Farm fields landscape

Fuel from Farms
A guide to Small-Scale Ethanol Production

Solar Energy Research Institute
United States Department of Energy

The United States has the potential for growing grains and other crops well in excess of the requirements for domestic and export markets. Economic factors have consequently played a major role in the institution of "set-aside land" and "land diversion" programs by the U.S. Department of Agriculture (USDA). However, growing grain or other crops on this land for fuel production would not detract from the production of food. Rather, if properly utilized, it would constitute a resource that would otherwise have been left idle. Furthermore, the crops grown on this land can still be held in reserve for emergency food, should that become necessary. In 1978, for example, the USDA has certified that the amount of cropland left fallow was 13.4 million acres under the set-aside program and an additional 5.3 million acres under the diversion program. If this acreage had been cultivated with corn for ethanol production, nearly 3.03 billion gallons of ethanol and 10 million tons of distillers' dried grains (DDG) could have been produced. (This assumes a modest average yield of 65 bushels of corn per acre per year with an average production of 2.5 gallons of 200-proof ethanol and 17 pounds of DDG per bushel of corn.) This is only ethanol produced from land left idle through two specific farm programs. The production of fermentation ethanol is not limited by the extent of this land, and additional unused land as well as some land currently under cultivation can be used for crops for production of fermentation ethanol. All this makes the production of ethanol even more promising, and a conservative estimate for the potential displacement of petroleum is at least several billion gallons per year in the near term.

Belt tightening alone will not help the United States solve the present economic difficulties. Farmers, like everyone else, do not like austerity programs and would rather increase our national wealth. This can be achieved by increasing productivity-the production of more goods tand services from every barrel of oil we use and development of new sources of energy.

Clearly, the agricultural sector has a role whose full potential is just beginning to be realized. A farm-based fermentation ethanol industry can provide a dccentralized system of fuel production and a measure of energy self-sufficiency for the farm community. This can be accomplished as an integral part of normal farming operations following sound agricultural practices.

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There are three areas in which there are benefits to the farm economy from small-scale, on-farm, ethanol production. These are direct sales, on-farm uses, and indirect farm benefits,

Farm-produced ethanol sold for profit provides an alternative market for farm commodities. It can provide a "shock absorber" for excess production and a "fall back position" if unforeseen events adversely affect crop or yields.

Farming, perhaps more than any other single occupation, offers the opportunity for self-reliance. The on-farm production of ethanol expands this opportunity. Ethanol can be used in farm equipment as a blend with gasoline in spark ignition engines, as anhydrous or hydrated ethanol fuels in modified spark ignition engines, as a blend with diesel fuel in diesel engines, and as a dual-carbureted mixture with water in diesel turbochargers to enhance efficiency. Protein co-products, such as stillage, can be fed to farm animals as a replacement for other protein sources. Cellulosic coproducts, if sufficiently dry, can be burned as fuel.

Farm overproduction is generally planned to meet anticipated demand in the event of possible reductions in crop yield. However, the cumulative result of consistent overproduction in the absence of alternative markets is depressed commodity prices. Consequently, the financial health of many farms depends on the opening of new markets. Fermentation ethanol production provides several alternative markets for a broad variety of farm commodities.
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Fermentation ethanol has replaced a significant portion of petroleum-derived ethanol in India and Brazil [5, 6]. In fact, ethylene is produced from fermentation ethanol in these countries. Similar programs are being developed in the Philippines, South Africa, Australia, and other countries, and it is reasonable to assume that such a development could also occur in the United States.

Other Uses. Other possible uses of ethanol are as fuel for

  • crop drying,
  • general heating, and
  • electricity generation with small generators.


Stillage can be fed to farm animals as a protein supplement either whole (as produced), wet, solid (screened), or dry. The stillage from cereal grains ranges from 26% to 32% protein on a dry basis. The basic limitation on the amount that can be fed at any one time to an animal is palatability (acid concentration caused by drying makes the taste very acrid). Mature cattle can consume about 7 pounds of dry stillage per day or, roughly, the stillage resulting from the production of 1 gallon of ethanol. The feeding of whole stillage is limited by the normal daily water intake of the animal and the re- quirements for metabolizable energy and forage fiber. The feeding value to swine and poultry is somewhat limited. Wet stillage cannot be stored for long periods of time, and the lack of locally available herds of animals to consume it may lower its value. Stillage from grains contaminated with aflatoxins cannot be used as animal feed.

