Exploring the profitability of using electric bus fleets
for transport and power grid services
Wenzhe SUN, Pos-doc researcher
Kyoto UniversityMay 7, 2024

Forces pulling the transition of public transport

CompetitivenessSustainability

Reliability

Resilience2Forces pulling the transition of public transport

CompetitivenessSustainability

Reliability

Resilience3

Long-term transition of bus fleet and financial sustainability
Long termtransition andinvestment
Fossil-bus fleet

Energy (operation)
cost savings

Electric-bus fleet

Bus purchase cost

New energy
revenues

Charger purchase
cost
Government
subsidies

4Batteryreplacement cost……

Newservices

Passenger andother newrevenues

Innovative solutions to the transition of PT: Cooperation, electrification,and new services

Competitionorcooperation?

Electrification?
How tofinance it?

Newservices?

5

•
•
•
•

• Services (activities)
aggregation as delay
remedy• Leveraging therailway station area
as an activity hub andproviding premium
service subscription

Improve travel time and network reliability
Create new services
Open up new source of revenues
Shape financially and environmentally sustainable PT

Multi-systems• Free taxi as delay(disruption)compensation• Providing transit farewith a delay
insuranceMulti-services

Multi-modes

Integrating multi-modes, multi-services, and multi-systems with PT

6• Bus-to-Grid services• Discharging theelectricity to thepower grid when theprice is high or
during disruptions(e.g. blackout)

Background
Global CO2 emissions by economic sector

Global distribution of CO2 emissions from fossil fuel andcement by sector 2020

Many countries focus on developing
greener transportation

7

Increasing number of EVs

Global electric car stock by region and mode, 2010-2020

The number of EVs are increasing(especially e-buses)

Background: Vehicle-to-grid (V2G)
Vehicle-to-grid (V2G)
V2G is a system in which EVs communicate with the power grid to either sell orpurchase electricity. EVs function as a distributed but mobile energy storage unit
which can also perform grid demand side management services.

8

Background: Virtual Power Plant (VPP)
Virtual Power Plant (VPP)
A cloud-based distributed power plant that aggregates the capacities ofheterogeneous distributed energy resources (DER) for the purposes of enhancing
power generation, as well as trading or selling power on the electricity market.

9Battery capacity
per bus:50-500 kWh••Energy consumption
per person per day:
10kWh (World)
20kWh (Japan)

E-buses are considered as
potential power storage in thisresearch
Advantages compared withprivate vehicles• Larger battery capacity• More callable electricity

The Bus-to-Grid (B2G) concept and contracts
Traditionalenergy (fossilfuels)

Renewableenergy (solar,wind)

Energydemand(householder)Power system
Selling energy byMarket price

Virtual PowerPlant

101) SbMP
Selling energy to gridby market price2) FCR
Set aside a certain
number of e-buses todischarge energy on
request for Frequency
Control Reserve
purposeBus to Grid(B2G)

Passenger

The Bus-to-Grid (B2G) concept and contracts
Traditionalenergy (fossilfuels)

Renewableenergy (solar,wind)

Energydemand(householder)Power system
Selling energy byMarket price

Virtual PowerPlant

111) SbMP
2) FCRBus to Grid(B2G)

Demandchanges

Change inservice quality

Passenger

Objectives and contribution

12Research objective• Understanding the feasibility of the concept by modelling the interactions among energy providers, bus operator andpassengers.
• Showing the service quality impacts and optimal condition for bus operator.
Finding out optimal bus fleet, timetable and energy exchange plans.

Contribution• Promoting the electrification of bus transit.
• The profitability of bus operator is enhanced by new incomes from grid
• Greener bus transport may attract more users• Reducing the fluctuation of renewable energy supply and therefore stabilizing the energy market price.

Fan Fei, Wenzhe Sun, Riccardo Iacobucci, & Jan-Dirk Schmöcker. (2023). Exploring the profitability of using electric bus fleets for transportand power grid services. Transportation Research Part C: Emerging Technologies, 149, 104060.

Models: An optimization approach from an aggregate energy perspective(SbMP contract)
Objective function: Total profit ofpublic transport operator

Max𝑓 𝑡 ,𝐸 − 𝑡 ,𝐸 + 𝑡 ,𝑅 𝑡 ,∀𝑡{1,2,…,𝐻 ሽ

13𝑃 = ෍ 𝑃𝑝 𝑡 + 𝑃𝑔 (𝑡) − 𝐶𝑒 (𝑡൯ − 𝐶𝑚𝑡

Decision variables: Bus frequency, charging energy, discharging energy, and bus fleet allocation

Subject to:
Running buses constraint

𝑈 𝑡 ≤ 𝑁, ∀𝑡 ∈ {1,2, … , 𝐻ሽBuses connected to the grid𝑅 𝑡 ≤ 𝑁 − 𝑈 𝑡 , ∀𝑡{1,2, … , 𝐻ሽ

