How BMW is cutting CO2 emissions from its diesel truck by 50%

How can you make a long-haul diesel truck emit 50% less CO2 without changing anything about it? Sounds like a puzzle, doesn’t it? However, the new BMW Group Logistik pilot solution provided by partner company Trailer Dynamics here in Germany can do just that. I spoke with BMW’s Mo Koellner and Trailer Dynamics’ Michael Nemech about this technology in a phone call earlier in the week.

As for the answer to the puzzle above: This is a semi-truck trailer that has a huge battery (up to 600 kWh) mounted on its floor, and this battery powers an electrically powered axle underneath the trailer. The solution is not conceptually new. E-trailers, or electrified trailers, have been on the market in various forms for several years (although the technology is still at a relatively early stage). The basic principle is also simple. By adding a battery-electric power source to a diesel tractor trailer, you can reduce the fuel consumption of the diesel portion of the system. In other words, you’ve created a great hybrid-electric platform. Pretty obvious, isn’t it?

What makes the Trailer Dynamics solution great is how “plug and play” it is. In fact, the company says its electric trailers can work with it any The truck they are physically able to access. No trailer-to-truck connection is used; The e-trailer operates completely autonomously. Trailer Dynamics says this makes its product unique* in this space, as most other e-trailer solutions require active communication with the connected truck to enable electrically assisted driving. BMW is currently testing the TD solution on the BMW Group Logistik fleet. (*US-based Range Energy also claims to work with basically any truck, and their solution looks quite similar to Trailer Dynamics. We covered it back in May. The biggest distinction I’ve seen is that Trailer Dynamics offers a much larger batterys It is designed for use with European tractor trailer configurations. BMW’s own fuel economy numbers also seem to indicate that the TD solution may be more efficient, but it’s hard to know how those numbers are calculated apples-to-apples given differences in package size.)

The way TD achieves this is down to a special sensor package that lives in the main body of the trailer. There, a computer control model takes input from sensors (used to monitor various forces on the main axle) and turns that data into a decision about when and how much power to apply to the electric motors in the axle. The system’s logic takes into account the kind of things you expect. For example, if the trailer knows that the truck is currently parked and starts moving — when large trucks tend to use their fuel inefficiently — it will use too much energy to move the truck. The result is a significant reduction in the amount of diesel used. Likewise, if the system detects that the truck is heading uphill, electric assistance will be applied generously to reduce the effects of a high fuel consumption condition. According to TD’s website, factors such as weather conditions, road terrain, and traffic can also be taken into account, though it wasn’t clear to me how these factors come into play when the trailer is applying power. The system can also be configured to disable itself if the battery capacity reaches a pre-set cut-off point (important, as fleet operators ideally want to guarantee a minimum charge level at any given moment).

The system itself, by electric passenger vehicle standards, is heavy-duty stuff. Both 400 kWh or 600 kWh battery packs are used (a 200 kWh unit will come later), with the 600 kWh configuration being the most preferred among potential TD customers. This is because the efficiency economies seem to pay off better for longer routes, where a larger battery will be needed. The electric motor unit produces up to 580 kW (777 hp), which is impressive, but it’s the insane 13,000 Nm of torque that does the heavy lifting (literally). Charging is also very fast, with the 800V architecture supporting 44kW AC and up to 350kW of fast charging. The big numbers here make sense when you consider impact weights — BMW tests TD trailers with payloads of 16 metric tons, or more than 35,000 pounds. (Specifically, BMW has been using it to power electric drive units for its passenger cars.)

As for final efficiency, BMW sees a reduction in fuel consumption nearly 50% On some of the longer routes being tested, which means reduced emissions on those roads half. Even on shorter routes, this figure is more than 45% fuel savings. Because BMW uses 100% carbon neutral sources to recharge its trailer batteries, it estimates that each e-trailer can cut up to 120 tons of CO2 emissions from its fleet every year. For comparison, assuming a “typical” ICE vehicle emits about 5 tons of CO2 per year, each optimally used trailer is like taking 60 cars off the road. All of this is to say: It’s hard to overestimate the amount of fuel used by a real big truck.

BMW has also tested TD trailers with electric trucks, where the system effectively works as a range extender. Depending on the truck, the load and the specific route, BMW says the electric truck’s range can be extended by a factor of 2-3x, opening up entirely new scenarios for the use of BEV tractor units. In one test, BMW used an unspecified Volvo e-truck with a large TD trailer to travel more than 600 kilometers (373 miles) without recharging.

In an ideal world, diesel trucks would be replaced wholesale by electric trucks. But in reality, the principle of designing trucks as long-life assets means that ICE trucking will last a little longer than combustion-powered passenger cars. If we can get to a point where e-trailer systems like Trailer Dynamics reduce truck fuel consumption at scale, we can still have a real net positive impact on emissions as this transition occurs. Because this type of system benefits both ICE and EV tractors (arguably, the latter more so), this is a scenario where a gradual hybrid transition makes more sense. There’s nothing redundant being designed here for ICE trucks; These trailers will retain their utility in the age of electric vehicle (BEV) trucking.

For BMW, the electric trucking side of the equation has an added bonus – the low-profile “mega-trailer” configuration it uses for a significant amount of its haulage fleet significantly limits the range of electric truck options available. Using TD’s jumbo trailer solution as a range extender is an excellent way to overcome this challenge. (Large trailers are a class of high-capacity trailers developed specifically for use in the European Union, where they remain very popular. These maximum-space trailers require a specific class of truck body with a very low deck floor for towing, which leaves very little room for the battery.)

As for the challenges of stuffing a massive battery into the bottom of an already heavy trailer? They are not destitute. According to BMW, TD solutions are best for shipping in “cubic” configurations – that is, using the maximum container volume, not its maximum weight. The battery certainly frees up some available space for charging. But over time and as the system develops and improves (weight reduction is one of the immediate goals of TD), it will become possible to increase payloads. Human behavior is another big factor to consider. Suppose the tractor driver is still driving his car like a front-end. In this case, it is possible to reduce a fair amount of fuel economy in the system (BMW experienced fuel consumption variation of up to 20% during testing depending on the driver). From an economic standpoint, BMW believes that e-trailers will significantly reduce fleet operating costs, offsetting the initially high acquisition costs of the equipment.

In the future, TD suggests it could also start using its technology to aid on-road safety for tractor trailers, applying power or engine braking force to manage stability (for example, if the truck is at risk of being jacked). Right now, the company is just getting started, and currently has seven trailers in operation (the eighth was just delivered).

While cleaning up our passenger cars will have a real impact on global CO2 emissions, the impact of trucking is something we should all take into consideration too. According to data from the International Energy Agency, road freight accounts for 30% of total global transport emissions, making it the second largest contributor after passenger cars – and by a significant margin. (For comparison, air and maritime transport contribute just over 10% of global emissions each. Rail is just 1%.)