In physics, a semi-scientific "dimensional method" is sometimes used to solve problems, when knowing the dimension of the desired quantity, we can guess what to divide, add, multiply in order to get the correct answer. I decided to take the dimension "energy" and compare "apples with bananas", namely man as an energy system with other systems.

### The person is the energy consumer. 2 kWh, 100 W

The average person consumes about 2000 kcal per day, which gives about 2 kWh or about 100 watts, average power. One can imagine that a person eats as one large 100-watt incandescent bulb.

The power consumption of a person is relatively small compared to the devices that surround us. It can be said that man has made a technical revolution. A man takes in himself less energy than he uses "for himself", even only at home (the average calculation is more than 100 kWh per month).

### Man is a computer. 30 W

It is widely estimated that the brain eats 200 to 1000 kcal (stressful situations), that is, from 20% to 40% of energy, which gives an average power rating of 30 W.

The brain is an extremely effective system. Yes, modern laptops perform operations much better than us and the average power is about 30 watts, and phones generally 0.5-1 watts. But modern graphics cards consume an average of 250 watts and still can not compare with the brain in terms of speed and accuracy of processing visual information. So, the person is a very good processor, though only for specific tasks.

### A man is a battery. 10 kWh

They say a person can not eat 3-7 days. It is clear that without eating, a person will consume less energy for internal and external needs. You can assume that by eating a double daily rate, the person will be active for 2 days (in the presence of water), which gives a rough estimate of 10 kWh.

If we calculate the energy intensity of a person, then we can get extremely different figures, the weight of people who can live Nth number of days and produce some useful work varies very much from 50 kg to 150 kg. Most likely, the average energy intensity is 0.1 kWh / kg, which is not so good and not so bad. We are between gasoline (10 kWh / kg) and Liion (0.1 kWh / kg), closer to the batteries.

### A person is a consumer of solar energy. 1-2 solar panels

Today's solar panel gives about 300 watts in peak, in moderate latitudes the average CIUM is up to 20% (the sun shines only during the day and weakly). We know that a person is short-lived, but still a battery, so an average of 2 panels is enough for a person to eat only the sun.

If you drop convention and make small breakthroughs in technology (using expensive elements allows you to achieve up to 40% efficiency in the panels ), It will be enough for a person to wear "sunny clothes" in order to receive all the necessary energy.

### Man – heater

I will quote an article about clothes: at rest the human body generates 80 watts of heat, but loses at the expense of breathing 10 watts, thermal radiation – 30 watts, thermal conductivity and convection – 20 watts, evaporation of moisture – 20 watts.

The person turns out to be an extremely "weak" heater. Home heaters consume 1 kW and they cover heating needs only partially. Heating of water and heating of premises in principle is the largest energy consumption of a household. I will quote my annual report:

– Movement (transport, fuel): 8,000 kWh per year

– Electricity: 2,500 kWh per year.

– Heating water and heating: 30 000 kWh per year.

It turns out for an average daily heating of water and heating goes up to 100 kWh per day, which is 50 times more than people consume in principle.

### A man is a means of transportation (car, pedestrian, bicycle)

Man as an active living entity can move in space. Suppose a person can move 30 km per day on foot and 120 km per day by bike. This is not the maximum values, of course, athletes run up to 100 km and travel up to 1000 km per day.

Let's try to compare a person as an effective system of human movement.

– A car with ICE spends an average of 5 liters per 100 km , 1 liter = 10 kWh, which gives ** 500 Wh per km **

– Electric vehicle – ** 150-200 W * h per km **

– Pedestrian – 2 kWh divided by 10-50 km, ** 50-200 W * h per km **

– Slow / small electric vehicle – ** 50-100 W * h per km **

– Electric bike – ** 10 W * h / km ** (average speed of 10-15 km / h)

– Cyclist – 2 kWh divided by 100-1000 km, ** 2-20 W * h per km **

You know more interesting coincidences – write in the comments.

Thank you for your attention.

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