The cellulosic coproducts may be directly fermented to produce methane gas or dried for use as boiler fuel.

Carbon dioxide (CO2) produced by fermentation can be compressed and sold to users of refrigerants, soft drink bottlers, and others. It also has many agricultural applications which are beyond the scope of this handbook.

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Market Assessment

Before a decision to produce can be made, it is necessary to accurately determine if markets for the ethanol and coproducts exist close enough to allow for economical distribution. The size of the market is defined by the quantities of ethanol and coproducts that can be used directly on the farm and/or sold. The ethanol on-farm use potential can be determined from the consumption of gasoline and diesel fuel in current farming operations. Then, a decision must be made on the degree of modification that is acceptable for farm equipment. If none is acceptable, the on-farm use will range from 10% to 2040 of the total gasoline consumption. If direct modification to spark ignition equipment is acceptable, the on-farm potential use can be 110% to 120% of cur- rent gasoline consumption. If the risks associated with attempting undemonstrated technology are considered acceptable, the ethanol replacement of diesel fuel will be roughly 50% of current diesel fuel consumption [3].

The sale of ethanol off the farm will be dependent upon local conditions and upon the type of Bureau of Alcohol, Tobacco, and Firearms (BATF) license obtained. (Currently, a commercial license from BATF is required for off-farm sale of ethanol.) Market estimates should be based on actual letters of intent to purchase, not an intuitive guess of local consumption. The on-farm use of stillage must be calculated on the basis of the number of animals that are normally kept and the quantity of stillage they can consume. The potential for sale of stillage must be computed on the basis of letters of intent to purchase, not just on the existence of a local feedlot. The value of stillage wit1 never exceed the directly corresponding cost of protein from other sources. Direct on-farm use of carbon dioxide is limited; its principal value may come from sales. If Jerusalem artichokes, sorghum, or sugarcane are used, the bagasse and fiber that remain after the sugar is removed may be sufficient to supply the entire energy requirements of the ethanol plant. This value should be calculated in terms of the next less expensive source of fuel.

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Production Potential


The mix of feedstocks determine in part the actual pro- duction potential. Chapter IV discusses the use and production of the various feedstocks individually and in combination. The guidance offered in that chapter will help define the sizing of the plant from the viewpoint of output, once the potential of the available feedstocks is determined. Additional feedstocks may also be pur- chased and combined with products available on-site.


Significant amounts of water are used in the ethanol production process (about 16 gallons of water per gallon of ethancl produced). This demand includes require- ments for generating steam, cooling, and preparing mashes. Also, it may be desirable to grow a crop not normally produced in the area. If additional irrigation water is necessary for this crop, the increment must be included, but it is likely that stillage liquids can be directly applied to fulfill this need.

Heat Sources

Heat is required in the conversion of feedstocks to ethanol, primarily in cooking, distillation, and stillage drying. An accurate assessment must be made to deter- mine the type and quantity of available heat sources. Waste materials can contribute as energy sources and, from a national energy perspective, the use of petroleum fuels is not desirable. In some cases, other renewable sources of energy such as methane, solar, wind, and geothermal may be used as supplements.

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Financial Requirements

Considerations to Proceed

Once the considerations for equipment selection are completed, the capital and operating costs may be roughly computed.

The capital cost considerations are:

real estate and buildings,
permits and licenses, and
availability of financing.

