# Minimization of Construction Costs for an All Battery-Swapping Electric-Bus Transportation System: Comparison with an All Plug-In System

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## Abstract

**:**

## 1. Introduction

^{2}, and it has a population of approximately 100,000. The Penghu Low Carbon Island Project began in 2011 with the aim to transform the archipelago through eight dimensions, namely renewable energy, energy conservation, green transportation, low-carbon construction, resource recycling, environmental greening, low-carbon living, and low-carbon education [4]. The impetus of this study was the promotion of electric buses (e-buses) in the green transportation section of the Penghu Low Carbon Island Project. The use of public transportation vehicles in the confined Penghu Islands will substantially increase as the tourism industry develops. The exhaust gas emitted by conventional diesel-powered vehicles is a source of air pollution, and reducing the emissions of these diesel-powered vehicles will improve the air quality. Public transport operators in Taiwan have begun promoting low-carbon transportation with hybrid e-buses. Although these hybrid e-buses consume fewer resources and generate less carbon emissions than diesel-powered buses do, they still emit carbon dioxide. A pure electric bus can run without generating any carbon dioxide and creates no environmental burden throughout the service route. Replacing all diesel buses in the Penghu Islands with e-buses could thus alleviate vehicle-generated carbon emissions [5,6,7]. Coupled with other green transportation equipment, a green traffic network can conserve energy by reducing carbon emissions, alleviate environmental hazards caused by human activities, and establish a comfortable living environment.

#### 1.1. Literature Review

#### 1.2. Motivation and Contributions

## 2. System Modeling and the Calculation of Construction Costs for a Battery-Swapping Electric-Buses Transportation System

#### 2.1. Modeling a Battery-Swapping Electric-Buses Transportation System

- (1)
- The operating models in both systems were formulated according to the existing bus schedule. However, because the two models required different durations for recharging and battery swapping, the operation–line and number–line sequence diagrams varied between the two systems.
- (2)
- Both systems required fast charging during daytime and slow charging during nighttime. Because they required different charging equipment and back-up batteries, the battery capacity and recharging sequence diagrams varied between the two systems.
- (3)
- The round-trip durations in both systems were 20 min (10 min for each one-way trip), and each bus required 10 min for changing destination signs, cleaning, and driver change before being redispatched. The PI-Ebuses were recharged immediately at the charging station in the depot upon their return, whereas the BS-Ebuses required 15 min for battery swap according to the e-bus manufacturers.
- (4)
- Identical fast- and slow-charging curves were employed in both systems. To prolong the battery life, the minimum battery capacity of the on-board batteries was maintained at ≥20% in both systems.
- (5)
- The optimization parameters of the PI-Ebus system were RBC and battery-charging time (BCT), whereas those of the BS-Ebus system were RBC and BCE.
- (6)
- The electricity costs of the two e-bus systems were calculated according to the latest price quoted by Taipower Company.
- (7)
- The research considers a complex problem spanning the life expectancy of batteries. Some assumptions have been made, including no disruptions, schedule-based operations, and installation of a unique charging point. The costs are based on expected values, and no reliability analysis was fulfilled.
- (8)
- Because of the complexity of road and traffic conditions, a microscopic simulation could not be executed in this study. The energy consumption of each e-bus line was calculated by the constant energy consumption rate per kilometer. The energy consumption rates per kilometer were 1.6 and 0.74 kWh for large and medium e-buses, respectively.

