New Delhi, Oct. 10 -- India's race to expand clean energy is running into a transmission bottleneck. Even as new power generation capacity has nearly tripled to 26.8 GW so far this fiscal year, expansion of the transmission backbone is faltering. Just 1,998 circuit kilometers (ckm) of new lines were added till August, 30% less than a year ago, against a full-year target of 15,382 ckm, according to data from the Central Electricity Authority (CEA).

The gap between generation and transmission is already stranding projects. A JMK Research study estimates that nearly 50 GW of renewable capacity nationwide cannot be evacuated because of inadequate infrastructure, inflating per-unit transmission costs, weakening project viability and deterring...