While most North American growers and farm equipment dealers don’t share much enthusiasm for electric-powered field tractors and harvesters, the recent demonstration of a highly-modified John Deere tractor using anhydrous ammonia as fuel for its electric motors could spark some interest in both groups.
Earlier this year, in a custom research report on the 5-year outlook for the electrification of farm equipment, Ag Equipment Intelligence found only limited interest in electric high-horsepower tractors and combines among broad-acre farmers surveyed in Canada, Mexico and the United States. Similarly, equipment dealer interest mirrored the growers’ largely underwhelming support for replacing diesel power with batteries — especially where long duty cycles at high loads are the norm.
Both groups cited serious concerns about the lack of “run time” available with today’s lithium-ion battery technology, the non-existence of rapid rural charging infrastructure for current battery designs and the apparent need for expensive alternate sets of batteries to keep their equipment rolling during various crunch times of the agricultural calendar.
In early June, however, Amogy, Inc., opened some eyes with its successful demonstration of a mid-size, electric farm tractor at New York’s Stony Brook University’s Center for Advanced Energy. Using its “Ammonia to Power” system, Amogy’s researchers gutted the diesel power train of the John Deere FWA tractor and replaced it with electric motors, a 100 kW hydrogen fuel cell (roughly 75 horsepower equivalent) and a standard 60-gallon liquid-storage tank suitable for anhydrous ammonia fuel to create a tractor which produces no harmful emissions of its own.
Unlike most hydrogen-powered tractors which burn the light, colorless gas in a spark-ignited internal combustion engine, Amogy’s demonstration machine uses widely-available anhydrous ammonia (NH3) and a hybrid fuel cell to power the electric motors. The demonstration model can run several hours on the ammonia stored in the tank behind the cab, and, to answer the skepticism of those concerned with the refueling time of “battery-electric tractors,” Amogy’s team says it refilled the fuel tank with liquid ammonia for on-lookers in a “fast and simple” process.
While ammonia can be used as fuel for internal combustion engines, its energy density vs. pure hydrogen makes it attractive for use in fuel cells such as that on display with Amogy’s tractor.
Fuel Cell Operation 101
The U.S. Department of Energy says fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is available.
With apologies to the DOE, this is a paraphrase of their explanation of the workings of a fuel cell:
“A fuel cell consists of two electrodes — an anode (negative charge) and a cathode (positive charge) sandwiched around an electrolyte.
“Fuel such as hydrogen is fed to the anode, and atmospheric air is fed to the cathode. In a polymer electrolyte membrane fuel cell, a catalyst separates hydrogen atoms into protons and electrons — which take different paths to the cathode. The electrons go through an external circuit which creates electron flow to power motors, lights and other loads, and the protons migrate through the electrolyte to the cathode where they reunite with oxygen and the electrons to produce water and heat.”
Compared with elemental hydrogen, which is made up of two hydrogen atoms, an equivalent tank of anhydrous ammonia with its three hydrogen atoms has 50% more energy density than compressed pure hydrogen, so more fuel can be stored in smaller spaces. And across the globe, because NH3 is widely used as an agricultural fertilizer, there is an infrastructure for manufacturing, storing, transporting and quickly refilling ammonia tanks.
These advantages are what has drawn Amogy scientists to powering their electric tractor with NH3 rather than H2 — which is difficult and expensive to store. Additionally, outside of the West Coast of the U.S., there is little infrastructure for handling hydrogen.
Amogy’s “Ammonia to Power” system doesn’t use ammonia directly, because its fuel cell is specifically designed to use hydrogen to produce electricity. The system, therefore, is designed with an on-board reactor to “crack” the NH3 compound to free hydrogen atoms on demand, which enables the system to outperform a typical hydrogen fuel cell in terms of energy density.
While electric vehicle (EV) technology appears to be quite technologically feasible for personal transportation and urban service and delivery vehicles (if you agree the nation’s power grid and charging infrastructure can match estimated demands), the weight, expense and low energy-density of batteries required for long-duration, heavy-load applications has substantial engineering challenges. Amogy researchers, however, say their technology is scalable, and they plan to have a Class 8 ammonia fuel-cell over-the-road demonstration truck within the year.
It’s quite conceivable ammonia-driven fuel cells might also find a home on the world’s farms and ranches if the market is allowed to sort out the most practical technologies for a variety of power demands.