# <mark>1. INTRODUCTION</mark>

# <mark>1.1 PRIORITIZATION OF TRANSMISSION THROUGH BETTER PLANNING IS NEEDED</mark>

When it comes to decarbonization of the power sector, it is eminently clear that the primary focus ought to be on cleaning up the generation side, which includes scaling up renewable energy (RE) as well as phasing down of coal/gas plants. World Bank (2022) made this point emphatically during the COP27. There has been the desired focus initially on the RE scale up for at least a decade and increasingly on phasing down of coal over the second half of it – most prominently in some of the EU countries and the UK. The World Bank’s internal works on decarbonization pathways, accelerating coal transition (ACT: Huang et al, 2021), Country Climate and Development Reports (CCDR; World Bank, 2021-2023) and most recently the _Scaling Up_ work (World Bank, 2023) have also done a comprehensive array of analytical work covering these aspects. This paper highlights the importance of the transmission investments in upgrading and expanding the grid as they obviously play a critical role in reorienting the network to accommodate clean generation. In a decarbonized state, the transmission infrastructure often needs to connect to remote RE hubs and has a significant role to manage its variability amid other challenges. Transmission and distribution (T&D) network systems will, for instance, need to cope with higher and less predictable load (as EV, heating etc. loads get added), deal counterflows in traditional “one way” distribution networks, require significant digitalization, and smartening up to deal with a much greater degree of variability of both supply and demand, low inertia and reactive power deficient system. These roles are now widely recognized in the literature and practical ways to deal with these issues are being implemented in countries where the share of renewables has gone up. However, the role of T&D and particularly transmission as the key and the first enabler that should be on an equal footing as generation is somewhat understated. The central policy research questions that this paper address are (a) What categories of transmission projects should qualify as “green”? and (b) What should be the methodology to assess their benefits?

The process needs to start by planning generation and transmission together so that the complementarity of these two resources is fully captured, including the variable generation and load related issues that to a large extent require coordinated planning of the two. The fundamental point that coordinated planning of generation and transmission subsystems can lead to a cost-effective solution with or without any environmental considerations has, however, been well known to power system planners for several decades. Sophisticated research-grade methodologies that can do this has also been known for at least a decade. Linear/mixed-integer programming (LP/MIP) based models for generation or transmission planning models have been around for a long time, albeit the computational burden meant that the early models used a sequential method for the transmission plan to follow the generation plan. For instance, a nonlinear programming (NLP) based transmission planning model was proposed back in 1989 by Youssef and Hackam (1989) that can be solved sequentially taking a generation plan as an input. Bahinese et al (2001) and Akbar and Mina (2014) used MIP to undertake transmission planning. Leite de Silva et al (2010) have used meta-heuristic methods like the ant colony system to get around the difficulties of solving a very large combinatorial problem in a real-life system. Hemmati et al (2016) also use a particle swarm optimization (PSO) technique to solve the non-linear MIP model. Coordinated planning can lead to a better optimization of resources often reducing the need for generation resources with less capital-intensive transmission resources. The composite 2