Green Transmission: Context, Rationale, and Planning Methodology

Transmission is a key enabler of clean generation as the lines and substations need to bebuilt first to encourage investments in generation. However, there has been limited attention to readying the gridthrough upgrades of existing transmission lines/substations and expansion of the grid. As a result, transmission hasbecome a major bottleneck, not only in developing countries, but also in their developed counterparts, including theUnited States, which has seen accumulation of 930 gigawatts of clean generation “queued up” waiting for transmission tobe built. To prioritize upgrading and expansion of the transmission grid, there is a need to adopt a more holisticsystemwide view from a long-term perspective and develop a methodology that recognizes transmission as an enabler ofclean generation. Such a methodology can be devised around a composite generation-transmission co-optimization model.This paper sets the context within which “green transmission” needs to be viewed and further proposes amodeling framework that brings together the critical elements in generation and transmission planning, includingsystem security constraints as a mixed-integer linear programming problem. The model formulation attempts tostrike a reasonable balance between the technical rigor of a network model and computational tractability. There are alsoimportant implementation details such as making the planning period sufficiently long to elicit the value oftransmission. The shadow prices of key constraints extracted from the model can be useful in prioritizing transmissionprojects, especially if the duals of transmission capacity and carbon dioxide limits are combined. These issues arediscussed around a set of illustrative examples. It is expected that the model and associated discussion would provide a starting point to refine the model further andapply it to practical case studies to develop a holistic definition of green transmission and sustainablegeneration-transmission plans.