#### 2.1.1. Battery-Swapping Process

#### 2.1.2. Battery-Charging Process

#### 2.2. Calculation of the Construction Costs of a Battery-Swapping Electric-Buses System

- (1)
- E-bus cost: The BS-Ebus system in this study included two types of e-buses, namely medium- and large- e-buses. The bus cost was calculated by multiplying the number of buses with the price. The number of buses was determined according to the actual number of scheduled buses in the timetable.
- (2)
- On-board and additional battery costs: The minimum battery capacity of the on-board batteries was maintained at ≥20% in this study, and the installation interval of the on-board battery was set at 10% (i.e., possible battery capacities include 30%, 40%, 50%, ..., and 90%). The percentage of both on-board and back-up battery capacities of each bus was calculated to obtain the battery cost. The battery cost can be related as follows:$$\begin{array}{c}{\mathrm{C}}_{\mathrm{BA}}\left({\mathrm{N}}_{{\mathrm{BLB}}_{\mathrm{i}}},{\mathrm{N}}_{{\mathrm{BMB}}_{\mathrm{i}}},\text{}{\mathrm{N}}_{\mathrm{ELB}},\text{}{\mathrm{N}}_{\mathrm{EMB}}\right)\hfill \\ ={\displaystyle \sum}_{\mathrm{i}=3}^{10}\left[{\mathrm{N}}_{{\mathrm{BLB}}_{\mathrm{i}}}\cdot {\mathrm{C}}_{\mathrm{BLB}}\cdot \mathrm{i}\cdot 10\text{\%}+{\mathrm{N}}_{{\mathrm{BMB}}_{\mathrm{i}}}\cdot {\mathrm{C}}_{\mathrm{BMB}}\cdot \mathrm{i}\cdot 10\text{\%}\right]+{\mathrm{N}}_{\mathrm{ELB}}\cdot {\mathrm{C}}_{\mathrm{BLB}}+{\mathrm{N}}_{\mathrm{EMB}}\cdot {\mathrm{C}}_{\mathrm{BMB}}\hfill \end{array}$$
- (3)
- Battery-charging and -swapping system cost: The batteries that were replaced during daytime were quickly recharged in the battery-swapping facilities. Each battery-swapping facility could accommodate both medium and large buses and simultaneously recharge four batteries. After all scheduled trips were completed, all on-board and back-up batteries were slow charged during nighttime, and all batteries were fully charged by the following morning before the bus schedule commenced. During the slow-charging process, each charger could simultaneously recharge two buses. The battery-charging and -swapping system costs can be related as follows:$${\mathrm{C}}_{\mathrm{CH}}({\mathrm{N}}_{\mathrm{LB}},{\mathrm{N}}_{\mathrm{MB}},\text{}{\mathrm{N}}_{\mathrm{BC}})=\mathrm{ceil}(\frac{1}{2}{\mathrm{N}}_{\mathrm{LB}})\cdot {\mathrm{C}}_{\mathrm{CLB}}+\mathrm{ceil}(\frac{1}{2}{\mathrm{N}}_{\mathrm{MB}})\cdot {\mathrm{C}}_{\mathrm{CMB}}+{\mathrm{N}}_{\mathrm{BC}}\cdot {\mathrm{C}}_{\mathrm{BC}}$$
- (4)
- Electricity cost: Generally, the electricity rate consists of two parts, the flat and meter rates. To simplify the calculations, only the meter rate was included in this study. The meter rate includes summer and nonsummer prices, and the summer price is divided into peak and off-peak periods. The off-peak period starts at 22:30 and ends at 07:30, and the peak period starts at 07:30 and ends at 22:30. The peak price was applied to the daytime charging in this study, whereas the off-peak price was applied to the nighttime charging.

## 3. Optimization Methods

#### 3.1. Optimization Variables

#### 3.2. Particle Swarm Optimization

#### 3.2.1. Particle Coding and Initialization

#### 3.2.2. Particle Movement

#### 3.2.3. Update the Best Known Particle

#### 3.2.4. End Loop

#### 3.3. Particle Swarm Optimization–Genetic Algorithm

#### 3.3.1. Early Stage of Optimization

#### 3.3.2. Later Stage of Optimization

## 4. Results and Discussion

#### 4.1. Penghu Bus Transportation System

#### 4.2. Minimization of the Construction Cost of the Battery-Swapping Electric-Busesc System

#### 4.2.1. Case 1: No Daytime Charging

#### 4.2.2. Case 2: Optimize the Residual Battery Capacity and Battery-Charging Energy by Using the Genetic Algorithm

#### 4.2.3. Case 3: Optimize the Residual Battery Capacity and Battery-Charging Energy by Using the Particle Swarm Optimization–Genetic Algorithm

#### 4.3. Comparission of Battery-Swapping Electric-Buses and Plug-In Electrice-Buses System Results

## 5. Conclusions

## Acknowledgment

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**Constructing the battery-swapping e-buses (BS-Ebus) transportation system [32].

**Figure 4.**Flow chart of particle swarm optimization–genetic algorithm (PSO–GA) algorithm application in this study.

**Figure 5.**Penghu bus transportation system [32].

**Figure 6.**Results of Case 1. (

**a**) Number of electric-buses (e-buses) for various residual battery capacity (RBCs); (

**b**) number of additional battery units for various RBCs; and (

**c**) construction costs for various RBCs.

Price | Bus Type | |
---|---|---|

Large | Medium | |

E-buses (NT$/unit) | 6,000,000 | 4,000,000 |

On-board batteries (NT$/unit) | 2,600,000 | 1,200,000 |

Chargers (NT$/unit) | 950,000 | 750,000 |

Energy-filling facilities (NT$/unit) including battery-swapping equipment and battery chargers | 19,435,000 | |

Electricity cost (NT$/kWh) | Summer: Peak 3.89 Off-peak 1.99 Nonsummer: Peak 3.79 Off-peak 1.88 |

**Table 2.**Minimized construction costs in the BS-Ebus system without daytime charging. Unit: Million NT$.

System Construction | Cost Calculation | ||||
---|---|---|---|---|---|

E-Bus Type | Large | Medium | Item | 10-Year Cost | |

On-board battery capacity when dispatched | Full | 5 | 0 | On-board battery cost | 117.8 |

