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Do Now: What are the 4 steps of the Water Cycle? What is the difference between transcription and evaporation? The Water Cycle Evaporation & Transpiration 2. Condensation 3. Precipitation 4. Infiltration, Storage & Runoff 1. The Parts of a Hydroelectric Plant Essential Questions How is moving water an energy source? How can flowing water do work? What is hydropower’s potential? The Water Cycle The 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. 2. 3. 4. 5. 6. 7. 8. Reservoir Penstock Turbine Blades & Shaft Generator Step-up Transformer Transmission Lines Tailrace Dam & Spillway Reservoir The 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. Penstock Penstock 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 & Shaft The turbine blades transform the kinetic energy of the water into mechanical energy which the shaft transmits on to the generator. Generator The generator transforms the mechanical energy transmitted from the turbine blades into electricity, into electrical energy. Step-up Transformer The step-up transformer increases the voltage of the electrical current generated so that it can be transmitted long distances more efficiently. Dam & Spillway A 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: 3. 1. 2. Run-of-River Traditional Pumped Storage Hydro Turbines: Power & Efficiency The Potential Energy of Reservoirs The amount Dams force water of energy to back stored up behind is proportional them into to reservoirs the head –which the height store of thewater gravitational in the reservoir potential energythe above of water. turbine. The stored energy can be used to generate power. head, h Volumetric Flow Rate Volume Flow Rate Through a Pipe Example: Water flows at a rate of 1 In this case, the pipe we’re m/s through a round pipe with a talking about is theis the diameter of 3 cm. What volumetric ratechannels [L/s]? penstockflow that water from the reservoir to the turbines where power is transmitted to Q =the AVgenerators. Q, volumetric flow rate A, cross-sectional area V, average fluid velocity How much power does a hydro turbine produce? Power = hrghQ h, efficiency r, density Q, g, h, acceleration of gravity head 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 Large h Small Q Average h Average Q Small h Large Q Thiswe As image means follow shows that, theinrun-off atheory, cross-section from it would A toofC, be surface the possible vertical run-off to drop achieve at of three the water same separate power flow locations: decreases when installing (A) (h goes a small, a down), hydroelectric fast-flowing, but thepower steep mountain volumetric plant at any stream; flow of the rate (B) three increases a deep, locations quick (Q goes shown. flowing up).river in a narrow channel; and (C) a very wide, but shallow, slowmoving river. Types of Turbines Impulse ◦ Pelton Wheel - large h, small Q Reaction ◦ 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