Nepal's NEA rules out winter load-shedding, plans 1,154 MW of imports

What happened

On 26 August a flood on the Bhote Koshi destroyed the 220 kV Upper Trishuli-3B hub substation in Nuwakot. Plants with 176.1 MW of capacity were not damaged but could no longer send power to the national grid. According to the Post, more than 256 MW of national generation was damaged in the disaster. At a meeting in September, the NEA decided to speed up its preparations for winter supply.

Managing Director Dirghayu Kumar Shrestha said there would be no winter load-shedding. The NEA formed a five-member committee, coordinated by the director of its Bagmati Provincial Office. The committee must send daily progress reports and raise problems at once. The NEA also set deadlines for finishing transmission and distribution projects in Kathmandu Valley before winter demand rises, and sent a team to check whether the damaged Devighat substation can be restored.

More floods followed. Khabarhub reported on 28 September that rain from 25 September had shut more plants. At that time eight projects with 230 MW were out of operation. Damage to towers on the 220 kV Kaligandaki corridor line in Myagdi blocked 190 MW from seven plants. Khabarhub said 430 MW from the Bhote Koshi and Trishuli area was still out of the system. Some losses from the second flood were short. By the same report, 262 MW had restarted on the Seti and Madi corridors and 190 MW on the Marsyangdi corridor.

The engineering behind it

The key idea is the gap between installed capacity and firm capacity. Installed capacity is what all plants could produce together at full flow. Firm capacity is what they can be relied on to produce when conditions are poor. According to the NEA plan reported by Khabarhub, Nepal has 3,739.40 MW installed and expects about 320.60 MW more by Mangsir, for roughly 4,060 MW. Only about 30 percent of this is available in the dry season.

The reason is the river. A run-of-river plant uses the water that flows past each day, with little or no storage. When river flow falls after the monsoon, such plants lose much of their output. The NEA figure of about 30 percent shows how much of the national capacity depends on that flow, because only the Kulekhani reservoir can hold water back for winter. The NEA expects 1,218 MW of domestic generation this dry season.

Storage is the other tool. The Kulekhani cascade in Makawanpur has three plants of 60, 32 and 14 MW that use the same water one after another, for 106 MW in total. It is fed by the Indra Sarobar reservoir and is normally saved for the dry months. The Post reported on 12 September that all three plants were running around the clock to cover the flood loss.

That choice has a cost. According to the Post, continuous running lowered the reservoir by 20 to 25 cm a day, while inflow added back only 15 to 18 cm. Silt has also cut the usable depth from 57 m at commissioning in 1982 to about 46 m. Water used in the monsoon is water that cannot be used in January.

What it means in Nepal

To fill the gap, the NEA plans to import 1,154 MW from India. Khabarhub listed the routes: 600 MW through the Dhalkebar-Muzaffarpur line, 54 MW through Tanakpur-Mahendranagar, 350 MW from several points in Bihar, and 150 MW through a round-the-clock (RTC) arrangement. Each figure depends on the capacity of a cross-border line and on an agreement to buy power.

Adding imports to domestic generation gives 2,372 MW of expected supply. Last year's dry-season peak demand was 2,292 MW. The margin is therefore about 80 MW, if every import route works and demand does not grow. A single line fault or a higher peak could use up that margin. This is why the committee is pushing to finish Kathmandu Valley transmission and distribution work before the peak.

The situation also shows how one substation can change the national balance. The plants behind the Trishuli-3B hub usually help the Kathmandu Valley in winter. With them cut off and Kulekhani drawn down early, more of the winter load rests on imports. The NEA's promise depends on how quickly lines are repaired and how much water stays in Indra Sarobar.

The reservoir itself has limits. The Post reported that a flood in July 1993 raised the lake bed by about 6 m overnight, and that NEA studies count more than 170,000 cubic metres of silt, sand and gravel on the bed. Annual generation potential has fallen to 144.7 million units. Cracks found in the main dam after the 2015 earthquake also mean engineers take extra care once the level passes 1,527 m, below the 1,530 m maximum.