High-resolution spatial and electrical modeling for efficient BIPV system design

Johannes Hofer, Arno Schlueter

Architecture & Building Systems, Institute of Technology in Architecture, ETH Zurich

6th PV Performance Modeling and Monitoring Workshop

Fraunhofer Institute for Solar Energy Systems ISE

October 24 and 25, 2016 | Freiburg | Germany

Opportunities for BIPV and thin-film PV

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• Growing opportunity for PV in buildings due to energyregulation (EU NZEB, MuKEn)

• Increasing efficiency andreduced cost of thin-film PV (CIGS, CdTe, OPV, etc.)

• Lightweight and flexible, partial transparency, different colors

• New integration possibilities(buildings, transport, consumerelectronics, etc.)

• Low cost production andinstallation

Source: www.beautiful-light.eu

Source: www.pv-magazine.com

BIPV Applications

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www.coltinfo.co.uk

SwissTech convention centerwww.archiexpo.com

Adrian Smith + Gordon Gill Architecture

NEST HiLo Project

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HiLo building to be constructed in 2017 at NEST (EMPA, Switzerland)

• Leightweight integrated roof and floor

• Thin-film PV applications (curved roof modules, adaptive solar facade)

Further information:

www.empa.ch/web/nest/

www.hilo.arch.ethz.ch

Challenges and Objective

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Challenges

• Non-uniform irradiance (due to partial shading or curvature) generatesimbalance between PV cells and modules

• Performance of thin-film modules in partial shading and under curvaturenot well known

• No adequate design and planning tools

Objectives

• Creating a modeling framework coupling high-resolution geometry, irradiance, electrical simualtion

• Compare and validate with experimental analysis

• Apply in context of NEST HiLo project

Modelling Workflow

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Electrical model(Matlab/Python)

IV characteristicsPower generation

Irradiance model(RADIANCE/DIVA)

Shading calculationModule irradiance

CAD model(Rhinoceros

3D/Grasshopper)

PV geometryModule positioning

Building parameters

PV system parameters

Electrical designWeather data

Geometric Model and Shading Analysis

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J. Hofer et al., Energy Science and Engineering, 4, 2, 134-152, 2016

A. Groenewolt et al., Int J Energy Environ Eng, 2016

PV modules on the roof PV modules on the facade

• Parametric model (Rhino/Grasshopper) to

simulate PV modules on roof and facade

• Triangulation method for layout of PV strips

• Parameters: module dimension, module

distance, strip orientation, etc.

Irradiance Analysis

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Sun directions

• Cumulative sky approach (Radiance): matrix of sky patch values using the Perez all-weather model and hourly weather data

• High resolution sky using the Reinhart sky patch subdivision

• Backward ray tracing to calculate irradiance on geometry

• Irradiance model with sub-cell resolution (same as the electrical model)

PV Electrical Model

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Modules

• Cells split in sub-cells, simulated with one diodemodel

• Reverse breakdown

• Bypass diodes

PV system

• Series-parallel interconnection of modules

• Distributed electronics(power optimizer ormicroinverter)

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

PV Module Layout

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Electrical layout parameters

• Cell dimension

• Cell arrangement andinterconnection

• Module bypass diodes

Designs investigated

• Commercial CIGS modules

• Modules defined byindustrial partner

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Performance in Partial Shading

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Longitudinal shadingLateral shading

• Measurement of I-V curves in various partial shading conditions

• Module design and shading pattern strongly affect power loss

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

lateralshaded

not shaded

longitudinal

shaded not shaded

Performance in Partial Shading

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• Comparison of model vs. experiment (module 1)

• Further comparison model/experiment for other module designs andinterconnected modules

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Design of PV as Shading Element

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• Parametric 3D design of different adaptive shading system configurations

Horizontal louvers (1-axis) Vertical louvers (1-axis) Diamond pattern (2-axis)

• Calculate electric performance and

optimize system design

• Module arrangement and spacing

• Cell orientation

• String interconnection

• Bypass diode integration

J. Hofer et al., Energy Science and Engineering, 4, 2, 134-152, 2016

Facade cover ratio (FCR) =

module area / facade area

Design of PV as Shading Element

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• Applied in context of Adaptive Solar Façade (ASF) project

• PV cell orientation and placement of bypass diodes strongly affect energy yield

P. Jayathissa et al., European Solar Energy Conference, Munich, Germany, 2016

J. Hofer et al., Energy Science and Engineering, 4, 2, 134-152, 2016

Performance of Curved PV Modules

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• Simulation of irradiance and power outputof curved modules (design 1)

• Flat horizontal module for comparison

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Performance of Curved PV Modules

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• Flat horizontal: efficiency mainly determined by temperature

• Curved: mismatch of irradiance between cells leads to efficiency loss

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Performance of Curved PV Modules

• Experimental measurements using digitally fabricated prototype with same predefined geomtery

• Very similar dependence of efficiency observed (for this module design)

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Application to HiLo Building

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J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

PV Module Layout

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Irradiance and electricity yield vs. orientation

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

PV System Electrical Design

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• Simulate irradiance distribution between

cells and modules

• Optimize electrical layout

• Power optimizers to balance mismatch

J. Hofer et al., European Solar Energy Conference, Munich, Germany, 2016

Conclusions

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Summary

• Framework for modeling of PV modules in non-uniform irradiance

• PV module and system layout strongly influences the performance

• Can be used for efficient system design

Outlook

• Identify PV module designs less sensitive in partial shading / curvature

• Measurements with a full scale ASF and a section of actual HiLo roof

• Evaluate module level electronics to balance mismatch

Acknowledgement

• NEST HiLo team

• Industrial partner

• Sponsors

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Contact: hofer@arch.ethz.ch

Architecture& Building Systems: www.systems.arch.ethz.ch