UK and Europe - With the introduction of increasingly stringent CO2 emission reduction deadlines for on-highway road transport in Europe and North America starting as soon as next year, many industry members are discussing whether hybrid electric drivelines should be part of the wider strategy to meet those targets.

Previously, we featured an article on Voith’s mild-hybrid product offering, and to help us understand the situation further we spoke to BAE Systems, an electric propulsion supplier with thirty years of proven experience of delivering hybrid electric drivetrains. They are proposing its parallel hybrid technology to help truck OEMs meet their emissions obligations on both sides of the Atlantic.

Commenting on parallel hybrid solutions, Laurence Homer, Business Development Manager at BAE Systems, said:

The emissions targets that need to be met by the truck sector in the coming years are very challenging. Hybrid electric technology is mature and dependable, and while it may not be the desired ‘end-state’, as an interim solution it can bring immediate and very significant reductions in fuel usage and emissions, without the cost and performance burdens that zero-emission alternatives can bring with them.

Laurence Homer, business development manager at BAE Systems

The regulatory environment

In the U.S. the new EPA "Phase 3" GHG standards for heavy-duty vehicles (HDV) target substantial reductions in CO2 emissions, with up to 60% reductions for vocational trucks by 2032 and 40% reductions for tractor trucks by 2032. These standards will apply to HDV manufactured from 2027 to 2032. Currently, in Europe, the targets are set at reducing emissions by 15% and 45% in new HDV by 2025 and 2030 respectively, as encompassed in the recently passed Euro VII emissions legislation. While the adoption rates of zero-emission transit buses in Europe has shown that battery electric technology is the logical answer and therefore makes such targets achievable, it is in no way clear that this is the case for many applications within the truck market.

EU legislation: Euro VII

This year saw the European Commission propose and adopt new CO2 emissions targets for new HDV from 2030 onwards, to incentivise the uptake of zero-emission vehicles as part of the European ‘Green Deal’. Compared with 2019 emissions levels, the Commission proposed a mandatory 45% emissions reduction from 2030, a 65% emission reduction from 2035, and a 90% emissions reduction on all HDV from 2040. The policy aims to improve air quality and overall public health in cities, while at the same time driving down the use of fossil fuels.

EU Parliament, Brussels, Belgium

The European Automobile Manufacturers’ Association* (ACEA) has made some calculations, claiming that in order to meet the 45% reduction by 2030 more than 400,000 zero-emission trucks must become operational in Europe. These would require over 50,000 charging stations and 700 hydrogen refilling stations, infrastructure which still needs to be built! In all likelihood this seems incredibly unlikely, which leaves industry leaders scratching their heads looking for solutions. So given the slow adoption of zero-emission trucks, should the industry be considering a more diverse strategy for reducing our carbon emissions; one that includes hybrid electric technology?

Smog in Paris

Electric buses vs electric trucks

There is no doubt that battery electric technology is already the logical answer for use cases such as city buses and last-mile delivery vans, especially in increasingly infrastructure-ready cities. The statistics back this up. According to market analysis by Wim Chatrou of Chatrou CME Solutions (CME), in 2023 the total number of city bus sales with alternative drivelines in European Union 27 countries plus the UK, Norway (NO), Iceland (ICE) and Switzerland (EU 27+4) totalled 13,466 units. These comprised 6,354 battery electric buses (excludes trolley buses), 4,022 hybrid electric, 2,883 CNG, and 207 hydrogen (fuel cell).

According to ACEA, in 2023 5,279 battery electric trucks were registered in Europe, which represents 1.5% of the market, up from 0.8% in 2022. Of these, 2,486 units were heavy-duty (trucks over 16 tonnes) and 2,793 units were medium-duty (3.5 to 16 tonnes).

Battery electric city buses are now seeing a far more rapid rate of adoption, but it is worth noting two things – hybrids still make up a significant proportion of bus sales (~30%), and that while the electrification of trucks is accelerating, it is doing so at a much slower pace.

Battery electric city buses have proven to be a more suitable and attractive option for urban public transport compared to electric trucks for freight. The question is why? Well, city buses typically operate on fixed routes with known distances, making it easier to plan for charging infrastructure and battery capacity. The buses will always return to a depot where they can be charged overnight. Furthermore, buses generally cover shorter distances per day at much lower speeds than long-haul trucks, aligning better with current battery technology limitations. Finally, the stop-and-go nature of city bus routes is ideal for regenerative braking, enabling the recovery of energy along its journey, and therefore improving the energy efficiency of the vehicle compared to its diesel counterpart. Other factors include the policy, regulatory and financial support afforded to public transport operators by governments.

