New PV system design strategy avoids oversizing, curtailment

Researchers from King Mongkut’s University of Technology North Bangkok in Thailand have proposed a new methodology to conduct techno-economic assessments of distributed PV systems considering overvoltage-induced curtailment.

The scientists stressed that, unlike previous methods for PV system sizing, the new approach is not intended to identify the optimal size of a solar array based on profit maximization and self-consumption policies. They rather suggested avoiding oversizing and an “exaggerated profitability,” but said this choice leads to a significantly improved levelized cost of energy (LCOE), especially in scenarios where curtailment is expected to increase, due to a higher penetration of renewable energy resources.

The research group conducted a sensitivity analysis to assess the impacts of different voltage thresholds of overvoltage-induced generation curtailment on the techno-economic performance of distributed PV systems based on the electricity tariffs set by the Metropolitan Electricity Authority (MEA) in Thailand.

The academics monitored the load for an entire year in 2018 and found maximum loads were at 21.00, with consumption being the highest in April. “As a result, air-cooling loads increased considerably,” they explained. “The load tended to decrease when the season changed from summer (March to May) to winter (November to February). The lowest load was identified in December because the temperature was usually pleasant, substantially reducing air-cooling loads.”

Electricity prices in the analyzed area ranged from $0.176/kWh to $0.057/kWh and a volt-watt droop curtailment strategy was assumed to be implemented. This method requires deploying an additional controller at the point of common coupling (PCC) and is generally used for local PV power curtailment. “This strategy curtails the PV generation when the voltage reaches the threshold of 1.06 p.u., according to the ANSI C84.1-2016, IEEE 1547-2018, and IEC 60038-2009 standards,” the researchers specified.

Their analysis considered techno-economics parameters, such as the self-consumption rate (SCR), self-sufficiency rate (SSR), net present value (NPV), and LCOE.

They also adopted the so-called Jiménez-Castillo PV system sizing optimization approach, which is aimed at maximizing NPV values, and considered four different scenarios: Scenario 0, where overvoltage and curtailment are neglected; Scenario 1, where overvoltage-induced generation curtailment and PV installation location are considered and PV systems are installed at every node in each area; Scenario 2, where PV systems are installed at every node in two areas; and Scenario 3, where PV systems area installed at every node in every area of the feeder.

Through this assessment, the scientists found that, to avoid curtailment and overvoltage, PV system sizing could be reduced by up to 58.33%, depending on the number of PV systems and their location. This would lead to a reduction in NPV of 21.34% but also to an increase of LCOE by 22.96%.

“Additionally, the findings indicate that the SCR mildly increased by up to 11%, but the SSR marginally decreased by up to 4% when implementing overvoltage-induced generation curtailment,” they added. “Finally, the sensitivity analysis revealed that the optimal PV capacity remained unchanged even though different voltage thresholds were applied. However, the NPV significantly decreased by up to 25%, and the LCOE increased by up to 20.72% as the voltage threshold decreased to 1.01 p.u. The SCR tended to increase by approximately 10%, whereas the SSR remained unchanged.”

Their findings are available in the study “Techno-economic assessment of grid-connected residential photovoltaic systems considering overvoltage-induced generation curtailment,” which was recently published in Energy Reports.