Novel method to calculate variations in temperature coefficients of solar modules


Researchers from the Federal University of Rio Grande do Sul in Brazil have developed a new way to measure variations in temperature coefficients (TCs) in solar modules.

“Our work provides an improved description of the behavior of PV modules at different irradiance levels and describes some aspects that were not fully present in the scientific literature,” researcher Fabiano Gasparin told pv magazine. “The results can be applied to any type of PV system with crystalline silicon cells.”

The scientists said that they wanted to identify a general relationship between the dependence of TCs and irradiance based on experimental data, which could be used for PV module performance modeling, they claim.

The researchers assessed the TCs of eight PV modules with different efficiencies at different irradiances. They measured the I-V curves of the panels in a large area pulsed solar simulator (LAPSS) with irradiance from 100 to 1,000 W/m2 and temperatures from 25 C to 65 C.

“From a matrix of 50 I-V curves for each module, the TCs of open-circuit voltage (VoC), short-circuit current (IsC), and maximum power (Pm) were calculated for different irradiances,” said Gasparin.

The scientists tested the modules in a thermostatic chamber that heated them to a controlled temperature. They found that the TC of VoC varies logarithmically with irradiance for c-Si PV modules.

“This behavior was well described by a new empirical logarithmic function derived from measured data,” said Gasparin. “This behavior was also described by theoretical equations derived from the physical principles of a solar cell model, and both models are equivalent.”

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They determined that the TC of IsC is practically constant with irradiance for conventional c-Si PV modules and increases slightly at lower irradiances for modern half-cell PV modules.

“This behavior was not investigated further because it plays only a minor role in modeling the energy conversion of PV modules,” they said. “The TC of Pm, by contrast, is fairly constant with irradiance for the half-cell PV modules studied.”

Gasparin said the group has yet to simulate its findings in the modeling of systems.

“We do not yet know how the actual impact on system power generation over time will compare to the simulated results,” he said. “A new development for the future would be to compare the models and evaluate the impacts. New simulations can show us the differences, but from the perspective of investors and developers, they seem secondary. Perhaps a small improvement in simulated results can be achieved.”

The researchers introduced their novel methodology in “Assessment on the variation of temperature coefficients of photovoltaic modules with solar irradiance,” which was recently published in Solar Energy.

The results can improve the PV accuracy of PV device modeling in a wide range of solar irradiance and temperature, including an effect not usually considered in engineering applications,” the scientists concluded.

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