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Chemical, Biological and Environmental Engineering Cost of Electrical Energy AC Power Concepts.

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Presentation on theme: "Chemical, Biological and Environmental Engineering Cost of Electrical Energy AC Power Concepts."— Presentation transcript:

1 Chemical, Biological and Environmental Engineering Cost of Electrical Energy AC Power Concepts

2 Advanced Materials and Sustainable Energy Lab CBEE Housekeeping Issues Changed way #2 is stated (replaced n 2 with T 2 for clarity) Timeline: Midterm planned for Tuesday 2/8 (date OK?) Class on 2/3: Intro to Nuclear Energy Plan to issue HW4 on 2/1(due on 2/8 before midterm) GS: Need to discuss class presentation subject Reminder: visit to Energy center on 2/1 at class time.

3 Advanced Materials and Sustainable Energy Lab CBEE

4 Advanced Materials and Sustainable Energy Lab CBEE Baseload, Intermediate and Peaking Supply

5 Advanced Materials and Sustainable Energy Lab CBEE Baseload, Intermediate and Peaking Supply Load demand on utilities fluctuates constantly –During peak demand most plants are operating –During light demand many plants are idling Power plants are categorized as –Baseload Large coal, nuclear, and hydroelectric plants Expensive to build, cheap to operate –Intermediate Combined-cycle plants Cycled up during the day, cycled down during the evening –Peaking Simple-cycle gas turbines Inexpensive to build, expensive to operate

6 Advanced Materials and Sustainable Energy Lab CBEE Costing Power Other fixed costs –Regular maintenance (e.g., groundskeeping) –Administration –Insurance Variable Costs (primarily fuel) –Cost of fuel Coal ~ $2.21/MMBTU ($43.74/ton) Gas ~ $4.74/MMBTU –Operations and Maintenance (Repair & Spare parts, etc) Variable Costs ($/yr) = [ Fuel($/BTU)xHeat rate(BTU/kWh) + O&M($/kWh)] xkWh/yr

7 Advanced Materials and Sustainable Energy Lab CBEE Costing Power - II Total cost of operating power plant then is the sum: Then, depending on how many kWh are generated in a typical year, This levelized cost per unit of energy is useful to compare various projects

8 Advanced Materials and Sustainable Energy Lab CBEE Graphical Version of Costing Power

9 Advanced Materials and Sustainable Energy Lab CBEE New Generation Costs Summary Capital Costs ($/kW) Fixed O&M ($/kW) Heat Rate (BTU/kWhr) Variable O&M (¢/kWh) Conventional Coal 2,200288, IGCC (Integrated Coal Gasification Combined Cycle) 2,600407, IGCC with CCS 3,800478, Gas Combined Cycle 1,000126, Gas CC w/CCS 2,000207, Gas Turbine , Nuclear 3, , Wind 2, Wind-Offshore 4, Hydro 2, Geothermal (US average) 1, , Solar PV 6, Solar Thermal 5, Adapted from EIA publication Electricity Market Module of the National Energy Modeling System 2010, DOE/EIA-M068(2010)

10 Advanced Materials and Sustainable Energy Lab CBEE Costing Power

11 Advanced Materials and Sustainable Energy Lab CBEE Screening Curve Plot costs for different plants on the same graph Plot as Cost = Fixed Cost ($) + Variable Cost ($/kWh) *kWh Cost ($) Energy Produced (kWh) [or rated power (kW) x hours of operation (h)] Fixed Costs Plant 1 ($) Variable Costs Plant 1 ($/kWh * kWh) Fixed Costs Plant 2 Variable Costs Plant 2

12 Advanced Materials and Sustainable Energy Lab CBEE Using Screening Curves Combustion turbine is lowest-cost option for up to 1675 h/yr of operation Coal plant is the lowest-cost option for operation beyond 6565 h/yr The combined cycle plant is the cheapest option if it runs between 1675 and 6565 h/yr

13 Advanced Materials and Sustainable Energy Lab CBEE Capacity Factor The capacity factor is defined as CF = [produced energy per year (kWh/yr)] / [ Rated power (kW) x 8760 h/yr] Essentially fraction of plant on-line time at full power averaged over year Why would the plant not operate at full rated power for full year? 1-Time down for maintenance (try to minimize this…) 2-Power it produces is not cost effective (use screening curve to find out how many hours on-line)

14 Advanced Materials and Sustainable Energy Lab CBEE Load-Duration Curves

15 Advanced Materials and Sustainable Energy Lab CBEE Load-Duration Curve

16 Advanced Materials and Sustainable Energy Lab CBEE Determining Optimum Mix Transfer crossover points onto load duration curve to identify optimum mix of power plants

17 Advanced Materials and Sustainable Energy Lab CBEE LOAD-DURATION CURVES

18 Advanced Materials and Sustainable Energy Lab CBEE Determining Optimum Mix Baseload Intermediate Peaking + Reserve

19 Advanced Materials and Sustainable Energy Lab CBEE Baseload, Intermediate and Peaking Supply

20 Advanced Materials and Sustainable Energy Lab CBEE Cost of Power The CF with cost parameters allow us to determine the cost of electricity from each type of plant

21 Advanced Materials and Sustainable Energy Lab CBEE Cost of Energy to User The final price is the weighted average of the costs of all generation: From example on previous slide:

22 Advanced Materials and Sustainable Energy Lab CBEE Costing Power Load duration curve needs to be padded with reserve excess capacity (reserve margin) –To deal with plant outages, sudden peaks in demand, and other unforeseen events Process of selecting which plant to operate first at any given time is called dispatching If you have renewables, they will be dispatched first, although they are intermittent (and require extra spinning reserve) –Energy Policy Act 1992/2005

