This document discusses using bifacial solar modules in east-west orientations to better match solar power generation to load profiles. Simulations show bifacial modules in east-west orientations can generate more total power over a day compared to south-facing monofacial modules due to light collection from both sides. However, shading losses increase at high density spacings. Using reflective material between modules can significantly increase power output by over 60% by reflecting more light to the rear side. Proper system design accounting for load profile, storage costs, reflectivity and other factors is needed to determine the most economical solar solution. Further measurements on real systems are still required to improve simulation accuracy for bifacial modules.

1. Zürcher Fachhochschule
New opportunities of grid integration
by the use of bifacial modules
H. Nussbaumer, T. Baumann, F. Carigiet, N. Keller, D. Schär,
F. Baumgartner

2. Zürcher Fachhochschule
ZHAW –SoE - IEFE PV
• ZHAW = Zurich University of Applied Sciences
• Close to 11.000 students
• School of Engineering located in Winterthur (~15km
away from Zurich)
• IEFE = Institute of Energy Systems and Fluid
Engineering

3. Zürcher Fachhochschule
ZHAW –SoE - IEFE PV

4. Zürcher Fachhochschule
ZHAW –SoE - IEFE PV
• Focus
Silicon Wafer Solar cell Module System
Integration,
Batteries

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Increasing share of PV
Lost energy or energy storage

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Power distribution / storage
In the near future many regions will face the problem
of an over PV capacity during midday and too low
capacity in the evening
We do not only have to think about the maximum
energy harvest but also about the load profile!
We need energy storage or have to adapt the
energy production profile on the load profile

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Load distribution, example Chile
• If we want to supply energy to a copper mine we
have to ask:
• “What is the load profile of a copper mine?”

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Solution:Energy storage
Peak shift - battery storage & costs
N. Kreutzer, C. Allert, J. Weide, M. Rothert, F. Thim; 4BV.1.31
25th European Photovoltaic Solar Energy Conference /5th World Conference
on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain
produce it
0.18 USD/kWh
store it
> 0.42 USD/kWh+ = use it
> 0.60 USD/kWh
4 person household
5kW PV
20% to 40%
PV self consumption
0.74€/kWh; F. Baumgartner et. al. EUPVSEC 2012, Plenary Talk, www.zhaw.ch/~bauf

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Solution: Energy storage
Peak shift - battery storage & costs
Copper mine
Power
Load profile copper mine
PV power generation profile
Transfer this energy adds
significant cost
Time
store it
> 0.42 USD/kWh

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Solution: Energy storage
Peak shift - battery storage & costs
Energy storage significantly increases the cost of
generated PV energy
Due to large scale production of batteries cost of
storage tend to go down but even, if they were cut by
half, the cost of generated kWh of PV will by at least
doubled-
Can we modify the PV energy generation profile?

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Solution 2 ?: East/west orientation of
bifacial modules
N
W

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Bifacial Module
Measurement - Setup
• Bifacial: vertical - azimuth 90° Pn1=255.6 / 232.6 WSTC
• Bifacial: 30° inclination / azimuth 0° Pn2=255.3 / 231.7 WSTC

13. Zürcher Fachhochschule
Bifacial module east/west
Measurement results:
+8.4% Power @ 2014-05-18
5 8 11 14 817 20
Irradiance
Power East/West
Power South

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=> With a bifacial module in east/west orientation you
would need less peak shift, if your load is in the
morning and the evening!
• What happens in the PV system?

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PV System bifacial
south orientation
d
𝑓 = 𝑏/𝑑 b
Characteristics:
• Depending on mounting height and albedo higher energy harvest as
compared to standard modules
• Energy peak during midday
• Shading losses below 5% (Zurich) for f = 0.5
south

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PV system bifacial
east/west
Characteristics:
• Broader distribution of the daily energy production
• Very low chance of soiling
• Possibility of using alternative, maybe cheaper, mounting systems
• Chance of further enhancing the energy harvest by use of reflective underground
• Higher energy harvest as compared to south oriented module but
• Enhanced shading losses based on the same degree of land utilisation as
compared to south orientation
S
E

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Simulation with PVSyst
• Simulation parameters
– 2 standard modules = 1 bifi module
– Variation of tilt angle and azimut
– Albedo = 0.2, model Perez
• Degree of area utilization 𝑓 = 𝑏/𝑑
• Limitation: No complete row of modules as shading barrier
Bifi Module simulated
d = Distance between modules
S
b

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First Simulation results using PVSyst
Using a standard utilization factor of 0.5 a relative difference of 10% in
shading is observed- but?
0%
5%
10%
15%
20%
25%
30%
35%
1,00 0,50 0,33 0,25
LossinPercent
Degree of area utilization
Bifacial east/west
orientation
South 37°
South 30°
Shading losses resulting from neighbored modules

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Simulation with PVSyst
 A PV System consisting of east/west bifacial modules can be superior to
monofacial modules with the same area utilization rate, if a reflective
material is positioned in between the modules- this overcompensates the
higher shading by far!
 First measurements with a white foil
have shown an increase of power
by ~60% (no shading)
f=0.5 PR
Monofacial 30° South oriented, Albedo 0.2 100.8%
Monofacial 30° South orientated Albedo 0.85 101.2%
Bifacial East/West orientated 90° Albedo 0.2 96.4%
Bifacial East/West orientated 90° Albedo 0.85 126.8% 2
_
/1 mkW
P
E
E
PR
N
InputSolar
AC

-5%
+25%

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Simulation with PVsyst
Albedo 0.2
6 8:45 16:3014
Measured data
Power
Simulated data
=>The simulation with PVsyst does not show a good fit to the measured data!

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Conclusion
• There is a need for PV power generation profiling in order to adapt to the
power load
• Bifacial modules in east/west orientation are a possible solution if the
highest load is in the morning and evening
• Shading has a severe impact on the energy harvest for PV systems with
east/west oriented modules for high area utilization rates.
• Using a reflective ground in between the modules can have a significant
impact on the energy harvest, especially for east/west oriented modules
• The most economic solution for a certain energy system using PV
depends on
– Energy load distribution
– Cost for energy storage
– Area related costs
– Conditions for soiling
– Wind loads
– Reflectivity of the ground
Designing a PV system is
getting more complex

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Outlook
• Simulation models have to be adapted to bifacial
modules in order to give better predictions
• Measurement on real bifacial PV systems with
east/west orientation will be made and compared to
simulated data using various reflective
undergrounds, heights of the modules, area
utilization ratios

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Acknowledgement
Many thanks to our friends at the ISC for the good
cooperation
and for your attention!