Researchers in Ireland have proposed for the first time a deterministic approach to designing the inverter load ratio (ILR) in utility-scale PV projects. The new methodology is claimed to simplify the design process and reduce performance variability, while increasing investment security.
A team of scientists from University College Cork in Ireland has proposed a new approach to designing the inverter load ratio (ILR) for utility-scale PV power plants.
The researchers described the ILR as the ratio of the output power of the DC PV array to the rated AC power of the Power Conversion Unit (PCU). “If the ILR value is low, it may result in reduced economic viability of the system,” they explained. “On the other hand, increasing the ILR value can cause problems with the dispatch down operation and clipping losses.”
In the study “A refined method for optimizing inverter load ratio in utility-scale photovoltaic power plants”, published in Energy reportsThe research group said that identifying the optimal ILR design for large-scale solar is “an ongoing effort” at both industry and research levels, and emphasized that to date no deterministic ILR approach has been developed that will enable PV project developers could help identify the best value of DC/AC PCU under specific geographic, climatic and economic conditions.
“Unlike metaheuristic or heuristic methods, this approach simplifies the design process and reduces performance variability,” the academics emphasized, noting that the proposed methodology, instead of focusing on oversizing, increases the rated power of the installed inverter for a given Optimizes PV array installation. “By increasing investment certainty, it provides a reliable estimate for maximizing economic returns with minimal risk.”
The new approach is implemented in two steps. Firstly, it is assumed that the inverter does not need to connect the PV system to the electricity grid. Secondly, it also assumes that the electricity grid runs on alternating current, which requires an inverter. “The optimal inverter capacity is then determined to optimize revenue, taking into account the additional investment costs for the DC/AC PCU,” the academics further explained, noting that the system’s algorithm takes into account the specifications of the DC /AC PCU. the feed-in tariff and the estimated PV DC generation.
The group tested the new approach in a 5 MW PV power plant in Kelmoney, Ireland, with the aim of maximizing annual profitability. The facility uses 16,380 solar panels from Chinese manufacturer Longi, with 26 modules in parallel and 630 strings. It also uses 29 string inverters supplied by China’s Huawei. Temperature and radiation data were collected from a site simulation using the PVsyst software.
The researchers claim that this analysis allows them to find the optimal ILR value for the plant at 1.4528, which they highlighted is lower than the 1.4656 designed by PVsys. “The analysis shows that energy clipping occurs at 5.22 MW, which is the optimal power of the inverter,” they said. “Only generation above 5.22 MW is cut off, and energy below this threshold is used to calculate estimated system revenue annuities.”
Inverter clipping occurs when the DC energy from a PV system exceeds the maximum input size of the inverter. This causes the inverter to become saturated and the excess DC energy is not converted into AC power.
The scientists emphasized that the lower ILR value corresponds to an increase in annual profit distributions.
They also stated that the proposed methodology could also be used for rooftop PV systems or to assess the economic viability of the site for existing photovoltaic power plants. “It can then make recommendations for upgrading PVPP components to achieve greater profitability,” they concluded. “This approach is particularly useful in addressing the potential increase in inverter or PV module obsolescence.”
In March, an international research team published a study on the effect of inverter clipping on limiting pollution losses in PV systems and explained that this strategy may not be as effective as commonly thought.
Later in July, researchers in Malaysia proposed a proposal new approach to identify the optimal power size ratio to balance PV energy collection with inverter cost. The calibrated model is said to accurately reflect the relationship between inverter efficiency and real-world system behavior.
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