## 2 BESS Dimensioning Methodology  
The BESS dimensioning methodology described in this section aims at reducing the fixed term of the electricity access rate by introducing a BESS that deals with the peaks of the industrial consumption. A few assumptions made by the authors in the development of the BESS dimensioning methodology are presented in the following.  
Firstly, both the BESS (\(P_{BESS}\)) and the electrical grid (\(P_{GRID}\)) must cover the customers' demand (\(P_{LOAD}\)) and the losses (\(P_{LOSS}\)):  
\[P_{BESS}+P_{GRID}=P_{LOAD}+P_{LOSS} \tag{1}\]  
Moreover, the BESS must account for enough energy to cover the energy to fulfill the extra energy demand not supplied/covered by the grid. Besides, a BESS must be able to fully recharge the same amount of energy as dispatched in a specific scenario. If not, the mean SoC will be decaying as the scenario repeats over time, being eventually unable to fulfil the load power demand.  
The methodology comprises a set of steps, as seen in the flow chart of Figure 1.  
1. Step 1: Models parameterizations. The different models, which are mathematical representations of physical systems or devices, account for variables (inputs and outputs) and parameters. In order to particularize the models (grid, BESS, and industrial consumption) to a specific system or device, those parameters must be adjusted to a fixed value.
2. Step 2: Define test cases. The variable that defines the test cases is the maximum fixed power that the grid can deliver (\(P_{LIMIT}\)). Reducing this power limit implies adding a greater contribution from the BESS, which yields to the different scenarios, which consequently will result in different BESS configurations and different BESS ageing.
3. Step 3: Simulate test case, calculate BESS requirements, and BESS configuration. Once the scenarios have been defined, a simulation is performed for every value of \(P_{LIMIT}\). Each scenario implies different necessities from the BESS, regarding power and energy. This requirements give different BESS configurations, in terms of number of cells in series and in parallel. The charge/discharge profile for the BESS is also obtained from the simulation. If the energy available for charging is unable to match the amount of energy dispatched by a BESS in a specific scenario, that scenario will not be considered for the dimensioning process. As previously noted, this situation will force the BESS to, eventually, not being able to feed the load when the scenario repeats over time.
4. Step 4: Calculate BESS ageing. Once the minimum BESS configuration that satisfies the power and energy requirements is selected for each scenario, a BESS ageing analysis is performed, based on the BESS model and configuration, and on the charge/discharge profile for each specific scenario. As a result of this step, the number of days until the BESS loses a 20% of capacity retention is obtained.
5. Step 5: Cost-benefit analysis. Prices and fees for both a BESS (as a function of the kW and kWh of the system) and the fixed access power are needed for their incorporation into a cost function. BESS standard prices as well as Spanish fixed access rates are provided in Section 4, with a case example. The cost can be computed yearly, taking into account the net present cost, and the capital recovery factor. The base scenario, i.e., when there is no BESS, is then compared to the rest of scenarios in terms of cost, and the final solution can be chosen.