The operating costs are: .
cost of money.
chemicals, enzymes, additives,
costs of delivery, and

These considerations are then compared to the specific financial situtation of the individual. If the results of this comparison are not acceptable, then other options in equipment specifications and plant size must be con- sidered. If all possibilities result in an unfavorable posi- tion, the decision to produce is no. If a favorable set of conditions and specifications can be devised, detailed design considerations should be examined (see Chapter V, Plant Design) and an appropriate organization and financial plan developed (see Chapter VI, Business Plan).
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Decision & Planning Worksheets

[See separate document on this web site]

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The production of ethanol is an established process. It involves some of the knowledge and skill used in normal farm operations, especially the cultivation of plants. It is also a mix of technologies which includes microbiology, chemistry, and engineering. Basically, fermentation is a process in which microorganisms such as yeasts convert simple sugars to ethanol and carbon dioxide. Some plants directly yield simple sugars; others produce starch or cellulose that must be converted to sugar. The sugar obtained must be fermented and the beer prod:uced must then be distilled to obtain fuel- grade ethanol.

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Production of fuel-grade ethanol is a practical operation to include in farm activities. Texts in microbiology and organic chemistry portray it as a complex pro- cedure, but this is not necessarily true. Fermentation is affected by a variety of conditions. The more care used in producing optimum conditions, the greater the ethanol yield. Distillation can range from the simple to the complex. Fortunately, the middle line works quite satisfactorily for on-farm ethanol production.

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Grain processing as practiced in large plants is not feasible for small plants. However, a simple form of processing to produce human food may be feasible. Wheat can be simply processed to separate the starch from the combined germ, gluten, and fiber. They form a cohesive, doughy mass which has long been used as a base for meat-analogs. This material can also be incorporated into bread dough to enhance its nutritional value by increasing the protein, fiber, and vitamin (germ) content.

Work at the University of Wisconsin has resulted in the development of a simple, practical processing machine that extracts about 60% of the protein from forage crops in the form of a leaf juice [6]. The protein in the juice can be separated in a dry form to be used as a very high quality human food. The fibrous residue is then in good condition to be hydrolyzed to fermentable sugars. Most of the plant sugars are in the leaf juice and, after separation of the protein, are ready for fermentation. Forage crops have the potential for producing large amounts of ethanol per acre together with large amounts of human-food-grade protein. The protein production potential is conservatively 1,000 pounds per acre, equivalent to 140 bushels per acre of 12%-protein wheat [7].

6. Besken, K. E.; et al. "Reducing the Energy Require- ments of Plant Juice Protein Production."Paper presented at the 1975 Annual Meeting of the American Society of Agricultural Engineers; paper no. 75-1056, 1975.
7. Mann, H. 0.; et al. "Yield and Quality-Sudan, Sorghum-Sudan, and Pearl Millet Hybrids." Prog- ress Report, Colorado State University, Fort Collins, co; 1975.

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Agronomic Considerations

A simple comparison of potential ethanol yield per acre of various crops will not rank the crops in terms of economic value for production of ethanol. The crops vary considerably in their demands on the soil, demands for water, need for fertilization, susceptibility to disease or insect damage, etc. These factors critically influence the economics of producing a crop. Fortunately, forage crops which have the potential for producing large amounts of ethanol per acre have specific agronomic advantages relative to some of the principal grain crops (e.g., corn).

The nonfruiting crops, including forage crops, some varieties of high-sugar sorghum, and Jerusalem artichokes, are less susceptible to catastrophic loss (e.g., due to hail, frost, insects, disease, etc.), and, in fact, are less likely to suffer significant loss of production due to adverse circumstances of any sort than are fruiting crops such as grains. Furthermore, forage crops and Jerusalem artichokes are less demanding in their culture than almost any grain. Their cost of culture is usually lower than for grains on the same farm, and they have great potential for planting on marginal land.

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Plant Design

[See separate document on this web site]

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Flexibility in Operation and Feedstocks

Plant profitability should not hinge on the basis of theoretical maximum capacity. Over a period of time, any of a myriad of unforeseen possibilities can interrupt operations and depress yields. Market (or redundant commodity) variables or farm operation considerations may indicate a need to switch feedstocks. Therefore, the equipment for preparation and conversion should be capable of handling cereal grain and at least one of the following:
ensiled forage material;
starchy roots and tubers; or
sugar beets, or other storable, high-sugar-content plant parts.

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[See separate document on this web site]

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