|Almas, Lal -|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2010
Publication Date: June 1, 2011
Citation: Vick, B.D., Almas, L. 2011. Developing wind and/or solar powered crop irrigation systems for the Great Plains. Applied Engineering in Agriculture. 27(2):235-245. Interpretive Summary: A significant amount of crops in the United States are grown in the Great Plains, and most crops can significantly increase yield when they are irrigated. Because the energy used to pump water from underground aquifers for irrigation is primarily from fossil fuel sources that produce greenhouse gases, (natural gas, diesel, electricity from coal), it is important for farmers to begin switching to renewable energy resources like wind and solar energy in order to continue to provide a stable food supply. Renewable energy-powered irrigated crop production in southwestern Kansas and the northern Texas Panhandle is potentially cost competitive compared with existing fossil fuel powered irrigation systems. The ability of solar, wind, and a hybrid combination of solar and wind energy to meet irrigation energy requirements in the northern Texas Panhandle was analyzed. Average monthly data for solar energy resource, wind energy resource, rainfall, and crop moisture requirements were used to assess the renewable energy systems. Combining a winter crop (like winter wheat) with a summer crop (like corn or soybeans) resulted in a better match of crop irrigation power electrical demand to renewable energy electrical generation than if only a winter or summer crop was grown. The solar resource matched irrigation energy requirements better than the wind resource, but combining a wind turbine with a solar photovoltaic (PV) array increased reliability over just having a solar PV array. However, when the economics were analyzed for the wind and solar irrigation systems, some wind turbines in the 40 to 100 kilowatt (kW) range were less expensive than the solar PV systems in that range, so it is currently more economical to irrigate with just wind turbines in the Great Plains. If no loan was required and excess wind generated electricity was used on the farm instead of selling back to utility; payback periods in the seven to eight year range were possible with no Federal incentives. With 55% Federal incentives, payback periods in the four to five year range were possible. At times when wind or solar energy is insufficient to power irrigation, either electricity from utility or bio-fuel, such as bio-diesel from soybeans (which can be grown and processed on farm), can be used to power irrigation pumps. Spikes in the prices of natural gas and diesel in recent years will occur again in future as demand exceeds supply, so switching to wind and solar energy for irrigation energy requirements and other farm energy requirements will enable farmers in the Great Plains to continue farming. It will also decrease the dependence of the United States on foreign countries for energy and food.
Technical Abstract: Some small scale, off-grid irrigation systems (less than 2.5 ha) that are powered by wind or solar energy are cost effective, but this paper discusses ways to achieve an economical renewable energy powered center pivot irrigation system for crops in the Great Plains. It was found that partitioning the center pivot irrigation system between a winter crop and a summer crop improved the match of wind turbine generation to irrigation energy required. It was also found that a solar-photovoltaic (PV) array was a better match to the irrigation energy requirement of a winter and summer crop than using only a wind turbine, but a wind/solar hybrid was a better match than wind alone. Although solar PV systems were shown to be a better match than wind turbines for irrigation power requirements, solar PV systems are more expensive than small wind turbine systems for large scale irrigation water requirements in the Great Plains. Including on-farm uses for the excess wind and solar electricity instead of selling the electricity back to a utility company at usually low prices, improves the profitability of a renewable energy powered irrigation system significantly. For a utility electrical price of $0.10/kWh, a wind turbine installed price of $3000/kW, no loan required (e.g. no loan costs), and the excess renewable energy generated electricity used for on-farm use only, a payback period of seven to eight years was possible with no state or federal incentives. With 55% Federal incentives and the same assumptions, a payback period of four to five years was possible. Also, if the assumed operations and maintenance costs doubled, the payback period increased about two years. However, cost reductions are still required for both wind and solar energy systems in order that renewable energy systems can be competitive without the need for state or federal incentives when loans at 90% of installed cost with a 6% interest rate are required.