Presention At The Caribbean Renewable Energy Symposium, Kingston, Jamaica – Solar Applications in U.S. Agriculture | 1981

Presented by Roger Blobaum, At Caribbean Renewable Energy Symposium, Kingston, Jamaica, July 28-30, 1981

Although the agricultural production system consumes only about 3 percent of the energy used in the United States, the concept of energy self-sufficiency for agriculture has received a good deal of attention.  Steadily rising energy prices and the possibility of supply interruptions during planting and harvesting periods provide a special incentive for farmers to begin moving in that direction.

Energy self-sufficiency is one way to reduce agriculture’s vulnerability to energy shortages and price increases.  Although rising energy costs in the 1970s had little adverse impact on agricultural output, there is considerable evidence that shortages or interruptions could result in-much[i] higher production costs and substantial production cutbacks.

These possibilities, along with the clear need to reduce agriculture’s dependence on nonrenewable forms of energy, influenced the U.S. Department of Agriculture’s decision three years ago to encourage the self-sufficiency concept.  The department’s announced goal of energy self-sufficiency for production agriculture by 1990 would be reached by conserving energy and developing and applying alternative sources.[ii]

Preliminary estimates indicate that solar, wind, and biomass energy could account for 25 percent of the net energy required to reach self-sufficiency.  Energy conservation, including minimum tillage and conversion to diesel-powered equipment, would contribute the balance.

These preliminary estimates are little more than educated guesses prepared on the basis of energy research and demonstration projects carried out over the last five years.  Some data has been collected from farmers on how they use energy.  But little is known about the performance of alternative energy systems on farms or the kinds of incentives needed to gain widespread farmer participation in energy-saving and energy-producing efforts.  Most commercial-size farms are still energy-intensive and this is not likely to change as long as energy price increases are not out of line with increases in the prices of other production inputs.

A long-range research plan prepared by the U.S. Department of Agriculture has identified 27 use categories where energy savings are possible.[iii] The categories with the greatest potential are irrigation, tillage, crop drying, greenhouse heating, space heating of livestock and poultry buildings, and water heating for dairies.  A related area with considerable potential for energy savings is farm residences, which use the equivalent of about 22 barrels of oil per home per year.

Although research on alternative energy applications for agriculture began in the 1950s, most of this work has been done the last five years.  The research at the land grant universities has emphasized low-temperature, moderate-cost applications, including systems that could be built on the farm or retrofitted to existing buildings.

The U.S. Department of Agriculture has identified five solar energy approaches that have been developed at land grant universities and appear to have the greatest near-term economic potential:

–A passive solar farrowing house developed at Kansas State University.

—A solar-heated greenhouse developed at Rutgers University.

–A combination solar tobacco-curing barn and greenhouse developed at North Carolina State University.

—A solar-heated broiler house developed at Mississippi State University.

—A solar grain dryer that draws heat from a nearby building roof modified to perform as a solar collector.  This system was developed at the University of Illinois.

Several of these renewable energy technologies are being demonstrated and monitored on farms.  The main ongoing government-initiated demonstration is a program that began in 1978 and now involves model projects on about 90 farms in 10 states.[iv]   This effort is testing systems designed to reduce fossil fuel consumed in drying grain and other crops, heating livestock and poultry houses, and heating greenhouses.

Some of the systems being tested have been provided by private companies that are getting into the agricultural market. Others have been built by farmers themselves with plans made available by the Cooperative Extension Service.  The purpose of this program, of course, is to commercialize agricultural applications and provide information to research engineers and extension specialists.

Individual farmers also are demonstrating that they can move toward energy self-sufficiency by producing alcohol in hand-built stills for use in tractors and farm vehicles, generating electricity with small wind systems, building solar grain dryers and space heating systems, and adopting agronomic practices that reduce or eliminate the need for pesticides and commercial fertilizer.  A few are experimenting with sunflower and other vegetable oils as a fuel for diesel engines.