90% | 1 | 0 | |||

80% | 13 | 0 | |||

70% | 5 | 0 | |||

60% | 2 | 1 | |||

50% | 0 | 1 | |||

40% | 1 | 0 | |||

30% | 2 | 1 | |||

Number of e-buses | 29 | 3 | E-bus cost | 186 | |

Number of extra battery modules | 5 | 0 | Extra battery cost | 26 | |

Number of chargers | 15 | 2 | Charger cost | 15 | |

Number of charging facilities | 1 | Facility cost | 19.4 | ||

Nighttime BCE (kWh) | 5418.6 | 124.8 | Electricity cost | 35.7 | |

- | Total cost | 399.9 |

System Construction | Cost Calculation | ||||
---|---|---|---|---|---|

E-Bus Type | Large | Medium | Item | 10-Year Cost | |

On-board battery capacity when dispatched | Full | 10 | 0 | On-board battery cost | 112.8 |

90% | 2 | 0 | |||

80% | 7 | 0 | |||

70% | 1 | 1 | |||

60% | 2 | 0 | |||

50% | 2 | 1 | |||

40% | 1 | 0 | |||

30% | 1 | 1 | |||

Number of e-buses | 26 | 3 | E-bus cost | 168 | |

Number of extra battery modules | 3 | 0 | Extra battery cost | 15.6 | |

Number of chargers | 13 | 2 | Charger cost | 13.9 | |

Number of charging facilities | 1 | Facility cost | 19.4 | ||

Daily BCE (kWh) | Day | 855.8 | 0 | Electricity cost | 42.5 |

Night | 4674.6 | 124.8 | |||

- | Total cost | 372.2 |

**Table 4.**Minimized construction costs optimized by the particle swarm optimization–genetic algorithm (PSO–GA). Unit: Million NT$.

System Construction | Cost Calculation | |||||
---|---|---|---|---|---|---|

E-Bus Type | Large | Medium | Item | Decade Cost | ||

On-board battery capacity when dispatched | Full | 7 | 0 | On-board battery cost | 108.2 | |

90% | 3 | 0 | ||||

80% | 10 | 0 | ||||

70% | 1 | 1 | ||||

60% | 1 | 0 | ||||

50% | 2 | 1 | ||||

40% | 2 | 0 | ||||

30% | 0 | 1 | ||||

Number of e-buses | 26 | 3 | E-bus cost | 168 | ||

Number of extra battery modules | 3 | 0 | Extra battery cost | 15.6 | ||

Number of chargers | 13 | 2 | Charger cost | 13.9 | ||

Number of charging facilities | 1 | Facility cost | 19.4 | |||

Daily BCE (kWh) | Day | 576.4 | 0 | Electricity cost | 42.5 | |

Night | 4875.6 | 124.8 | ||||

- | Total cost | 367.5 |

**Table 5.**Optimized results of the plug-in e-buses (PI-Ebus) and BS-Ebus systems according to various algorithms. Unit: Million NT$.

Cost Items | PI-Ebus System | BS-Ebus System | ||||||
---|---|---|---|---|---|---|---|---|

Non Day-Charging [32] | Day-Charging | Non Day-Charging | Day-Charging | |||||

PSO | GA [32] | PSO-GA | PSO | GA | PSO-GA | |||

E-bus cost | 222 | 174 | 168 | 168 | 186 | 174 | 168 | 168 |

On-board battery cost | 102.2 | 117.0 | 109.7 | 105.0 | 117.8 | 121.1 | 112.8 | 108.2 |

Extra battery cost | --- | --- | --- | --- | 26 | 10.4 | 15.6 | 15.6 |

Charger cost | 29.8 | 23.4 | 22.6 | 22.6 | 15.0 | 14.8 | 13.9 | 13.9 |

Battery swapping system | --- | --- | --- | --- | 19.4 | 19.4 | 19.4 | 19.4 |

Energy cost | 38.9 | 58.3 | 50.4 | 53.0 | 35.7 | 41.7 | 42.5 | 42.5 |

Total cost | 392.9 | 372.7 | 350.7 | 348.7 | 399.9 | 381.5 | 372.2 | 367.5 |

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## Share and Cite

**MDPI and ACS Style**

Fang, S.-C.; Ke, B.-R.; Chung, C.-Y.
Minimization of Construction Costs for an All Battery-Swapping Electric-Bus Transportation System: Comparison with an All Plug-In System. *Energies* **2017**, *10*, 890.
https://doi.org/10.3390/en10070890

**AMA Style**

Fang S-C, Ke B-R, Chung C-Y.
Minimization of Construction Costs for an All Battery-Swapping Electric-Bus Transportation System: Comparison with an All Plug-In System. *Energies*. 2017; 10(7):890.
https://doi.org/10.3390/en10070890

**Chicago/Turabian Style**

Fang, Shyang-Chyuan, Bwo-Ren Ke, and Chen-Yuan Chung.
2017. "Minimization of Construction Costs for an All Battery-Swapping Electric-Bus Transportation System: Comparison with an All Plug-In System" *Energies* 10, no. 7: 890.
https://doi.org/10.3390/en10070890