Photovoltaic (PV) or solar technology is a widely known and promising technology to facilitate the transition to a sustainable energy system. To ensure efficiency and reliability, EnergyVille investigates new materials for PV and PV-cell/module technology. For a widespread implementation, the integration of PV in buildings, vehicles or other infrastructure is another topic of research. As these applications require a decent lifetime and reliability, EnergyVille studies PV module ageing and reliability as well as PV module-level convertors.  Last but not least, we conduct research in energy yield prediction and forecasting.

Philip Pieters

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Philip Pieters

Business Developer Solar at EnergyVille/imec
Kris Baert

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Kris Baert

Business Developer Solar and Electrical Energy Networks at EnergyVille/KU Leuven
Lieve De Doncker

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Lieve De Doncker

Business Developer Solar and Storage Materials at EnergyVille/UHasselt
Electrical

New Materials for PV

While the average consumer might only be acquainted with standard Si-based solar cell technology, the field of photovoltaics is still in continuous evolution. Cells based on new thin-film absorber materials, like perovskites, are approaching conversion efficiencies of Si cells. However, stability and upscaling need to be further improved. EnergyVille has built up the infrastructure to investigate such new materials and to develop highly efficient large area and stable cell architectures.

For other materials systems, like CIGS, the absorber interface is meticulously controlled to enhance the output voltage while maintaining very thin films. Understanding and describing the materials properties is crucial to generate high performing photovoltaic devices. This is why EnergyVille enables the demonstration of these new device architectures not only on small lab-scale devices but on large area (30x30cm²) modules and even full integration in final applications like buildings, vehicles and infrastructure.

High efficiency PV-cell/module technology

Solar cells transform incoming light from the sun into electrical current. In Si solar cells current is generated uniformly across the full area of the cell and is collected by the so-called “fingers” of the metallization grid (a set of parallel metal lines every 1-3 mm). The current from those fingers is then collected into wider metal lines perpendicular to the fingers: “busbars”. To improve electrical performance and reduce optical losses in PV modules, the trend in Si cell interconnection is towards more and narrower busbars which then deliver the generated current to the ribbons that are soldered on top (the thin strips of copper or aluminum between cells that conduct electricity). Ultimately this is evolving to module interconnection through multi-wire technologies instead of busbars and ribbons. Because the multi-wire interconnections capture the current over a more distributed area of the cell, the width of the fingers can be strongly reduced, decreasing the cost of the metallization on cell level.

Building further on these evolutions, we have developed the concept of woven interconnection sheet by weaving encapsulant ribbons and metal wires in one fabric. This concept saves on materials and eliminates multiple process steps while it can still be run on industry-standard laminators, which are all significant advantages. Hence, this interconnection technology is a valuable new building block for our work in building and vehicle integrated PV.

Integration of PV in building facades, vehicles and infrastructure

Bringing the energy generation closer to consumption and increasing its integration in the built environment is the foundation of a swift and sustainable energy transition. Therefore EnergyVille explores the integration of PV in building facades, vehicles and other applications. This requires a close collaboration between architecture, building physics, electrical engineering and PV experts. Application-defined requirements drive our research in module convertors and electronics, PV cell and module technology, reliability testing and energy yield simulation. Through large-scale demonstration projects we validate these technology and simulation results in real-life conditions.

We research aesthetic and reliable interconnection technology that enables mass customization. Aesthetics and bespoke dimensions are a must in building integrated PV. We envisage a module assembly tool which, based on the input of architectural software, automatically assembles custom-made modules. Our multi-wire cell interconnection technology can flexibly adapt to module dimensions and will facilitate the implementation of Industry 4.0 principles.

Both for integration in buildings and vehicles, we also explore changing the PV module’s shape and dimensions in the EnergyVille labs. Integrating PV in buildings or vehicles will often cause non-uniform illumination, which calls for novel module technologies that enable efficient energy yield harvesting in non-uniform and dynamically varying conditions. By combining reconfigurable module topology with the multi-wire interconnection technology, EnergyVille aims to bring a paradigm shift for the next generation of PV modules.

PV-cell/module analysis and performance optimization

Since PV modules are applied in a variety of ways, assessment of their performance beyond the standard laboratory conditions is required. This has been largely recognized by the industry preparing a wide range of novel IEC standards in this area. We are closely involved in this process and it is based on these insights that we have selected our tools. EnergyVille has a first of a kind large area module tester using LED lighting in which we can simultaneously illuminate the front and back-side of full size PV modules. Spectral and light intensity variations can be all resolved to fully mimic varying outdoor conditions.