23 Advanced Materials and Sustainable Energy Lab CBEE New Generation by Fuel Type (USA 1990 to 2030, GW) Source: EIA Annual Energy Outlook 2007

24 Advanced Materials and Sustainable Energy Lab CBEE Upcoming Challenges to Grid Plug in Electric Vehicles: What do you think that will do to the daily load profile? People come home at about this time In absence of incentive to charge at other time peak will get higher (worse)

25 Advanced Materials and Sustainable Energy Lab CBEE Smart Grid Q: Why should someone using power off peak pay rates using peak power? (subsidizing peak power?) Adding information layer to power distribution grid Allows utilities to charge differential rates depending on mix Allows utilities to inform customers about changing rates Allows customers to decide when to consume power Can also be used (voluntarily) to turn off non-essential loads at customers –Pool Pumps, Washer/Drier, A/C –Demand Side Management Also Increases ability of users to add distributed generation Increases resilience of grid

26 Advanced Materials and Sustainable Energy Lab CBEE Time of day metering: Different rates depending on time of day

27 Advanced Materials and Sustainable Energy Lab CBEE Example of Distributed Generation: Microturbines Very small gas turbines (aeroderived) 1kW to several 100 kW 30 to 60 kW unit about the size of a refrigerator Have only one moving part –Spins at ~96000 rpm on air bearings… Particularly good for CHP

28 Advanced Materials and Sustainable Energy Lab CBEE MICROTURBINES Generator makes variable frequency AC that is rectified and inverted to grid frequency ac (50 or 60 Hz) Some microturbines are designed for power and heat

29 Advanced Materials and Sustainable Energy Lab CBEE MICROTURBINES

30 Advanced Materials and Sustainable Energy Lab CBEE Microturbines Source: Capstone 65 kW Microturbine 230 kW fuel 80% CHP Heat Utilization 120 kW hot water 65 kW electrical 45 kW waste heat

31 Advanced Materials and Sustainable Energy Lab CBEE DG/CHP: Fuel cells Example: ClearEdge Power (Hillsboro – OR!) PEM fuel cell operating on natural gas (reformate) No moving parts (but membrane degrades) ~40% Efficiency, ~85% Energy Utilization

32 Chemical, Biological and Environmental Engineering Evaluating power consumption in AC

33 Advanced Materials and Sustainable Energy Lab CBEE AC Power Instantaneous Power = VI What is the power transferred if V=120V, I=10A,

34 Advanced Materials and Sustainable Energy Lab CBEE AC Power Note: because i is also used for current, the imaginary number basis i is usually replaced by j

35 Advanced Materials and Sustainable Energy Lab CBEE Phasor Representation

36 Advanced Materials and Sustainable Energy Lab CBEE AC Power Previous problem reduces to: What is the instantaneous power transferred if V=120V, I=10A and =0 What if =90 o instead? P=VIcos

37 Advanced Materials and Sustainable Energy Lab CBEE Real vs. Apparent Power Real power is the capacity of the circuit for performing work in a particular time Apparent power is the product of the current and voltage of the circuit If Voltage and Current out of phase, apparent power can be greater than real power

38 Advanced Materials and Sustainable Energy Lab CBEE Real, Apparent, Reactive Power; Power Factor Real Power usually written as P, given in Watts Apparent Power is S, Given in Volt-Amperes (i,.e., based on system voltage and current) The difference is Reactive Power, given as Q Basically, current flowing 90 o (π/2) out of phase with voltage Given in Volt-Amperes Reactive (or VARs) S can be calculated as S 2 =P 2 +Q 2 Power factor =P/S (fraction of power that is useful) Can be shown that P=S cos, therefore =cos

39 Advanced Materials and Sustainable Energy Lab CBEE About the Power Factor A load with low power factor draws more current than a load with a high power factor for the same amount of useful power transferred Higher currents increase losses in the distribution system, and require larger wires and other equipment Causes utilities to charge higher cost for low power factor – it is in your interest to correct power factor

40 Advanced Materials and Sustainable Energy Lab CBEE AC Power Further, power varies continuously what is the power at the point V (or I) crosses 0? Use Root Mean Squared (RMS) power instead

41 Advanced Materials and Sustainable Energy Lab CBEE Root Mean Squared Values

42 Advanced Materials and Sustainable Energy Lab CBEE Where RMS comes from For a continuous function, its rms value is

43 Advanced Materials and Sustainable Energy Lab CBEE Impedance In general you know that power is dissipated by a current flowing against a voltage (V=IR) In AC you have to consider the effect of sinusoidal voltage waveform The generic resistance is called impedance –Purely resistive (R) –Capacitive (X C ) –Inductive (X L )

44 Advanced Materials and Sustainable Energy Lab CBEE Complex Impedance In general impedance is called Z –R is still the resistance –X is the reactance The relationship is

45 Advanced Materials and Sustainable Energy Lab CBEE Inductive Reactance We define a quantity called the Inductance, L From Faradays law

46 Advanced Materials and Sustainable Energy Lab CBEE Inductive Reactance In other words, current lags voltage change Units of inductance is the Henry written as H

47 Advanced Materials and Sustainable Energy Lab CBEE Capacitive reactance How does capacitor work? Current flows onto capacitor electrodes Charge accumulation builds voltage This causes current to lead voltage Impedance of a capacitor is called capacitance measured in farads

48 Advanced Materials and Sustainable Energy Lab CBEE Capacitive reactance Therefore current leads voltage in a capacitor

49 Advanced Materials and Sustainable Energy Lab CBEE In Phasor Diagrams…

50 Advanced Materials and Sustainable Energy Lab CBEE In Phasor Diagrams…

51 Advanced Materials and Sustainable Energy Lab CBEE You can combine impedances In Series… In Parallel… Etc…


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