The Case for the Electric Tractor

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30 Jun 2007
View all related to biofuel | Renewables
View all related to Jason Bradford | David Fridley

The Case for the Electric Tractor
Christoffer Hansen and Jason Bradford
Post Carbon Institute - Energy Farms Program

The discourse has been heating up around biofuel for well over a year now. The classic food versus fuel debate has been engaged recently by the United Nations, while scientists, climate change experts, and farmers begin to question the scale and logistics of biofuel replacement of the current liquid fuel demand.

This June, one of us (Dr. Jason Bradford) interviewed Lawrence Berkeley National Laboratory staff scientist and Post Carbon Fellow David Fridley on the bi-weekly radio show the Reality Report. The topic for the interview: “The Myths of Biofuels” finds Bradford and Fridley engaged in a devastating analysis of the scale and logistics of replacing our current fossil fuel demand with ethanol and biodiesel. In short, a large scale industrial biofuel system will wreak havoc on the soil, require an entirely new distribution infrastructure (due to the corrosive nature of ethanol), not easily adapt to the current fleet of USA autos, will compete heavily with food production and natural ecosystems that are seen as potential cellulosic biofuel feedstocks, and will do little to actually replace the current (or future) energy demands of liquid fuel.

Two weeks later, the Reality Report picked up where the Fridley show left off and we both joined Yokayo Biofuels President, Kumar Plocher on the show. The question was: If biofuel is not going to be sustainable on a large industrial scale, then would a local biofuel system be an appropriate response to the limitations of long-distance transport and petrol dependent methods of cultivation and processing of biofuel? If biofuel is produced for local consumption how much land would be needed, what crops would be used, and how would they be processed? Again, simple math painted a picture of an inflated hope and hype. We ran the numbers and with the 35,000 acres (14,000 hectares) of remaining prime farm land in Mendocino County approximately 84,900 acres (34,000 ha) would be needed to replace current county diesel consumption if canola was used as the prime feedstock.

Additionally, approximately 231,100 acres (94,000 ha) of farm land would be needed to replace the current gasoline consumption with corn-based ethanol. It doesn’t really matter much which crops, or combination of crops, are considered--the land base isn’t available to support a biofuel industry even on a local scale that meets current fuel demand. These analyses also absurdly assume the use of all agricultural land for fuel production, leaving no room for food! This is unconscionable and not the direction that any serious farmer or environmentaly aware person desires to advocate.

As the hype around biofuel already begins to dissipate, serious researchers and planners are advocating curtailment of long distance transport and the adoption of electric vehicles as one of the most sustainable options to replace the work and carbon footprint of the internal combustion engines. Vegetable oils and ethanol are useful products and should not be omitted from agricultural production, but their uses require further consideration. Why do we have to burn these useful feedstocks when they have multiple alternate uses? Should biodiesel production be limited to the reuse of waste food oil?

In an article published by AlterNet, David Morris from the Institute of Local Self Reliance makes two important observations related to the uses of vegetable oils and plant-based sugars that are consistent with the position of the Local Energy Farm Program. Morris suggests that

“human nutrition is the highest use of plants, followed by medicinal uses and possibly clothing [and…] we should first use biomass to substitute for industrial products that use fossil fuels rather than for the fuels themselves. [W]hile there is insufficient biomass to displace a majority of fuels; there is a sufficient quantity to displace up to 100 percent of our petroleum and natural gas-derived chemicals and products. And these are much higher value products.”

Additionally, he recognizes that: Electricity, not biofuel, will be the primary energy source [note: we consider electricity an energy carrier, with wind, solar radiation, etc. being renewable sources] for an oil-free and sustainable transportation system. But biofuel can play an important role in this future as energy sources for backup engines that can significantly reduce battery costs and extend driving range.

