Re: How much energy can a Robo hamster generate and can it be harnessed?

Hi Gina,

Thanks for submitting your question to the MadSci Network. I think that there is a relatively straightforward answer to your question, but that answer will depend on some information that will be specific to the hamster in question (see below). The important thing to realize is that hamsters (Roborovskii Hamsters or any other hamster, or any other animal) do not generate energy. Animals convert the chemical energy stored in the food that they eat to the mechanical energy that we observe when we see them doing things, like turning a hamster wheel. So, to get an idea of how much energy a Roborovskii Hamster has available to turn a wheel, we have to look at what that hamster is eating, and how much it is eating. The caloric content of a given hamster's diet will tell us what the limits on its output are.

I took a look at various packaged hamster foods to get an idea of how much a hamster might eat in a day, and what the caloric composition of that food is. Now, the caveat here is that a different hamster food might have a different caloric composition, and that different hamsters will eat different quantities of each food. The numbers that I am including here come from the PetCo.com entry for one particular brand of hamster food, so you should feel free to recalculate them using a different food if you like.

A calorie is defined as the amount of energy necessary to raise the temperature of one gram of water by one degree centigrade. The caloric content of food derives from three sources -- proteins, fats, and carbohydrates. I should note here, that there is a somewhat confusing system for describing caloric units. The packing on food products lists the caloric contents in terms of Calorie units (written with a capital-C), but for considering chemical and mechanical energy, we use calorie units (written with a lower-case-c). One Calorie is equal to 1000 calories, and so we also call one Calorie one kilocalorie, or one kcal. So one Calorie is enough energy to raise the temperature of one thousand grams of water by one degree centigrade.

So, the caloric content of proteins and carbohydrates differs from the caloric content of fats. One gram of protein or carbohydrate contains 4 kcal of energy, while one gram of fat contains 9 kcal of energy.

With that in mind, we can take a look at the caloric content of the hamster food that I am using for this answer. If you look at the "directions" for that food, the serving size for one hamster is between 0.5 and 1 ounces of food per day. If you look at the "Ingredients and G.A." for that food, you will see that it is 17% protein, 6% fat, and 8-11% fiber. I chose to average that and use an average of 9.5% fiber. Plugging the caloric content of 4 kcal per gram for protein and carbohydrate (fiber) and 9 kcal per gram for fats, that gives us 1.6 kcal per gram for this hamster food.

1 ounce is about 28.35 grams, so that gives us a total caloric intake of 22.7 to 45.4 kcal per day for a healthy (not overeating and not starving) hamster. However, what we need to know is how much of that energy is available to the hamster to convert into mechanical energy. As you will see in this answer (1070824959.Bc), which I wrote a few years ago, most (69%) of the energy in the food that we mammals eat is used to keep us warm; that energy is "lost" in the form of heat. Less than 1/3 (31%) of the energy in the food we eat is available to us for metabolism and activity.

So, that means that of the 22.7 to 45.4 kcal consumed by a hamster in a day, only 7-14 kcal contribute to the activity that we observe as happy hamster behavior. So, the output of a normal hamster is limited to about 7-14 kcal per day. We do know that high-performing human athletes consume much more food than a regular human, so presumably, a high-performing hamster would consume more as well, but I assume that your question pertains to regular hamsters that you've seen going about their everyday business, so this number gives us a good starting point. Obviously, the mechanical energy output of a hamster will be even lower than this number, because some of that 7-14 kcal is used for breathing, pumping blood, thinking important hamster thoughts, etc., so we can think of this as an upper limit on the output for a regular hamster.

In terms of how we can harness that energy, we can convert from units of energy to units of power. Power tells us how much energy is generated/consumed per second. Power is measured in watts, which is the equivalent of one joule of energy per second. A 60 watt light-bulb consumes 60 joules of energy per second. One kcal is equal to 4148 joules, so we can convert our daily caloric output for a hamster by multiplying 7 to 14 kcal by 4148 and then dividing the whole thing by the number of seconds in a day (24 hours * 60 minutes * 60 seconds = 86,400 seconds).

(7 * 4148) / 86,400 = 0.337 watts
(14 * 4148) / 86,400 = 0.675 watts

So, our hamster is putting out a maximum of somewhere between 1/3 and 2/3 of a watt of power (of course, this is an average; while the hamster is sleeping its power output is lower). So it would take between 90 and 180 hamsters to power that 60 watt light bulb, assuming that we could capture all of that energy; in reality, the energy spent on turning a hamster wheel is much less than 7 - 14 kcal.

There is one final point that I want to make about all of this. Remember that 2/3 of the caloric energy in food is used to keep the hamster warm. This means that using any mammal to convert the chemical energy stored in food to mechanical energy is extremely inefficient. When a hamster eats food, it ultimately converts that food to carbon dioxide and water (with the exception of the food that is not digested, but I won't go into that) by combining it with oxygen, which is the same thing that happens when we burn that fuel in a furnace, except that we can capture a lot more of the energy that results from the burning. So, instead of using a hamster to generate power, it would be much more efficient to burn the hamster food, and use the resulting heat to turn a steam turbine, generating electricity.

So, all that means that I doubt that we will be able to meet our energy needs using hamsters (something I believe the hamsters will be thankful for). That doesn't mean that your idea wasn't a good one though, just that the numbers don't look too promising; keep thinking about this issue and don't be afraid of unconventional ideas. Someday you may be the one to find a great solution!

Keep asking questions!