Mitigation of carbon dioxide releases from power production via “sustainable agri-power”: The synergistic combination of controlled environmental agriculture (large commercial greenhouses) and disbursed fuel cell power plants

There has recently evolved in the United States a number of independent power plants producing power for the grid while cogenerating heat for use in large, commercial greenhouse operations. The state-of-the-art of these greenhouses is 10 to 50 acres under glass with productivities on the order of 300,000 pounds of tomatoes per acre per year which is achievable through computer controlled climate, hydroponic growing systems, supplemental carbon dioxide, and energy conserving structures and systems. While the greenhouse structures and growing systems are high tech and capital intensive, the combination of high productivity in the wintertime when the prices are highest and the relatively low cost for cogenerated heat result in economic attractiveness as a commercial venture. Furthermore, from an environmental perspective, these state-of-the-art systems can be designed for zero water releases to soil or surface waters and very efficient point application of both fertilizers and pesticides compared to field crop broadcast applications. The primary objective of this paper is to present an engineering systems analysis of how such systems can mitigate, through greenhouse photosynthesis, carbon dioxide releases from both from fossil-fuelled power production at the greenhouse site and from the avoidance of fossil energy for field crop production and distribution. A second objective is to propose the use of environmentally benign fuel cells as the power production technology of choice (200 to 500 kilowatts/acre) to not only produce electricity with high efficiency (40 to 50 percent or more as electricity) and cogenerate useful heat for greenhouse winter warming, but also “trigenerate” useful carbon dioxide in the form of exhaust. This exhaust, which is very low in NOx and SOx coming from the fuel cell, can be used directly in the airspace of the greenhouse for both heat and the value of the carbon dioxide as a fertilizer, which can further increase crop productivity by 10 to 20 percent. The third objective is to show that when greenhouse biomass residues, along with other locally available agricultural wastes, can be anaerobically digested to produce a biogas that fuels the fuel cell, the system can produce power and food with a net short term sequestering of carbon dioxide in the form of food. In summary, this linking of technologies can result in both “sustainable power” and “sustainable agriculture,” the combination of which might be called “sustainable agri-power.” Also to be briefly explored will be applications to crops other than vegetables, such as fruits, flowers, spices and forest products, supplemental lighting for increased productivity, summertime cooling and thermal energy systems, and even more novel applications such as wastewater treatment through constructed wetlands, short rotation tree crops for energy production and, even further along, biotechnology applications.