Source: Rocky Mountain Institute outlet
(Editor’s Note: This is the second in a series examining vehicles powered by natural gas. Read the first post here.)
The value proposition of natural gas vehicles varies widely by application. Fleets with high utilization and poor gas mileage, for example, can reap significant near-term value from the switch to natural gas.
In April, Colorado Governor John Hickenlooper sent a letter to the CEOs of 19 automakers, asking them to commit to manufacturing natural gas vehicles (NGVs). His letter included signatures from governors of 12 states, all committing to a bulk purchase of NGVs—the idea being to spur the growth of a relatively niche market and reduce costs through economies of scale.
It’s a powerful idea. If 13 states can agree upon a specific vehicle type for their respective fleets, they can achieve significant cost reductions with an aggregated purchase. But wouldn’t the same approach work for any alternative-fuel vehicle that is currently more expensive than standard gasoline and subject to economies of scale?
Wouldn’t it work for electric vehicles (EVs), too? In general, car fleet buyers (such as taxi cab companies) see many economic similarities when weighing EVs vs NGVs. The differences emerge when considering electricity vs. natural gas for fleets of heavier vehicles: medium trucks, heavy trucks, and buses.
Fleets of Passenger
Vehicles Both NGVs and EVs can offer a compelling business case for centralized fleets of passenger vehicles with high utilization rates (e.g. 60,000 miles per year) that accelerate the payback from the nine to 10 years typical of non-fleet vehicles to about three to four years. EVs pay back slightly faster due to the current federal tax credit.
Many of the same considerations and tradeoffs that would apply to individual buyers of passenger vehicles also apply to fleet buyers:
- EVs currently have less range than NGVs.
- The most efficient and least greenhouse-gas-intensive way to use natural gas is to burn it to generate electricity that powers EVs.
- The learning curve for manufacturing EV powertrains is steeper than it is for NGV powertrains, potentially leading to drastic EV price reductions within as few as three years.
- Refill/recharge rates for both NGVs and EVs vary according to the refilling/recharging technology employed.
- Stop-and-go city driving would favor EVs because their powertrains deliver the same torque and efficiency regardless of speed and don’t consume energy idling during stops (as internal combustion engines do).
- Investment in EV recharging stations offers reduced exposure to fuel volatility because EVs are fuel agnostic and can get their electricity from fully renewable sources.
Fleets of Heavy Vehicles
Per unit of mass, batteries carry much less energy than any type of liquid fuel or compressed natural gas. Batteries are currently expensive; a typical passenger EV battery pack costs about $10,000. As vehicles get heavier and require more power, battery costs become prohibitive relative to liquid fuel technologies because of a difference in scaling characteristics. If the power requirements double, it is much cheaper to double the capacity of a fuel tank than it is to double the quantity of batteries.
For this reason, natural gas is an attractive alternative fuel technology for heavier vehicles, with compelling paybacks depending on yearly mileage and fuel prices.
Heavy truck fleet owners can, relatively cheaply, convert their trucks to natural gas and achieve paybacks in the three-year range (assuming yearly mileage of about 120,000 miles and current fuel prices). One challenge is the increased volume of the fuel tanks (compressed natural gas has four times the volume of diesel fuel). For trucks that “cube out” (loads whose critical limit is determined by freight volume rather than weight), the consequence is decreased freight revenue. If volume is not sacrificed, range is.
Garbage trucks are another application offering an attractive payback of three to six years, and given the stop-and-go nature of their routes, a start-stop device can be installed to reduce idling waste.
Electric buses are common, but most use direct electricity from overhead lines rather than batteries. These are by far the most efficient and cost-effective types of buses if cities can invest in electric lines. For rural routes where electric lines are unavailable, however, natural gas again offers an attractive payback of three to five years.
A long-term perspective again reveals additional economic considerations. While switching to natural gas from diesel or gasoline offers a compelling economic case for heavy vehicles, their fuel must be delivered via specialized filling stations.
The size of the fleet now comes into play; for a small municipality with a single garbage truck, the high cost of a single CNG filling station may not pay back within the life of the vehicle. If, on the other hand, the single expenditure of a filling station can benefit multiple vehicles, such as heavy trucks traveling along a main freight corridor, the economic case may still hold up.
In general, when choosing between natural gas and electricity for vehicles, natural gas tends to make economic sense in the short term for fairly large fleets of heavier vehicles, and electricity tends to make economic sense, in both the short and long term, for passenger vehicles.
With so many complex variables—vehicle type, gas mileage, and utilization patterns; fleet size; natural gas vs. diesel prices; battery prices; and infrastructure costs—the decision merits a case-by-case and real-time examination by fleet managers considering the switch to alternative fuel.