Due to the discrepancy in electricity production in the dry and wet season, turbines are not going to operate in their optimum condition - in the dry season, because of inadequate discharge, and in the wet season, because of excess energy. Operating turbines in part load conditions and frequent start-up and shut down might also reduce their life-span
Extensive discussions are being held at the moment regarding domestic consumption of surplus electricity and what to do when there is a deficit during the peak hours and dry season. While the budget of Nepal for FY 2079/80 BS has given priority to establishing charging stations to encourage the use of electric vehicles (EVs) to enhance power consumption, it is hard to understand why excise and customs duty of 30-60 per cent have been slapped on EVs in the range of 100 kW to 300 kW.
The budget has announced distributing one electric stove per family and removing the LPG subsidy to discourage the use of cooking gas in favour of electricity. Concessions of 2 to 15 per cent have been provisioned for large industries, which consume electricity worth more than Rs 100 million annually.
Hence, the government has taken a number of measures to handle the energy excess.
Nepal currently has a yearly trade deficit of over Rs 1.7 trillion, out of which 25 per cent goes into importing food items. Exporting the surplus energy to neighboring countries can help narrow this deficit. Besides, numerous schemes have been planned in the current budget for strengthening the agricultural sector, including the establishment of a green fertiliser factory in the country. These interventions will provide a basis for utilising the additional energy in food-based or other industries.
The monthly energy generation according to Nepal Electricity Authority (NEA) in 2077/2078 ranged from 326,370 MWh in the month of Shrawan to 139,908 MWh in Falgun. This tremendous decline by more than 57 percent shows that electricity production in Nepal depends heavily on rainfall and river discharge.
This is mainly due to the fact that hydropower production in Nepal is dominated by run-of-river projects.
Hence, although domestic consumption of electricity is emphasised through the use of electric appliances and EVs, meeting the energy demand during the peak time in the dry season will remain a challenge.
Reservoir type hydropower projects are an alternative for storing the energy of water to be used during the peaking periods.
However, as experienced from the famous Budhi Gandaki hydropower pro ject, reservoir projects multiply the social complications manifold, which generally results in deferral of the project initiation.
Some planning from the government for developing storage projects is reflected in the present budget, with Rs 1 billion allocated for the start of the Upper Arun Hydropower Project (1,060 MW) and Rs 940 million for the Dudhkoshi Hydropower Project (635 MW). These types of storage projects will help to maintain the reliability of power plants by balancing the load throughout the year.
Sedimentation and erosion of the turbine components due to suspended sediments have been a major operational challenge for the power plants of Nepal.
Run-of-river projects are equipped with desilting basins, which help to settle the sand particles at intake, with efficiency of more than 80 percent for particles larger than 0.2 mm.
With additional investments, the size of these basins can be extended for more efficiency.
However, even particle sizes of less than 0.1 mm, which are ultimately carried into the power house, are found to be vulnerable for the mechanical components.
Reservoir projects could also be crucial to addressing the issues of operation and maintenance of power plants in Nepal, since sand particles will get ample time to settle and prevent turbines from eroding.
The possibility of using pumped storage hydropower projects have also been identified and studied in Nepal. These projects are designed using two reservoirs at different elevations with an electromechanical system that can be utilised as both turbine and pump.
The plant runs as a pump when the demand is low to force the water from the lower reservoir to the upper reservoir. When the demand is high, it runs as a turbine to bring the water back to the lower reservoir and generate electricity. At different tariff rates for pumping and generating mode, the overall losses arising from the turbines and generators can be compensated.
Some sites in Nepal, such as Sunkoshi II and Sunkoshi III, Rupa and Begnas lakes, and Tanahu hydropower projects were studied as suitable sites for these projects. These projects could also be integrated with solar and wind energy, which also requires storage facilities. However, no significant schemes have been mentioned in the current budget in this sector.
The government of Nepal, through the budget of FY 79/80, has made an ambitious plan of providing electricity access to its entire citizens within two years. Within this fiscal, a total of 715 MW of electricity will be added to the national grid. Solar PV, micro and mini hydropower plants have been targeted for inaccessible regions, and an annual per capita electricity consumption of 400 units is aimed by the end of this fiscal year.
It is quite evident that with the present discrepancy in electricity production in the dry and wet season, turbines in the power plants are not going to operate in their optimum condition – in the dry season, because of inadequate discharge, and in the wet season, because of excess energy. Operation of turbines in part load conditions and frequent start-up and shut down might also reduce their life-span.
It is high time these aspects were considered, also because of the reason that maintenance challenges in Nepali turbines are already high due to sediment issues.
Chitrakar and Lama are with Turbine Testing Lab, Kathmandu University
A version of this article appears in the print on June 15, 2022, of The Himalayan Times.