Recent extreme weather and disasters have been raising the awareness of the serious issue of climate change. The attainment of low-carbon energy, especially in renewable electricity (RE), is a key mitigation and adaptation goal under the United Nations Framework Convention on Climate Change (UNFCCC) and is therefore central to implementing the Paris Agreement. In general, policies to promote RE have produced uncoordinated, frequently high-cost measures. Large subsidies are usually necessary to give impetus to RE development. However, such a subsidy-thirsty regime may threaten the important world order of international economic law (IEL) and trade law. Recent cases in the World Trade Organization (WTO) concerning green-power industrial policies have signaled a paradigm shift in the conflict between trade and the environment. How to strike a balance between the international climate law regime and IEL will become more and more important in the future. The main purpose of this chapter is to answer the core question: Can a regional trade agreement (RTA), particularly a mega-RTA, contribute to RE development? And in what aspects? (For example, can it reduce tariff or non-tariff barriers?) This chapter also analyses the dynamic interaction between the IEL/RTA system and the regulatory regime of RE, where the regulatory regime involves incentives for and regulation of RE development. The second research question is: How are regulatory divergence and convergence affected by the IEL/RTA system?