## 2 Methodology  
The analysis of the economic benefits of PV/BESS application of BTM in this study shows that the load is the priority to use the electricity generated by the PV system to reduce the demand for purchased electricity. The BESS with TOU price is considered to adjust the charge and discharge schedules during the period of off-peak electricity price and the period of on-peak electricity price, respectively, in order to obtain the profit from the electricity price difference and reduce the cost of annual contract capacity. Therefore, the sum above two reductions in electricity bills is the PV/BESS project benefit. This research uses the contract capacity of the actual industrial user as a research case and performs PV/BESS techno-economic simulation analysis through the HOMER Grid software.  
According to Taiwan's policy of contracted capacity, the objective of the analysis shows the reduced contracted capacity related to the most economical PV/BESS capacity allocation and optimal contract capacity scheme under the condition that the electricity demand is met and the PV power generation is fully used. Figure 1 shows the flowchart of the economic benefit analysis. Without a waste of excess PV power, the excess electricity fraction is limited within 3% to the analysis and effective use of energy for the economic benefit evaluation of PV/BESS.  
From several cases of contract capacity reduction, the economical combinations of the PV system and BESS capacity are analyzed to find the most economical combination scheme of contract capacity reduction and the corresponding PV/BESS capacity. The research methods and analysis are as follows:  
(1) Through on-site surveys, the load power consumption from industrial users in 2019 is obtained. The basic data for simulation is as statistic interest rate, inflation rate, and time price of electricity in Taiwan in recent years, as well as the cost of equipment obtained from the market survey;  
(2) According to the load conditions of industrial users, the result analyzes the electricity expense without the energy storage system installed as a benchmark for comparison of project benefits;  
(3) According to the conditions of load and TOU electricity price, the simulation has considered that PV electricity can be fully used and the excess electricity fraction must be limited to less than 3%. The result addressed to calculate the highest project benefit for PV/BESS capacity allocation schemes under different contract capacities, and they are corresponding electrical and economic results, respectively;  
Figure 1: The flowchart of the economic benefit analysis.  
(4) According to the simulation result of (3), the most economical scheme is from several reduction cases of contract capacity to find the combination plan of contract capacity with the highest project benefit and their operation capacity of PV/BESS;  
(5) Based on the combined plan of contract capacity of the highest project benefit and PV/BESS capacity, the sensitivity analysis carries out to know the degree of impact on economic benefits by the parameters such as global horizontal irradiation (GHI), electricity price, key components cost, and real interest rate.