Energy use is often categorized into either direct or indirect use. Direct energy usage in agriculture is a measure of annual consumption of gasoline, fuel, and oil, as well as utility charges for electricity, water, telephone, and internet services. Indirect energy use is the embodied energy used to produce certain materials used on the farm, such as fertilizers and pesticides. Figure 1 shows a breakdown of US farm energy use. This energy use accounts for 15% of a farm’s total expenses.
Average energy-use data
Direct energy accounts for 5% to 7% of farm expenditures and indirect energy represents 9% to 10%. Because small farms, in particular, operate on profit margins well below 10%, improving energy efficiency can make a real difference in their budgets.
Turn things off
Every 1,000 kilowatt-hours (kWh) you save by shutting off equipment when it’s not in use cuts $100 off your utility bill (assuming an average electricity cost of $0.10/kWh).
LightsTurn off lights at night when they’re not in use. Installing a timer, photocells (which turn lights on at dusk and off at dawn), or motion sensors on outdoor lighting systems can help, although motion sensors may not be suitable for all applications. A less expensive alternative is to encourage employees to switch off lights when not needed, especially at the end of the day.
Air conditionersWindow air conditioners in outbuildings such as machine shops or garages are energy hogs, consuming up to 1 kilowatt per hour on average. Install a timer to shut off the air conditioner when no one’s in the space and set the timer to turn the unit back on a half hour before you expect to return.
Install programmable thermostatsTurning your heating systems down and cooling systems up while buildings are unoccupied is a simple way to save energy. Choose a programmable thermostat that allows multiple start/stop times to accommodate your schedule.
Clean and maintain equipment
Clean fansFailure to clean fans and shutters, which provide ventilation and circulation in buildings such as machine shops, can reduce ventilation efficiencies by as much as 40% and increase the possibility of fire. You should lubricate any motor bearings and shutter pivot points with machine oil at least once a month to ensure optimal operation. Also, check fan blades for damage regularly—replacing them is much more cost-effective than replacing an entire fan.
Keep lights cleanClean light fixtures and bulbs to ensure that they perform as designed and provide acceptable light levels for workers.
Replace beltsBelts transfer power from motors to pumps and fans. The majority of belt applications use standard V-belt drives. They’re the least expensive belt but they’re also the least efficient. When new, a V-belt typically achieves efficiencies between 90% and 95%, but a worn belt’s efficiency can decline considerably due to slippage caused by slackening and worn grip surfaces. Cogged V-belts are similar to standard V-belts except that the normally flat underside has grooves across the width of it, allowing better grip and less slip. Cogged V-belts typically offer a 2% to 5% efficiency gain over standard V-belts.
Perform system tune-ups
Tune irrigation and crop-drying equipment at the beginning of each season for optimal performance. Thoroughly clean and lubricate the equipment at the end of the season to prevent deterioration during long periods of disuse.
Ensure that parts of the irrigation system such as motors, switches, and control panels are free of dirt, insects, and bird nests. Be sure connections are tight and lubricate moving parts as needed. Check for correct impeller alignment, worn nozzles and shaft sleeves, leaking gaskets and drains, and dried-out pump packing and bearings. Clean and lubricate as needed at the end of the season.
Test the well pumpLocal utilities or water agencies will often test pumps free of charge or at low cost. Depending on the level of pump efficiency the test shows, you can:
- Adjust the impeller (for pumps with 55% to 60% efficiency)
- Adjust the impeller; if there’s no improvement, repair or replace the pump (for pumps with 50% to 55% efficiency)
- Repair or replace the pump (for pumps with less than 50% efficiency)
Tune up the crop-drying systemIf you have a crop-drying facility, be sure to:
- Clean screens and aeration floors
- Check belt drives (make sure safety guards are in place)
- Clean fan housings and blades
- Calibrate temperature-sensing devices
- Clean and check burners for proper operation
- Have utility personnel check gas-pressure regulators
- Calibrate grain-moisture testers and sensors annually
- Clean all debris from screens, aeration floors, and fan housings and blades at the end of the season
Although the actions covered in this section require more involvement or investment, they can dramatically increase the energy efficiency of your farm without compromising productivity. Ask your local utility representative for more information about available funding or guidance for such projects.
