Factors Affecting Hydropower Plant Capacity

Evaluating Head and Flow

The generating capacity of hydropower plants is expressed in kilowatts (KW) or Megawatts (MW) and is selected based on the evaluation of several important parameters.

The first parameter is the Head (H): the approximate vertical distance through which the water falls.

The second is the flow rate or discharge (Q): the volume flow rate of the water that passes through the plant.

Since the power output of a hydro plant is proportional to the product of the head and flow rate, the relative frequency that various head-flow combinations occur must be considered in selecting the generating capacity to be installed at a particular site.

Look at the equation:

The actual form of the equation

• Using project hydrologic data and economic criteria, project planners analyze a range of project capacities by evaluating the capital costs and economic benefits of each alternative capacity.
• If the project capacity appears economically feasible, the planner can evaluate other plant capacities and alternative machinery solutions in the same manner until the optimal plant capacity is determined.
• If the initial plant capacity is not feasible, the planner can evaluate smaller capacities in a similar manner.

Determining Optimal Plant Capacity

The flow diagram, as shown above, illustrates the basic steps in determining the optimal capacity of the hydropower plant.

The initial input for the process is determining: (1) the hydraulic resource or river flow and (2) the economic criteria to evaluate the project’s economic feasibility, including the value of energy, the value of capacity, escalation rates, discounts rates, etc.

The project hydrological data (water availability versus time) is obtained by reviewing historical records or estimated by other techniques. As a result of this analysis, an initial plant capacity is assumed. A trial number of turbine-generator units is also assumed at this stage. The next step is to obtain, from manufacturers or other sources, estimates of the performance characteristics of the selected turbines and generators, and other major equipments are used to estimate the powerhouse dimensions and costs. This analysis is usually done by the project developer or his engineer.

Economic analysis for a range of project alternatives typically is conducted for the various capacities, annual generation, capital costs, and economic criteria. If the project appears feasible, other plant capacities and alternative machinery solutions would be evaluated in the same manner until the optimal plant capacity is determined. If the initial plant capacity is not feasible, smaller capacities would be evaluated in a similar manner. After evaluating several alternatives, a range of solutions available for consideration can be provided the potential developer with a basis for selection.