ECE 333 Renewable Energy Systems Lecture 7 Power
ECE 333 Renewable Energy Systems Lecture 7: Power System Operations, Wind as a Resource Prof. Tom Overbye Dept. of Electrical and Computer Engineering University of Illinois at Urbana-Champaign overbye@illinois. edu
Announcements • • Start reading Chapter 7; also read Prof. Sauer's article on course website explaining reactive power HW 3 is posted; it will be covered by an in-class quiz on Thursday Feb 13 – Material from Power Systems history and operations will be covered on exams (such as true/false) 1
Power Flow • A common power system analysis tool is the power flow – • Solves sets of non-linear equations enforcing "conservation of power" at each bus in the system (a consequence of KCL) – – • It shows how real and reactive power flows through a network, from generators to loads Loads are usually assumed to be constant power Used to determine if any transmission lines or transformers are overloaded and system voltages Educational version Power. World tool available at – http: //www. powerworld. com/gloversarmaoverbye 2
Power. World Simulator Three Bus System Load with green arrows indicating amount of MW flow Used to control output of generator Note the power balance at each bus Direction of arrow is used to indicate direction of real power (MW) flow 3
Area Control Error (ACE) • The area control error is the difference between the actual flow out of an area, and the scheduled flow. • Ideally the ACE should always be zero. • Because the load is constantly changing, each utility must constantly change its generation to “chase” the ACE. MISO ACE| (in MW) from 9/19/12. At the time the MISO load was about 65 GW https: //www. misoenergy. org/Markets. Operations/Real. Time. Market. Data/Pages/ACEChart. aspx 4
Automatic Generation Control • • BAs use automatic generation control (AGC) to automatically change their generation to keep their ACE close to zero. Usually the BA control center calculates ACE based upon tie-line flows; then the AGC module sends control signals out to the generators every couple seconds. 5
Three Bus Case on AGC 6
Generator Costs • • • There are many fixed and variable costs associated with power system operation. The major variable cost is associated with generation. Cost to generate a MWh can vary widely. For some types of units (such as hydro and nuclear) it is difficult to quantify. Many markets have moved from cost-based to pricebased generator costs 7
Economic Dispatch • • Economic dispatch (ED) determines the least cost dispatch of generation for an area. For a lossless system, the ED occurs when all the generators have equal marginal costs. IC 1(PG, 1) = IC 2(PG, 2) = … = ICm(PG, m) 8
Power Transactions • • • Power transactions are contracts between areas to do power transactions. Contracts can be for any amount of time at any price for any amount of power. Scheduled power transactions are implemented by modifying the area ACE: ACE = Pactual, tie-flow - Psched 9
100 MW Transaction Scheduled 100 MW Transaction from Left to Right Net tie-line flow is now 100 MW 10
Security Constrained Economic Dispatch • Transmission constraints often limit system • • economics. Such limits required a constrained dispatch in order to maintain system security. In three bus case the generation at bus 3 must be constrained to avoid overloading the line from bus 2 to bus 3. 11
Security Constrained Dispatch is no longer optimal due to need to keep 12 Line from bus 2 to bus 3 from overloading
Multiple Area Operation • • • If Areas have direct interconnections, then they may directly transact up to the capacity of their tie-lines. Actual power flows through the entire network according to the impedance of the transmission lines. Flow through other areas is known as “parallel path” or “loop flows. ” 13
Seven Bus Case One-line Diagram System has three areas Area left has one bus Area top has five buses Area right has one bus 14
Seven Bus Case: Area View System has 40 MW of “Loop Flow” Actual flow between areas Scheduled flow Loop flow can result in higher losses 15
Seven Bus System – Loop Flow? Transaction has actually decreased the loop flow 100 MW Transaction between Left and Right Note that Top’s Losses have increased from 7. 09 MW to 9. 44 MW 16
Pricing Electricity • • • Cost to supply electricity to bus is called the locational marginal price (LMP) Presently PJM and MISO post LMPs on the web In an ideal electricity market with no transmission limitations the LMPs are equal Transmission constraints can segment a market, resulting in differing LMP Determination of LMPs requires the solution on an Optimal Power Flow (OPF) 17
Three Bus Case LMPs: Line Limit NOT Enforced Gen 2’s cost is $12 per MWh Gen 1’s cost is $10 per MWh Line from Bus 1 to Bus 3 is over-loaded; all buses have same marginal cost 18
Three Bus Case LMPS: Line Limits Enforced Line from 1 to 3 is no longer overloaded, but now the marginal cost of electricity at 3 is $14 / MWh 19
Generation Supply Curve As the load goes up so does the price Natural Gas Generation Base Load Coal and Nuclear Generation Renewable Sources Such as Wind Have Low Marginal Cost, but they are Intermittent 20
