Model of Photovoltaic Generation During Cloudy Days

Transcription

1 Model of Photovoltaic Generation During Cloudy Days Dionysios C. Aliprantis, Chengrui Cai Iowa State University Sandia National Laboratory June 11, 2012

2 Outline Motivation Literature review on cloud pattern synthesis Fractal shape of clouds Proposed irradiance model Conclusion 2

3 Motivation Increasing PV installed capacity: GW worldwide by the end of Germany (24.7 GW) : No. 1 Italy (12.5 GW), Japan (4.7 GW) and the United States (4.2 GW). Need for simulation model. Need for simulation data: irradiance. Jyosai town pilot project, Ota-City, Japan 2.13 MWp, sq. mile Nellis Solar plant, NV, U.S MWp sq. mile 3

4 Motivation cont. Current practice: single-point measurement: Good: readily available data (NREL). Bad: overlook the smoothing effect over the area. Consequence: Overly conservative result and over-estimated cost. Source: J. Marcos, L. Marroyo, E. Lorenzo, D. Alvira and E. Izco, Power output fluctuations in large scale PV plants: one year observations with one second resolution and a derived analytic model, Prog. Photovolt: Res. Appl., Volume 19, No.2, Irradiance vs. normalized PV plant output

5 Motivation cont. Solution for high resolution irradiance data: Make use of satellite images. - Lack of images with fine resolution. Synthesize cloud pattern. - Adopted method in our study. 5

6 Literature review W. Jewell and R. Ramakumar, The effect of moving clouds on electric utilities with dispersed photovoltaic generation, IEEE Trans. Energy Convers., vol. EC-2, no. 4, pp , Dec

7 Literature review cont. D. L. Garrett and S. M. Jeter, A photovoltaic voltage regulation impact investigation technique. I. Model development, IEEE Trans. Energy Convers., vol. 4, no. 1, pp , Mar

8 Literature review cont. H. G. Beyer, A. Hammer, J. Luther, J. Poplawska, K. Stolzenburg, and P. Wieting, Analysis and synthesis of cloud pattern for radiation field studies, Sol. Energy, vol. 52, no. 5, pp , May

9 Contribution Extend Beyer s work in following way: Synthesis of a cloud pattern of arbitrary time duration. The irradiance levels during clear and shaded time periods are determined using real meteorological data. The model can represent variable meteorology conditions. 9

10 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 10

11 What is a fractal? A fractal is defined as a rough or fragmented geometric shape that can be split into parts, each of which is, at least approximately, a reduced-size copy of the whole. --by Mandelbrot Fern leaf 11

12 Generate a fractal surface Midpoint displacement algorithm. Takes log 2 ( N ) stages to generate a (N+1) x (N+1) fractal surface. 2 steps in each stage. Added noise ε ~ N (0, δ 2 ). In each step δ is reduced. 12 5x5 grid example (N = 2)

13 Generate a 33 x 33 Surface Stage 0 (initialization) 13

14 Generate Surface Stage 1 14

15 Generate Surface Stage 2 15

16 Generate Surface Stage 3 16

17 Generate Surface Stage 4 17

18 Generate Surface Stage 5 18

19 A 513 x 513 fractal surface 513 x 513 fractal surface Cloud pattern 33.4% cloud coverage Z = 0 19

20 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 20

21 Facility in ISU 270 Wp DC-off grid PV station Pyranometer. RTD: model temperature. GE RH&Temp sensor. NI ENET 9205 sampling card MPPT tracking. Irradiance measurement: LI-COR LI

22 Solar Irradiance Characteristics Global irradiance Clustering technique High/Low pattern Four quantities to capture this High/Low pattern: 22 High/low pattern for irradiance

23 Solar Irradiance Characteristics Scatter plots of the duration and the relative irradiance magnitude of clear periods (a) and shaded periods (b). Clear periods within one minute. Shaded periods within 200 s. 23

24 Solar Irradiance Characteristics Scatter plots and marginal histograms of the duration and the relative irradiance magnitude for clear periods within one minute (a) and shaded periods within 200 sec. (b). 24

25 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 25

26 Cloud Coverage Ratio 26 Feb. 14, :30 Feb. 14, :30

27 Upper Air Wind Speed : NREL 1-min wind speed data measured at Power law equation: 27

28 HBI and HDI HDI: Horizontal Diffuse Irradiance (NREL data) HBI: Horizontal Beam Irradiance (Modeled) 28

29 Clear Sky GHI Solid line: clear sky global horizontal irradiance Dashed line: measured global horizontal irradiance (NREL BMS) 29

30 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 30

31 System Layout 31

32 Wind direction A: study area. Wind direction: SW. 9 frames of 513 x 513 fractal surface contour. 4.5 s to generate using Matlab running on an Intel i QM 2.2 GHz CPU. 32

33 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 33

34 Fractal and Cutting Surface Gray: fractal surface Black: cutting surface 34

35 Generate Shading Pattern (a) Sampled fractal value (dashed line) and sampled cutting surface value (solid line). (b) Shading condition. 35

36 Proposed Method - Outline Basics of fractal Solar Irradiance Characteristics Meteorological Factors Geographic Factors Generation of Shading Condition Synthesis of the Irradiance Pattern 36

37 Synthesize Irradiance (b) Shading condition. (c) Synthesized irradiance pattern. 37

38 Area Averaged Irradiance (c) Synthesized irradiance pattern. (d) Averaged irradiance pattern over the entire area. 38

39 Conclusion Propose a simulation model for irradiance pattern generation. Passing clouds are modeled and generated in fractals. High/Low irradiance pattern analyzed with data collected by the experimental station in ISU. Synthesize the irradiance pattern based on the shading condition and the statistics of irradiance levels. Emulate the spatial smoothness of irradiance pattern over an area. Future work: i) further capture and model the transition period; ii) extend the model to other types of cloud; iii) combine with the PV energy conversion model to conduct system side analysis. 39

40 Thank You 40