development of an optical model for simulating energy...
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Development of an optical model forsimulating energy yield of a bifacial
PV array
25-26.10.2017
Dimitrij Chudinzow,
Ludger Eltrop
Picture: http://www.desertmodule.cl/
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IER Universität Stuttgart 226.10.2017
1. Introduction into bifacial PV
2. Methodology for energy yield modelling
3. Results
Agenda
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IER Universität Stuttgart 326.10.2017
… with monofacial PV (!)
PV electricity market prices set new world record in 2016 in Chile
1: https://www.pv-magazine.com
2: https://www.pv-magazine-latam.com
Imagine, how much more efficient could PV become
(even in less sunny regions than Chile)
if using both sides of the module!!!
Introduction ResultsMethodology
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IER Universität Stuttgart 626.10.2017
Utility-scale bifacial power plants
• Pel= 1.25 MW
• Inauguration: 2013
• Fixed tilt
1: Photovoltaic Technical Solutions Presentation, 2016
2: isc-konstanz.de
3: pv-magazine.com
• Pel= 2.5 MW
• Inauguration : 2016
• Fixed tilt
La Hormiga PV Power Plant (commercial), Chile2
Sunpreme PV Power Plant (commercial), USA3
• Pel= 12.8 MW
• Inauguration : 2016
• Fixed tilt
Hokuto PV Power Plant (test facility), Japan1
Introduction ResultsMethodology
Bifacial Gain = EnergyrearEnergyfront
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IER Universität Stuttgart 726.10.2017
Which bifacial gain can one expect from bifacial PV plants?
Hokuto bifacial PV Power Plant, fixed-tilt, 1.25 MW1
1: World First Large Scale 1.25MW Bifacial PV Power Plant on Snowy Area in Japan, 3rd bifi PV workshop in Miyazaki, Japan, 2016
Introduction ResultsMethodology
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IER Universität Stuttgart 826.10.2017
These factors directly influence the
shading constellation and thus the
ground-reflected irradiation from
DNI & DHI (albedo)
SunEdison PV Power Plant, Chile1
Influencing factors on absorbed irradiation
1: pv-magazine.com
1. Location
• Weather conditions
• Ground albedo factor
2. Field layout
• Elevation (installation height)
• Orientation
• Row spacing
• Slope
Introduction ResultsMethodology
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IER Universität Stuttgart 926.10.2017
Absorbed irradiation by conventional (monofacial) PV
DNI
DHI
Introduction ResultsMethodology
DNI: Direct Normal Irradiation
DHI: Diffuse Horizontal Irradiation
DNIground, albedo
DHIground, albedo
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IER Universität Stuttgart 1026.10.2017
Absorbed irradiation by bifacial PV
DNI
DHI
Ground albedo
from DHI
Shaded area:
calculable size &
position
Ground albedo
from DNI + DHIUnshaded area: unknown
size & position
„How can one properly take ground albedo
irradiation (from DNI & DHI) into account?“
Introduction ResultsMethodology
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IER Universität Stuttgart 1126.10.2017
Definition of „view fields“
Dashed lines
seperate front
and rear side
Ground albedo:
DNI + DHI
Length
Width
Introduction ResultsMethodology
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IER Universität Stuttgart 1226.10.2017
Definition of „view fields“
• Length of front and rear view fields depends on row
spacing, elevation and slope
• FVF of first and RVF of last row are treated differently
• Width of view fields is defined exogeneously:
• Higher widthmore albedo energy (how much
more?), but also higher land purchase costs
For a fixed-tilt configuration, the view fields are
time-invariant
front rear
Length of front view field (FVF) Length of rear view field (RVF)
Introduction ResultsMethodology
Sideview
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IER Universität Stuttgart 1326.10.2017
View fields implemented in Matlab
Here no self-shading occurs (7h after sunrise) Here self-shading occurs (12h after sunrise)
Introduction ResultsMethodology
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IER Universität Stuttgart 1426.10.2017
View fields implemented in Matlab
Here no self-shading occurs (7h after sunrise) Here self-shading occurs (12h after sunrise)
Introduction ResultsMethodology
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IER Universität Stuttgart 1526.10.2017