Some of the research on farm energy production is directed toward capital-intensive systems, such as methane digesters that utilize manure produced in livestock confinement buildings and large feedlots. Most of this work has emphasized development of energy systems that are not affordable for most farmers.  The cost effectiveness of large digesters is enhanced by the fact that they provide important pollution abatement benefits as well as producing methane gas and an odor-free effluent that is an excellent fertilizer.[v]

The U.S. Department of Energy also is sponsoring a major energy integrated farm system program to demonstrate energy conservation and production.  The seven farms selected are being modified to show how diverse on-site energy sources can be utilized to provide a continuous supply of energy and reduce their dependence on nonrenewable sources. The technologies involved include production of alcohol fuel, crop drying, methane digestion, energy-conserving tillage practices, solar heating of farm buildings, and wind generation of electricity.

The sites selected include Granja Caribe, a large modern poultry farm operated by the University of Puerto Rico. [vi] The integrated energy concepts to be demonstrated there include use of wind energy for water and effluent pumping; generation of electricity with methane produced from poultry wastes; use of solar-heated water in brooding operations; production of feed and fertilizer by anaerobic fermentation of manure, feathers, broken eggs, and other wastes, and the use of a solar energy aquaculture system to recycle waste nutrients as a feed supplement.

Other farm energy research is being carried out by the Tennessee Valley Authority, the National Center for Appropriate Technology (NCAT), nonprofit and community-based groups and organizations, and by private companies. NCAT’s newest farm-related project involves assisting a small farmer in equipping his farm with the full range of small-scale energy technologies.  This includes both monitoring and detailed record keeping.[vii]

Several engineering firms are marketing large custom-built methane and solar systems for farms. A growing number of wind and solar companies have entered the agricultural market.  Although networks of distributors and dealers will be needed in rural areas, this market development effort has been slow. Materials needed for on-site construction of solar systems are becoming available at lumber and hardware retail outlets and plans for a wide range of low-cost systems can be purchased.

A growing number of farmers, viewing alcohol production as a valuable addition to their existing operations, are exploring the possibility of purchasing or constructing on-farm ethanol distilleries. Although the technology for the fermentation and distillation of corn and other grain crops is well known, dependable manufactured small-scale stills are not yet widely available.  Several hand-built stills now operating on farms produce alcohol fuel plus an animal feed byproduct.  It is not difficult to modify existing gasoline-powered farm equipment to run on high-proof ethanol. Diesel tractors present special but not insurmountable conversion problems.”[viii]

The most practical and economically-feasible solar application in agriculture is heating water for dairies.  These systems are cost effective because the daily requirement for hot water spreads the cost over the entire year.  This application was adapted from research on solar water heating for residential and industrial uses. These systems pre-heat water that goes into conventional water heaters, assuring temperatures that meet dairy sanitation standards.

Milk-to-water exchangers that capture heat removed from milk when it is cooled also are being used by dairy farmers. Similar exchanger systems that recover heat from warm air expelled by livestock ventilation systems also are being used on farms in cold climates.  These commercial waste heat recovery systems save enough energy to pay for themselves in a relatively short period of time.

The most advanced solar research effort relating to agriculture-specific applications focuses on grain and crop drying.  The main emphasis is on drying corn, which is picked and shelled in the field on most farms when it still has a moisture content of 20 to 25 percent.  It is then dried to a safe storage level with natural air, natural gas, or propane. The energy consumed in drying corn can exceed the energy used to produce the crop. Most of the drying units are on farms although some large dryers are located at elevators or other storage sites.

Research also is underway on the use of desiccants, mainly over-dried corn.[ix] Part of a previous year’s crop is solar dried in the summer to 10 percent moisture or less, then mixed with wetter corn at harvest time.  The desiccant takes up moisture and the new corn releases it, resulting in an equalized moisture level for the entire mixture.

