Hydro Power

Question 1

With the aid of a sketch, describe a pumped storage hydro scheme.

Answer 1

• In generating mode the plant operates as a conventional hydro power plant.
• However, the generator can function as a motor, and the turbine as a pump.
• When demand for electricity is low, power may be taken from the grid to pump water into the upper reservior, to act as an energy store for future use when demand for electricity is high.

NOTE: All reaction turbines will operate efficiently as pumps; impulse turbines will not, because the reaction turbine can create a static pressure difference similar to a centrifugal pump.

Question 2

Provide 3 key arguments for or against the construction of a large scale hydro project.

Answer 2

For:

1. Generate 100% carbon neutral energy
2. Pumped schemes provide a means of energy storage to be used when required
3. Are built to last a long time
4. Contribute to the reliability of the base load of the grid

Against:

1. Capital cost is relatively high compared to generated output
2. Can be said to spoil the aesthetic of a landscape
3. With such large mass, they cause negative geological and seismic effects
4. Decommissioning is very difficult, and likely highly expensive
5. Damage to the reservoir/dam structure can lead to severe flooding and devastation of the nearby ecosystem

Question 3

Explain how a pumped hydro scheme could be of use in the operation of a power system featuring significant quantities of wind power.

Answer 3

• By building a secondary reservoir, the water
  can drive the turbine as a standard hydro
  plant would, but the work done by the turbine
  is now equivalent to the head between the
  reservoirs and the losses in the system.

- This means that when supply is above
demand, the excess, lower rate electricity,
can be used to power the generator as a
motor, and the turbine will operate as a
pump. 

-Therefore, if an intermittent power
such as a wind turbine were to be used cooperatively with the hydro scheme, the wind power could be used to return the tail-race water to the reservoir. This would provide reliable base load from the reservoir when required. This also acts as a method of energy storage when wind is generating large quantities of electricity
but demand is low.