Recap of developed methodology
Introduction ResultsMethodology
„How can one properly take ground albedo
irradiation (from DNI & DHI) into account?“
Definition of view fields
+
using theory of view factors to compute
share of ground albedo irradiation that hits
the module‘s surfaces
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IER Universität Stuttgart 1626.10.2017
Simulation set-up
Introduction ResultsMethodology
• Location: Atacama Desert, Chile
• Weather data in hourly resolution
• Computation resolution: 20 min
• PV Array: 80 modules in 4 rows (≈21 kWel)
• Ground reflectivity: 20%
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IER Universität Stuttgart 1726.10.2017
Monthly absorbed irradiation
Introduction ResultsMethodology
Slope=25°, elevation= 3.5m, row spacing=4m
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IER Universität Stuttgart 1826.10.2017
Annual absorbed energy
Introduction ResultsMethodology
Slope=25°, elevation=2m, variation of row spacing
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IER Universität Stuttgart 1926.10.2017
Annual bifacial gain of absorbed irradiation (AI)
Introduction ResultsMethodology
Row spacing=5m, variation of slope and elevation
Bifacial GainAI =Absorbed IrradiationrearAbsorbed Irradiationfront
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IER Universität Stuttgart 2026.10.2017
Conclusions
Introduction ResultsMethodology
• The definition and implementation of „view fields“ for both sides of a module is
suitable to take into account different irradiance contributions
• Bifacial gain highly depends on array desing
(slope, elevation, row spacing, assumed width of view fields)
• Simulations show that a bifacial gain of over 40% of absorbed energy is possible
• Next step is to implement a submodel to calculate produced electric energy
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Muchas Gracias!
Telefon +49 (0) 711 685-87870
Fax +49 (0) 711 685-87873
Universität Stuttgart
Heßbrühlstraße 49a
70565 Stuttgart
Dimitrij Chudinzow, M. Sc.
IER Institut für Energiewirtschaft
und Rationelle Energiewendung
IER Institut für Energiewirtschaftund Rationelle Energieanwendung
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Annex
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IER Universität Stuttgart 2326.10.2017
𝜙12 =diffuse energy leaving A1directly toward and intercepted by A2
total diffuse enrgy leaving A1
1
𝜙12 =1
𝜋𝐴1𝐴1
𝐴2cos 𝛽1 ∙cos(𝛽2)
𝑠²𝑑𝐴1𝑑𝐴2
1
Theory of „view factors“
1: Heat Transfer Handbook, 2003
2: VDI Wärmeatlas, 2013
Theory of „view factors“ 2
Assumption: All surfaces radiate diffusely
View factor is a solely geometric quantity
Sum of all view factors for one surface is always 1
(conservation of energy)
Introduction ResultsMethodology
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IER Universität Stuttgart 2426.10.2017
• The time-variant view factors from „ground shadowmodule row“ and „view fieldmodule row“
are calculated using an algorithm in Matlab, developed by Nicolas Lauzier1
• Time-invariant view factors „module row sky“ (Perez model) are calculated using methodologies
from:
• For inner rows: View factors of photovoltaic collector systems, Maor, T.; Appelbaum, J., 2012
• For outer rows: FC→sky =1+cos(𝛽)
2, 𝛽 = 𝑚𝑜𝑑𝑢𝑙𝑒′𝑠 𝑠𝑙𝑜𝑝𝑒
(Both approaches for time-invariant view factor calculation assume infinitely long module rows)
Calculation of „view factors“
1: https://de.mathworks.com/matlabcentral/fileexchange/5664-view-factors
Introduction ResultsMethodology
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IER Universität Stuttgart 2526.10.2017
Daily absorbed energy
Introduction ResultsMethodology
San Pedro de Atacama, slope=25°, elevation=3.5m, row spacing=4m
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IER Universität Stuttgart 2626.10.2017
Annual absorbed energy
Introduction ResultsMethodology
Slope=25°, elevation=3.5m, row spacing=4m
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IER Universität Stuttgart 2726.10.2017
Low Solar Bids
https://c1cleantechnicacom-wpengine.netdna-ssl.com/files/2016/08/low-solar-bids.png
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IER Universität Stuttgart 2826.10.2017
Annual bifacial gain of absorbed energy
Introduction ResultsMethodology
Row spacing=4m, variation of slope and elevation
Bifacial GainAI =Absorbed IrradiationrearAbsorbed Irradiationfront