The Current Situation and Perspectives on the Use of Hydropower for Electricity Generation:Efficiency of the Hydropower Plants

Efficiency of the Hydropower Plants

According to Kumar and others (2011), the potential for energy production in a hydropower plant is determined by several parameters, which are dependent on the hydrology, topography, and design of the power plant. These parameters are the following:

• The amount of water available;

• Water loss due to flood spill, bypass requirements, or leakage;

• The difference in head between upstream intake and downstream outlet;

• Hydraulic losses in water transport due to friction and velocity change;

• The efficiency in energy conversion of electromechanical equipment.

The total amount of water available at the intake will usually not be possible to utilize in the turbines because some of the water will be lost or will not be with- drawn. This loss occurs due to the following reasons:

• Due to water spill during high flows when inflow exceeds the turbine capacity;

• Due to bypass releases for environmental flows;

• Due to leakage.

In the hydropower plant, the potential (gravitational) energy in water is trans- formed into kinetic energy and then mechanical energy in the turbine and further to electrical energy in the generator. The energy transformation process in modern hydropower plants is highly efficient, usually around 97 % mechanical efficiency in turbines and over 99 % in the generator. The inefficiency is due to the following reasons:

• Hydraulic loss in the water circuit (intake, turbine, and tailrace);

• Mechanical loss in the turbo generator group;

• Electrical loss in the generator.

In addition, some energy losses occur in the headrace section where water flows from the intake to the turbines, and in the tailrace section taking water from the turbine back to the river downstream. These losses, called head loss, reduce the head and hence the energy potential for the power plant. These losses can be classified either as friction losses or singular losses. Friction losses depend mainly on water velocity and the roughness in tunnels, pipelines, and penstocks.

The total efficiency of a hydropower plant is determined by the sum of these three loss components. Hydraulic losses can be reduced by increasing the tur- bine capacity or by increasing the reservoir capacity to get better regulation of the flow. Head losses can be reduced by increasing the area of headrace and tailrace, by decreasing the roughness in these and by avoiding too many changes in flow velocity and direction.

The efficiency of electromechanical equipment, especially turbines, can be improved by better design and also by selecting a turbine type with an efficiency profile that is best adapted to the duration curve of the inflow.

Hydropower is one of the largest sources of energy, and for well-resourced countries, it accounts for the majority of the energy. Compared to other sources of energy, hydroelectric power is one of the cheapest, non-carbon emitting, non- polluting, and mature energy sources. Hydropower plants have been developed to almost full potential in developed countries because of their superior characteris- tics and many more are being constructed by developing countries such as China and India.

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