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• Condensed script of the video:
Today we are gonna make experiments with human power. Our goal, will be to produce as much power as possible by ourselves. We will first try our set up which transforms a regular bike into a generator, then we will give you interesting information about human power.

The most difficult point is to link the generator to the bike’s wheel, we use a scooter wheel held to a wooden mount. The torque, that means rotational force, is transferred with screws till the motor sprocket. By adjusting wisely the pressure between the bike and the scooter’s wheels, it’s possible to communicate power with a reasonable efficiency. The size of the scooter wheel has been chosen so that a normal cycling cadence makes the generator revving around it’s rated value.

We sit on the bike and go for a voltage measurement without any load.
We reach easily 36V, the rated voltage of the motor, it’s then possible to reach up to 50V. Ok for the voltage, but power is voltage times current, and for now the current is 0 as there is no load, so no useful power is produced in this test. That’s also why we don't feel any resistance from the pedals.
Now we’re gonna try 21W car light bulbs, and to get straight to the point, we’re gonna start directly with 9 bulbs, in a 3 series times 3 parallel layout.
When the voltage will exceed 36V, the power will be at least 189W.
It’s a success, and it's not even difficult.

We managed to produce up to 555W but can we produce more? This power corresponds to the output power of the generator, but from the pedals to the resistor there are many losses, in the bike’s mechanics, between the scooter and the bike’s wheels and finally in the generator. The loss in the generator can be calculated precisely. Its efficiency is 80% in our test, it means the mechanical energy at the motor shaft is around 700W.

It's more difficult to estimate other losses but they are not negligible, we estimate that the mechanical power on the pedals close to 900W. More recently, we managed to produce up to 750W with another simpler set up. It’s based on an efficient 1000W brushless hub motor. The overall efficiency is also better thanks to a direct mechanical transmission. The power on the pedals is again around 900W but we retrieve more of it. The energy is stored in li-ion cells, and it is possible to look for the most suitable cycling cadence by shifting the number of cells in series.

Here is simple test to estimate the maximum power we can deliver. This consists of climbing a precise height as quickly as possible. Overcoming gravity consumes energy, that can be released downhill. By measuring his weight and the duration of the climb, it’s possible to calculate the power, in our test it’s at least 1075W.

Of course, it’s impossible to hold this tremendous effort a long time, our muscle stock of ATP, which allows us to make an intense effort at any time, runs out quickly, and slower metabolisms are used over time. A healthy person can go up to 1000W during seconds, but for one hour, the maximum is around 250W.

For an 8 hours working day, it would be something like 125W only. It makes only 1 kWh of energy per working day. Doing this work as a job for an entire month would pay off less than 3 bucks of electricity. Even if it would be enough to supply many low consumption devices, the overall consumption of these devices can be insignificant compared to just one high consumption device.

Now a question, is human energy environmentally friendly? It’s possible to compare our body to an engine. For instance, we can simplify our metabolism by the combustion of sugar and the petrol engine chemistry by the combustion of the isooctane hydrocarbon. Both reactions only release water vapor and carbon dioxide, the famous “CO2”. If we limit our environmental study to CO2 only, responsible for global warming, the amount of work released by unit of CO2 emitted is twice as more with the engine. Clearly, in this aspect, the petrol engine is the winner, but an average car engine is 500 times more powerful than its driver continuous power capability. The best aspect of human power is not its energy or CO2 efficiency, but it’s sobriety. Sport is necessary for the balance of the human body and using its own energy for an useful purpose is always a plus.

Another major point is the origin of the chemical energy. Oil comes from the lithosphere whereas the food we eat comes from the biosphere.
The carbon cycle in the biosphere is quick and well balanced, the CO2 emitted by an human has been captured and will be captured by food plants.The CO2 emitted by the combustion of hydrocarbons found in the lithosphere is highly unbalanced, with current rates, only 5% of the carbon returns to the lithosphere so 95% of current emissions will remain in the atmosphere as long as nothing is done to change that.

Thanks for watching!