Energy Use in Food Production and Transportation

Transcription

1 Energy Use in Food Production and Transportation Joey Klonowski HSA10 section 5 5/17/2011 I. Introduction What is the energy cost of feeding a human? Is fresh food more energy efficient than processed food? How is energy used in the food industry? These are very large questions, but we can get a rough estimate of how energy is used in the food industry fairly easily, with a little research and basic arithmetic. The idea of this paper is not to provide a broad, sweeping answer to these very large questions, but to develop and present a method of obtaining first approximations to quantitative values, not for the entire nation, but in a very specific test case, with a bit of a backstory. Students at Harvey Mudd College have been working hard on their essays, and have decided to stop for a bit because they are hungry and thirsty. Is it more energy-efficient if they eat fresh or processed food? We'll say a student can choose either processed calories in the form of high-fructose corn syrup, or fresh lettuce for a salad. How much energy is used in each case? II. US Agriculture Industry: A Quick Primer For the last 5000 years, farming has been sustainable. Energy and water were both used at a renewable rate. Most people lived in rural areas and grew their own food within a few hundred yards of their house, because they did not have the technology to transport food long distances. In the last hundred years or so, farming has become nearly unrecognizable. Crops are squeezed together to fill as little space as possible. They are planted in industrial-scale monocultures. We sometimes farm in climates that do not provide enough water, and use imported water for irrigation. We create chemicals to use as fertilizer, adding artificial nutrients and chemical energy to the crops. We load the crops onto trucks, trains and airplanes to be shipped for hundreds or thousands of miles, either to a supermarket or to be turned into magical things like high fructose corn syrup, maltodextrin, or natural grill flavors. Critics of this system say that it takes too much energy to grow, process and transport food produced in this fashion. They generally suggest eating local as an an alternative. The argument is that if we eat fewer processed foods, and instead eat only seasonal produce that can be grown in a one to twohundred mile radius, we'll save a good deal of energy on fertilizer, processing and truck fuel. The downside is that produce, unless you grow it in your backyard, must be refrigerated, which is itself a large energy cost. III. Processed Food Corn is the most common crop grown in the US; 300 million tons were produced in It is used to feed people and animals, as a fuel, as a sweetener, and to produce chemicals and medicines. This is partly because corn is easy to grow and partly for political reasons. Corn is especially well adapted to industrial production; the plants can grow very close together, require much less water than other crops (because it uses C4 carbon fixation instead of C3), and the harvesting and planting processes are easily mechanized. It has also evolved to be able to absorb nutrients from artificial fertilizer. These fertilizers, however, require energy to produce; in this paper I will estimate how much energy is used to produce fertilizer for farmer Bob's corn. Another energy problem in the US food system is transportation. Foods shipped across the country or across the globe are very energy-intensive, especially if they need to be 1

2 refrigerated or frozen while they travel. The problem is that no one in Iowa wants farmer Bob's corn, and no one at or near Harvey Mudd College grows their own. The corn must be shipped about 1700 miles. That requires a good deal of energy, but can we estimate how much? And what about the processing and packaging of the corn? How much energy does that use? These general questions are too big and complex to answer in a short paper; we need something a little shorter and more specific. So let's return to our burning question: how much energy is required for farmer Bob to grow a bushel of corn in Iowa and send it to Harvey Mudd College in California? To find an estimate of how much energy, I'll focus on two main steps: the energy required to produce the fertilizer and the energy required to transport the corn from the farm to the consumer. There also could be some energy used in processing the corn, although that would depend on what the corn was being processed into, and therefore difficult to quantify. So how much energy does it take for farmer Bob to produce a bushel of corn in Iowa? The corn gets some energy from the sun, of course, but that energy is entirely renewable. I'll focus here on the energy used to produce the fertilizer. Most of the facts and numbers in the following section are from a study on farm energy published by Iowa State University. 2 Crops generally need three nutrients from fertilizer to achieve optimal yields: nitrogen, phosphorus and potassium (abbreviated N, P and K, respectively). Of the NPK fertilizers, nitrogen requires much more energy to produce. In fact, the manufacturing processes of phosphorus and potassium fertilizers actually release more energy than they use. Our main concern, then, is the energy used to make nitrogen fertilizers. How much nitrogen does farmer Bob use? The Iowa State study found a formula for the optimal (profit-maximizing) amount of fertilizer in terms of the price of fertilizer and the price of corn. I found that the price of anhydrous ammonia (a common nitrogen-based fertilizer) was $499/ton in , and the price of corn was $6.40/bushel 4. Using these numbers and Iowa State's Corn Nitrogen Rate Calculator, I found the profit-maximizing nitrogen rate to be 150 lb N/acre (see first graph). 5 This is a good number, but we want a nitrogen/corn ratio, so we need to find an estimate of yield; how many bushels of corn will that acre produce? The Iowa State study estimated a yield of 180 bu/acre at 150 lb N/acre (see second graph), 6 so Image from 6

