January 6, 2022 Emiliano Bellini

From pv global magazine.

Researchers from Singapore Solar Energy Research Institute (SERIS) proposed a new design for shingle solar modules that they claim to make these products less sensitive to shading and hot spots, which remain the main obstacles to overcome for a wider commercial adoption of this photovoltaic technology.

“Rather than offering a particular interconnect or module architecture as a single solution, our work offers a design framework based on minimizing potentially dangerous hot spot temperatures while giving manufacturers the flexibility to play with different design parameters. “, The author, Carlos Clement, said pv magazine. “Ideally the way it would work is for a manufacturer to choose a cell technology, be it p-type PERC or whatever they choose, and through our model, we would generate a matrix of parameters. of modulus such as chain length, cell fraction and number of chains, where the hotspot risk for each specific combination is quantified. Analysis can also be performed in the opposite direction, with specific modulus characteristics constrained first, then appropriate cell technologies and characteristics determined thereafter.“

In the newspaper “Shade and hot spot resistant shingle module design”, which was recently published in Progress in photovoltaics, the SERIS team has developed a electrothermal template intended to create a framework for the design of shading and hot spot resistant shingle panels. “For the purposes of this study, we chose to model and test shingle modules made from pPERC cells that were cut into one-fifth of pieces by thermal laser separation for better mechanical properties,” said the researchers. scientists. “From our previous study, we learned that p-type cells exhibit a lighting-dependent effect on their leakage current as the cell nears failure.”

Through the modeling approach, the researchers first simulated the power of a shingle module and the response of the access point to shading. They built mini-modules from 12 shingles that have been laminated to 20x20cm glass with the same encapsulant and backsheet as used in full size modules. These panels were tested under negative voltages and standard irradiation conditions and their cell parameters were extracted.

The model was then validated by experimental dayour. “The precision of this model largely depends on the ability of our split cell subcircuit to capture the cell behavior at negative voltages approaching failure, ”they further explained, noting that a simulation was performed on the module power responses for different shingle module configurations. The developed electrothermal model was found to adequately capture the hot spot and the shading response of the panels.

This information was then used to set up the framework for design hot spot resistant shingle modules. This requires, as a first step, to understand, via Monte Carlo simulations (MCS), which characteristics of the input cell are most suitable in a multivariate system where the parameters vary together. “From the point of view of minimizing power losses, it is advantageous to have cells that have more leakage current,” the academics pointed out. “This can be explained by how larger leakage currents allow the shaded cell to match the current of other cells connected in series without being pushed further into reverse bias.”

According to the research group, the increase in the number of chains determines, for the shaded cells, a delay in the activation of the bypass diode and higher reverse voltages, which in turn result in higher maximum temperature measured in the cell itself. This, in their opinion, made of string length one of the most influential design levers to determine the hotspot Temperature. With an increasing number of parallel strings per block, the shaded string becomes capable of operating at lower currents and a lower hot spot temperature.

“The work described here is perfectly compatible with existing manufacturing techniques for shingle modules, ”said Clément. pv magazine.