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Load management can reduce costs of irrigation systems

In the same manner that farmers seek to cut their production costs, energy companies do, likewise. Both parties can end up doing this with load management programs.

A problem energy companies face is that power consumption by customers is never steady throughout the day. During certain parts of the day — peak loads — customers use more energy. And just like the city which has to construct and maintain road networks large enough to handle rush hour traffic, utility companies have to invest in generating and grid capacity to handle peak loads.

Energy companies in the Bootheel of Missouri, however, are willing to sell energy at cheaper rates if the customer helps out by refraining from drawing energy during peak use periods. Reducing the peak by balancing out customer energy consumption during the day leads to lower capital costs for energy companies.

Peak energy loads occur during the heat of the day when air conditioning use is at its highest, around 4 p.m. to 8 p.m.

SEMO Electric Coop in Sikeston, Mo., has about half of its 1,135 irrigation accounts using load management. Irrigators in the program are not able to irrigate during the four-hour peak period all week during July and August. This is managed by a circuit board timer installed in the control panel that turns off units around 4 p.m. and then back on four hours later at 8 p.m.

The actual cut-off and re-start time is staggered among the 500 plus pumps in a 45-minute time band to avoid power surges.

The financial incentive is that a typical pivot user will decrease his energy bill by 30 percent. Flood irrigators will save even more, with up to a 60 percent reduction in cost savings possible.

The reason flood irrigators can save more is that they normally have much higher flow rates per acre than pivots. A pivot user might typically have a pump that makes 1,250 GPM for his 125 acres, or 10 GPM per acre. A 40-acre flood field may have a pump that produces 2,000 GPM, or 50 GPM per acre.

These high capacities (about 10 times what a crop would ever use) allow the irrigator to water the field all at once with polypipe.

Figure 1 shows energy costs for both pivot and flood with and without load management based on the size of the field involved. The assumptions were gross depth = 12 inches, pumping water level = 50 feet, pump efficiency = 50 percent, operating pressure = 35 psi (pivot) and 5 psi (flood), and pumping season = 4 months. Flow rate assumptions were already discussed.

Figure 2 shows the seasonal savings for flood and pivot. An 80-acre flood field will have a savings of about $2,000. Since the normal Missouri Bootheel irrigator has about eight irrigated fields, a farmer could save almost $16,000 per year with load management from this company. The pivot owner with comparable irrigated acreage would save about $4,000 per year.

Stan Estes, general manager of Ozark Border Electric Co-op in Poplar Bluff, Mo., says that 93 percent of his company's 2,614 irrigation accounts participate in the load reduction program. They use the honor system regarding farmers shutting off when they are suppose to. One-third of the group shuts down from noon to 4 p.m., while the remaining shut down from 4 p.m. to 8 p.m. The program cuts pivot energy costs 30 percent and flood energy costs a whopping 78 percent.

However, there are the down-sides of load management that should be considered:

Short water supply

If the amount of available water is limited, the savings in energy could be overshadowed by a loss in yield. It would only take about an 11-bushel per acre decline in corn yield to evaporate that $2,000 savings on the 80-acre field talked about earlier. Water supplies of less then 6 GPM per acre would dictate that load management might be too risky, unless under super management.

Added wear and tear on equipment

Turning the pump on and off adds to the wear and tear of the pumping plants, especially if there is sand in the well.

Terminates flood irrigation before reaching the end

Some irrigators may consider this a drawback, but it might actually be beneficial. Cutting off the irrigation, in effect, turns the field into a surge flow field and may actually help irrigation uniformity.

Using siphon tubes

The irrigation group that would be the most affected by energy interruption are those irrigators who use siphon tubes. An interruption in power means that all the siphon tubes need to be reset.

Load management incentives are worth exploring with your electric co-op. However, not every co-op provides the load reduction program. Check with yours to see if it does. If your co-op does offer one, and demand charges (also called stand-by charges) are part of the billing schedule, many irrigators, especially those flooding with high-capacity wells, could benefit from load management.

Joe Henggeler is the State Irrigation Specialist at the University of Missouri Delta Center, Portageville, Mo.

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