors from flue gas; the higher the condensation fraction, the higher the energy saving is. The experimental study refers on the heat gained and fuel cost saving by condensing water vapors from flue gas in the case of a heating system with two condensing boilers having nominal outputs of 25 kW and 35 kW, respectively. The maximum condensation fraction of the heating system, determined in real operating conditions, was 0.52, which corresponds to an energy saving rate of roughly 2 MJ/m³ of fuel. The cost of the energy saved, converted into fuel saving cost, is 22.28 Euro/1000 m₃ for the natural gas price of 426 Euro/1000 m₃ (39.9 Euro/MWh or 0.01108 Euro/MJ) in Ia.i, Romania, February 2020.