Primary and secondary energy (Nepali calendar months)

Primary energy is the energy available throughout the year from the minimum usable flow; secondary energy is the extra energy from usable flows above that minimum. No design discharge is given, so the plant is assumed to use all the usable flow. Each month is taken as 730 h (Nepali months vary from 29 to 32 days, but the yearly total is the same).

Environmental flow

Minimum flow of the series = 400 m³/s (month 10, Magh).

$$Q_{env} = 0.10 \times 400 = 40\ \text{m}^3/\text{s}$$

Usable flow = Q − 40.

Power per unit discharge

$$P = 9.81 \times Q \times 155 \times 0.80 = 1216.44\,Q\ \text{kW}$$

Primary energy

Minimum usable flow = 400 − 40 = 360 m³/s.

$$\begin{aligned} P_f &= 1216.44 \times 360 = 437{,}918\ \text{kW} \approx 437.9\ \text{MW} \\ E_p &= 437{,}918 \times 8760 = 3836.17\ \text{GWh} \end{aligned}$$

Total energy

$$\begin{aligned} E_{total} &= 1216.44 \times 13{,}180 \times 730 = 11{,}703.86\ \text{GWh} \\ E_s &= 11{,}703.86 - 3836.17 = 7867.69\ \text{GWh} \end{aligned}$$

Answer: Primary energy ≈ 3836.2 GWh/yr; secondary energy ≈ 7867.7 GWh/yr (total ≈ 11,703.9 GWh/yr).