Hydroelectric Generation CEE 6490 David Rosenberg

Learning Objectives 1.Explain how hydroelectric generation complements and enhances an energy generation system. 2.Describe the basic components of a hydroelectric generation system. 3.Differentiate hydropower generation systems. 4.Apply the laws of thermodynamics to calculate available power and generated energy. 5.Simulate the energy generated by a time- series of reservoir releases. CEE 6490David Rosenberg 2

Motivation CEE 6490David Rosenberg 3 Hydropower is a significant part of the U.S. energy supply

U.S. Energy production by source over the last 60 years (EIA, 2007) CEE 6490David Rosenberg 4 U

Base load and peak demand Fossil fuel production good at meeting base load. Why? Hydropower really flexible to meet peak (and economically valuable) demand. Why? Energy Demands CEE 6490David Rosenberg 5 energy demand 24 hours base load (thermal, nuc.) low-cost peaking (hydro) peaking (oil)

Basic Components 6

Some examples 7 Right: Norris Dam (TVA) Left: Moccasin penstock and dam (Hetch Hetchy, CA) CEE 6490

Types of Hydropower Systems Run-of-river (no storage) Pondage (small storage; days - week) Storage (seasonal) Re-regulating (after bay reservoirs) Micro (small head; off-stream) Pump-storage (bi-directional) CEE 6490David Rosenberg 8 Conventional

Oroville Reservoir and Thermalito Fore- and Afterbays (CA DWR) CEE 6490David Rosenberg 9

CEE 6490David Rosenberg 10 Example #1: What type of project is 1 st Dam?

Energy Generation Principles 1 st law of Thermodynamics –Conservation of energy –Can not create or destroy energy – no free lunch – … or mass. Why? –How does this apply to a dam? CEE 6490David Rosenberg 11

1 st Law of Thermo (cont.) A dam stores energy in the form of the elevation difference between two pools of water datum channel bottom 1 T 2 z1z1 z2z2 the “potential” David Rosenberg 12 CEE 6490

Energy Generation Principles 2 nd law of Thermodynamics –Entropy increases over time –Irreversible effects –You can not break even – Why? CEE 6490David Rosenberg 13

Some energy is lost in the process 2 nd Law of Thermo (cont.) datum channel bottom 1 T 2 z1z1 z2z2 entrance bends exit friction David Rosenberg 14 CEE 6490

2 nd Law of Thermo (cont.) And more energy is lost in the conversion –The power provided to the turbine by water moving through the penstock is: (dimensions: force length / time) –Energy supplied to the turbine = multiply the amount of time by which the power is provided: (dimensions: force length) CEE 6490David Rosenberg 15

2 nd Law of Thermo (cont.) And more energy is lost in the conversion (cont.) –The turbine is not 100% efficient at converting the energy of falling water into energy of motion to turn the generator η T = Turbine efficiency (< 1) [a function of flow, head, turbine design, etc.] –The generator is not 100% efficient at converting energy of turbine motion into electric energy η G = Turbine efficiency (< 1) –Transmission lines are not 100% efficient either (η C < 1 – 0.08) CEE 6490David Rosenberg 16

Example #2. Available Power What is the power delivered, respectively, to the turbine, generators, and end users (a long distance away) from a run-of-river project operating with a flow of 2,200 cfs, 70 feet of available head, and turbine and generator efficiencies of 80% and 90% respectively? –1 ft-lb/sec = 1.36 watts Solution: CEE 6490David Rosenberg 17

Turbine Design CEE 6490David Rosenberg 18 Source: Mays (2005), p. 502

Turbine Efficiency CEE 6490David Rosenberg 19 Source: Mays (2005), p. 502

Simulating Reservoir Energy Generation Recall –E = γ η Q H T Δt –Constants: γ (specific gravity of water) and Δt (time step) –State variables: H T (net head) and η (efficiency) –Decision variable: Q (flow through turbine) Keep in mind –Flow through turbine may differ from reservoir release Integrate into a spreadsheet model of reservoir operations –H T, η, Q, and E as new columns (state variables and outputs) –Specify formulas for each new state variable –Copy down formulas for subsequent time steps CEE 6490David Rosenberg 20

Conclusions Hydropower is a versatile and valuable energy source to meet peak energy demand Different types of system designs and configurations Convert energy of falling water to mechanical energy and onto electrical energy Inefficiencies along the way Can integrate energy generation into spreadsheet (and other) models that simulate reservoir operations CEE 6490David Rosenberg 21