Challenges hampering the adoption of electric trucks

When hauliers and transport operators are looking at procuring zero-emission trucks, it is difficult to get away from the very high, often prohibitive, upfront cost, of both the truck and the necessary charging infrastructure. Just last year, the recently launched Mercedes Benz eActros 600 long-haul battery-electric tractor unit purchase price was announced at around 2.5 times higher than its diesel equivalent. Very few operators are willing to absorb that initial cost, in an industry already operating on notoriously thin margins. The challenge facing the adoption of hydrogen-powered trucks is even greater.

The Mercedes-Benz eActros 600

Alongside the upfront cost and lack of charging infrastructure, current battery technology is better suited to the range requirements of city buses rather than most truck applications. In terms of battery capacity needs, we also know that the weight and physical volume of the batteries required by many trucks reduces their payload capacity, adversely affecting their economic viability. The trade-off between batteries and payload also results in the majority of zero-emission trucks having less range than the fossil-fuelled incumbents. This is coupled with the trucking industry having more varied operational requirements, making it harder to develop standardised electric solutions.

In other words, one drivetrain configuration does not fit all uses, as there are massive variations in vehicle types, weights, sizes, duty cycles (the route/operation they are used on), and operating environments. These may even vary from day-to-day for the same individual truck! A large investment is required to electrify all of these vehicle types from the OEMs, while providing the same level of flexibility to truck operators.

What is a parallel hybrid drive system, and how does it work?

There are two broad hybrid electric architectures: series and parallel. While a series system is most applicable to city buses, it is the parallel set-up that is most suited to the truck use-case we are discussing here.

In a parallel hybrid-powered vehicle, the diesel engine and electric motor work in coordination to propel the vehicle. The diesel engine acts as the primary power source, it provides the bulk of the power when the truck is travelling at higher speeds or when heavy loads are involved. The diesel engine is connected in a traditional manner, via a transmission, to the wheels. The electric motor is also connected to the transmission and is able to use energy stored in batteries to turn the wheels. The electric motor can either propel the truck independently (an ‘EV mode’) or assist the diesel engine by providing additional power during acceleration or while the truck is at high payload. The energy in the batteries is generated by a combination of regenerate braking, and the diesel engine itself (with the same electric motor being utilised as a generator). For areas where electric charging infrastructure is available, a version of this system is possible that incorporates a larger battery and a charging plug, both increasing the range it can drive with the diesel engine turned off, as well as further reducing tailpipe emissions.

The key feature of the parallel hybrid system is that both the diesel engine and the electric motor can operate simultaneously or independently, depending on driving conditions, vehicle demands, and the capability of the system fitted. At low speeds, or in mandated zero-emission zones, the truck may use only the electric motor to move, which is especially useful in urban or stop-and-go driving where diesel engines are less efficient and more polluting. At higher speeds the diesel engine typically takes over, as it is more efficient at maintaining continuous highway speeds and powering the truck over longer distances. The electric motor can also assist the diesel engine during acceleration, helping the truck reach higher speeds quickly and more efficiently, reducing the load on the diesel engine and improving fuel economy.

Benefits of a parallel hybrid-powered truck

The system can optimise fuel consumption, ensuring that the truck uses the diesel engine more efficiently (at higher speeds and loads), while relying on the electric motor to reduce fuel consumption and emissions in urban and low-speed environments. By relying on the electric motor during low-speed operation, the truck creates significantly less noise, and uses less diesel fuel, leading to lower emissions. This makes these vehicles more suitable for densely populated residential areas, or urban areas with stricter emission regulations such as the Low Emission Zones (LEZ) found in big European cities. Proponents of these parallel hybrid diesel-electric trucks will tell you, “operational flexibility is the name of the game”!

