Retail price of food per energy content

Food is energy. Look on the back of any food package and you will see the energy content of the item plain and clear – Calories, specifically nutritional calories (or kilocalories). What is a calorie? It is a energy unit, and for an exact definition let’s look to its wikipedia entry:

“The large calorie, kilogram calorie, dietary calorie or food calorie (or Cal) approximates the energy needed to increase the temperature of 1 kilogram of water by 1 °C. This is exactly 1000 small calories or about 4.18 kilojoules.”

With that said, food is also much more than just energy, providing us both vitamins and minerals. The cost of any food includes its monetary value for energy, vitamins, minerals, etc. But, for the moment, I just want to consider food’s energy content. Because the thought dawned on me – if food is just energy, then what is its price per unit energy?

With my background (electrical engineering), I live in the energy world which has the units of kilowatt-hours (kWh). A kWh is just another unit of energy. Specifically, the ratio between kWh and Calories is 1kWh equals ~860 Calories (kilocalories). With this conversion in hand, it is easy to change the back-of-the-box Calorie listing to kWh(s). Then, by dividing the retail price of the package by the energy content of the food, a cents per kWh value can be obtained. When I did this for a grocery list that I had just purchased, I learned a very interesting fact about food. It is really expensive on a cents per kWh (cents per energy unit) basis!!!

For example, the cereal I buy costs $3.99 for the box, and contains 2640 Calories (3.07 kWh). So, 399 cents per 3.07 kWh = 130 c/kWh!!!

In contrast, electricity costs about 11 c/kWh, vehicle fuel about 9.7 c/kWh, and natural gas at 2.97 c/kWh.

Although the comparison between these prices is dramatic (one order of magnitude difference), the comparison is a little apples to oranges. The retail price of food includes not just the energy content, but also the packaging, vitamins, minerals, nutrition, manufacturing, transport, etc . The retail price of other forms of energy includes taxes, marketing, manufacture, and transportation (if any).

Although there are differences, the price of food as seen in just an energy lens is a striking thing to see. The c/kWh for individually package, retail, consumer food is very high. This fact just hits home the point about using food for fuel. It can be an expensive enterprise (at least if you are using individually packaged food products…).

For ethanol makers, the basic economics looks okay. Dry corn has 2.34 kWh per dry pound, and at 4.5 cents per pound ($18 per 400 lb dry), the cost would be 1.92 c/kWh.

Just an interesting food for thought. Or thought for food (thanks Colbert).

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