Package delivery by drones is expected to take off in the next few years. That should reduce energy use and cut greenhouse gas emissions, but only if done with care, new research published in Nature Communications finds.
The environmental impact of drone delivery depends on the size and efficiency of drones, the source of electricity used to recharge their batteries, and, most importantly, on the warehouses that would have to be built to support them.
Small drones carrying packages up to 0.5 kilogram in weight would have lower emissions than any truck or van, researchers calculated. But larger drones carrying packages weighing up to 8 kg could generate much more emissions than trucks in regions with fossil fuel-powered electricity.
“To realize the environmental benefits of drone delivery, regulators and firms should focus on minimizing extra warehousing and limiting the size of drones,” researchers from Lawrence Livermore National Laboratory and Carnegie Mellon University write in the paper.
Small, battery-powered drones will mostly replace large diesel trucks and vans to cover the last few miles from warehouses to customers. A previous study has shown that drones emit less carbon dioxide than trucks when they cover short distances and deliver fewer packages.
In the new work, researchers consider the energy use of delivery vehicles but also the logistics system built around them. Companies like Amazon are promising a delivery time of 30 minutes from the time of purchase. That will require building a several local warehouses that stock goods. So while drones use less energy per package than diesel trucks, the additional energy used by warehouses waters down that benefit, the researchers found.
The team estimated energy use and greenhouse gas emissions per package delivery from a truck and two different types of drones: four-rotor and eight-rotor. They included emissions from warehouse energy use in both scenarios. For drone emissions, they took into account electricity grids in two regions with different fuel mixes: California, where the electric grid is cleaner, and Missouri, which has a high-carbon-intensity grid.
Small drones emitted less carbon dioxide than trucks and vans in both states, according to the results. But the impact of larger drones was fuzzy because the carbon intensity of the grid mattered more. In this case, drones had 9 percent less emissions than truck delivery in California, but had 77 percent higher emissions than truck delivery in Missouri.
“The focus of drones should be on light packages, with heavier packages left for ground vehicles,” the researchers say. “The continued reduction in the carbon intensity of the electricity system, coupled with energy efficiency improvements in associated commercial buildings, are essential to realize the potential environmental benefits of freight delivery by drones.”
Source: Joshuah K. Stolaroff et al. Energy use and lifecycle greenhouse gas emissions of drones for commercial package delivery. Nature Communications. 2018.