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Energy-Efficient Grain Drying Resources
NCAT Agriculture Specialists
Pub Date Here
ATTRA Publication 2009
Abstract
The ambient air system for grain drying recommended for the United States by The Ohio State University and other grain belt research institutions, as well as the Saskatchewan Ministry of Agriculture, is now state of the art and slowly replacing systems using fossil fuels, chiefly natural gas. Although not as much recent research has focused on solar technology for grain drying, solar was shown by University of Maryland studies to be feasible for small- and medium-size facilities for drying grain for on-farm use. Payback time for installing a solar system varies with the cost of fossil fuels and the costs of labor and materials for a solar installation. Resources for evaluating these two systems include links to key sources and a condensation of two reports from the University of Maryland.
Table of Contents
Introduction
Major objectives of grain farmers include completing harvest as quickly as possible with the lowest possible crop loss and minimizing cash costs. The use of low-input technology can maximize energy efficiency while meeting other objectives.
U.S. crop drying systems are used principally for shelled corn that must be stored on-farm. Changing markets and uncertain fuel costs have caused farmers to consider alternatives to hot-air drying. New farming techniques and improved seeds that enhance achievement of optimum moisture content in harvested grain make low-impact systems more feasible. Bins equipped with electronic monitoring provide the precision needed to operate such systems effectively.
Two low-impact technologies are natural-air drying and solar drying.
Natural-air drying (NAGD) differs from hot-air drying in many ways. The main advantages of natural-air drying are flexibility and low operating costs. Disadvantages include reliance on ambient air conditions, extended operating time and alternate grain handling requirements (Hansen et al., 2008). Contracts for U.S.-grown food-grade crops, such as low-linolenic soybeans, popcorn, food-grade white or yellow corn, high-amylase corn, canola and rice, often specify that the crop be stored on the farm and kept in good condition. The government of Saskatchewan recently published natural-air drying guidelines applicable to 18 crops including wheat, legumes, barley, oats and canola (2008).
Adoption of natural-air grain drying has not been rapid since its introduction around 1990. In connection with an online energy efficiency audit, Purdue Extension's Renewable Energy program is currently collecting data on in-state grain drying systems.
The In-Bin Drying System Energy Audit Questionnaire, which covers natural-air and solar drying, and the Continuous Flow Dryer Energy Audit Questionnaire are available at: www.extension.purdue.edu/renewable-energy/on-farm-efficiency.shtml.
Solar drying
In the North American grain belt, solar drying systems must employ solar collectors. The term sun drying is sometimes used in connection with direct use of solar heat to dry household grain crops in lower latitudes. The solar energy available at a particular location depends on the latitude and local weather conditions. Associated costs are labor and construction materials. Although solar grain drying has been researched extensively in the United States for several decades and found technically feasible in replacing significant amounts of energy in some grain drying systems, initial installation costs have not decreased as much as hoped. Based on 1980 construction costs, the University of Maryland Extension estimated payback times at from 7.2 to 8.1 years. A United Nations Food and Agriculture Organization grain expert predicted that fuel costs for hot-air drying would need to at least double from 1980 levels to make solar drying feasible (Bakker-Arkema, 2001).
Farmers in the Maryland demonstration constructed their own solar installations using Purdue University plans. [Reader using this link must select Energy Production and Conservation section. Doc. AE-108 is linked to its full text.]
In addition to payback time, feasibility may depend on other factors, including the cost of fossil fuels and the scale of operation. The Maryland studies involved a single bin on each farm and the corn was intended for on-farm use.
