Quantile integration order of decarbonized energy series using a Fourier function in the deterministic trend

The logic of analysing the stationary features in energy series lays in the policy potentials that unit root assessments confer. This paper identifies the integration properties of renewable energy consumption series in Germany, Italy, Poland, France, Spain, and Netherlands: six energy leaders but also top carbon emitters in the Schengen area. A stepwise integration property testing framework is applied on data spanning more than five decades. It includes a set of univariate unit root tests (ADF, PP, DFGLS, and Kwiatkowski-Phillips-Schmidt-Shin tests); stationary procedures allowing for endogenously determined structural breaks in the intercept and the time-trends (CMR, ZA); double breaks in the deterministic trend (LS); along with the Bahmani-Oskooee et al. (2017)'s extension of the Koenker and Xiao (2004) Fourier Quantile Unit Root test incorporating smooth breaks in the deterministic trend. In neither France, nor Italy, Poland, or Spain, renewable energy consumption series reject the null hypothesis of non-stationarity. This contrasts with German data displaying quantiles-varied integrational properties, whereas the Netherlands presents stable stationary features along each stage of the procedure. In addition to prospects for future research, policy suggestions involving bridging fuels are proposed to offer a secure and less volatile supply of green energies, reach IPCC climate targets, and avoid transitory shocks transmitted back to macroeconomic variables.