Another critical factor for determining PV module performance is temperature. That is why we have designed a system where PV modules can be heated during the measurement. We have also outdoor measurement sites in rack and façade configuration, complementing our indoor measurement capabilities.  In these systems we can measure PV module power with high precision and at very small time intervals. Combining this with extensive weather measurements, our research in BIPV, reliability and energy yield simulation and forecasting is excellently equipped. Focused on exploration of new materials and technologies we ensure that both industrial and small research samples can be measured in all our characterization tools.

Our cell and material and reliability characterization research is supported by vast variety of opto-electrical characterization tools (e.g. spectral response, reflectivity mapping, spectroscopy, high-resolution electroluminescence imaging) and material analysis tools (e.g. optical and electron microscopy, cross-section preparation tool, adhesion tester). Combining these broad set of characterization capabilities together with the insights of our specialists enable us to understand the root causes of PV module performance failure and devise routes for performance optimization.

PV Module ageing and reliability study

In reducing the levelized cost of electricity, lowering the degradation rate of PV modules is equally important as efficiency. ‘Design for reliability’ is the foundation of various research activities EnergyVille conducts in the field of PV module reliability.

EnergyVille conducts in-depth reliability investigation of the next generation of PV module materials and technologies. We design targeted reliability studies to investigate the weak points of the material or technologies. By combining opto-electrical characterization with destructive material analysis, we are able to uncover the underlying failure modes. These investigations and insights are further deepened through finite-element modelling of thermo-mechanical stresses. EnergyVille offers standardized testing and is involved in the International Electrotechnical Commission (IEC) standardization committees.

PV module reliability also plays a crucial role in reducing the ecological footprint of PV. One element is technology design and material selection for improved recycling and elimination of toxic materials. Through prolongation of the operational lifetime and refurbishing or reuse of PV modules, we aim to further lower the environmental impact of PV panels. EnergyVille is involved in public funded projects and consultancy to the EU commission to contribute to this effort.

PV Module-level convertors (including modelling, testing and reliability)

Current mismatch within a PV module or in between PV modules may affect the PV energy production. Due to (partial) shading of one or more series connected cells in a module or one or more series connected modules in a string, the total PV module current or the total string current will be limited. This results in a significant reduction of the overall PV module or system power.

In Building Integrated Photovoltaics or BIPV the same problem of non-uniform illumination (due to shadowing from obstacles) exists. To maximize the energy production, novel module technologies that enable efficient energy harvesting in non-uniform and dynamically varying conditions are needed. One of the most innovative but also challenging solutions is based on the idea of changing the electrical interconnection between the PV cells in real time as the PV module adapts to its environment. We propose a reconfigurable smart PV (RSPV) module concept that considerably increases energy harvesting in non-optimal conditions. This module integrates switches and intra-module converters into its own volume in order to make the self-reconfiguration possible.

Both for standard and reconfigurable PV modules, module level and intra-module convertors must be compact for integration and must match the stringent reliability requirements. This asks for reliability testing and understanding of the failure beyond the current standard metrics and measurements. We aim to not only measure failure rate but also degradation rates of such novel convertor designs. For this we use accelerated synthetic mission profiles.

PV energy yield metrology, simulation & forecasting

When it comes to solar energy, an optimal energy yield is key. Nowadays, the energy performance of PV modules is measured indoors under standard testing conditions. However, in reality, outdoor conditions vary significantly from these standard defined conditions. To bridge the gap between indoor and outdoor performance and to come to the highest yield of solar energy, EnergyVille has developed both indoor and outdoor testing setups and an accurate energy yield simulation model.

EnergyVille’s energy yield simulation model is a scenario-based software which accurately simulates the expected daily energy yield of solar cells and solar modules under varying meteorological and irradiation conditions using available historic weather data. The model combines optical, thermal and electrical parameters to provide detailed insight on thermal variations in the solar module. The model integrates the effect of these variations, resulting in a significantly better accuracy than commercially available software packages for energy yield estimation. In contrast to most existing models for energy yield calculation, our energy-yield simulation model starts from the physical parameters of the solar cells and the used materials, and includes on top of that the variations due to changing external conditions. This way, a ‘closer to reality’ model is obtained, enabling a more precise analysis of the effects of solar cell and module technology changes on the energy yield of these photovoltaic cells and modules.