The effectiveness of R&D investments for efficient energy use in Türki̇ye: A recent fourier approach on renewable energy use, energy prices, energy imports, and foreign direct investment

The increasing demand for energy in Turkey, dependence on external sources, and the necessity of sustainable environmental policies have made the effectiveness of R&D investments focused on energy efficiency a strategic policy area. This study examines the effects of foreign direct investment, energy prices, energy imports, and renewable energy use variables on energy efficiency R&D investments using annual data from 1990 to 2022. The theoretical framework is built upon the Resource-Based Approach, the Sustainable Development Approach, Porter's Hypothesis, and the Endogenous Growth Theory. The stationarity levels of the series were analysed using ADF and Fourier ADF tests; long-term cointegration relationships were investigated using Fourier Engle-Granger and Fourier ADL tests. Long- and short-term coefficient estimates were obtained using FMOLS, CCR, and DOLS methods. The findings show that foreign direct investment significantly increases the effectiveness of energy efficiency R&D investment in the long term, while energy prices encourage the effectiveness of energy efficiency R&D investment in both the short and long term. The use of renewable energy has a positive effect on the effectiveness of energy efficiency R&D investment, while energy imports have been the main factor reducing effectiveness in both periods. Consequently, it has been determined that the success of energy efficiency policies depends not only on the level of expenditure but also on the tangible efficiency and environmental gains generated by each unit of R&D resources. In order for Turkey to advance its energy transition in a sustainable manner, energy efficiency R&D policies must be implemented within a long-term, stable and technology-focused strategic framework.