Number of chargers constraint

𝑃𝑝 (𝑡) = 𝜌𝑌(𝑡)𝑃(𝑓൯

Revenue from the grid𝑃𝑔 (𝑡) = 𝑐𝑒 (𝑡)𝐸 − 𝑡

Energy costs

𝐶𝑒 (𝑡) = 𝑐𝑒 (𝑡)𝐸 + 𝑡

Maintenance costs

𝐶𝑚 = 𝑁𝑐𝑚

Passenger demand loss
due to reduced frequency

𝑃 𝑓 =𝑅 𝑡 ≤ 𝑆, ∀𝑡{1,2, … , 𝐻ሽAggregate energy of bus line at theend of t

𝐸𝑚𝑖𝑛 ≤ 𝐸 𝑡 ≤ 𝐸𝑚𝑎𝑥 , ∀𝑡{1,2, … , 𝐻ሽEnsure the energy for running back𝐸𝑐 𝑡 𝑇𝑓 𝑡 ≤ 𝐸𝑚𝑖𝑛 , ∀𝑡{1,2, … , 𝐻ሽThe amount of charging anddischarging will be limited by thenumber of buses connected to thegrid and battery capacity

𝐸− 𝑡
𝐸+ 𝑡+
≤ 𝑅 𝑡 , ∀𝑡{1,2, … , 𝐻ሽ
𝛾−𝛾+Non-negative constraints

Revenue from passengers

𝐸 + 𝑡 − 𝐸 − 𝑡 ≤ 𝑅 𝑡 𝐵, ∀𝑡{1,2, … , 𝐻ሽ𝑓 𝑡 , 𝐸 − 𝑡 , 𝐸 + 𝑡 , 𝑅 𝑡 ≥ 0, ∀𝑡{1,2, … , 𝐻ሽ2𝜅2− 𝜅2
1 + 𝑒 −𝜅1 𝑓

Passenger demand elasticity to service frequency
2𝜅2𝑃 𝑓 =− 𝜅2
1 + 𝑒 −𝜅1𝑓

14

• An increase in service
frequency will attract
new passengers butwith an upper bound tolimit the total potential
demand.
• Since the service isalready in operation, it islikely that some kind of
demand equilibrium has
been reached with thecurrent f = 3.

Models: An optimization approach from an aggregate energy perspective(FCR contract)
Objective function: Total profit ofpublic transport operator

Subject to:

Max𝐾,𝑓 𝑡 ,𝐸+ 𝑡 ,𝑅 𝑡 ,∀𝑡{1,2,…,𝐻ሽ𝑈 𝑡 ≤ 𝑁, ∀𝑡 ∈ {1,2, … , 𝐻ሽBuses connected to the grid𝑅 𝑡 ≤ 𝑁 − 𝑈 𝑡 , ∀𝑡{1,2, … , 𝐻ሽ𝐸𝑚𝑖𝑛 ≤ 𝐸 𝑡 ≤ 𝐸𝑚𝑎𝑥 , ∀𝑡{1,2, … , 𝐻ሽEnsure the energy for running back𝐸𝑐 𝑡 𝑇𝑓 𝑡 ≤ 𝐸𝑚𝑖𝑛 , ∀𝑡{1,2, … , 𝐻ሽBuses for FCR no more than thoseconnected the grid𝐾 ≤ 𝑅 𝑡 , ∀𝑡{1,2, … , 𝐻 ሽNon-negative constraints𝑡

Revenue from passengers

𝑃𝑝 (𝑡) = 𝜌𝑌(𝑡)𝑃(𝑓൯

Revenue from the grid

𝑃𝑔 = 𝜀𝐾𝛾 −Energy costs

𝐶𝑒 (𝑡) = 𝑐𝑒 (𝑡)𝐸 + 𝑡

Maintenance costs

𝐶𝑚 = 𝑁𝑐𝑚

Passenger demand loss
due to reduced frequency

𝑃 𝑓 =𝑅 𝑡 ≤ 𝑆, ∀𝑡{1,2, … , 𝐻ሽAggregate energy of bus line at theend of t

Charging amount constraints

𝑃 = 𝑃𝑔 − 𝐶𝑚 + ෍ 𝑃𝑝 (𝑡) − 𝐶𝑒 (𝑡൯Decision variables: Buses for FCR contract, bus frequency, charging energy, discharging energy,and bus fleet allocation

Running buses constraint

Number of chargers constraint

15𝐸 + 𝑡 ≤ 𝛾 + 𝑅 𝑡 , ∀𝑡{1,2, … , 𝐻 ሽ
𝐸 + 𝑡 ≤ 𝑅 𝑡 𝐵, ∀𝑡{1,2, … , 𝐻 ሽ
𝐾, 𝑓 𝑡 , 𝐸 + 𝑡 , 𝑅 𝑡 ≥ 0, ∀𝑡{1,2, … , 𝐻 ሽ