While biofuel might remain a short-term transition technology, it is being recklessly advocated by the United States Senate as a panacea for the liquid fuel appetite. One response is to advocate appropriate uses of biofuel, including its role in agriculture. Another is to adapt to new information and seek alternate ways of powering crucial societal infrastructure. One such component is a relocalized agricultural system.

We should remember that biofuel was originally produced by farmers for on-farm use. Just because you can power an internal combustion engine on bio-blends does not necessarily mean that it is a suitable energy replacement or clear cut solution to salvage the industrial model which is so deeply dependent on cheap liquid petroleum.

Before agriculture began to juggle the burdens of constant soil degradation, increased mechanization, and cheap labor (see Steinbeck’s ‘Grapes of Wrath’), animals were used for the cultivation of crops. However, like a biodiesel tractor, some land must be dedicated to feeding a team of horses. On good pasture land it is estimated that 5 acres (2 ha) of land is needed per horse. Marginal land could require about 13 acres (5 ha) per horse, and possibly much more.

Similarly, to produce 1000 gallons (3,800 liters) of biodiesel requires the cultivation of 10.25 acres (4 ha) of canola. This is assuming you have access to processing equipment and methanol (which is normally derived from natural gas). Whether you consider horses, oxen or biofuel to reduce dependence of fossil fuels, cropland is used that will often compete with land needed to grow food.

For example, data from the Nebraska Tractor Test Laboratory shows that the performance of small, modern tractors at around 20 hp requires about 1.7 gallon (6.4 liters) of diesel fuel per hour of work. If we estimate that a tractor will be in use about 1000 hours per year, this would require 1700 gallons (6,400 l) of fuel. In biodiesel terms, it would take 17 acres (6.9 ha) of prime crop land to grow the fuel for one small tractor per year. Of course we should also think about how much land such a tractor could cover in a year. A small tractor could cultivate about 25 acres (10 ha) in those 1000 hours, meaning that after fuel crop use only 8 acres (3.2 ha) would remain for non-fuel crops.

Post Carbon Institute’s Energy Farm Program is addressing the tension between food vs. fuel, or land vs. energy. In our search for ways to reduce these tensions comes the latest Energy Farm Demonstration Project: The Electric Tractor.

We have made connections with activist and inventor Stephen Heckeroth and are seeking to test cutting edge agricultural equipment for a post-petroleum world. The electric tractor does not compete for food and prime agricultural land for fuel, has a significantly reduced carbon footprint, increases the scale of acreage that can be cultivated, and is easy to operate for the 50 Million New Farmers that Richard Heinberg is calling for in the coming century. Stephen is not the only person who has made the electric tractors. John Howe has been working on retrofits of agricultural equipment powered by electricity.

This week we took a (petroleum-powered) scenic drive through the redwoods to the Mendocino coast to visit Stephen Heckeroth and demo his “Solar Electric Tractor.” Stephen has been working on alternatives to fossil fuel use in both his private and professional life since 1970. His company, Homestead Enterprises, has been doing electric tractor conversions since 1993, and has become an internationally recognized consultant on industrial and agricultural electric equipment. In 1996-97, Ford-New Holland commissioned Homestead Enterprises to build an electric tractor prototype. In 1997-98, a Japanese company, Eifrig Ltd. Commissioned another prototype. A fully functional design was completed in July 1998 and several provisional patent applications were filed in August 1998.

As Stephen points out: Our future is only as sustainable as the tools we use to get there. The daily energy income from the sun is gigantic and it is feasible to use already existing renewable energy infrastructure to “re-fuel” the Electric Tractor. If the farm has yet to invest in renewable energy infrastructure, it is also possible to charge the batteries with standard 110V power (or 240 volts in other parts of the world).