Waterers provide drinking water for livestock and use energy to keep the water from freezing in the winter. Install low-energy waterers and insulate the water tank to prevent heat loss. To prevent leaks, ensure that you’ve correctly installed the float that indicates the water level.
Pumping water to irrigate crops can account for as much as 30% of a farm’s total energy use. Installing efficient technologies will reduce energy consumption and save money. For more information on the various forms of irrigation presented here, review the guidelines and line drawings at the National Center for Appropriate Technology’s Energy Saving Tips for Irrigators.
MotorsImprove motor efficiency by repairing or rewinding existing motors or by upgrading to premium-efficiency models. Be sure to consider costs when evaluating your options. When upgrading, keep in mind that premium-efficiency motors have high up-front costs, but they make up for the expense in energy savings, higher service factor (resilience to overload), longer life of parts such as bearings and insulation, and less vibration. Consider purchasing a premium-efficiency motor when the cost of repairing or rewinding the existing motor exceeds 65% of the cost to replace it. Some premium-efficiency motors draw a larger start-up current, so verify that your system has the appropriate capacity before you buy a new motor.
PumpsReplace diesel pumps with energy-efficient electrical pumps. If the irrigation system uses old electrical pumps, rebuild them by replacing shaft sleeves, wear rings, and packaging. This cost-effective repair will improve the pump’s efficiency. If the cost to rebuild the pump is high, consider replacing it with a new, energy-efficient pump.
DrivesInstalling variable-frequency drives (VFDs) on irrigation pumps cuts energy use in several ways. Pumps are often oversized and therefore don’t operate at their most efficient speeds. But a VFD can better accommodate this discrepancy because it changes speed in response to the flow rate. Flow-rate requirements change over time, and in a single-speed system, a pump must either bypass the extra flow or dissipate the extra pressure that builds up at the lower flow rate. Either method wastes energy. A variable-speed pump, however, will reduce energy use when flow rates are low and will allow the pump to start and stop more slowly. This will reduce the potential for cavitation, a condition in which air bubbles form and collapse, producing potentially damaging shock waves inside the pump.
Irrigation schedulingA computer-based tool or app that works with sensors, software, and hardware allows you to track the moisture available to the crops and to more accurately forecast the crop’s water needs. By irrigating crops only when necessary, you can reap annual savings on water, energy, fertilizers, and labor to pay back the cost of the scheduling tool.
Fittings on a centrifugal pumping systemTechnicians will sometimes connect a pump to the mainline distribution pipe using undersized fittings because they have a lower initial cost. Unfortunately, any abrupt change in diameter can increase friction losses, which will result in significantly higher pumping costs. Consider these fitting guidelines to achieve maximum efficiency in a pumping system:
- Install a concentric expansion joint on the pump discharge to create a smooth transition from the smaller pump outlet diameter to the larger mainline distribution pipe diameter.
- Ensure that the check and shut-off valves are the same diameter as the mainline distribution pipe.
- Use a flexible joint of the same diameter between the shut-off valve and the mainline distribution pipe. This will minimize friction losses from misalignment, axial movement, and thermal expansion.
- Install a pipe support just downstream of the flexible joint to minimize pipe movement.
- Install the discharge pressure gauge downstream of the expansion joint. Use a ball valve to isolate the gauge, which will facilitate winter removal.
Surface-water pumpingEnergy-efficient pumping from rivers or canals should adhere to several design parameters. Take these actions to be sure your system is operating efficiently.
On the suction side of the pump that pulls water from the source:
- Ensure that pipe joints are airtight under vacuum conditions.
- Eliminate any high spots where air can collect.
- Be sure that the suction lift (the distance from the pump impeller to the water surface) is no more than 20 feet.
