Parameters for planning and sizing a plant

Planning, selecting and sizing a plant means deciding the type, installed capacity, number of units and commissioning time of a new plant so that it fits the forecast demand, is economically viable and suits the overall system plan.

1. Parameters from load/demand forecast

• Peak demand (MW) and growth rate: decide how much capacity is needed and when.
• Energy demand (GWh): decides required annual and firm energy.
• Load curve shape: base, intermediate or peak load. Base load suits ROR/thermal; peak load suits storage, PROR or gas turbines.
• Load factor: a high load factor favours base-load plants with high capital and low running cost.
• Seasonal pattern: in Nepal winter evening peak with low river flow favours storage/PROR plants.
• Location of load centres: affects transmission cost.

2. Economic parameters

• Capital cost per kW and O&M/fuel cost per kWh.
• Levelised cost of energy (LCOE) and comparison with alternatives.
• Economic indicators: NPV, IRR (typically above 10–12%), B/C ratio, payback period.
• Plant factor / capacity factor: higher plant factor lowers cost per kWh.
• Tariff / PPA rate (e.g. NEA wet and dry season rates), royalty and taxes.
• Financing: debt–equity ratio, interest rate, construction period.

3. System planning parameters

• Reserve margin and reliability (LOLP, spinning reserve).
• Unit size relative to system: loss of the largest unit must not endanger the system; usually unit size below about 10% of system peak.
• Number of units: decided by flow variation (FDC), part-load efficiency, maintenance and transport limits.
• Transmission availability: voltage and distance to nearest grid substation.
• Fit in generation mix: hydro–thermal–solar balance, firm power need.
• Stability: short-circuit ratio, inertia, voltage support.

4. Site and technical parameters (for hydro)

Design discharge (e.g. Q40–Q65 from FDC), net head, turbine type, sediment, geology, access, environmental flow (riparian release).

5. Environmental and social parameters

Land acquisition, resettlement, emissions, river ecology, local benefit sharing.

The final size is the one that gives the least cost per kWh to the system while meeting reliability and constraints.