available datasets may differ to the 10min average calculated by the inverter. As a result, the datasets don’t give the complete picture of the voltage conditions to be able to separate anti-islanding tripping from sustained voltage tripping. In this study, all tripping curtailment is analysed together – this is an important limitation and should be considered in future work.
4.2.2.1 D-PV tripping (anti-islanding and limits for sustained operation) curtailment The D-PV ‘tripping’ analysis applied the methods developed in [1] to identify the start and end points for periods in which D-PV generation reduced to near zero. The linear method is applied to non clear-sky days, whilst the polyfit-iteration method is applied to clear-sky days in most cases, as described in [1]. These methods output an estimate of the D-PV energy curtailed at each site for each day in the 10 month dataset, as well as the estimated profiles for all sites over the period. The results are then analysed to assess the following: • • •
Significance of curtailment: how much energy is being lost due to D-PV ‘tripping’? Distribution of impacts: are some sites more impacted than others? Seasonality of curtailment: when is ‘tripping’ curtailment occurring most throughout the year?
The five most impacted sites are presented as case studies.
4.2.2.2 BESS tripping (anti-islanding and limits for sustained operation) curtailment It was more challenging to define the tripping (anti-islanding and limits for sustained operation) curtailment for BESS compared to D-PV systems. This is because BESS has storage capability and for the instances where BESS could not discharge due to tripping, the unused stored energy will be available for later use. Similarly, for the instances where BESS could not charge due to tripping, the excess-D-PV generation can be exported (assuming there is no export-limitation which is out of the scope of this study). Therefore, identifying and quantifying ‘loss’ due to BESS tripping is not straightforward. Nevertheless, the analysis focused on the instances where BESS’s operational capabilities were limited by the identified tripping instances and assessed curtailment under two categories: 1. BESS tripping curtailment when BESS could be discharging. 2. BESS tripping curtailment while BESS could be charging. Further details for the BESS tripping (anti-islanding and limits for sustained operation) curtailment calculation are given in the Appendix.
4.2.3 Volt-VAr curtailment D-PV and BESS inverters have rated Volt-Amp (VA) ratings which is made up of real and reactive power components. Volt-VAr (V-VAr) curtailment can occur when D-PV or BESS absorbs or injects high reactive power (VArs) which limits the real power output (i.e., when a D-PV inverter with 5 kVA rating injects or absorbs 3 kVAr, it’s real power output will be capped at 4 kW and any real power output over 4 kW will be curtailed). V-VAr curtailment analysis is carried in three steps. Firstly, BESS and D-PV system VAr characteristics are investigated using real operational data. In the next step V-VAr curtailment is investigated using real operational data and in the final step, future V-VAr curtailment scenarios are modelled under different V-VAr curves referenced from different regulations and standards.
4.2.3.1 V-VAr characteristics Before quantifying V-VAr curtailment, preliminary analysis was done to reveal the operational VAr characteristics of BESS and D-PV inverters. Analysis focused on the following points: • • •
How often do BESS and D-PV inverters inject and absorb VArs? What are the statistics of the injected and absorbed VArs? Are there any specific months or hours of the day where VArs were observed more significantly than others?
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