## 4 Results and Discussion
### Study of Net Emissions of CO\({}_{2}\) Eq
This is justified because power (GW) from more sustainable sources of energy generation (hydro, solar) has gradually and progressively increased to replace traditional types such as coal, natural gas, etc. Hence, by 2025, the CO\({}_{2}\) eq emission factor coefficient will be \(-\)8.01 g CO\({}_{2}\) eq for each kWh produced in the Spanish electricity grid. However, it should be noted that there was a 68.71% reduction in the emission factor over the time series for which there is recorded data (2007-2023), which implies the reduction of the emission of the producing electricity in the Spanish electricity grid from 390 g CO\({}_{2}\) eq to a value of 122 g CO\({}_{2}\) eq for each kWh produced. The scenario of obtaining negative emission factor values is a scenario with a very optimistic assumption for a very near horizon. These negative values are justified because they are the results of the previously calculated trend line. However, they were considered to adopt this assumption and to obtain the subsequent results of the net balance of the emissions. The results of the net balance of the CO\({}_{2}\) eq emissions are plotted in Figure 9. Firstly, it is indicated that only the test characteristics that produced a charcoal with a fixed carbon content of 75% or higher were shown, a condition taken from the previous optimisation process, considering this type of charcoal to be of acceptable quality. For this reason, only tests with characteristics of 350 \({}^{\circ}\)C for 2 h and for 3 h onwards are plotted. As can be seen in Figure 9, the net balance of the CO\({}_{2}\) eq emissions follows a similar trend to that of Figure 8, as the emission factors that directly affect the energy consumption are decreasing. It is also highlighted that the test characteristics with high temperatures and times, such as 450 \({}^{\circ}\)C for 3 h, are the ones that produce the highest net CO\({}_{2}\) eq emissions, at least until 2023, as they are associated with higher energy consumption. The turning point of the simulation is in the year 2023, where for the 350 \({}^{\circ}\)C for 2 h carbonisation test, values of \(-\)7.54 g CO\({}_{2}\) eq are recorded, which implies that producing this charcoal from vine shoot wastes in a conventional muffle furnace behaves as a CO\({}_{2}\) sink, which is a relevant result. If we continue with the time scenarios (2024 onwards), a very interesting feature is that the trials with the highest energy consumption, i.e., the 450 \({}^{\circ}\)C for 3 h trial, have the best net CO\({}_{2}\) eq emission balances, as can be seen in Figure 9. The justification for this condition is that, from the year 2025 onwards, the emission factor  
Figure 8: Historical series of 23 years of CO\({}_{2}\) emission factors per kWh produced in the Spanish electricity grid, as well as those obtained from the regression function (2024 onwards). estimated according to the previous regression function becomes negative (\(-8.01\) g CO\({}_{2}\) eq/kWh), implying that consuming electricity from the grid helps to sequester CO\({}_{2}\) eq, consequently, the test whose energy consumption is higher will bring a higher amount of CO\({}_{2}\) sequestered. In addition to these values, CO\({}_{2}\) must be added the \(-60\) g of CO\({}_{2}\) eq sequestered by the mass of the vine shoot to be tested during its vegetative cycle. All this means that, for instance, for the year 2030, pruning wastes (vine shoots) for test conditions of 450 \({}^{\circ}\)C for 3 h will generate approximately 10-12 g of charcoal with a high carbon content (\(-80\%\)) and in addition to sequestering values of \(-522.74\) g CO\({}_{2}\) eq. Based on these results, the possibility of scaling up these results to an industrial production scenario, where the quantities of the charcoal produced are higher, should be discussed. In this case, it should be taken into account that, logically, if more charcoal is to be produced, more raw material from the vine shoot wastes is needed.