## 6 Conclusions  
This paper has performed an economic evaluation of smart PV inverters with a three-operation-phase Watt-Var control scheme for enhancing PV penetration in distribution systems in Taiwan. The annual PV power injection and curtailment were estimated according to the annual duration curve of solar irradiation, and a Taipower distribution feeder was selected for economic evaluation. Some concluding remarks for the test feeder are listed as follows.  
1. There is no need to have a smart inverter for the cases with PV capacities less than 1500 kWp since their PV real power injection will not violate the voltage variation limit and no curtailment occurs.
2. When the PV capacity is greater than 1500 kWp, the smart PV inverter can enhance the injection of PV real power into the feeder and the utilization of PV power generation, and thus increase the PV grid-connected capacity in distribution feeders.
3. When the PV capacity is between 1500 kWp and 3500 kWp, the smart PV inverter with control ability _pf_ = 0.95 will be sufficient to play the role to increase the PV power injection to the distribution system since there is almost no curtailment for _pf_ \(\leq\) 0.95.
4. When the PV capacity is greater than 3500 kWp, the smart PV inverter with control ability _pf_ = 0.9 will be sufficient to play the role to increase the PV power injection to the distribution system since there is almost no curtailment for _pf_ \(\leq\) 0.9.
5. According to the cost-benefit analysis, to gain a positive NPV or a BCR greater than 1, the maximal allowed PV capacities are around 2200 kWp, 3500 kWp, and above 5000 kWp for smart inverters with control ability _pf_ = 1.0, 0.95, and 0.9, respectively. That is, smart PV inverters with _pf_ \(\leq\) 0.95 can increase the PV capacities by at least 59%. This result may convince the Taiwan government to set a new standard on PV systems to have a smart inverter with power factor control ability of _pf_ \(\leq\) 0.95 for enhancing PV penetration in distribution systems.
6. According to the sensitivity analysis, the NPV is increased to NT$ 77 million for a FIT rate at NT$ 7.3268/kWh and to NT$ 76.6 million for a PV cost at NT$ 28,175. The BCRs are increased  
Figure 12: BCR sensitivity graph for four key parameters.  
by 50% and 22.7%, and decreased by 11.2% and 33.3% for a 50% increase of FIT rate, economic life, discount rate, and PV cost, respectively. That is, the most sensitive parameter is the FIT rate, followed by the PV cost; the third is the economic life and the least sensitive parameter is the discount rate. Moreover, increase in the FIT rate and reduction in the PV cost will raise the values of NPV and BCR.  
Conceptualization, S.-C.H.; Methodology, S.-C.H.; Formal Analysis, S.-C.H.; Writing-Original Draft Preparation, S.-C.H.; Writing-Review and Editing, S.-C.H.; Project Administration, Y.-D.L. and Y.-R.C.  
This research was funded in part by the Ministry of Science and Technology of Taiwan, R.O.C., under Grants MOST 106-3113-E-214-001, MOST 106-2221-E-214-033, MOST 107-3113-E-214-001 and MOST 107-3113-E-042A-001-CC2.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study, in the collection, analyses, or interpretation of data, in the writing of the manuscript, and in the decision to publish the results.