3 the ratio of corn:nitrogen is 180bushels/150lb N, or 1.2 bu/lb N. Next, we need to find how much energy is required to produce a pound of nitrogen. Nitrogen fertilizers are produced by the Haber- Bosch process, where nitrogen from the air and hydrogen from natural gas combine to form ammonia (NH 3 ). A very large amount of energy is required to break the nitrogen (N 2 ) molecule, because the two nitrogen atoms are held together by a triple bond, the strongest possible bond between two atoms. Energy is also required to produce the hydrogen from natural gas. According to the Iowa State study, the exact amount of energy is 39.8 million BTU/ton N, which is equivalent to 5.83kWh/lb N. If we divide this number by 1.2 bu/lb N, we get 4.9 kwh/bu. In other words, farmer Bob needs 4.9 kilowatthours of energy to produce fertilizer for one bushel of corn. We now turn to the second question: how much energy does it take to transport a bushel of corn 1700 miles from Iowa to Claremont, California? This is a bad question farmer Bob's corn doesn't fit very well on a truck or a train, so shipping it across the country would not be profitable. Part of the reason corn is refined into high fructose corn syrup and other processed foods is that these are easier to transport. High fructose corn syrup is a liquid, so it's cheap to put in a tanker and send to California. So let's edit our story question a bit: let's say that instead of shipping his bushel of corn to California, farmer Bob sells his bushel to Cargill, who sends it to a refinery in Iowa, where it is magically transformed into high fructose corn syrup, which is transported to Claremont. Students are hot and sweaty from Southern California weather and demand for sodas is very high, so Cargill sells its high fructose corn syrup to The Coca-Cola Company, which puts the HFCS in soda sells the soda to the Hoch to be consumed by thirsty students. If a student drinks 20 oz of coke, how much energy was used to produce and transport the corn used to make that coke? A bushel of corn yields about 15 kg of high fructose corn syrup. 7 A 20 oz bottle of coke has 65g of sugar, all of which is high fructose corn syrup. 8 This means that one bushel of corn is equivalent to 4600 oz of coke, or oz bottles. It took 4.9 kwh to produce that bushel of corn, so it takes kwh to produce corn for a 20 oz coke. But remember, we're trying to answer the second question: how much energy is used transporting the corn, which is now high fructose corn syrup? We'll assume the HFCS makes most of its journey on a train. On average, a train can move a ton of freight 436 miles with a gallon of diesel fuel. 9 A gallon of diesel fuel contains 130,500 btu. 10 If we throw these numbers together, with some other simple conversions, we find that it takes 9.6x10-8 kwh to transport one gram of freight a distance of one mile. Adjust for 65g instead of one tonne and 1700 miles instead of one mile, and it comes out to kwh. If we assume the sweet stuff is transported by truck instead of train, this number comes out to 0.12 kwh. We'll use the figure for trains and say kwh. So how much energy is needed for that bottle of coke? If we add the kwh it took to produce the corn, to the kwh it took to transport the liquid sweetener, we get kwh total. Considering the can contains 260 Calories, or about 0.3 kwh of energy, that's a very low number. The moral of this story is that highly processed foods are energy efficient, at least in terms of transportation; putting HFCS on a train and shipping it across the country requires less than a tenth of the energy that the HFCS contains in calories. Transporting refined calories like HFCS is efficient for two reasons. The first is that HFCS is a liquid, so more can be transported in the same amount of space. The second is that HFCS doesn't need to be kept cold while it is shipped. Fresh or frozen foods require a great deal more energy because they must be kept cool as they are transported. This requires more energy both for the actual refrigeration and because they must be shipped quickly, which greatly decreases efficiency. Fresh food can't be shipped by train, so trucks and planes are the only option. Trucks, as we saw above, use about ten times more energy to transport the same amount of weight the same distance, and planes are even worse. We still