MISO LMPs on Sept 19, 2012 (11: 50 am EST which is CDT) Available on-line at https: //www. misoenergy. org/LMPContour. Map/MISO_All. html 21
MISO LMPs on Feb 6, 2015, 1 pm Central Available on-line at https: //www. misoenergy. org/LMPContour. Map/MISO_All. html 22
MISO Annual Load Duration Curves https: //www. misoenergy. org/Library/Repository/Report/Annual%20 Market%20 Report/20 13%20 Annual%20 Market%20 Assessment%20 Report. pdf 23
MISO Average Prices and Wind Output https: //www. misoenergy. org/Library/Repository/Report/Annual%20 Market%20 Report/20 13%20 Annual%20 Market%20 Assessment%20 Report. pdf 24
Wind Power Systems Photos taken Kate Davis near Moraine View State Park, IL 25
Historical Development of Wind Power • The first known wind turbine for producing electricity was by Charles F. Brush turbine, in Cleveland, Ohio in 1888 • • 12 k. W Used electricity to charge batteries in the cellar of the owner’s mansion Note the person http: //www. windpower. org/en/pictures/brush. htm 26
Historical Development of Wind Power • First wind turbine outside of the US to generate electricity was built by Poul la Cour in 1891 in Denmark • Used electricity from his wind turbines to electrolyze water to make hydrogen for the gas lights at the schoolhouse http: //www. windpower. org/en/pictures/lacour. htm 27
Historical Development of Wind Power • In the US - first wind-electric systems built in the • • late 1890’s By 1930 s and 1940 s, large numbers in rural areas not served by the grid for pumping water and sometimes electricity generation Interest in wind power declined as the utility grid expanded and as reliable, inexpensive electricity could be purchased Oil crisis in 1970 s created a renewed interest in wind until US government stopped giving tax Renewed interest again since the 1990 s Photo: www. daviddarling. info/encyclopedia/W/AE_wind_energy. html 28
Global Installed Wind Capacity Total worldwide electric capacity is 4500 GW, so wind, at almost 250 GW, is 5. 6% of total Source: Annual Market Update 2013, Global Wind Energy Council, 29
Wind Capacity Additions by Region Source: Annual Market Update 2013, Global Wind Energy Council, 30
Top 10 Countries - Installed Wind Capacity (as of the end of 2013) Source: Annual Market Update 2013, Global Wind Energy Council, 31
US Wind Resources http: //www. windpoweringamerica. gov/pdfs/wind_maps/us_windmap. pdf http: //www. windpower. org/en/pictures/lacour. htm 32
US Wind Capacity by State, 12/31/14 33
Wind Map for Illinois at 80 m 34
Worldwide Wind Resource Map Source: www. ceoe. udel. edu/Wind. Power/Resource. Map/index-world. html 35
Types of Wind Turbines • • “Windmill”- used to grind grain into flour or pump water Many different names - “wind-driven generator”, “wind turbine”, “wind-turbine generator (WTG)”, “wind energy conversion system (WECS)” Can have be horizontal axis wind turbines (HAWT) or vertical axis wind turbines (VAWT) Groups of wind turbines are located in what is called either a “wind farm” or a “wind park” 36
Vertical Axis Wind Turbines • • • Darrieus rotor - the only vertical axis machine with any commercial success Wind hitting the vertical blades, called aerofoils, generates lift to create rotation No yaw (rotation about vertical axis) control needed to keep them facing into the wind Heavy machinery in the nacelle is located on the ground Blades are closer to ground where windspeeds are lower http: //www. absoluteastronomy. com/topics/Darrieus_wind_turbine 37
Horizontal Axis Wind Turbines • • • “Downwind” HAWT – a turbine with the blades behind (downwind from) the tower No yaw control needed- they naturally orient themselves in line with the wind Shadowing effect – when a blade swings behind the tower, the wind it encounters is briefly reduced and the blade flexes 38
Horizontal Axis Wind Turbines • • “Upwind” HAWT – blades are in front of (upwind of) the tower Most modern wind turbines are this type Blades are “upwind” of the tower Require somewhat complex yaw control to keep them facing into the wind – • • Need to search for the wind to start turning Operate more smoothly and deliver more power Largest turbines are on the order of 6 MW with 1. 5 MW a quite common design 39
Number of Rotating Blades • Windmills have multiple blades – – • • need to provide high starting torque to overcome weight of the pumping rod must be able to operate at low wind speeds to provide nearly continuous water pumping a larger area of the rotor faces the wind Note, most seem to write “wind speed” as two words Turbines with many blades operate at much lower rotational speeds - as the speed increases, the turbulence caused by one blade impacts the other blades Most modern wind turbines have two or three blades 40
Worldwide Wind Energy Company Market Share, 2013 Installations Source: http: //www. statista. com/statistics/272813/market-share-of-the-leading-wind-turbine-manufacturers-worldwide/ 41
Vestas Stock Price https: //uk. finance. yahoo. com/echarts? s=VWS. CO#symbol=VWS. CO; range=my 42
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