European PV Solar Energy Conference and Exhibition

The European PV Solar Energy Conference and Exhibition (EU PVSEC) is one of the major events of the PV research. This year hold in Marseille from September 9 to 13, several PVLAB members will attend. Peter Fiala will present on textured single-junction perovskite solar cell while Lionel Bloch will discuss incentives mechanism to promote high penetration of PV in the distribution network while keeping the network operation in bounds. Finally, Alessandro Virtuani will present results of the temperature behavior of light-weight building integrated PV module and a novel model for predicting potential induced degradation  in crystaline silicon modules.

Peter Fialas's abstract:
In the field of perovskite thin-film solar cells (PSC), solution-based deposition methods dominate as the most common means to fabricate the perovskite absorber. Typically this restricts PSC architectures to thin, planar layers, which experience optical losses through reflection and transmission. PSC could in theory employ a textured absorber interface for ideal light management in order to eschew the optical losses typical of thin films, but this would require new methods and materials. In this work, we first perform optical simulations to determine the effect of different texture designs, optimize a conductive textured substrate, and finally fabricate proof-of-concept PSC on these substrates. Optical ray-tracing simulations were done using atomic force microscopy scans of various textured surfaces. These textures were formed by KOH-etched silicon wafers and boron-doped zinc oxide (ZnO), deposited by low-pressure chemical vapor deposition. Optically optimal ZnO surfaces were then used to fabricate PSC in the p-i-n architecture on ZnO substrates via a 2-step evaporation/spin-coating method previously reported [1]. Demonstrated PSC verified the trends predicted by simulation, with increased short-circuit current density (J_SC) and removed interference fringes from external quantum efficiency curves. However, improved optical performance and J_SC are not the only factors relevant to the overall performance of our PSC. Optimization of the full device and the impact of textured interfaces on other device parameters will be discussed at the conference.

Lionel Bloch's abstract:
In the path toward a decarbonized society, the integration of a large share of renewable energy source is a mandatory step. In this context, the EU commission set the goal of a 32% penetration of renewable energy by 2030. To achieve this goal, distributed PV energy has to be widely deployed in the low voltage distribution grids. However, the variability and uncertainty inherent to PV generation bring, in case of high penetration, new challenges for distribution grids. In this context, this work proposes a novel approach to investigate how regulation and tariff-based incentives allow maximising the PV penetration in any distribution network without requiring high grid reinforcement cost. The first step of this approach uses a developed model that optimally allocates electricity demand profiles in the distribution grid based on available GIS data. This allocation presents the benefit of preserving the stochastic nature of the electricity demand, essential for any grid scale analysis. Then to evaluate the impact of a specific incentive on the design and control of building energy systems, a full year optimisation for each building is performed combined with a power flow simulation to ensure both optimality of the solution in terms of profitability as well as feasibility in terms of network operational constraints. The results show the effectiveness of tariff-based incentives and regulation to increase the potential PV penetration.

Alessandro Virtuani's abstract on BIPV monitoring:
In the case of older buildings undergoing renovation, excessive loads are often not well tolerated by roofs or other building structures (e.g. facades) [1], [2], which limits the adoption of PV in these contexts. The idea of lightweight modules is very attractive especially for the building‑integration of photovoltaics (BIPV) thanks to their reduced weight and strong improvements in durability [3]–[5]. On the other hand, the thick backsheet structure of lightweight modules may be seen as a disadvantage, because it may induce higher module operating temperatures (OT). In a fully-integrated BIPV installation, module operating temperature can be even higher due to the limited rear ventilation. Consequently, the high temperature may contribute to a faster module degradation and reduced energy-yield. This work demonstrates that lightweight (~6 kg/m²) photovoltaic module based on a composite sandwich backsheet and a polymeric frontsheet can reach equivalent (or lower) operating temperatures of standard glass‑glass modules thanks to a careful material selection. Additionally, we propose an innovative installation based on Velcro that allows a fast and easier mounting that comply with the static mechanical load test present in the IEC 61215.

Alessandro Virtuani's abstract on PID:

We propose a mathematical model to predict PID in photovoltaic (PV) crystalline silicon modules in the field. This model is based on empirical equations that relate the time-evolution of the module’s power with the stress factors for PID (e.g. temperature or humidity), obtained from a matrix of accelerated tests in the laboratory. Then we apply the set of equations with weather data as inputs to predict what the power evolution of our mini-modules would be if they were operating in different climates.
This paper is a continuation of a work that we presented in a previous contribution, where only the phase of power degradation was taken into account. Here, we improve this model by including the mechanism of regeneration. Moreover, we improve the simulations of the different phases of the PID mechanism providing some elements of novelty with respect to previous works.
One contribution of our work is to analyze the regeneration process that occurs during lightexposure, when samples are exposed to negative voltages towards ground resulting in an interaction between the degradation and the regeneration mechanisms. We observe that, in conditions of low humidity and high temperature, regeneration takes place as well for samples exposed to a high negative bias voltage (−1000 V). This effect, for which little evidence existed from field monitoring, is clearly proven by our experimental tests. Moreover, suitable thresholds on the weather conditions are set to properly simulate different phases of PID. For instance, we integrate in the predictive model a condition that allows to treat the particular case where the module surface is wet (rain or condensation).
The results show that our simulations are able to reproduce the seasonal trend of power degradation and regeneration as it was observed in the field in the same climate. Moreover, by employing the dependence of power degradation on the voltage level, we are able to simulate the effect of PID on an entire string of modules. Starting from our experimental work, we also propose a sequence of accelerated PID tests beyond the current IEC Technical Specification 62804-1:2015 that allows for better prediction of PID in real field conditions. Finally, we are confident that the mathematical adaptation we developed for our simulations can be applied to simulate other degradation mechanisms that induce a non-monotonous behavior on the power evolution of the module, therefore leading to an improved prediction ofreliability of photovoltaic modules in different climates.