Let’s run through some numbers to help us evaluate the land requirements of electric tractors versus tractors operating with biofuel. Electric motors are about 90% efficient at converting energy to work, and solar panels are the most efficient way of converting radiant sunlight energy into electricity (approaching 20% vs 1% or much less for plants). Stephen’s tractor can hold 5 kWh of battery packs that will give the same kind of performance in terms of work over a year as the 1700 gallons of diesel fuel in a small tractor. 5 kWh of batteries can be recharged each day with a 1 kW photovoltaic system covering about 40 sq ft (3.7 sq meters) of roof space. By contrast, 43,000 sq ft (4,000 sq m) are in an acre (which is 0.4 hectares).

In terms of fuel dollars, 1700 gallons of diesel cost about $5,100 in 2007. Installing a 1 kW photovoltaic system might cost about $10,000. By investing once in double the annual cost of fuel, a farmer could power a tractor for decades.

Not only does this appear to be an economically wise investment, but electric tractors are a pleasure to use. As you would expect from an electric motor there is no diesel exhaust emissions and no loud engine noise. While driving the tractor we could actually hear birds chirping (a rare experience when operating heavy machinery). With an electric tractor there is no longer a need for engine oil or oil filters, a radiator and coolant, no need for fuel filters, no engine overhauls, and it offers a lower operating cost ($0.50) to charge the 5kWh battery pack. There is a 1500W charger/inverter on the tractor and a complementary AC power outlet. This is a useful feature because it allows the use of electrical equipment in the field (e.g. sorghum press, or thresher and winnower). The ability to process certain crops in the field (like sorghum) is a good way to circumnavigate the need to transport large amounts of material to a central processing facility.

We plan to put the tractor through its paces and provide data that farmers will find useful as they begin to evaluate the efficacy of this exciting technology. Although in theory we should have great performance from an electric tractor, a lot of questions exist related to how long the tractor can work (similar to the range of an electric car) and whether or not the machine has enough power for the rigorous demands of cultivation. To test the machine we will attempt to run a dryland grain demonstration in Willits, CA. We intend to plant a fall crop of wheat or oats using a disk, harrow, and seeder. These classic implements used to be horse-drawn and do not require the intense energy that PTO (Power-Take-Off) implements require (less draw-down on the battery bank). The over-winter rains will help to get the crop established without relying on intensive irrigation and we plan to come back in the next summer to harvest and process the cereal crop. The experiment is two-fold in which we get a chance to demonstrate and produce grains with minimal amounts of fossil fuel and high energy inputs while also collecting data related to operation time and power capacity of the prototype electric tractor.

Aside from John Howe and Stephen Heckeroth, we have not heard of other people using electric tractors for other than mowing; we hope that many are out there. We would like to hear from you. We invite readers to check our numbers and the assumptions above and please tell us how realistic we are, based on your data, calculations and experience.

If you want to see Stephen’s tractor in operation, check out this link.

For more information about the Willits/Brookside Energy Farm and about the electric demonstration, please contact Dr. Jason Bradford or Christoffer Hansen.

For more information about the Energy Farms Program, please contact Julian Darley, President Post Carbon Institute (email or call 1 800 590 7745)


Electric Tractor Front View


Jason Testing The Front Suspension on a Hill


1500 Watt Charger/Inverter with Battery Bank (Mounted Over Rear Tires)


AC Power Outlet to Use Tools In the Field


testing and Q

How has the testing gone? Is this system really feasable for larger tractors - 200 to 300 hp range? thanks

Update? And questioning some of your calculations

Just wondering if there is any new info on the electric tractor? Also, your calculations seem a little suspicious to me. "a small tractor could cultivate 25 acres in 1000 hours of use" - this works out to 40 hours per acre. Not sure if you are referring to plowing + weeding, etc; but I thought a more reasonable estimate of plowing was 90 minutes/acre (with a 20HP tractor). It seems like you are off by a factor of ten in hours; fuel usage; and ground needed for a fuel crop. And I'm curious how many hours of use you would get from the battery? It seems like frequently tractor use is a rush item, you want to get the hay baled before the rain, or work up a field when the soil moisture is just right. It could be an issue to only be able to work two(?) hours and then have to wait for your battery to re-charge.