Electric buses are propelled by motors and run on electricity. Unlike traditional diesel-powered buses that are fitted with internal combustion engines, electric buses are zero-emission and produce less noise.
Given their environmental benefits, several cities have adopted electric buses for public transport solutions. In Singapore, electric buses are being explored for wide-scale future use. While still in its early stages, electric buses are expected to gain traction in the coming years with the Land Transport Authority (LTA) spearheading efforts to incorporate them into the public bus fleet.
Advantages of Electric Buses
For a highly urbanized environment like Singapore, electric buses offer clear advantages. With zero tailpipe emissions, the bus does not contribute to urban air pollution within the immediate vicinity, while also reducing noise pollution. In the mechanical aspect, electric buses have far less moving parts as compared to buses with internal combustion engines, thus requiring less maintenance. Operating costs are further lowered without the need for diesel fuel.
Types of Electric Buses
There are several main types of electric buses, differing in their method of energy storage and operating principal. The most prevalent type is the battery electric bus, which stores energy onboard in a chemical battery, with Lithium-Ion and Iron-Phosphate varieties being most popular.
A variant of this technology is used on the supercapacitor or ultracapacitor bus, where capacitors are used instead of batteries to store their energy. While capacitors store far less energy (~5%) for the same weight as compared to conventional batteries, they are able to charge and discharge very quickly, making them more suited for bus routes that stop frequently and predictably. NTU’s Supercapacitor Bus (discussed later) is based on this principle. However, for conventional bus operations, battery electric buses are most suited for public bus routes.
There are also vehicles that need a constant source of electricity (such as trolleybuses), but such vehicles are confined to a network of overhead lines and thus lack deployment flexibility. Apart from the infrastructure cost of building and maintaining overhead lines, they are also regarded as unaesthetic.
Finally, the plug-in hybrid bus combines the plug-in charging capabilities of electric buses with a conventional hybrid bus drivetrain (thus, essentially hybrid buses with larger-capacity batteries and external battery charging capabilities, designed for prolonged electric-only running). Only a small handful of such bus models exist, with examples being the Volvo 7900 Electric Hybrid and the ADL Enviro400VE.
Battery Electric Bus – Design Philosophies
Among battery-electric buses, two distinct design philosophies have been adopted. The conventional, depot-charging approach (still favoured by Chinese bus manufacturers) is to place a large number of batteries on every bus to achieve sufficient operating range over a day’s worth of revenue service. However, equipping buses with heavy batteries makes them more expensive and heavy (and to some extent, decreased cabin space), which increases the strain on the battery, raising both energy consumption and life-cycle costs.
On the other hand, the Opportunity Charging approach is favoured by European bus manufacturers. Charging points are erected at the end-points of a bus route, which sufficiently recharges the bus in a short amount of time (usually several minutes) before the bus continues on its next trip. With fewer batteries required per bus, its advantages translate to a more spacious bus interior, lower environmental cost of battery production, and lower electricity consumption through reduced vehicle weight. Disadvantages include the lack of deployment flexibility (on non-infrastructure-equipped routes) and the possible impact on bus operations should a charging station break down, and some redundancy is thus required, such as installing multiple chargers at terminating points.
Around the world, the majority of Opportunity Charging systems have largely used pantograph-down charging (with a pantograph extending down from a fixed overhead mounting position). A minority of systems use pantograph-up (with a bus-mounted pantograph), plug-in charging, and ground-based inductive charging. Currently, efforts are focused on expanding the use of opportunity charging on suitable routes and the adoption of a common charging interface across different bus manufacturers, allowing multiple bus models to use the same charger.
Challenges facing Electric Buses in SG
Singapore is a demanding environment for electric buses. To avoid compromising the efficiency of the current public bus network, electric buses must operate at levels of high availability throughout the day (at similar levels as their diesel-powered counterparts), which often requires buses to operate for over 20 hours per day.
Two major issues facing electric buses are range and charging. Not only must electric buses have an adequate range for performing several trips of a bus service, they must also be supported by charging infrastructure installed in depots and/or bus interchanges, usually in the form of cable charging or overhead charging.
