## 4 Results and Discussion
### Study of Net Emissions of CO\({}_{2}\) Eq  
Charcoal is gaining attention as a sustainable alternative to traditional fuels to reduce emissions and mitigate environmental impact [36]. It was decided that in order to assess the sustainability of the charcoal production from vine shoots, a net balance of the CO\({}_{2}\) emissions from the tests would be carried out. This balance was sought by comparing the CO\({}_{2}\) emissions, which were generated due to the consumption of electrical energy from the grid used in the muffle furnace for the tests, with the CO\({}_{2}\) capture that the vine plant itself carried out during its growth. The energy input during the pyrolysis process was a key factor in determining its energy balance [35]. It has been estimated [26] that in the Autonomous Community of La Rioja, vine cultivation fixes a value of 9.12 tonnes of C per hectare to the soil, which is equivalent to the vine directly absorbing a value of 6.26 HCO\({}_{2}\)/ha from the atmosphere [27]. Based on these data and also knowing the average generation of vine shoots in the Autonomous Community of La Rioja, calculated at 4.18 tonnes per hectare [38], it is possible to obtain the amount of CO\({}_{2}\) that the vine shoot residue accumulates during its annual cultivation. This value is 1.50 g of CO\({}_{2}\) captured for each g of vine shoot generated. The trials had an average mass of 40 g per shoot, so the amount of CO\({}_{2}\) captured per trial could be set at \(-\)60 g CO\({}_{2}\) eq; this value was the same for all the pyrolysis trials as it did not depend on the temperature of the trial but on the amount of vine shoot to be tested and remained constant. This amount of CO\({}_{2}\) captured should be subtracted from the amount of CO\({}_{2}\) emitted as a result of using an energy source for the test. A key aspect to highlight is that, in a scenario of charcoal production from this waste at an industrial level, the vine shoots would undergo a prior transport process from the vineyard to the production plant, as well as a mechanical cleaning and preparation process for their respective carbonisation. All these processes logically added an environmental burden to the raw material of the vine shoot, negatively influencing its sustainability. However, in this research, due to the fact that these operations have been carried out manually, it was decided to exclude them from the analysis process, leaving their accounting for future research. In the case of this research, the energy used in the pyrolysis tests came from electricity from the grid, so it was necessary to collect the amount of CO\({}_{2}\) eq emitted by the consumption of one kWh from the Spanish electricity grid. For this purpose, the Spanish electricity grid databases [39] and their annual data history were used to develop the emission factor of g CO\({}_{2}\) eq per kWh produced in the national grid. The data series only covered the time frame from 2007 to 2023, as shown in Figure 8, so it was decided to calculate a polynomial regression function of degree 3. The rationale for using a polynomial of this degree was that it is a fairly efficient fit (see R\({}^{2}\) value in Appendix A, Table A3). Furthermore, this regression function allowed us to approximate and estimate the emission factors for the consecutive years such as 2030, which coincided with the sustainable development plan. The aim of creating this future scenario was to determine whether there was any point on the near horizon where producing charcoal from vine pruning waste would result in a net negative balance of CO\({}_{2}\) eq emissions. The coefficients of the regression function are shown in Appendix A, Table A3. Figure 8 also shows the error bars between the real data of g CO\({}_{2}\) emission factors and the results obtained according to the regression function. It should be noted that the emission factor has been decreasing significantly over the years.