Are We Ready for Electric Concrete Trucks?

The economics of switching from diesel to electric—and what must be done to reach viability

The Ford flathead V8 from 1932 is near-mythical. The engine’s rumble and power transformed road vehicles into speedsters that were often favored by moonshine runners. The 1909 Harley-Davidson V-twin engine, with its patented sound, is equally iconic. So why are we messing with the fabled internal combustion engine in favor of electric? The answer includes “green”—for the environment and the money.

Research by Patrik Sved of Heidelberg Materials is leading the effort to convert ready-mixed concrete (RMC) trucks to electric. Heidelberg has full-volume electric mixers on the road today in Sweden. Given the country’s abundant hydropower, the energy usage is roughly 30 percent lower than the cost of diesel. The wildcard is the rapid pace of technological innovation, which will reduce the now higher capital cost.

Sved points out that electrification of all phases of material extraction, processing, and logistics can substantially reduce the carbon footprint of placed concrete. Noise will be mostly eliminated in sensitive environments like congested cities and air consumption in enclosed areas like tunnels.

Let’s look at the fundamental energy economics of switching to electric.

Consider Tesla Model S, known for its impressive range and performance. It has 50 kWh and a range of over 270 miles, with 7,104 lithium-ion cells of battery type 18650. Maintenance and operating costs are lower than those of an internal combustion engine, and the operating emissions are much less than gasoline or diesel. The problem is recharge time and the scarcity of key battery ingredients.

We need a lower-cost battery that can charge in minutes. Enter sodium rechargeable batteries. Lithium (Li-3) and sodium (Na-11) are alkali metals. Lithium is scarce, expensive, and often found in geographies unfriendly to Western democracies. Sodium is cheap and plentiful.

Sodium-ion batteries are supercapacitors that can charge up in seconds and release their charge quickly. They have a long lifecycle and operate over a wide range of temperatures. Sodium’s atomic weight is 3.3 times that of lithium, so sodium-ion batteries have a lower “specific energy” in terms of kilowatt-hour per kilogram than lithium-ion. However, they also tend to lose their charge over time.

Just how much energy does it take to deliver a cubic yard of concrete? We can calculate the energy needed based on the National Ready Mixed Concrete Association’s estimation of 1.08 gallons of diesel (and cross-referencing that number with numerous producers to confirm the estimate).

One gallon of diesel fuel contains 137,381 Btu of energy. Conversion to useful power for motion and hydraulics via the diesel combustion cycle is about 36-percent efficient. The delivery of 1 cubic yard, on average, requires 137,381 Btu/gallon x 1.08 gallon x 0.36—or ~53,400 Btu. Converting electricity to power via a motor has a relatively small power loss due to heat and friction, so let’s ignore it for now. There are approximately 3,412 Btus per kilowatt-hour, so the average delivery of 1 cubic yard requires 15.65 kWh.

Right away, we can see the battery size has to be huge. Tesla S is promoted as having a big battery at 50 kWh. That is only enough to deliver 3 cubic yards of concrete on one charge.

Four round trips per day at 10 cubic yards each trip would require 626 kWh. The Tesla battery appears to deliver ~0.16 kWh/kg and would require 4 metric tons of battery to go one day without a charge and no factor of safety. Given a cubic yard of concrete is ~2 metric tons with no other changes, that would reduce load capacities from 10 yards to 8.

While sodium-ion batteries are heavier than lithium-ion batteries, they recharge in minutes, not hours. A much smaller battery could be installed and recharged while the truck is being loaded at the expense of a few more minutes in the yard.

The best estimate of a comparable range on sodium, which has a specific energy of ~0.099 kWh/kg, would require a battery of 6-plus metric tons. Given that recharge is close to immediate, we could take a third of the size needed for the full day, reducing the range to just over 1.5 times the average trip distance. The reduced load size would be 9 cubic yards. We’re getting closer to viable with sodium.

At $0.20 per kWh in California, it would take $2.90 per cubic yard for delivery. Diesel varies, but we can assume an average price of $3.75 per gallon. This gives us about $1.15 per cubic-yard savings on variable costs to offset capital costs. At an average of 5,200 cubic yards per year, that gives us a capital offset of $5,980 per truck per year. That’s pretty thin when considering the battery cost and possible price differential from a diesel engine to an electric motor.

Of significant note is the current oversupply of renewable energy in many locations, such as the U.S. and EU, and its subsequent bargain prices. For example, German wholesale prices were negative in 301 of the 8,760 tradable hours last year. Instead of idling down wind and solar farms during the peak hours of the day, the energy can easily be consumed by our industry. Using current overcapacity at reduced prices will further tip the scale of electrification economics.

Assuming we can get five years of depreciation out of a battery and only need one per truck—and costs for diesel versus electric trucks are the same—that gives us around $30,000 and, depending upon electricity prices, perhaps up to $60,000 to work with for batteries. Sodium batteries are still too new to be available in volume, and there is no clear pricing information, but at least we know what we are working with.

Sweden is Heidelberg Materials’ battery electric mixer truck proving ground. Heidelberg Materials is a leading manufacturer of heavy construction materials such as cement and concrete.

Electrification of over-the-road and heavy-yard vehicles for RMC is coming. According to Patrik Sved, a new economic model must both evolve and remain flexible. Traditional trucks have an optimal life of five to six years and often require one-year lead time for procurement. For electric trucks, the technology for power and drivetrain is moving so fast that innovation will take place in the time between order and delivery.

While current technology presents some challenges, promising near-term developments will tip the scale in favor of the transition. On behalf of our industry, children, and grandchildren, let’s give Sved and his team at Heidelberg Materials a shout-out for their pioneering work.

Craig Yeack has held leadership positions with both construction materials producers and software providers. He is co-founder of BCMI Corp. (the Bulk Construction Materials Initiative), which is dedicated to reinventing the construction materials business with modern mobile and cloud-based tools. His Tech Talk column—named best column by the Construction Media Alliance in 2018—focuses on concise, actionable ideas to improve financial performance for ready-mix producers. He can be reached at [email protected].