Human Energy
Before machines took over the work, the human being was the engine. Whoever grasps this suddenly sees energy with different eyes.
We talk about power plants, oil and electricity as if energy always came from outside, from lines and tanks. Yet we ourselves are an energy store that works day and night. Every human being is a small, astonishingly economical engine, and a look at its output exposes something we take for granted and have long forgotten.
The human being as an engine
Physically speaking, we constantly perform work: we lift, carry, walk, push the pedals. The energy for this comes from food. What we eat is chemically bound energy that our body converts into motion and heat, much as an engine burns petrol. Only this engine never quite runs out as long as we live: even in sleep it keeps heart, breathing and body heat going.
How strong is this engine? A person exerting themselves can sustain only about 100 watts of usable muscle power, just about as much as an old light bulb. For short sprints a trained racing cyclist might manage 300 to 400 watts, but not for long. That sounds modest, and that is exactly the point.
Let's do the maths for once
A day has time for work around the clock, yet no one can give full strength for eight hours straight. Let us realistically assume that a strong person delivers on average 75 watts over a working day. Over eight hours that comes to about 0.6 kilowatt-hours, that is, a good half a kilowatt-hour of hard physical labour.
What does this half kilowatt-hour cost at the socket? In Germany roughly 15 to 20 cents.1 A whole day of human muscle power, then, is to be had for a few cents of electricity. Seen the other way round: a litre of petrol holds so much energy that a person would have to toil for weeks to match it. No wonder we so gladly hand manual labour over to machines.
The invisible helpers
From exactly this arises a revealing comparison. A person in a rich country claims, around the clock, sixty times what they could produce themselves.2 Put vividly: behind each of us dozens of "energy slaves" toil invisibly, never-tiring machines, motors and power plants that take over the work for which whole groups of people were once needed.
This is an enormous privilege, and it is worth becoming consciously aware of it. Whoever has once pumped water from a well by hand, ground grain or scrubbed laundry feels bodily how much work is contained in a single press of a button. That does not belittle us but makes us alert: it shows what our everyday life actually rests on.
Everything comes from the sun
Where does the energy in our muscles come from? From food, and that in turn from the sun. Plants capture sunlight and build sugar and starch from it. Whether we eat the vegetable directly or the animal that ate the plant: at the beginning there is always sunlight. When we carry a crate up the stairs, we move it with energy that fell weeks ago as light onto a field.
Seen this way, the human being is no exception in the great cycle but a part of it. The same sun that drives the wind and lifts the water into the rivers is also in our breakfast.
Why this is more than physics
The look at one's own energy has an emancipatory point. It relativizes the self-image of the all-powerful human who simply masters nature: in truth we are weak engines that have borrowed mighty tools. These tools cost energy, and this energy costs money, leaves traces and creates dependencies.
Whoever knows how little their own body produces and how much foreign energy is in everyday life judges differently. They more easily see through why cheap energy is so seductive, why its price often does not tell the whole truth, and why using strength more consciously is no sign of backwardness. To grasp with one's own body what a kilowatt-hour means is perhaps the best school for critical thinking about energy.