Although parallel hybrid-powered trucks are typically more expensive than their conventional ICE counterparts (obviously there is a cost to the electric motor, associated electronics and battery system – though the diesel engine can often be downsized reducing the delta cost), the relatively small battery capacity makes them far cheaper than equivalent battery electric trucks. The fuel savings over time can go some way to offsetting this higher upfront cost. Additionally, reduced maintenance costs may result from the use of the electric motor during lower-power operations, reducing wear on the diesel engine. The vehicle is not reliant on electric charging infrastructure, hence does not suffer from the range anxiety that comes with e-trucks. That said as previously mentioned parallel hybrid-powered trucks can be ‘plug-in’ enabled, allowing them to charge their battery when the opportunity arises, thus further reducing the use of diesel. Ultimately, a parallel hybrid-powered truck offers a versatile and efficient solution for the commercial trucking industry by integrating the strengths of both diesel and electric power, making it one of a number of key technologies enabling the future of sustainable freight transportation.

BAE Systems’ hybrid drive pedigree

BAE Systems is one of very few highly experienced suppliers of highly integrated, high-performing and reliable hybrid drivetrains to the global heavy-duty commercial vehicle sector.

Homer agrees that parallel hybrid systems could be a key part of meeting the challenging emissions goals facing the truck sector. He believes that the company is well placed to take advantage of this emerging market, based on their experience as one of only a handful of providers of heavy-duty hybrid drivetrains: “Over the last 25+ years BAE Systems has produced more than 18,000 hybrid drive systems, which have collectively run for five billion revenue miles. That makes us uniquely placed to understand the technology, and what it takes to bring it into the commercial truck market.”

Over the last three decades, BAE Systems has integrated hybrid drive systems into a wide range of medium and heavy-duty vehicles. These include working with leading OEMs to integrate series hybrid drive systems for the European and North American city bus markets, achieving class-leading fuel economy and reliability, as well as integrating parallel hybrid systems for both demonstration vehicles and trial fleets for both commercial and military applications. 

Homer continued:

The concept of a parallel hybrid is not new. BAE Systems completed its first parallel hybrid vehicle integrations more than 15 years ago. While they have always been successful in operation, the technology improvements flowing from continued investment in our broader family of electrification solutions combined with the emissions challenges facing truck operations, means the case for our parallel hybrid solutions is now more compelling than ever before.

The parallel hybrid system from BAE Systems

BAE Systems offers a proven parallel hybrid drive system for heavy-duty trucks. The system is suitable for vehicles ranging from 9 to 40 tonnes gross vehicle weight. It provides smooth power transitions between the diesel engine and the electric motor, with features like regenerative braking and energy management that optimise fuel usage and improve overall vehicle efficiency. Real world operations have seen fuel economy improvements and emissions reduced by more than 30% compared to conventional diesel engines. The product is versatile and can be applied to a wide range of medium and heavy-duty truck applications, including refuse collection, delivery, port tractors, utility and construction.

The investments made by BAE Systems across their broad family of low and zero emission drive solutions, such as more efficient battery systems, advanced energy management software, and more compact and efficient power electronics all read-across into their parallel hybrid solutions. Improvements in power electronics for example mean longer engine-off driving ranges, faster recharging, and better overall integration of power sources. These upgrades also increase the reliability and performance of the latest hybrid systems over previous versions, further reducing fuel consumption and emissions while enhancing operational flexibility.

So what is the conclusion - should hybrid diesel-electric drivetrains be a part of the solution to reduce carbon emissions by 45% in new trucks by 2030?

When the magnitude of the emission limitations being imposed in both the US and Europe are considered and compared to the recent uptake trends for zero-emission trucks, it is clear that alternative approaches need to be considered. The market is simply not ready to move entirely across to zero-emission solutions, but technologies are available today that would enable significant progress to be made.

Hybrid technology, and in particular parallel hybrid systems like those offered by BAE Systems, are very applicable to the truck market, and could go a long way in supporting the industry as it moves towards its end-goals.

It should certainly be amongst the alternative driveline technologies being considered to reduce the emissions of today, while the necessary changes in technology and infrastructure are made that will enable the industry to meet the massive reductions in local emissions being placed upon it.

*The European Automobile Manufacturers’ Association (ACEA) represents the 16 major Europe-based car, van, truck and bus makers: BMW Group, DAF Trucks, Daimler Truck, Ferrari, Ford of Europe, Honda Motor Europe, Hyundai Motor Europe, Iveco Group, Jaguar Land Rover, Mercedes-Benz, Renault Group, Stellantis, Toyota Motor Europe, Volkswagen Group, Volvo Cars, and Volvo Group.