**5. Conclusion**

Numerous DEA studies have incorporated the concept of production activities with multi‐ ple phases. They subsequently divided the DEA model into several sub-processes [60] [55] [33] [61] [62] [19]. Our first finding in this research is that there is a significant difference be‐ tween OE and DE. In other words, sub-process DEA model is suitable for measuring man‐ agement performance because of the characteristic of production activities in renewable energy industries [61].

OECD countries in response to United Nations climate Change Framework Convention and the relevant provisions of the Kyoto Protocol, In addition to adjusting the energy supply and demand side policies, and with the greenhouse gas performance of fiscal policy (subsi‐ dy) to promote energy conservation and reduce dioxide emissions [63]. Our second finding is that subsidies are positively correlated with OE and negatively correlated with DE. Pro‐ moting subsidy policies can reduce industrial production cost. However, if they are imple‐ mented inefficiently without carefully assessing the cost-efficiency and associated financial risks, a "free rider" phenomenon is created with consequent disadvantages; thus, the subsi‐ dies do not have a positive benefit. Therefore, renewable energy subsidies and DE may be negatively correlated [59].

In our study, we attempted to measure OECD countries' renewable OE and DE simultane‐ ously, to examine the OECD renewable energy's promote, employ, and the relevance to the development of research, and provide feasible suggestions for a renewable energy develop‐ ment strategy in Taiwan. For example, because Taiwan is an island country, and resources are difficult to obtain, efforts should be made to actively develop renewable energy technol‐ ogy to replace traditional energy sources. In addition, policy-makers should assess renewa‐ ble energy subsidy programs, promote renewable energy industry research and development, assist the industry in developing cost-efficient production technologies, and develop a new energy market. Furthermore, strengthen the use of renewable energy demon‐ stration and propaganda work, and to enhance the efficiency of the client to use.

Finally, this study has several limitations that require discussion. First, only 34 OECD sam‐ ples were selected that could provide the data required to conduct this study. Future re‐ search could include more countries, especially developing countries, such as Taiwan, China, and India to achieve more precise results. Second, non-financial data such as output quality and investment of renewable land were not included in our model. These variables are also critical factors for the evaluation of energy industry performance. Future research could include this as an additional evaluation variable. Finally, in this study, we independ‐ ently tested and verified the two phases of efficiency. However, future research could use a supply chain model that assumes that the two phases of efficiency are dependent and fur‐ ther evaluate the real scores of management efficiency.
