Proposal to increase the capacity of the Trisuli 3A hydropower from 60 MW to 90 MW, which is at present already under construction, could not have been justified on technical as well as economic grounds as explained hereinafter. The proposed modification would have worsen the financial situation of the NEA, which is already in great difficulties. Very recently government has taken a very wise decision not to raise the capacity of the Trisuli 3A hydropower from 60 MW to 90 MW.
It is unfortunate that in recent years our policy makers and planners are turning a blind eye to various techno-economic aspects of our water resources in general and the hydropower engineering in particular. As a result, we are ruining the potential of our hydropower projects to produce very cheap electricity in abundance. The Upper Trisuli hydropower project is one of the casualties of our wrong decision.
Ruin of Upper Trisuli Potential
The upper reaches of the Trisuli have a steep slope and high dry-season runoff which make them attractive for development of run-of-river type scheme. The Gandak Basin study carried out in 1979 under the UNDP assistance had identified a single super high head ( 835m ) Upper Trisuli project to use the potential of the Trisuli River on the stretch between Syabru Bensi and Betrawati.
In 1970s the demand for electricity in Nepal was not yet sufficiently enough to justify the implementation of a single large Upper Trisuli project. Thus an alternative study was also done to utilize the 835 m head in stages by building three projects in a series. The Upper Trisuli 3A project is one of them. At present our demand for electricity has sufficiently increased. So instead of Upper Trisuli 3A project, now the super high head mega Upper Trisuli project should have been preferred for implementation to produce abundant cheap firm power, like the Nechako Kemano high head ( 783 m ) project of Canada now supplying exceptionally cheap electricity to aluminum smelter industries. Unfortunately, now it is too late to revise the entire Upper Trisuli planning.
We Compromised on Tecchno-Economic Aspect
Demand for electricity in our country is the highest during the winter months when the flow of the river falls to a minimum. Contrary to it, during the wet season months when the run-of- river type hydropower plants can produce three times or even more electricity by comparison with the generation in winter season if the installed capacity is excessively increased, the demand for electricity is the lowest.
In the past implementation of projects, like the oversized Khimti, Bhote-Kosi etc , disregarding the mismatch between the seasonal variation of demand for electricity in our country and the extremely unfavorable fluctuation in availability of water in the river for generation of electricity has resulted in financial downfall of the NEA that precipitated our country into perpetual energy crisis. At that time the Water and Energy Commission had cautioned the ministry about the dire consequences. Unfortunately, the WECS suggestions were turned into deaf ears. Now we might have again been committing the same type of blunder if it would have been decided to increase the capacity of the Trisuli 3A from 60 MW to 90 MW to produce additional seasonal energy during the monsoon period. We should bear in mind that just few years from now when the construction of the much awaited giant Upper Tama-Kosi project would be completed, as assured by the government, the NEA would be laden with enormously large surplus seasonal energy because that project would be generating perhaps about three times more energy in each monsoon month by comparison with that of its monthly generation in winter.
When Capacity Increase Justified
The increase in capacity of run-of river type hydropower can be justified to a certain extent if the power station is provided with sufficiently large daily water storage reservoir to enable the hydropower to operate in full capacity even in the driest months when the river flow falls to a minimum. The hydropower of this type could be virtually shut down during off-peak hours to conserve water to run in full capacity during the hours when the demand for electricity is the highest. Almost all run-of- river type hydropower projects built under international donor agencies and also under bilateral aid like the Kali-Gandaki, Marshyangdi, Trishuli etc fall under this category. Peaking energy is usually priced two to three times higher than the energy supplied to meet the demand for base load. Unfortunately, almost all hydropower projects like Khimti. Bhote-Kosi etc built by private developers and also the proposed Upper Trisuli 3A project are not provided with daily water storage facilities. The latter type of hydropower projects are now producing enormously large seasonal energy which used to be wasted until recently.
Why Peaking Energy Expensive
Peaking energy is priced two to three times higher than the energy produced during the off-peak hours. This aspect of electric energy economics serves as the basis of feasibility of pump storage power plants. Pump storage projects built at costs almost comparable to that of a normal hydropower consume about three units of energy drawn from the power grid during the off peak hours to produce only two units during the peak hours.
Let us take the case of Karnali Project. This project with a capacity of 10.8 GW would be producing 20.8 thousands GWh peaking energy. The same power station merely with an installed capacity of 2.5 GW could also produce the same amount of firm energy at almost 1/3 cost if it is to be operated like thermal or atomic power plants to supply electricity to meet exclusively the demand for base load.
Above mentioned aspects of power engineering economics have been carefully considered in all feasibility studies carried out under bilateral and multilateral agencies. Unfortunately, our government agencies seem to be quite unaware about it. As a result, we make no distinction in making comparison between the seasonal energy produced by Khimti type hydropower and the firm peaking energy produced by Kali-Gandaki like projects.