Decision trees published by various states can assist in selecting an appropriate grain drying system. Success in employing natural-air grain drying often depends on management decisions such as choosing the appropriate variety for weather conditions and intended use. Grain cleaning to remove broken kernels and small pieces of broken grain, weed seeds and chaff, collectively known as fines, is integral to success.
| How does natural-air grain drying dry grain? Cleaning equipment is used to remove broken kernels and fines, which may be utilized as animal feed. Portable conveyers take grain to the grain cleaner and then to the top of the bin. The bin is equipped with a full perforated floor, one or more high-capacity fans, a grain distributor and stairs. Drying results from forcing unheated air through the grain at airflow rates of from 1 to 2 cubic feet of air per minute per bushel of grain (cfm/bu). Initial moisture content is normally limited to between 22 and 24 percent. If harvest must occur at 30 percent, corn must first be dried down to reduce moisture content. This situation can be avoided by foresighted crop management. The drying process is slow, generally requiring from three to four weeks. Grain is then stored in situ. Adoption of natural-air grain drying avoids costs associated with over drying in high-temperature, high-speed continuous-flow or batch dryers, as well as significant fossil fuel savings. Adapted from Hansen et al., 2008. American Society of Agricultural and Biological Engineers (ASABE) meeting presentation: ASABE Paper No. 084550, St. Joseph , MI . Cf. Hansen et al., 1996b; Wilcke and Morey, 1995 |
Subsidies
The North Carolina Solar Center, operated by the College of Engineering at North Carolina State University, maintains the Database of State Incentives for Renewables and Efficiency (DSIRE). It is updated weekly at www.dsireusa.org. While not specifically addressing farm energy efficiency, the site lists power companies that offer rebates on the efficient non-residential use of energy. Visit DSIRE for more information.
The U.S. Department of Agriculture (USDA) offers grants and loans for the installation of renewable energy systems and energy efficiency improvements. Many growers take advantage of programs such as the Rural Energy for America Program (REAP), formerly known as Section 9006 in the 2002 Farm Bill. REAP provides grants and loan guarantees to farmers, ranchers and rural small businesses to help purchase renewable energy systems or make energy efficiency improvements. Financing is available for up to 75 percent of eligible project costs. The USDA Rural Development program administers REAP. The 2008 Farm Bill authorized $255 million in mandatory funding for the four-year period from 2009-2012.
Many states have proactively offered extensive information online and held workshops to help with the application process by providing templates, guidelines and resources.
Application deadlines and the official Notice of Funds Availability (NOFA) will be published in the Federal Register at a future date. See http://farmenergy.org/tools/reap-faq for updates. Energy efficiency projects include improvements to facilities, buildings or processes that reduce energy consumption.
Maryland Cooperative Extension Services grain drying demonstrations, 1982
Summary of results
This summary is based on research reports by Larry E. Stewart and Gerald E. Berney of the University of Maryland Department of Agricultural Engineering.
Cool Springs Farm
This farm will be an excellent demonstration of low-temperature solar drying in combination with a high-temperature drying unit. The energy saving potential is quite high. As the operators gain additional experience in managing the system, full potential energy savings will be realized. This operator dried 32,400 bushels of grain from 20 percent to 14 percent moisture in 40 days.
Serenity Farm
The operator of this system, already convinced of the benefits of natural-air drying, feels that the solar collectors add enough reliability to his system that he will not have to resort to the use of his liquid propane gas heater again. The operator also states that the solar-supplied heat dried grain much faster than the natural-air method would have. This operator dried 4,800 bushels of grain from 26.7 percent to 15 percent moisture in 16 days.
Cool Springs Farm, Inc., is a father-son enterprise operated by James and Gary Schoonover. The farm is located about 1 mile from Greensboro, Md., near the center of Maryland's eastern shore, 8 miles north of Denton, the county seat of Carolina County, and 30 miles due east of the Chesapeake Bay Bridge. The Schoonover Farm is a 500-acre grain and broiler farm.
Approximately 300 acres of corn and 200 acres of soybeans are produced annually. The Schoonovers produce nearly 100,000 broiler chickens annually. The current drying system consists of a 100-bushel-per-hour dryer commonly operated at high temperatures of about 210 degrees Fahrenheit. The brand is a Brock SUPERB. Two storage bins are in place; one is 36 feet high by 24 feet in diameter and holds approximately 20,000 bushels. This bin is equipped with a 9.5-horsepower fan. The second bin is 27 feet in diameter, 18 feet, 4 inches high and holds 8,500 bushels of grain. This bin is equipped with a 9-horsepower fan.
