## 4 Component Cost and Financial Assumption
### Conditions with PV/BESS Installation  
Because of the installed PV system, the self-use type fully used can reduce the consumption of main power. The energy storage system uses energy arbitrage to obtain income through charge and discharge scheduling of TOU. The arbitrage method is to reduce the user contract capacity by charging electricity at off-peak electricity price and discharging electricity at peak electricity price to reduce the total electricity expense of users. To find the best project benefit of the PV system and BESS capacity, this simulation analyzes that the contract capacity is reduced from 7.5 MW to 5 MW, with each reduction level of 0.25 MW in the condition of excess electricity fraction less than 3%. After the analysis of each level is completed, the project benefit of the contract capacity of each level is compared with each other to find the reduced contract capacity with the highest project benefit and corresponding PV/BESS capacity combination. Table 5 shows the analyzed results of PV/BESS combinations corresponding to different contract capacities and the best plan is the contracted capacity of 6 MW after downgrading by the solution with a PV capacity of 8.25 MWp and the BESS capacity of 1.25 MW/3.195 MWh. The maximum project benefit of \(\$3.591\times 10^{6}\) can be obtained by resulting in the lowest LOCE of \(\$87.85\times 10^{-3}\)/kWh, NPC of \(-\$51.222\times 10^{6}\), IRR of 3.08%, ROI of 1.77%, discounted payback of 15.41 years, reduced electricity charge of \(\$18.449\times 10^{6}\), total electricity savings of 33.66%, RF of 29.6%, and excess electricity fraction of 2.93%. The total setup cost of PV/BESS presents \(\$11.888\times 10^{6}\) of which PV system setup cost is \(\$10.807\times 10^{6}\) accounting for a ratio of 90.91%, and BESS's total setup cost is \(\$1.08\times 10^{6}\) accounting for a ratio of 9.09%. The total O&M cost of PV/BESS equipment in 20 years is \(\$2.88\times 10^{6}\) of which PV system is \(\$2.078\times 10^{6}\) accounting for a ratio of 72.14%, and BESS is \(\$0.802\times 10^{6}\) accounting for a ratio of 27.86%. Figure 10 shows that when the contracted capacity reduces, more electricity charges can be saved. However, because the required capacity for PV/BESS increases, the equipment and maintenance costs will accompany by the increase to have lower project benefits. For example, the contract capacity sets at 5 MW which means the upper limit capacity of the utility power is limited to 5 MW. Therefore, the load maintain can let the system operate normally with the requirements of PV system capacity of 9 MWp and the BESS capacity of 2.25 MW/8.307 MWh, as shown in Table 5. Although the RF of contract capacity of 5 MW increases to 32.24%, the initial investment cost of the equipment has also increased by 1.22 times compared with the contract capacity of 6 MW, and the lower performance presents that the electricity charge is only reduction ratio of about 7% and the project benefit is \(\$3.32\times 10^{6}\). Although the installed capacity of the PV system is 7.25 MWp for the contract capacity at 7.25 MW, the best project benefit can be obtained with related to the lowest initial investment cost of the equipment in Table 5. The RF, electricity cost saving percentage and project benefit are all the lowest. Figure 9: NPC in each year without PV/BESS conditions. As an example to illustrate the electricity consumption in summer, it can be presented by taking the contracted capacity of 6 MW, PV capacity of 8.25 MWp, and BESS capacity of 1.25 MW/3.195 MWh. To TOU management, BESS charged during the off-peak period with low electricity price on 18 June as shown in Figure 11. The load power consumption appears at 6.179 MW, which is higher than the setting value of contract capacity, in the period with a high electricity price at 10:00 o'clock on the next day. Because of the energy management of power supply by PV system outputs of 3.856 MW and the BESS outputs of 1.25 MW, the immediate usage of main power drops to 1.073 MW.