- Use an eccentric reducer at the pump inlet to prevent the reducer from trapping air.
On the discharge side of pump, which delivers pumped water for distribution:
- Ensure that the shut-off valve is the same size as the mainline pipe.
- Verify that the check valve is a “nonslam” type to prevent the pump from spinning backward on shut-off.
- Ensure that there’s an air-relief valve if the mainline distribution pipe is buried.
- Shade the motor to reduce the potential for overheating.
Center-pivot systemsFlexible hose drops connected to the center-pivot system will dispense water a few feet above the crop and reduce evaporative losses and drift from the wind. Low-energy precision applicators and low-elevation sprinkler applicators, which deposit the water very close to or within three feet of the ground, will provide even higher efficiency. They allow 95% to 98% of the pumped irrigation water to get to the crop.
Drip and microirrigation systemsIn this type of system, emitters placed on the ground use the capillary action of the soil to bring water to each plant’s root zone, reducing the amount of water and energy required for effective irrigation. When buried, drip systems will deliver water directly to the roots. Surface and subsurface drip systems can effectively deliver nutrients directly to the plants, improving yields and reducing fertilizer use.
After harvesting, most field crops go through on-farm processing that requires additional energy. The most common process for crops with high moisture content is drying, which brings the crops to moisture levels necessary for storage and further processing. Grain-drying systems typically use electricity to run fans and move grain, and they use propane or natural gas to provide heat. With each energy source there are ways to make crop drying more efficient. Because corn requires more energy for drying than any other grain, we’ve used it as an example, but these processes will work for most harvests. For additional guidelines and line drawings of the drying options presented here, see the “Low-Temperature and Solar Grain Drying Handbook,” a publication of the Iowa State University Midwest Plan Service; the University of Minnesota Extension Service’s Natural-Air Corn Drying in the Upper Midwest; and Dryeration & Bin Cooling Systems for Grain, from the Cooperative Extension Service of Purdue University.
Ambient-air dryingIf a corn crop comes out of the field at less than 22% moisture, consider using ambient-air (or low-temperature) bin drying. This process uses warm, outside air for drying and is best suited for dry-weather regions. Electrical energy use is high because high-horsepower fans run for an extended period. But overall, the process is more efficient when compared to crossflow dryers. In one study conducted by the University of Wisconsin on grain drying in various climate zones, Reducing Grain Drying Costs (PDF), researchers found ambient-air drying to have the potential of saving 25% to 50% energy than the typical crossflow high-temperature dryer in certain climate zones.
To reduce some of the risks with ambient-air drying, such as unexpected and persistent humid weather, use a high-temperature dryer to dry corn to about 20% to 22% moisture and then finish with ambient-air bin drying. Transfer the hot grain to the bin dryer and start the aeration fans immediately. This practice can reduce energy requirements by up to 60% compared to high-temperature drying alone. Combination drying has high drying capacity and can improve grain quality because it results in fewer cracked kernels than high-temperature drying processes. However, capital cost is higher because all bins will need fans.
Continuous crossflow dryerIn this dryer, the grain flows down a column via gravity as air blows across it. This is a popular type of dryer but it results in poor grain quality. Compared to other dryer types, its lower airflow rate increases energy efficiency. However, the moisture content varies between grains in the inner area of the column and those on the outside. Some crossflow dryers come with stirrers to mix the grain and reduce the variation in moisture content.
In-bin coolingAfter drying, the farmer cools the crops before storing them. You can save fuel by cooling corn in the storage bin rather than in the dryer. In this method, the farmer moves the grain from the dryer to the storage bin when the grain moisture level is 1% to 2% higher than the desired level. This means that if the final moisture target is 15%, you can unload the corn from the dryer when the moisture reaches 16% to 17%. Start the cooling fans immediately when moving the grains to the storage bin. Since the corn leaves the dryer sooner, in-bin cooling saves 10% to 15% in fuel costs and increases dryer capacity by 10% to 20%.