Fuel and energy requirements for the system are .215 gallons of liquid propane gas per bushel and .1 kilowatt hours of electricity per bushel to dry at a rate of 100 bushels an hour.
Serenity Farm, owned by Franklin Robinson, produces crops on 300 acres plus another 100 leased acres. Crops include corn, tobacco, potatoes, soybeans and seed rye. The farm also has a large flock of sheep and a swine herd. About 15,000 bushels of corn and 3,000 bushels of rye for seed are harvested and dried annually. Liquid propane gas is used for fuel, with the annual usage varying considerably with weather conditions and the number of acres leased. Maximum liquid propane gas usage has been approximately 2,250 gallons annually.
Investigators considered Cool Springs "an excellent location to demonstrate the optimal effects of management and solar systems on energy conservation." Goals and objectives reported for the two sites were very similar.
Objectives
Demonstrate the practicality, in terms of energy and economic effectiveness, of a solar grain drying system at Serenity Farm and a combination high- and low-temperature grain dryer "with a solar system supplying the energy for the low-temperature portion" at Cool Springs Farm.
Specific goals
- Have the farmer construct the system
- Monitor construction and operating costs
- Monitor energy use and evaluate cost effectiveness
- Prepare a publication on the results and conduct field days
For each farm, a skid-mounted solar collector, closely patterned after a Purdue design was the basic element of the solar system.
Each collector has face dimensions of 12 feet high by 16 feet wide. The cover material is a single layer of .04-inch fiberglass-reinforced panel (FRP). The receiver is corrugated sheet metal painted black and located 1.5 inches behind the cover, with the corrugations in a vertical configuration. Another 3.5-inch air passageway was provided behind the receiver, and the back was constructed of half-inch plywood reinforced with ribs made from 2-by-4 boards. No insulation was added to the backing for grain drying, but can be added to panels as needed when panels are diverted to alternate uses. The tilt of the panels can be manually adjusted by moving pins in a sliding pipe brace. Only one position was used for the entire drying season. At Cool Springs Farm, three panels of 576 square feet each were used with the 36-foot bin.
Groups of panels were serially joined together by a wooden clamping system that could be vented if necessary. Air was drawn horizontally across both faces of the receiver. Thus, the total length of the air flow path across the three collectors was 48 feet. A second set of three panels was connected in parallel to the first set. The air movement was provided at Serenity Farm by two 7.5-horsepower Aerovent fans. Air movement was provided by the existing fans at Cool Springs Farm to maintain the 500-feet-per-minute face velocity recommended for the Purdue collector.
View the solar grain drying system designs for the Cool Springs Farm.
The 1983 report on Serenity Farm adds the following information:
A mixing box for each set of collectors was used to provide the fan air demands beyond the 5 cubic feet per minute per square foot of receiver at the 500-feet-per-minute face velocity recommended for the Purdue collector. The total collector area was 1,152 square feet.
The 36-foot diameter bin was used, and a layer mode of drying recommended to the farmer. The layer depths depend on initial moisture contents and prevailing weather conditions. The initial layer is normally 4 feet with subsequent layers at 3 to 4 feet. Grain moisture measurements were made to determine how frequently additional layers could be added. The rate is normally a layer every 5 to 7 days.
View the solar grain drying system designs for the Serenity Farm.
Alternate uses for the collectors during the winter season were recommended for both farms according to their different enterprise mixes.
System construction costs
| Note: All dollar figures are 1982 dollars. To convert benchmark 1.000 1982-1984 dollars to 2008 dollars, multiply following dollar figures by 2.131. [Source: Robert C. Sahr, Oregon State University , Political Science Dept., Inflation Conversion Factors for Years 1774 to est. 2019. Or, use local prevailing prices. |
Serenity Farm
| 1152-square-foot solar collector and ducting, constructed with farm labor | |
| Materials | $4,112.60 |
| Labor (428 man hours at $5 an hour) | $2,140.00 |
| Total | $6,263.60 |
Cool Springs Farm
| 576-square-foot solar collector and ducting, constructed by farm operators | |
| Materials | $ 2,233.10 |
| Labor (118 man hours at $4 an hour) | $1,272.00 |
| Total | $ 3,505.10 |
Assumptions were somewhat different, but the researchers calculated the average cost per square foot of collector including ducts at between $5.42 and $6.08. Knowing exactly what materials were used and plugging in a reasonable cost for labor, costs can easily be extrapolated to 2008.
