## 8 Developed Tool  
The main objective of this tool is to provide consumers with a clear and objective view that helps them make informed decisions about their energy consumption, considering the volatility of the European electricity market. These factors have directly influenced the design of the tool, ensuring that it can dynamically analyze tariff variations and assist consumers in making cost-effective decisions. The task of choosing the most suitable electricity tariff for each context is complicated by the instability of energy prices, driven by factors such as fluctuations in fossil fuel prices, the integration of renewable energy, and regulatory policies. Additionally, there is widespread ignorance among consumers regarding mechanisms for self-consumption, surpluses, and other options to reduce dependence on the electrical grid. To simplify the decision-making process for consumers, the tool follows a structured workflow that guides users step by step. The workflow is illustrated in Figure 6.  
In this context, the tool not only guides users on the most efficient electricity tariff according to their consumption profile, but it also advises on the economic viability of implementing a photovoltaic installation in their home. Its design responds specifically to the challenges posed by the European electricity market, such as frequent tariff fluctuations and evolving self-consumption policies, ensuring that users receive tailored and up-to-date recommendations. The adoption of renewable energy is crucial on the path to energy transition, not only to mitigate environmental impact but also to reduce dependence on fossil fuel markets and thereby avoid exposure to energy price volatility. These functionalities are especially relevant at this moment as self-consumption installations allow households not only to generate energy to meet their needs but also to sell excess energy back to the grid, contributing to the balance of the energy system and generating significant savings on electricity bills. As of today, the tool is developed in Spanish and designed to analyze electricity tariffs in that market. However, the goal is to expand its reach at the European level by translating the tool into various languages and adapting its functionalities to integrate tariffs from different countries, which will allow consumers across Europe to benefit from a greater understanding of the electricity market, with accurate and personalized information for each region, facilitating decision-making in a complex and constantly evolving energy environment. The application has been developed using Microsoft Excel para Microsoft 365 MSO (version 2502) and Visual Basic programming language. The tool is made up of five main sections, which are accessed through an interactive menu shown in Figure 7.  
* Data entry: This section, of which a screenshot is shown in Figures 8 and 9, is the starting point from which all the information required for the analysis is collected. Here, the user is asked to enter the customer's personal data, such as name, address and contact details. In addition, data specific to the installation under study is collected, which could include information on the location of the installation, the type of building (residential, commercial, industrial), the contracted power, the type of tariff, whether they had a social bonus, a photovoltaic installation, and other relevant details. Figure 6: Workflow. These data provide the necessary context for an accurate analysis of the customer's electricity situation. * Consumption: In this section, electricity consumption data are collected, as can be seen in Figure 10. The user must enter detailed information on monthly or annual consumption, specifying the consumptions obtained from his distributor. This allows for a detailed analysis of electricity consumption patterns over time. In addition, the tariff period to which each meter reading belongs can be considered, which is crucial to accurately calculate the costs associated with electricity consumption.