Energy Put into Food

Diana Kim
May 26, 2018

Submitted as coursework for PH240, Stanford University, Fall 2017


Fig. 1: Picture of fertilizer (Source: Wikimedia Commons)

Have you ever wondered how the food consumed by us is produced? If you have, have you ever wondered how much energy is put into producing all this food? Have you ever wondered what the source of the energy is? Were you aware of how much energy is put into as all the food we eat is produced? Food manufacturing is actually a very energy intensive process that people are not usually aware of. It is quite interesting to see how much energy is put into food until it arrives at our table.

Energy Put into Food in the United States

A myriad of Government and academic studies have examined energy use by food industry in the United States. Interestingly enough, all of these studies have indicated that food-related energy use has remained a significant share of the total national energy budget. Not only that, food-related energy flows have significantly increased over the past decades. [1] From 1997 to 2002, per capita energy use in the United States decreased by 1.8 percent. However, per capita food-related energy use increased by 16.4 percent. Considering the population growth, total food-related energy use has increased by 22.4 percent. [1] Are you yet surprised by the amount of energy used in producing food? If you think about it, though, it makes sense. Between planting and harvest, a diesel-powered broadcast spreader applies nitrogen-based fertilizers, pesticides, and herbicides. These chemicals are all manufactured using natural gas and electricity. Moreover, farms use electric-powered irrigation equipment throughout the growing period. [1] Granted, farm fuel efficiency has improved significantly since the 1970s, due to a switch from gasoline to diesel-powered farm machinery. However, large portion of food-related energy is used in the form of fertilizers and pesticides. In fact, the three most significant energy consumers are fertilizers, farm equipment, and pumping and irrigation. fertilizer and pesticide still represent the largest energy input into agriculture. [1] The primary function of fertilizers is to add potassium, nitrogen, and phosphorus to the soil. Fig. 1 is an example of fertilizer that is used daily for agriculture. For fertilizer, nitrogen is the most important of the farm chemical inputs as it is extracted primarily from the atmosphere using the energy-intensive Haber-Bosch process. According to world average, even when only considering nitrogen, phosphate, and potash put into fertilizer, total of 109,530 kJ per kg (= 1.09 × 108 J/kg) is used. Considering that in 2008 only, U.S. farmers used 58 million tons (= 5.26 × 1010 kg) of fertilizer, the total energy consumed was [2]

5.26 × 1010 kg × 1.095 × 108 J/kg = 5.76 × 1018 Joules

And considering the total US energy budget is approximately 1.0 × 1020 joules, the energy to make fertilizer constituted

5.76 × 1018 Joules / (1.0 × 1020 Joules) = 0.0576

or 5.76% of national energy budget! And keep in mind that this only considers nitrogen, phosphate, and potash put into producing fertilizer.

Our Future

Fig. 2: Picture of food on our table (Source: Wikimedia Commons)

CEF projects that energy consumption by the food manufacturing sector will increase by 19 percent from 1997 to 2020. [3] As such, increasing demand for fresh processed foods by customers has increased energy consumption by the food manufacturing industry. [4] Everything is so fast and convenient today and we can easily have access to any food. Look at Fig. 2 and think about how easily we can find those foods on our table every day. However, perhaps it is time for us to question about all this energy put into food sector and altogether think about ways to save energy and use it more efficiently. For instance, it is possible to replace natural gas with hydrogen created via water electrolysis using renewable wind or solar energy. Our future is all dependent on what we can do today.

© Diana Kim. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] P. Canning et al., "Energy Use in the U.S. Food System," U.S. Department of Agriculture, Economic Research Report No. 94, March 2010.

[2] T. Gerlagh and A. W. N. Van Dril, "The Fertilizer Industry and Its Energy Use," Energy Research Center of the Netherlands, ECN-C-99-045. January 1999.

[3] "Energy Trends in Selected Manufacturing Sectors: Opportunities and Challenges for Environmentally Preferable Energy Outcomes," U.S. Environmental Protection Agency, March 2007.

[4] J. S. Steinhart and C. E. Steinhart, "Energy Use in the U.S. Food System," Science 184, 307 (1974).