System performance
Solar radiation was measured at both sites with an Eppley B&W pyranometer and a Li-Cor millivolt integrator. The pyranometer was mounted at the same slope as the collector face. Measurements for a typical day at each farm were based on hourly integrated values.
The thermal performance of the solar collector was evaluated for a typical day during the drying season. The energy output of the system was calculated using measured values of air flow and critical temperatures. Because relative humidity and barometric pressures were not recorded on-site, a constant specific heat of .24 btu per pound and a constant volume-to-mass ratio of 14 feet cubed per pound were assumed. Hourly and full-day efficiencies were calculated by dividing the energy output by the solar energy incident on the collector surface.
Typical day collector performances for collectors at Serenity Farm and Cool Springs Farm are shown in Table 1. Solar insulation received and collector efficiency are indicated. Daily average efficiency for the Serenity Farm unit near Washington, D.C. was 57 percent. Daily average efficiency for the Cool Springs Farm unit on Maryland's eastern shore was 89 percent.
| Table 1. Results | ||
| Serenity Farm | Cool Springs Farm | |
| Bushels of grain dried | 4,800 | 32,400 |
| Percent moisture decrease | 26.75 to 15 | 20 to 14 |
| Days required for drying | 16 | 40 |
| Average cost per bushel, in cents | 3.86 | 8.09 |
| Electrical energy cost per kilowatt hour (fans) | $185.20/3660 kwh | |
| Million btu per replacing gallons of liquid propane gas | 29.8/342.27* | 46.9/539 |
| Purchased energy per pound of moisture removed | 291 btu per pound | 848 btu per pound ** |
| * extrapolated ** one-half of the previous year's requirement |
||
System payback
The following estimates do not take into account expected increases in costs of liquid propane gas or the energy savings that will accrue through other uses of the system. Also, energy tax credits are not considered in this computation.
Serenity Farm
Because the collector was available for only a portion of the drying season, it is necessary to extrapolate expected economic returns to the farm. Assuming the system will be fully utilized in subsequent years, it is believed that annual liquid propane gas savings will reach 1,150 gallons or 1 gallon for each square foot of collector surface per year. Assuming the cost of liquid propane gas to be 75 cents for a gallon, the simple payback period for the system will be:
$5.42 divided by .75, to equal 7.2 years
Cool Springs Farm
Based on one year of experience, it appears that the solar system can be expected to save liquid gas at the rate of 1 gallon per square foot of collector surface. Assuming the cost of liquid propane gas to be 75 cents for a gallon, the simple payback period for the system will be:
$6.08 divided by .75, to equal 8.1 years
Numerous minor operational problems were identified at both farms, requiring close attention by management and early correction to keep the systems operating properly. Some management changes are necessary for farmers moving from high-temperature to low-temperature solar drying.
Copies of the original FACTS 139 and 140 research reports on which this summary is based were obtained from University of Maryland. However, print copies are no longer available to the public—except from archival sources. Permission has been given by the UMd for this redaction. For supplemental information since 1982, please see the Resources section.
References
Bakker-Arkema, F.W. 2001. Update from 1986. Mycotoxin prevention and control in food grains. FAO Corporate Document Repository: Agriculture and Consumer Protection.
Hansen, Robert C., Eli Troyer, and Harold M. Keener. 2008. American Society of Agricultural and Biological Engineers (ASABE) meeting presentation: ASABE Paper No. 084550, St. Joseph , MI .
Hansen, R.C., H.M. Keener, R.J. Gustafson. 1996b. Natural-Air Grain Drying in Ohio. Fact Sheet AEX-202-6. Columbus , OH . The Ohio State University Extension.
