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

Concentrator photovoltaics (CPV) reach the highest efficiencies [1] and lowest energy payback times [2] of all photovoltaic technologies. By using an optical concentration of up to 1000-fold, the cell efficiency can be increased and the solar cell area reduced at the same time. This allows the more costly, yet highly efficient, III-V multi-junction solar cells to be used for terrestrial applications. The industrial implementation of CPV technology has already been demonstrated in numerous multi-MW power plant installations. [3] However, to become competitive, module costs must be further reduced. The »micro-CPV« project addresses this by evaluating synergies with technologies from the fields of microelectronics, optoelectronics and display manufacturing to significantly reduce high efficiency CPV module costs. The rapid progress in the areas of miniaturization, additive manufacturing, parallelization and self-alignment – technologies which have been driven by the development of µ-LED displays, among others – shows promise of a steep learning curve and cost reductions also for CPV module manufacturing.

In the project, a micro-CPV module with an inexpensive all-glass lens array is developed, which focuses the light onto ball lenses acting as secondary optics and then onto the miniature III-V concentrator solar cell. With a flat design of only a few centimeters module height, this configuration allows a sunlight concentration of 1000-fold as well as a high acceptance angle for the module alignment towards the sun.

For the base plate, advanced additive printed circuit board technology is combined with panel-level packaging processes. Micro-concentrator solar cells with an area of only a fraction of a square millimeter are separated without 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 level of innovation potential in this research and development project is primarily due to the outstanding technological competence of the various partners in the project consortium. Their areas of expertise  ranges across the entire value chain from the individual components and processes up to complete modules.

First test modules have been built in the course of 2021 to evaluate the different technology building blocks developed by the partners. Experimental investigation and evaluation is ongoing (see photo above). Among others we study different solar cell structures, printed circuit board designs, ball lenses as well as primary lens plates. For the evaluation and assessment, we take into account technological aspects and their effect on module performance as well as economic aspects. With a mono module, i.e. an assembly of a singular primary lens and a 5-junction micro solar cell with secondary ball lens in the focal spot, we have demonstrated a module efficiency of 35.6% in outdoor measurements (Fig.2).

Sources:

[1] Martin A. Green, Ewan D. Dunlop, Dean H. Levi, Jochen Hohl-Ebinger, Masahiro Yoshita, Anita W.Y. Ho-Baillie, Solar cell efficiency tables (version 54). Prog. Photovolt: Res. Appl. 27(7), 2019. DOI: 10.1002/pip.3171

[2] Halasah, Pearlmutter, Feuermann, Field installation versus local integration of photovoltaic systems and their effect on energy evaluation metrics. Energy Policy 52, 2013. DOI: 10.1016/j.enpol.2012.09.063

[3] Maike Wiesenfarth, Simon P. Philipps, Andreas W. Bett (Fraunhofer ISE) / Kelsey Horowitz, Sarah Kurtz (National Renewable Energy Laboratory NREL, USA), Studie: Current Status of Concentrator Photovoltaic (CPV) Technology, Version 1.3, April 2017, https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/cpv-report-ise-nrel.pdf