2𝜅2− 𝜅2
1 + 𝑒 −𝜅1 𝑓Input data

16Bus lines selected in this research

Energy market price

Number of buses
GPS &Smartcard Data

Number of passengers
Service frequency
Passenger fare

Source: Japan Electric Power eXchange (JEPX)
http://www.jepx.org/index.html

Input data

17Bus operation related input

Energy-related input

Variables

ValueVariablesValue𝜌

2 $/pas

𝐸𝑏𝑎200 kWh

𝐻6𝛾𝑑𝑖𝑠40 kW/bus

𝑁18𝛾𝑐ℎ𝑎𝑟

60 kW/bus𝜂

1.35 kW/km

𝜀0.2 $/Kw per bus

𝑇

1.15𝑃(𝑓)𝜅1 = −1.2, 𝜅2 = 1𝜏

1𝑆20𝑐𝑚

6 $/bus per day𝑆𝑂𝐶𝑚𝑖𝑛

30%

𝑆𝑂𝐶𝑚𝑎𝑥100%

𝑆𝑂𝐶0100%* The notation of these variables is given in Appendix

Results: Profit given different fleet sizes, SbMP contract18• Higher profit with B2G than
without if the size of the bus
fleet is larger than 10.
• Currently, the line operates
with 18 buses. The total
profit could increase fromUSD3702 to USD3749 perday.
• A new electrified fleet of 14
buses can maintain theprevious level of profit
obtained from 18 buses

Results: Timetables in the Winter and Summer, SbMP contract• Bus timetable does notchange significantly given
the significant changes inenergy price.
• Seasonal service
adjustment to meet thefluctuation of energy
price is manageable.
• In winter, there are twodischarging peaks
according to the two
price peaks. They offer
the operator moretrade-off opportunities.

19

Results: Profit given different fleet sizes, FCR contract

20• Compared to SbMP, therevenue from grid and therevenue from passengers
are lower though, the gap
between the total profits
with and without EBaPS isenlarged.
• The operation (charging)cost is reduced due to thereduced number of buses
available for transportation
service.
• The potential negative
impacts on passengers canbe further consideredConclusions
Findings•••

We show the feasibility and profitability of E-buses as power storage providing grid service toVPP by two types of contract, from the perspective of a bus operator.
The difference in bus timetables obtained from significantly varying winter/summer energy
price were found acceptable.
The optimal timetable, bus fleet size, charging and discharging plans can be rapidly found.

Further work•••

Illustrating the feasibility of the concept in more complex situations
A large-scale bus transit network, the competitions among multiple bus fleets operated bydifferent operators.
Timetable-based bus operation and scheduling constraints
If the operator is the government, the profit will be discussed from more aspects.
From the perspective of “social welfare”, government subsidies to encourage electrification,and so on.
The cost of E-buses, the cost of discharging, and other parameter settings could also be
considered in the future.

21

A long-term bus fleet electrification framework considering B2G

22

Ongoing research and collaboration: Energy consumption modelling23• Trip-based bus energy consumption considering speed, acceleration, roadgradient, …
• Variables are from bus GPS data, and parameters are from literature• Manage the E-bus fleet of a bus terminal having 22 lines, using current arrivaland departure times as constraints and energy consumption as input• Consider the charging and dispatching problem as a bin packing or a knapsackproblem, each trip with its energy consumption as an item

Taken from Kim Bottinelli (2023) Profitability of using electric bus fleets: A case study of Kyoto. Master’s thesis,
ETH Zurich. (Supervised by: Wenzhe Sun, Jan-Dirk Schmöcker, and Francesco Corman)

Data collection progress: E-bus GPS and battery status data24

Sustainable, reliable, comfortable, and enjoyablemulti-modal mobility holding PUBLIC TRANSPORT
at the center

Contact: wz.sun@trans.kuciv.kyoto-u.ac.jp
25Appendix: Notation
Variables

26

Expression

Unit

𝜏

The period in the unit of hourh𝑁

Bus fleet sizebus

𝐻Bus line operation hours in one day

h𝑇

Travel time between terminals

h𝑆

The number of charging points at terminals

point

𝛾𝑑𝑖𝑠

Energy discharging rate

kW/bus𝛾𝑐ℎ𝑎𝑟Energy charging rate

kW/bus𝜂

Energy consumption per bus

kW/bus𝑐𝑒 (𝑡)Energy market price in time period t$/kWh𝑐𝑚

Maintenance cost for a bus per day$/day

𝜀Discharge price to the grid (FCR contract)$/bus per day

𝜌The fee paid per passenger$𝐸𝑏𝑎

Battery capacity per bus

kWh𝑆𝑂𝐶𝑚𝑖𝑛

Minimum state of system energy%

𝑆𝑂𝐶𝑚𝑎𝑥Maximum state of system energy

%

𝑆𝑂𝐶0

The initial state of charge of system energy

%

𝑌(𝑡)

Passenger demand in time period tpas𝑃 𝑓

Demand multiplier considering service frequency%