Wilcke, William, and R. Vance Morey. 1995. Natural-Air Corn Drying in the Upper Midwest , BU-6577. University of Minnesota Extension. Illustrated. ca. 20 p.
Resources
General Resources
Iowa State University MidWest Plan Service. 1980. Low Temperature and Solar Grain Drying Handbook. MWPS-22. $3.00. Published and distributed by 12-state Extension publishing cooperative in the Upper Midwest. Part of a series. Available at www.mwps.org, by calling 1-800-562-3618 or by e-mailing mwps@iastate.edu
| Scott Sanford, a senior outreach specialist for Wisconsin Focus on Energy and UW Extension, recommends Purdue's comprehensive collection of "all known grain-drying information on the Web." |
Natural-air grain drying
Government of Saskatchewan. 2008. Natural Air Grain Drying. October. 14 p.
Hansen, Robert C., Eli Troyer, and Harold M. Keener. 2008. American Society of Agricultural and Biological Engineers (ASABE) meeting presentation: ASABE Paper No. 084550, St. Joseph, MI.
Hansen, R.C., H.M. Keener, R.J. Gufstafson. 1990. Natural-Air Grain Drying—Guidelines for Ohio. Agdex 110/62 Bulletin 805. Columbus, OH. Agricultural Research and Development Center and Ohio Cooperative Extension Service. 22 p. (Print only)
Hansen, R.C., H.M. Keener, R.J. Gustafson. 1996b. Natural-Air Grain Drying in Ohio. Fact Sheet AEX-202-6. Columbus, OH. The Ohio State University Extension.
Wilcke, Bill [William]. 2001. Saving Fuel in Corn Drying. Minnesota/Wisconsin Engineering Notes. August. p. 1.
Wilcke, William, and R. Vance Morey. 1995. Natural-Air Corn Drying in the Upper Midwest, BU-6577. University of Minnesota Extension. Illustrated. ca. 20 p.
Solar grain drying
Bakker-Arkema, F.W. 2001. Update from 1986. Mycotoxin prevention and control in food grains. FAO Corporate Document Repository: Agriculture and Consumer Protection.
Foster, George H., Bruce A. McKenzie, Sherwood S. DeForest. 1980. Solar heat for grain drying—Selection, Performance, Management. [Energy Production and Conservation, AE-108]
Stewart, Larry E., and Gerald E. Berney. 1982. Biological Engineering Resources, University of Maryland. (print only)
FACTS 139. The Serenity Farm Solar Grain Drying Demonstration
FACTS 140. The Schoonover Farm Solar Grain Drying Demonstration
Print copies are no longer available to the public—except from archival sources through InterLibrary Loan. See summary.
Sutherland, Susan G., and Steven T. Sonka. 1982. An economic analysis of solar energy for grain drying. North Central Journal of Agricultural Economics, Vol. 4, No. 1, January. p. 41-46. Agricultural & Applied Economics Association, The Ohio State University, Columbus, OH. (print only)
| Updated information pertaining to solar drying, supplied by David S. Ross, UMd. Supplements 1982 FACTS reports. Ackerman, M., and J. Chang. 1987. Performance evaluation of seven flat plate collectors for agricultural applications. Proceedings: Annual Meeting, American Solar Energy Society, Inc. p. 466-472. American Solar Energy Society. [ U.S. Imprint, orig., Alberta, CA] Andrews, David L. c2005. Energy Harvesting Materials. World Scientific Pub. Co., Singapore; Hackensack, NJ . 388 p. Argiriou, A. et al. 1989. Thermal study of the receiver of a focusing solar collector using infrared thermography. Solar Energy. Vol. 43, No. 1. p. 45-55. Bougard, J., M. Bouidida. 1981. Study and construction of a solar focusing collector using a deformable mirror, in the temperature range 100-200 degrees C. In: W. Patz and T.C. Steemers (ed.). 