DryerationAn alternative to in-bin cooling, dryeration uses a special bin as an additional step between the dryer and the storage bin. In the dryeration bin the grains temper, or steam in their own vapor, for 4 to 10 hours and lose 2% to 3% moisture before the cooling fans start. Delaying the cooling step will reduce energy use and drying time, and it will improve corn quality (as seen in better test weight and fewer cracked kernels).
Heat recoveryIf you’re using a cooling section on your continuous-flow dryer, consider adding a heat-recovery system to capture the hot air exhausted from the cooling system and reuse it for the burner. This could save 10% to 15% of energy. Alternatively, you can add a heat-recovery system to the lower portion of the continuous-flow dryer’s heating column or full-heat dryer to save an additional 5% to 10% in heating costs.
StirringAdding a stirring device to grain bins will loosen the grain and increase airflow, resulting in an increased drying rate. It also mixes dry grain from the floor of the bin with high-moisture layers above and decreases drying time. The University of Wisconsin report on reducing grain-drying costs suggests grain stirrers can reduce energy use by 20% to 25%.
High-efficiency dryersIf ambient-air drying isn’t an option, consider replacing your existing crossflow grain dryer with a continuous in-bin dryer—the most efficient type of high-temperature dryer. Because crossflow dryers use high velocities to blow air completely across the large but shallow layer of grain, the air is traveling too fast to become fully saturated. Fully saturated air wastes fan power. Continuous in-bin dryers work on a much smaller cross section of the bin, allowing them to exhaust fully saturated air. They use about 40% less energy compared to continuous crossflow dryers.
Solar-assisted heatingSolar-assisted heating uses solar energy to warm air and dry the stored grain. A study by Iowa State University, Grain Drying With Supplemental Solar Heat, showed that solar-assisted drying reduced energy costs by 9% to 13%. Because they use the equipment longer and result in shorter payback periods, the best candidates for solar drying are crops such as nuts, herbs, and fruits that dry all year long.
Dryer controlsUpdating your high-temperature dryer controls to two-stage modulated burners reduces the extreme temperature variation caused by on/off thermostatic controls. Moisture and temperature sensors placed in the grain can save energy by sensing when the grain is dry enough for removal from the dryer and preventing overdrying.
Computerized control systemsComputerized controls sense the crop’s moisture level and regulate the temperature of the dryer accordingly, offering more-precise control. Because the systems are automated, you don’t need to worry about constantly checking and adjusting temperature levels.
Low-profile drying binsLow-profile bins are shallower than conventional bins and have a larger footprint. They save energy and reduce costs by decreasing airflow resistance through the grain, reducing fan power requirements, and shortening the drying time. Typically, reducing the drying depth by 25% will reduce the energy cost per bushel by 33%.
LED lightingLEDs are more efficient than other lighting technologies, last longer, and are safer to use with controls. They perform better in cold conditions than other lamps types and they’re suitable for both indoor and outdoor use.
Lighting controlsInstall lighting controls such as photocells or timers on outdoor lighting. A photocell control will turn on a light at dusk and turn the light off when it detects daylight. Motion-controlled sensors dim lights or turn them off in the middle of the night when they don’t detect any motion.
Install indoor occupancy sensors that switch off lights during periods of inactivity and save energy. Daylighting systems maximize the use of natural light and use artificial lighting when light levels fall below a certain threshold. Buildings with agricultural operations such as fertilizer plants, which have a large footprint, can benefit from advanced systems such as networked lighting controls.
Solar PV systemConsider adding renewable electricity generation through a solar photovoltaic (PV) system on your farm. In addition to providing power for daily operations, installing solar panels creates another revenue stream for farmers and provides agricultural benefits. Under the panels, you can grow shade-friendly crops, which have lower water requirements, and potentially extend the growing season. The US Department of Energy’s Farmer’s Guide to Going Solar is an excellent resource for getting started with a solar PV system.
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