Regardless of charging mode, electric buses must have sufficient battery capacity to deliver sufficient operating range before the bus needs to be recharged. On the operational side, bus operators must ensure that buses are sufficiently charged whilst on revenue service, which also involves factoring in unforeseen traffic conditions that may cause the bus to be stranded away from a charging point for a prolonged period of time.
Singapore’s warm and humid climate poses challenges for the performance and longevity of electric systems. In addition, air-conditioning systems consume large amounts of energy particularly in Singapore’s climate, which puts additional strain on a battery and hence the bus’ overall range.
Electric buses must be supported by charging infrastructure installed in depots and/or bus interchanges, usually in the form of cable charging or overhead charging. Overhead charging via pantograph is a common charging method for electric buses using the opportunity charging principle, which quickly charges a bus at the end termini of a bus route (in as little as a few minutes).
Less common forms of charging which have been trialled overseas include wireless inductive charging (installed underneath the road surface, and requires no physical contact with the bus), and battery swapping buses (paired with battery swapping stations). These solutions are more complex (and more expensive) than commonly-adopted charging methods, and also suffer from a lack of availability should the charging station break down.
The power drawn from these charging stations (especially when implemented on a large scale) is significant, and power infrastructure must be able to cope with their power consumption. The lack of excess capacity in the existing electrical distribution network is a major hurdle to widescale electric bus adoption in Singapore, particularly due to the centralised location of bus facilities (i.e. bus interchanges and depots) which would necessitate the installation of many charging points, and in turn, draw a large amount of power from the grid. While new transport facilities can be built to support these increased power demands, the retrofitting of existing transport facilities proves to be more difficult.
Initial Trial – BYD K9
Go-Ahead Singapore trialled Singapore’s first fully-electric bus from November 2016 to May 2017. The BYD K9 bus was produced by established Chinese electric vehicle manufacturer BYD.
The e-bus trial was part of the EV testbed led by LTA and the Economic Development Board to trial fleet-based EV operations, a follow-up to the earlier phase which ended three years ago and involved individual corporate users. The LTA also added that the bus will operate trips on top of those scheduled, and hence will not cause an adverse impact on service levels.
Charging equipment and infrastructure was installed at Go-Ahead‘s depot in Loyang. to support operations of the e-bus. The K9 bus requires between 5 and 10 hours to be charged fully, allowing it to run for 250km, but its operating range in Singapore is likely to be significantly lower due to the high energy consumption of the air-conditioning system.
LTA Procurement of Electric Buses
Main Article: 60 Electric Buses Procured by LTA
During the Ministry of Transport’s Committee of Supply Debate in March 2017, Second Minister for Transport Ng Chee Meng announced that LTA would be calling tenders to purchase 50 hybrid buses and 60 electric buses in 2017. Contract PT323 – Procurement of Electric Buses was put up by LTA in December 2017, and awarded to three different tenderers in October 2018.
|S/No||Tenderer||Provision + Total Price|
|1.||BYD Singapore Pte. Ltd.||20 Single-deck buses
|2.||ST Engineering Land Systems
(Bidded as: Singapore Technologies Kinetics Ltd)
|20 Single-deck buses:
(Bidded as: Zheng Zhou Yu Tong Bus Co., Ltd.)
|10 Single-deck buses &
10 Double-deck buses:
The 50 Single-deck and 10 Double-deck Electric Buses are expected to be delivered between 2019 and 2020. A mix of charging solutions, such as opportunity charging (via pantograph), and overnight charging at depots, would be implemented.
The BYD C6 is a midibus with a capacity of around 24 passengers, and entered public bus revenue service on SMRT Bus Service 825 on 17 October 2019. In total, 4 BYD C6 buses are used for this service. These buses are leased by SMRT Buses from BYD (Singapore) Pte Ltd.
Similar to units operated by SMRT on revenue service.
The BYD C9 is a 12-meter battery-electric coach. There are currently 2 units registered in Singapore.
Special Use Electric Buses
A collaboration between BlueSG and NTU brought in a Bolloré Bluetram, an electric supercapacitor bus. Named the NTU-Blue Solutions Flash Shuttle, the vehicle was used as a short-haul shuttle bus, whilst the vehicle is performance evaluated on Singapore roads.