4 haven't accounted for energy use in processing the corn and making HFCS (I couldn't find these numbers on the internet after about an hour of searching perhaps because other people can make more money if I don't know), so this is by no means an exact estimate. IV. Fresh Food Calculating energy use for fresh food in this case, lettuce, is a bit easier, because we don't need energy in the form of fertilizer. If we use organic lettuce, artificial fertilizers are not allowed, but regular lettuce doesn't need much anyway. The main energy costs in our student's leafy green salad are transportation and refrigeration. Transportation is much more energy-intensive for lettuce than for HFCS, even though the lettuce can be grown in California, because lettuce takes up much more space per calorie. Let's assume a head of lettuce takes up about a cubic foot in a truck. A typical trailer in the US is 48x8x13 feet, or about 5000 cubic feet, so we can fit 5000 heads of lettuce per truck. Semi trucks get about 6 miles per gallon, and we already know how much energy is in a gallon of diesel fuel 130,000 btu or 38 kwh. Let's say farmer Joe in Bakersfield, CA, harvests his crop of lettuce and loads it onto a truck bound for a cafeteria in Claremont: 140 miles. Multiply and divide these numbers appropriately, and we find that it takes 0.17 kwh to transport our lettuce. Now, let's work on refrigeration. If our lettuce isn't kept cold, the students will have a very unpleasant surprise, so we're going to install a refrigerator on the truck. I don't know how much energy a refrigerator truck uses, but in the spirit of order-of-magnitude approximations, let's say it uses energy at a rate proportional to its surface area. Then if we know how much energy a household refrigerator uses, and it's surface area, we can estimate the energy use of a typical semi trailer. Remember, the dimensions on our truck are 48x8x13 feet. That's a surface area of 2,200 square feet. The government's energy-star program has a very helpful website for calculating energy use for household refrigerators. 11 According to their site, a 29x65x32 inch refrigerator (surface area 68 square feet) uses 1,475 kwh/yr. If it takes one day (instead of a year) to get the truck from Bakersfield to Claremont, and the lettuce is stored in a conventional refrigerator for two days before being fed to hungry students, the energy cost for refrigeration is 0.03 kwh for the refrigeration in the truck and 0.23 kwh for the refrigeration at the cafeteria. The total energy cost of our head of lettuce is 0.43 kwh. This is a lot higher than the cost of the bottle of coke, especially considering the coke has 260 calories compared to 110 calories for the lettuce. But keep in mind, we haven't accounted for the processing of the corn, which might change this analysis. V. Conclusion Processed foods are surprisingly energy efficient to produce and transport. Of course, this completely ignores the health question it's no secret that fresh fruits and veggies are better than a bottle of coke. But transporting fresh food a long distance, which is becoming more and more necessary as the global population moves away from rural areas and into cities, may not be economically viable in the future if the price of energy, especially fossil fuels, increases. This means we have two alternatives: eat processed food, if we can find efficient ways of processing, or grow food very close to home, so that there's no need for refrigeration. Processed food can be easily transported, as we have seen, but the processing process itself requires energy that we haven't yet investigated. Chemically, this process involves taking the starches in the corn and breaking them into smaller sugars. In other words, the bonds in the cornstarch molecules must be broken. Breaking bonds requires energy, which brings up another question: how much energy does it take to process a bushel of corn and turn it 11

5 into 15kg of high fructose corn syrup? It's a question for another paper, but it's important to keep in mind that I've overlooked it here. Of course, the ideal solution would be to find an economically viable way to grow food in or near the urban areas where it is needed, and not transport it hundreds or thousands of miles.