1982. Solar Energy Applications to Dwellings: Proceedings of the Contractors' Meeting (Athens, Greece, Nov. 11-13, 1981). D. Reidel Pub. Co., Dordrecht, The Netherlands. Edwards, D.K. 1978. Solar Collector Design. Franklin Institute Press, Philadelphia, PA. Lei, P.K., and J.M. Bunn. 1994. Evaluation of a solar-drive absorption cycle heat pump. I. Design theory, development, and basic evolution. Transactions of the ASAE. Vol. 37, No. 4 (July-August). p. 1309-1318. American Society of Agricultural Engineers, St. Joseph, MI . p. 1309-1318. Lei, P.K., and J.M. Bunn. 1988. Solar driven absorption cycle heat pump grain drying system. American Society of Agricultural Engineers, St. Joseph, MI. 19 p. Neyeloff, S., J.W. Bartok, Jr. 1981. Design, construction & evaluation of a low cost solar collector for rural applications. In: Agricultural Energy: Selected papers and abstracts from the 1980 ASAE National Energy Symposium. American Society of Agricultural Engineers, St. Joseph, MI. Schmidt, C., A. Goetzberger. 1990. Single-tube integrated collector storage systems with transparent insulation and involute reflector. Solar Energy, Pergamon Press, Elmsford , NY . Vol. 45, No. 2. p. 93-100. Vox, G., E. Schettini , A. Lisi Cervone, and A. Anifantis. 2008. Solar thermal collectors for greenhouse heating. Acta Horticulturae. No. 1 (November). p. 787-794. |
Decision trees and assessments
Edwards, W. 2006. Grain drying cost calculator. Version 1.0. Univ. Extension, Iowa State University, Ames.
Government of Saskatchewan. 2008. Natural Air Grain Drying. October. 14 p.
This chart shows how long grain may safely be stored as a function of moisture content, ambient air temperature and humidity.
Hill, Holly. 2008. Farm Energy Calculators: Tools for saving money on the farm. Butte, MT: NCAT.
Purdue University. 2009. West Lafayette, IN. In-bin Drying System Energy Audit Questionnaire and Continuous Flow Dryer Energy Audit Questionnaire
These questionnaires cover natural-air and solar grain drying.
Sanford, Scott. 2004. Reducing Grain Drying Costs. Winter Feed. University of Wisconsin-Extension. August 31. 5 p.
USDA Rural Development. Renewable Energy Grain Dryer Questions and Answers.
USDA National Agriculture Library. Heid, Walter G. 1978. The performance and economic feasibility of solar grain drying systems. Agricultural Economic Report. Vol. 396. USDA Economic Research Service.
Voth, Franklin. 2001. Grain Technical Information for Profitable Grain Harvesting. Grain News. Summer.
Patents
Hufford, Jack E. and William E. Mosmeier. 1981. Grain drying storage building. United States Patent 4285143 for solar-heated air drying storage of crops. Iron Horse Buildings, Circleville, OH, 43113.
Steffen, Sylvester L. 1977. Solar grain drying apparatus. United States Patent 4045880.
Other resources
Web
Talbot, Michael T. 2003. Grain Drying and Storage on Florida Farms. University of Florida Institute of Food and Agricultural Sciences. Gainesville, Fla. 10 p.
Purdue University links to Web information related to grain drying
University of Minnesota Extension Grain Drying, Handling and Storage Web site
MidWest Plan Service publications:
Grain Drying, Handling and Storage Handbook, MWPS-13. MWPS, Ames, IA. 1987.
Dry Grain Aeration Systems Design Handbook, MWPS-29. MWPS, Ames, IA. 1997.Midwest Plan Service publications can be ordered online at www.mwps.org, by calling 1-800-562-3618 or by e-mailing mwps@iastate.edu.
Wilcke, W.F., C.J. Bern. 1986. Natural-Air Corn Drying with Stirring: II. Dryer Performance. ASAE Transactions Vol. 29, no. 3, p. 860-867.
Energy-efficient grain drying resources
By Jeff Schahczenski, Katherine Adam and Mike Morris
NCAT Program Specialists
Holly Michels, Editor
Sherry Vogel, HTML Production
This page was last updated on: June 23, 2010
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