Technology and market perspective for indoor photovoltaic cells

https://iopscience.iop.org/article/10.1088/1361-6463/ab9c6a/pdf

The 2020 photovoltaic technologies roadmap

Photovoltaic (PV) solar energy recorded an exponential growth, in worldwide scale, over the last decade. Inevitably, mature PV markets are becoming highly competitive, boosting the need for research and development (R&D) on efficiency and reliability optimization, maintenance and fault diagnosis of key components, such as the PV modules. Indeed, a significant number of studies and technical papers have been published up today, based on an extensive feedback from both laboratory and real (field) investigations of faults and advanced diagnosis applications, especially for crystalline silicon (c-Si) PV modules. Undoubtedly, such experience is of particular interest for current PV plant operators, future investors, maintenance engineers and the R&D sector of PV industry. However, up today, such research, published in the form of reports, technical papers or even books, remains mostly dispersed and unclassified. This paper represents a comprehensive effort to review and highlight recent advances, ongoing research and future prospects, as reported in the literature, on the classification of faults in c-Si PV modules and advanced diagnosis in the field, by means of the increasingly popular method of infrared thermal (IRT) imaging. In particular, the first main part of this paper, reviews the characteristics of the most common fault types of operating PV modules, in terms of electrical and thermal response. Then, the second part gives a thorough review of recently published research, as well as the state-of-the-art, in the fields of IRT-based fault diagnosis and thermal image processing. On the basis of these two individual though supplementary review parts, an overview table is presented, followed by a discussion on the future prospects and challenges, towards the understanding and diagnosis of faults and their propagation in operating PV modules.

Faults and infrared thermographic diagnosis in operating c-Si photovoltaic modules: A review of research and future challenges

The power conversion efficiencies (PCEs) of flexible organic solar cells (OSCs) still lag behind those of rigid devices and their mechanical stability is unable to meet the needs of flexible electronics at present due to the lack of a high-performance flexible transparent electrode (FTE). Here, a so-called "welding" concept is proposed to design an FTE with tight binding of the upper electrode and the underlying substrate. The upper electrode consisting of solution-processed Al-doped ZnO (AZO) and silver nanowire (AgNW) network is well welded by utilizing the capillary force effect and secondary growth of AZO, leading to a reduction of the AgNWs junction site resistance. Meanwhile, the poly(ethylene terephthalate) is modified by embedding the AgNWs, which are then used to link with the AgNWs in the upper hybrid electrode, thus enhancing the adhesion of the electrode to the substrate. By this welding strategy, critical bottleneck issues relating to the FTEs in terms of optoelectronic and mechanical properties are comprehensively addressed. The single-junction flexible OSCs based on this welded FTE show a high performance, achieving a record high PCE of 15.21%. In addition, the PCEs of the flexible OSCs are less influenced by the device area and display robust bending durability even under extreme test conditions.

Realizing Ultrahigh Mechanical Flexibility and >15% Efficiency of Flexible Organic Solar Cells via a "Welding" Flexible Transparent Electrode.

The analysis of the performance of photovoltaic (PV) installations mounted on a floating platform is performed. Different design solutions for increasing the efficiency and cost effectiveness of floating photovoltaic (FPV) plants are presented and discussed. Specifically, FPV solutions that exploit the advantages of additional features such as tracking, cooling and concentration, are presented. The results of experimental tests are reported and they show a considerable increase in efficiency due to the positive tracking and cooling effects. Gains due to the use of flat reflectors are also analyzed. Finally, the possibility of exploiting the floating structure on water in order to develop an integrated air storage system is presented.

Floating photovoltaic plants: Performance analysis and design solutions

Spatial and orientational distribution of cracks in crystalline photovoltaic modules generated by mechanical load tests

Unified methodology for determining CTM ratios: Systematic prediction of module power☆

We introduce an approach to determine the operating voltage of individual solar cells in photovoltaic (PV) modules by electroluminescence (EL) imaging. The highest EL signal of each solar cell is proportional to its operating voltage. Moreover the sum of all operating voltages equals the externally applied module voltage. Thus the operating voltage of individual solar cells is determined from the measured EL signal. The reliability of this relation is verified by measurements on specially prepared PV modules allowing us to measure the individual operating cell voltage. The experimentally measured cell voltages are deduced with an uncertainty of ±1% from an EL image.



Moreover, the operating cell voltages determined from the EL image are used to calculate the module series resistance. Comparing experimentally determined values from the operating cell voltage and the total current flowing supplied to the module with calculated module series resistances using tabulated material and typical solar cell parameters, a very good correspondence is found. Copyright © 2010 John Wiley & Sons, Ltd.

Detection of the voltage distribution in photovoltaic modules by electroluminescence imaging

The long-term stability of photovoltaic (PV) modules is largely influenced by the module’s ability to withstand thermal cycling between −40°C and 85°C. Due to different coefficients of thermal expansion (CTE) of the different module materials the change in temperature creates stresses. We quantify these thermomechanical stresses by performing a Finite-Element-analysis of a 60 cell module during thermal cycling. We therefore start by the experimental characterization of each material layer. In particular, the polymeric encapsulant is characterized by three alternative models in order to stepwise consider the time- and temperature-dependence in the simulation. Experiments performed with laminated samples are used to validate the computational model. We find that taking into account the viscoelasticity of the encapsulation layers gives the best agreement with experiments. The Finite-Element-analysis of the complete module shows that the solar cells are under high compressive stress of up to 76 MPa as they are sandwiched between the stiff front glass and the strongly contracting plastic back sheet. The non-symmetrical structure of the 5.55 mm thick module with glass being the thickest component (4 mm) leads to bending during the thermal cycle.

Ulrich Eitner

Papers

Spatial and orientational distribution of cracks in crystalline photovoltaic modules generated by mechanical load tests

Unified methodology for determining CTM ratios: Systematic prediction of module power☆

Detection of the voltage distribution in photovoltaic modules by electroluminescence imaging

Thermal Stress and Strain of Solar Cells in Photovoltaic Modules

Multi-wire interconnection of busbar-free solar cells