micro-CPV – Development of a Highly Concentrating CPV Module Based on Modern Micro-Production Technology

Innovative manufacturing technologies, e.g. for large-area displays, enable the cost-effective production of units consisting of thousands of interconnected semiconductor devices by miniaturization, additive manufacturing, parallelization and self-alignment. The objective of the "micro-CPV" joint project is to develop a concentrator photovoltaic (CPV) module based on these technologies. This shall enable high PV performance while at the same time exploiting cost reduction potentials in production.

Concentrating photovoltaics (CPV) achieves the highest efficiency and lowest energy payback times of all photovoltaic technologies. The up to 1000-fold optical concentration increases the efficiency and reduces the solar cell area used. This means that more expensive but highly efficient III-V multi-junction solar cells can be used for terrestrial applications. In 2022, Fraunhofer ISE set a new record for the conversion of solar radiation into electrical power with an efficiency of 47.6% using a concentrator solar cell. The industrial implementation of CPV technology has already been demonstrated in numerous multi-MW power plant installations. However, module costs need to be reduced further in order to remain competitive. This is where the joint project "micro-CPV" comes in, in which synergies with products from microelectronics, optoelectronics and display production are evaluated for a significant cost reduction of highly efficient CPV modules. Rapid progress in the areas of miniaturization, additive manufacturing, parallelization and self-alignment, driven among other things by the development of displays based on µ-LEDs, promises a steep learning curve and cost degression.

In this project, we are developing a micro-CPV module with a low-cost lens array that focuses the light onto a spherical lens secondary optic and then onto the miniature III-V concentrator solar cell. This configuration allows both 1000-fold sunlight concentration and a high acceptance angle for module alignment with a flat design of a few centimeters.

Advanced additive circuit board technologies in combination with panel-level packaging processes are being evaluated for the base plate. Micro-concentrator solar cells with an area of just a fraction of a square millimetre are separated with little or no kerf loss and then mounted and interconnected directly onto the panel in a self-aligning manner. Because the solar cells are so small, the cell operating temperature remains acceptable in spite of the exposure to high sun concentrations and the absence of a dedicated heat sink.

The high innovation potential in this research and development project is primarily the result of the outstanding technological expertise of the various partners involved, who cover the CPV value chain from individual components and processes through to finished modules.

Initially, small test modules with 3×3 interconnected solar cells were produced in the project and used to evaluate the various technology components, such as solar cell structures, circuit board designs, spherical lenses and primary lens plates. Technological aspects and the impact on module performance as well as economic aspects are taken into account for the evaluation.

The first demonstrator module developed was an array of 6×10=60 cell-lens units with an aperture area of 205 cm². This demonstrator module has been undergoing field testing since April 2023. A filtered performance evaluation carried out according to IEC 62670-3 criteria shows a CSTC (concentrator standard testing conditions) efficiency of above 36%.

In addition to the development of new components and manufacturing technologies, the focus is also on model-based understanding of the interrelationships in the module. Using a new nested optical-electrical Monte Carlo modeling approach, we are investigating the effects of various tolerances, i.e. slight deviations in the size and arrangement of components as they prevail in real modules, on performance. The results help with further development and provide information on where further improvements have the greatest leverage or where slightly less stringent tolerances can offer techno-economic advantages.

Components and manufacturing processes as well as packaging technologies are currently being transferred to larger modules in the 24"×18" panel format (>2000 cm²), a standard format in PCB technology and panel-level packaging in microelectronics. Results of a first panel-format micro-CPV module are expected at the end of 2024.

More Information on this Topic:

• Cost Competitive Tracker Prototype for Next generation Concentrating Photovoltaics
• Young Scientist Award auf der CPV-18 Konferenz
• Forced Motion Activated Self-Alignment of Micro-CPV Solar Cells (IEEE Journal of Photovoltaics)
• Technical boundaries of micro-CPV module components: How small is enough? (Proceedings of the 17^th International Conference on Concentrator Photovoltaic Systems (CPV-17)