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.