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Environmental degradation has become one of the major challenges facing the global community. This paper aims to explore the more effective options to combat environmental degradation by investigating the linearity and nonlinearity (trade openness set as a threshold variable) of energy efficiency, natural gas, renewable energy and ecological footprint. To this end, linear and non-linear panel models were constructed using panel data from 60 countries. The results of the linear analysis show that improving energy efficiency, and increasing the consumption of natural gas and renewable energy are conducive to inhibiting environmental degradation. Energy efficiency has the most significant negative correlation with ecological footprint, followed by renewable energy, and then natural gas, implying that improving energy efficiency and developing renewable energy is a more effective strategy to combat environmental degradation. The results of the nonlinear analysis show that there are threshold effects of trade openness between energy efficiency and ecological footprint, and between renewable energy and ecological footprint. The negative impact of both renewable energy and energy efficiency on the ecological footprint increases when trade openness exceeds the threshold. This suggests that, in terms of curbing environmental degradation, enhancing trade openness may further increase the negative impacts of energy efficiency and renewable energy on ecological footprint. At the same time, this confirms the positive role of trade openness in environmental protection. [Display omitted] • Exploring more effective option to combat environmental degradation. • Energy efficiency, renewable energy, natural gas can reduce ecological footprint. • Trade openness help energy efficiency, renewables lower ecological footprint. • The most effective strategy is energy efficiency, followed by renewables and natural gas. [ABSTRACT FROM AUTHOR]

In this paper, two generic photovoltaic (PV) panels (poly-Si and mono-Si) were experimentally tested in typical Mediterranean climatic conditions. The focus of the applied experimental approach was to examine the effect of backside convective thermal profile and its impact on temperature distribution, i.e. on panel electrical efficiency. Therefore, a series of measurements was made in 2015, from April to July, as well as CFD modeling in order to obtain a detailed analysis of the possible working regimes. According to the obtained experimental and CFD results, the present design of typical PV panels have an unfavorable impact on PV panel electrical efficiency. Namely, typical contemporary panel designs lead to two typical backside convective air temperature profiles which have a direct impact on the effectiveness of natural cooling. As shown in the obtained measurements, the specific convective profiles at the backside of PV panels have a significant influence on the degradation rate of panel electrical efficiency in the estimated amount of 2.5% up to 4.5%. The results of the research discussed in this paper signal the need to provide a possible redesign of the backside surface in conventional PV panels, in order to increase their average efficiency (more efficient backside thermal dissipation). [ABSTRACT FROM AUTHOR]