# Total Cost of Ownership Model and Significant Cost Parameters for the Design of Electric Bus Systems

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## Abstract

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## 1. Introduction

#### 1.1. Different Types of Electric Buses

#### 1.2. Aim of the Paper

#### 1.3. Limitations

#### 1.4. Structure of the Paper

## 2. Model for Total Cost of Ownership

#### 2.1. Method

#### 2.2. Output of the Total Cost of Ownership Model

#### 2.3. Parameters Used to Determine Total Cost of Ownership

- Driver time per year;
- Energy use per year;
- Total driven distance per year;
- Trip distance per year;
- Number of places with chargers (i.e., number of grid connections);
- Total combined power of all chargers;
- Number of chargers;
- Number of buses;
- Bus battery size.

#### 2.4. Simplifications Aimed to Find General Trends Rather than Route-Specific Results

#### 2.5. Cost of Conventional Combustion Engine Buses

## 3. Model Input Parameters and Variables

#### 3.1. Route Variables

#### 3.2. Timetable Variables

#### 3.3. Bus, Driver and Battery Parameters

#### 3.4. Electric Grid Parameters

#### 3.5. Charger Parameters

#### 3.6. Other Parameters

## 4. Calculating TCO Input Variables from Timetable and Bus Route Parameters

#### 4.1. Battery Size and Need to Charge during the Day

#### 4.2. Determining the Number of Buses Needed to Drive the Trips

#### 4.3. Determining the Number of Extra Buses to Provide Time to Charge

#### 4.3.1. Extra Buses for End-Stop Charging for a Whole Day (EndStop1)

**EndStop1**in the calculations. The energy charged equals the energy used during the last trip, which means that the buses always starts each trip with the same battery state-of-charge. The number of extra buses required is determined by calculating how much time is required to charge the bus after each trip. The calculation is made for the peak periods, as that is when the greatest number of buses will be charging simultaneously. The amount of energy that the bus must charge at each end stop is:

#### 4.3.2. Extra Buses for End-Stop Charging during Off-Peak Time Only (EndStop2)

#### 4.4. Number of Chargers

#### 4.5. Calculating Energy Use and Driving Distance

#### 4.6. Calculating Total Driver Time

#### 4.7. TCO for Combustion Engine Buses

## 5. TCO Analysis

#### 5.1. Cost Comparison for Different Bus Types

#### 5.2. TCO Variations for Different Timetables

#### 5.3. TCO with Future Cost Levels

## 6. Concluding Discussions

#### 6.1. Main Findings

- A new model that demonstrates how to calculate the TCO for electric buses that depends on the nine most significant input variables. The calculations result in four operating and three annual depreciation cost parameters that forms the TCO.
- Testing of the method in a Swedish context from 2019 showed that the TCO for electric buses is generally in line with buses powered by biomethane and slightly higher than buses powered by HVO. However, the TCO can be both higher or lower depending on cost variations related to departures per hour, electric grid connections, the distance to the depot, and the length of the route. It is likely that future TCOs will be lower for electric buses when compared to buses powered by biomethane or HVO, mainly due to lower prices for batteries and buses and costs related to maintenance.

#### 6.2. Critical Assessment and Comparisons with Other Studies

#### 6.3. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**The calculation steps of the TCO model, its nine input variables in the white boxes at the top and its eight cost parameters as inputs from the left and right side of the model.

**Figure 3.**Steps 1–6 for how to calculate the nine TCO input variables, and information flow between these steps (to the left). The white boxes show some of the key variables calculated in different steps and the output variables.

**Figure 5.**Example of buses needed to drive the trips during early morning traffic and the morning rush hours.

**Figure 6.**Number of buses in traffic during the day. Derived from the timetable and route parameters.

**Figure 8.**How the number of buses during peak traffic can be reduced by moving charging to other times.

**Figure 9.**How the number of buses during peak traffic can be reduced by moving charging to other times, when the off-peak traffic is almost as high as the peak traffic.

**Figure 10.**How the number of buses during peak traffic cannot be reduced if the off-peak traffic is the same as the peak traffic.

**Figure 12.**The cost of different types of buses on the reference bus route and with the reference timetable. EndStop1 and 2 buses are powered by electricity, while the others are powered by biogas (CNG) or biodiesel (HVO). (Note that the y-axis starts at 18 SEK/km, so the driver cost is more than half the TCO).

**Figure 13.**The cost per km for end-stop-charged and biogas (CBG) buses with varying bus traffic density for a whole day. (Note that the y-axis starts at 18 SEK/km, so the driver cost is more than half the TCO).

**Figure 14.**The cost per km for end-stop-charged and biogas (CBG) buses with varying bus traffic density off-peak. (Note that the y-axis starts at 18 SEK/km, so the driver cost is more than half the TCO).

**Figure 15.**The cost per km for end-stop-charged and biogas (CBG) buses with cost parameters estimated for high production volumes. (Note that the y-axis starts at 18 SEK/km, so the driver cost is more than half the TCO).

**Table 1.**The cost parameters for buses powered by HVO, biomethane, and electricity when charging at the end stop, and at the end stop only during off-peak time. The values are relevant for Sweden 2019, and based on results from pilot projects.

Cost Parameters | HVO | Biomethane | Electricity | |
---|---|---|---|---|

End-Stop | End-Stop Off-Peak | |||

Price (Million SEK) | 2.2 | 2.5 | 3 (excl. battery) | |

Battery capacity (kWh) | - | - | 100 | 200 |

Max energy used between charging (kWh) | - | - | 25 | 75 |

Maintenance including chargers (SEK/km) | 3 | 3.6 | 3.3 | 3.3 |

Bus Economic Life (year) | 10 | 10 | 10 | 10 |

Battery Economic Life (year) | - | - | 7 | 7 |

Battery Price (SEK/kWh) | - | - | 4000 | 4000 |

Energy Cost (SEK/kWh) | 3.5 | 4 | 0.82 | 0.82 |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Grauers, A.; Borén, S.; Enerbäck, O.
Total Cost of Ownership Model and Significant Cost Parameters for the Design of Electric Bus Systems. *Energies* **2020**, *13*, 3262.
https://doi.org/10.3390/en13123262

**AMA Style**

Grauers A, Borén S, Enerbäck O.
Total Cost of Ownership Model and Significant Cost Parameters for the Design of Electric Bus Systems. *Energies*. 2020; 13(12):3262.
https://doi.org/10.3390/en13123262

**Chicago/Turabian Style**

Grauers, Anders, Sven Borén, and Oscar Enerbäck.
2020. "Total Cost of Ownership Model and Significant Cost Parameters for the Design of Electric Bus Systems" *Energies* 13, no. 12: 3262.
https://doi.org/10.3390/en13123262