The global surge in variable renewable energy adoption, particularly solar power, is reshaping electricity grids. With the decreasing cost of solar modules, countries are increasingly adopting higher DC/AC ratios, commonly around 1.3. This trend has led to a rise in inverter clipping and curtailment (C&C) for both residential and utility-scale solar installations. While these practices are generally seen as economically efficient, curtailment, in particular, can significantly impact the financial returns of solar projects.
However, there’s another critical impact that often flies under the radar. During periods of inverter clipping or curtailment, the electrical power output of solar modules is intentionally reduced. This reduction can lead to an increase in the operating temperature of the modules, a factor usually deemed inconsequential since the plant’s output is already limited. Standard simulation tools like PVSyst, SAM, and pvlib typically ignore this variable, not adjusting for cell or module temperature changes due to clipping at the inverter. But ignoring this factor could have serious implications for the long-term degradation of solar modules.
The Study
Our team conducted a comprehensive analysis across various locations within the Australian National Electricity Market (NEM). We focused on systems using either the FT (Fixed Tilt) or SAT (Single-Axis Tracking) mounting systems, ensuring identical module and inverter parameters to maintain consistency. By varying the DC ratios and utilizing historical NEM data, we were able to simulate and adjust plant output during periods of curtailment accurately.
To understand the operating temperatures of modules under clipping and curtailment, we utilized custom Python scripts that leveraged our high-precision thermal model. Further, we employed our advanced degradation model to investigate how different mounting systems and operating conditions influenced expected degradation.
Key Learnings
Figure 7 below illustrates the simulated module temperatures for a location in Victoria, comparing MAV and SAT systems, both with and without inverter clipping. It’s evident that MAV systems generally operate at cooler temperatures due to lower plane-of-array irradiance and are less affected by clipping.
Figure 8 presents the degradation results over a year for both configurations, distinguishing between thermal and UV-related degradation. Using our advanced model, we observed a much more rapid degradation rate during summer months, particularly when degradation mechanisms are thermally driven. The MAV systems’ lower operating temperatures and UV exposure are predicted to lead to significantly less degradation over the project lifespan.
Figure 7: A graph showing the simulated temperatures for SAT and MAV systems with and without inverter clipping.
Figure 8: Left: Thermal degradation across a year for modules on SAT and MAV systems with and without clipping. Right: UV-related degradation across a year for the same configurations.
Transferability
These findings are particularly crucial for developers in the utility-scale solar sector when making technology decisions. Current software lacks the capability to predict temperature differences or degradation effects stemming from design and technology choices, leaving this issue largely invisible. Our models offer a novel perspective, allowing developers to assess how mounting technology, DC ratios, and grid operations will influence module performance over the plant’s lifespan, especially when comparing MAV and SAT structures.
Implications for Future Projects
The extent of curtailment and its impact on plant degradation across the NEM was surprising. This discovery prompts the need for further exploration across more sites within the NEM to quantify the full scale of this issue. Additionally, we are developing a potential mitigation strategy for plants with high DC ratios and curtailment challenges. Using our model, we can simulate this strategy’s impact on plant degradation and evaluate the potential commercial opportunities it presents.
In conclusion, while the focus on higher DC/AC ratios and the economic efficiency of inverter clipping and curtailment is warranted, the overlooked impact on module degradation requires urgent attention. By leveraging advanced thermal and degradation models, solar professionals can make more informed decisions, optimizing plant performance and ensuring the longevity of solar investments.
Written by Dr. Phil Hamer