# Energy Efficiency Improvement of Diesel-Electric Trains Using Solar Energy: A Feasibility Study
## 5 Results and Discussion
### Base Case  
We chose London as the base case of study. Figures 5 and 6 show London's location and some meteorological data from the RET Screen database [32].  
Figure 5 shows that the climate data's location is Leeds Weather Center. Figure 6 shows that the average annual air temperature is 10.3 \({}^{\circ}\)C, and the daily solar radiation (horizontal) is 2.54 kWh/m\({}^{2}\) per day. Moving to the energy section, and as shown in Figure 7, we consider the following inputs:  
* Fixed panels for the \"solar tracking mode\", the most straightforward model installed on the train's roof.
* Canadian Solar Poly-Si--CS34-365P-FG-KuDymond for the type of panels, with a total rated power of 365 W and total efficiency of 18.4%. At the same time, its high relative efficiency makes it a good choice.
* 27 PV solar panels are installed on the available area of each wagon's roof. The panels' total area is 53.6 m\({}^{2}\), which is slightly less than the available area of the roof (54.49 m\({}^{2}\)).
* 5% and 1% are the losses for the solar panels and inverters. The choice of these values is recommended in the RET Screen guide.
* 2500 $/kW and 33 $/kW-year for the initial costs and O&M costs, respectively. An experienced worker has validated the choice of these values in the field of PV solar panels.
* 0.3 $/kWh for the annual electricity export rate, as explained in the methodology section. This is the cost of diesel generated electricity production, which is avoided.  
Figure 5: London’s location, United Kingdom.  
Figure 6: Meteorological data for London, United Kingdom.  
After the energy section, the GHG emissions reduction and main finance parameters should be inserted. We considered them as follows:  
* 1.075 t CO\({}_{2}\)/MWh and 50 $/t CO\({}_{2}\) for the GHG emission factor (excluding T&D) and GHG reduction credit card, respectively, as shown in Figure 8. The emissions correspond to diesel generator electricity production, while the carbon credit corresponds to the market's actual values.
* 2%, 20 years, 50%, 5%, and 10 years are the values used for the inflation rate, project life, debt ratio, debt interest rate, and debt term, respectively, as shown in Figure 9. These values' choice corresponds to actual market conditions and similar PV solar panel projects.  
The main results from RetScreen are: (1) the annual solar energy production (MWh), which is the same as the \"electricity exported to grid\", shown in Figure 6. For London, it is 8.6 MWh, with a 9.9% capacity factor, which is directly affected by the local meteorological conditions; (2) the ROI (payback), which appears at the bottom of Figure 8 and is equal to 9.1 years; (3) and, finally, the GHG (CO\({}_{2}\)) reduction value and associated revenues (Figure 8).  
On the other hand, considering the duration of travel per day (9.33 h) and the number of trips per year (seven trips/week) for the case of London (shown in Table 2), the required energy is 16.21 MWh, 12.14 MWh, and 8.06 MWh for the first class, second class, and third class wagons, respectively. Therefore, we determined the percentage of each wagon's supply with solar energy as 53.05%, 70.85%, and 106.65% for the first class, second class, and third class wagons, respectively.  
Thus, the PV solar panels provide around 50% of the total energy consumed per year for the first class wagon. Therefore, the annual fuel bill of the auxiliary generator is reduced by 50%. In the same context, the PV solar panels provide 100% of the total energy consumed for the third class wagon. An additional 6% can be stored in batteries. This stored energy can be a supplementary source for other train charges.  
Figure 7: Energy data input for the case of London, United Kingdom.  
In the following sections, we use the same inputs as the base case for all other trains' cases. The results will be affected by the local solar resource and the train operation schedule, i.e., journey duration and frequency.