Successful solar applications also have been developed for drying tobacco, peanuts, hay, rice, soybeans, and small grains. Their effectiveness is determined to some extent by humidity (a problem in the Southeast) and by lack of sunny days (a limitation in the Northeast).

Low-temperature systems that utilize flat plate collectors are economically feasible now and will become more cost effective as energy prices go up. Most of these systems are being installed where additional drying capacity is needed, a conventional dryer must be replaced, or fuel supply interruptions or cutoffs are a possibility. [x]

A serious economic limitation is that solar drying systems normally are used only a few weeks during the fall harvest season.  The season can be extended if small grains like barley, which are harvested during the summer, are dried or if the desiccant method is used.  This short-term utilization problem is being addressed through development of portable collectors and other multiple-use solar units that can be used for space heating, for example, when the grain-drying season is over.

Low-temperature solar drying systems are considered too slow for large farm operations that may have 50,000 bushels or more to run through a dryer over a period of a month or six weeks.  Past dryers with heaters fueled by crop residues have been developed and demonstrated and are coming on the market.  High-volume dryers heated by small gasifiers fueled by corncobs are being demonstrated by seed corn companies in the Corn Belt. [xi]

Farmers also are constructing their own solar systems, which reduces the cost considerably and makes a wide range of agricultural applications economically feasible. Many of these utilize large simple collectors built into the roofs and south walls of machine storage buildings and other large farm structures.  The solar heat produced can be ducted in the fall to an adjacent grain facility to provide hot air for drying.  It can then be utilized throughout the winter months to heat a nearby machine repair shop, a milking parlor, or a hog farrowing facility.

These site-built applications, which utilize glazing and other readily available materials, normally cost one-third to one-half as much as factory-built systems.  This owner-built approach is receiving some encouragement from the Cooperative Extension Service and other government agencies that work with farmers.

The owner-built effort includes development of a low-cost methane digester that utilizes a continuous plug flow system developed at Cornell University and rubber bags from a water-bed manufacturer.  These digesters, scaled down for small hog farms with liquid manure systems, are designed for nearly automatic operation.  The small number built so far have a daily output of 400 to 500 cubic feet of methane, cost as little as $3500 each, and can be constructed on the farm by two persons in about two weeks.[xii]

A 3-year research and demonstration project in Nebraska used the site-built approach in helping a group of small, low-income farmers adopt a wide range of proven technologies for saving and producing energy. [xiii] The 24  farmers involved invested approximately $I,200 each for materials, provided all the labor required, and completed more than 100 energy projects.  The energy use data collected showed they were spending an average of $1,138 per farm per year less for energy at the end of the demonstration period than operators of comparable farms in the area.

The systems built by these farmers that appear to be most appropriate for small farmers are vertical wall collectors for heating homes, solar crop and food dryers, attached solar greenhouses, roof-mounted solar collectors for farrowing houses, and portable solar heaters for crop drying and space heating. The project also demonstrated the interfacing of a 4-KW wind generator with the local rural electric system serving the area. One of the advantages of demonstrating alternative energy systems on working farms is that it provides an opportunity to test their appropriateness, practicality, and adaptability in ways that are not possible in a laboratory or university farm situation.

The move toward energy self-sufficiency in U.S. agriculture is proceeding slowly.  Its continuation is assured, however, by regular increases in energy prices and the growing awareness of farmers of solar and other renewable energy alternatives.  One of the most important challenges is to scale down the renewable energy systems involved so they will be affordable and appropriate for the more than 2 million operators of small and moderate-size farms.  The availability of technical assistance for farmers who want to build their own systems and the development of an industry that can provide local dealers to sell and service factory-built systems also are critical needs.  It is highly unlikely that U.S. agriculture will be energy self-sufficient by 1990, as some energy experts had hoped. But farmers will continue moving toward that goal in the 1980s.  It appears to be a realistic objective that will be reached eventually.

By Roger Blobaum, Roger Blobaum & Associates, Inc,
1346 Connecticut Avenue, N.W. Washington, DC 20036