Do Now:What are the 4 steps of the

Water Cycle?What is the difference between

transcription and evaporation?

The Water Cycle

1.Evaporation & Transpiration2.Condensation3.Precipitation4.Infiltration, Storage & Runoff

The Parts of a Hydroelectric Plant

Essential QuestionsHow is moving water an energy

source?How can flowing water do work?What is hydropower’s potential?

The Water CycleThe Water Cycle ensures that water flows from mountain peaks, down rivers and streams back into the ocean. That continuous flow of water carries with it a large amount of kinetic energy.

…kinetic energy that can be transformed into electrical energy, with the aid of hydroelectric power plants, to power our homes and businesses!

Hydroelectric Power Plants

Water enters hydroelectric plants from a river or reservoir; each plant has essentially 8 different elements:

1. Reservoir2. Penstock3. Turbine Blades &

Shaft4. Generator5. Step-up Transformer6. Transmission Lines7. Tailrace8. Dam & Spillway

ReservoirThe reservoir for a hydroelectric

plant is a man-made lake/pond where water stored so that it backs up behind a dam; the height of such a mass of water is a way of storing gravitational potential energy.

PenstockPenstock is the pipe that

channels water from the reservoir to the blades of the turbine. As the water moves through the penstock, its potential energy is transformed into kinetic energy.

Turbine Blades & ShaftThe turbine blades transform

the kinetic energy of the water into mechanical energy which the shaft transmits on to the generator.

GeneratorThe generator transforms the

mechanical energy transmitted from the turbine blades into electricity, into electrical energy.

Step-up TransformerThe step-up transformer

increases the voltage of the electrical current generated so that it can be transmitted long distances more efficiently.

Dam & SpillwayA Dam is a barrier that blocks

the regular flow of a river or stream, causing the water to back up behind it.

Spillways are holes in the dam that can be opened to allow water to flow past the dam to prevent water from overflowing the dam.

Types of Hydroelectric Plants

There are 3 main types of hydroelectric plants:

1. Traditional2. Pumped Storage3. Run-of-River

Hydro Turbines:Power & Efficiency

The Potential Energy of Reservoirs

Dams force water to back up behind them into reservoirs which store the gravitational potential energy of water.

head,h

The amount of energy stored is proportional to the head – the height of water in the reservoir above the turbine. The stored energy can be used to generate power.

Volumetric Flow RateVolume Flow Rate Through a

Pipe

Q = AVQ, volumetric flow rateA, cross-sectional area

V, average fluid velocity

In this case, the pipe we’re talking about is the penstock that channels water from the reservoir to the turbines where power is transmitted to the generators.

Example: Water flows at a rate of 1 m/s through a round pipe with a diameter of 3 cm. What is the volumetric flow rate [L/s]?

How much power does a hydro turbine produce?

Power = hrghQ

h, efficiency g, acceleration of gravity

r, density h, head

Q, volume flow rate

 Example: A hydroelectric plant employs a turbine with an overall efficiency of 85% in conditions where the flow rate is 30000 liters per second and the surface of the reservoir is 20m above the turbine. How much power is produced [kW]?

Power, Head & Flow Rate

This image shows a cross-section of surface run-off at three separate locations: (A) a small, fast-flowing, steep mountain stream; (B) a deep, quick flowing river in a narrow channel; and (C) a very wide, but shallow, slow-moving river.

As we follow the run-off from A to C, the vertical drop of the water flow decreases (h goes down), but the volumetric flow rate increases (Q goes up).

This means that, in theory, it would be possible to achieve the same power when installing a hydroelectric power plant at any of the three locations shown.

Large hSmall Q

Average hAverage Q

Small hLarge Q

Types of TurbinesImpulse

◦Pelton Wheel - large h, small QReaction

◦Kaplan - small h, large Q◦Francis - large h, large Q

Pelton Wheel Kaplan Francis

Choosing Turbines

Which type of turbine would you choose if you were designing a hydroelectric power plant for a site similar to the conditions at location C? Why?

What’s Coming Up?Impacts on Environment/Society

Homework Due Tomorrow

Homework 3 Water Flow