It is manufactured by French transportation company Bolloré, of which BlueSG is a subsidiary. The bus can travel 2km on a single charge, with backup power that provides for an additional 30km.
More details on the trial and bus at the main article, Bolloré Bluetram.
Two units of the ST Autobus are being used as a testbed for autonomous development. More details on the trial and bus at the main article, ST Autobus. Both buses also took part in the Autonomous Bus Trial at Sentosa back in 2019, which was open to members of the public.
Two Volvo 7900 Electric buses are being used as a testbed for autonomous development in a tie-up between NTU, LTA, Volvo and SMRT. One unit is based at NTU/CETRAN, and another unit is based at SMRT’s Woodlands Bus Depot where depot trials are underway (involving navigation into washing bays and parking at charging stations). See Autonomous Buses in Singapore for more information.
More details on the trial and bus at the main article, NTU-LTA-Volvo Autonomous Bus Trial.
The MAN A22 Retrofitted Electric Bus is the product of an electric bus conversion project undertaken by ST Engineering and Linkker on an existing MAN A22 (Euro V) bus as a proof-of-concept. The bus was shipped to Finland for modification work before returning to Singapore. Only one unit of this bus has been produced, and charging is primarily via an inverted pantograph connection (Oppcharge).
ST Engineering (Land Systems) are bringing in several electric buses as a testbed for autonomous bus development. The electric bus will be based off the Linkker 12+, a full-size electric city bus made by Finnish manufacturer Linkker. It was rebranded the STROBO Series 12 in October 2019, and charging is primarily via inverted pantograph connection (Oppcharge).
Privately-operated Electric Buses
ShareTransport, a subsidiary of Commute Solutions, owns several 24-seater BYD C6 electric buses for use on on-demand routes.
HDT Singapore Taxi owns a 12-metre BYD C9 coach (registered PC6284C) equipped with a wheelchair ramp.
More Electric Buses
Opportunity Charging in Europe
Opportunity charging of electric buses is gaining popularity in Europe with bus manufacturers producing buses capable of supporting overhead charging. One such overhead charging platform is OppCharge, an open and competition-neutral interface supplied by Swiss-Swedish engineering group ABB. By being compatible with multiple bus manufacturers, Oppcharge offers bus operators choice and flexibility of buses without the need to modify existing charging infrastructure. These overhead pylon chargers with extendable pantographs are usually installed at the end stops of bus routes, allowing buses to quickly receive a full charge in-between trips.
Charging is fully automatic and secured by a two-way WiFi communication sequence. The driver gets a clear indication in order to stop within the specified ± 200 mm from the reference point. The charging sequence is started by activating the parking brake, and the driver can interrupt it at any time.
While OppCharge is the main vehicle-agnostic opportunity charging platform being rolled out in Europe, companies continue to offer proprietary charging solutions. For example, Alstom offers the SRS ground-based static charging system for trams or electric buses, where a current collector device deploys from the underside of the vehicle which makes contact with a charging plate installed on the road.
Electric Buses in Malaysia
Electric buses have also entered the Malaysian market. The BRT Sunway Line in Kuala Lumpur is fully operated by 15 battery-electric BYD buses (some of which were later redeployed outside the Bus Rapid Transit network). In addition, the Putrajaya region trialled 10 pantograph-charging electric buses in 2016 and has since procured 150 more units on delivery. These buses are operated by Nadi Putra. Most recently, electric buses were rolled out in the city of Kuala Terengganu on the myBAS service, a new series of residential bus routes to boost the existing bus network.
In addition, an Elektrik Bas Inovasi Malaysia (EBIM) program is researching and developing domestic electric bus technology.
Large Scale Rollout
A large-scale rollout of electric buses is prevalent in China where government grants for electric vehicles are strong. Even before the rollout of electric buses, natural gas buses were increasingly prevalent in Chinese cities.
Shenzhen is leading the way in electric bus usage with all 16,359 buses running on electricity, making Shenzhen the first in the world to have a citywide all-electric bus fleet. It also aims to convert all 17,000 taxis to electric ones by 2020, and as of early 2018, more than 63 per cent of them are electric.
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