24 Mar / Bio-mechanical energy for powering products:
The energy generators/harvesters using the human bio-mechanical energy are a common and recurrent idea when thinking in a new product development. One should consider the human body limitations in order to do a feasible and a realistic design.
The rules of the energy: there is no such thing as a free lunch:
One of the most important branch on physics is the thermodynamics, and the first law says something like:
“The amount of energy that you get from a system is never more than the energy that you put previously on it.”
And not only that, but you always get less, as the efficiency is never perfect. So the first step is to forget about any system that can generate extra energy, like the “over unity”, “perpetual movement”, “free energy”, etc, technologies. As you probably know already, that simply will not work.
Energy always comes with a price, If for instance you have a device that gets energy from a walking person, this person will need to make more effort and therefore will need to eat more food(energy).
Usually the key is to harvest what it’s called the negative energy, as for example the regenerative brakes in the trucks, it gathers the energy when breaking, as otherwise that energy will be dissipated in heat, better to gather it with a dynamo.
The human body as an energy generator:
Every way to generate(read transform) energy from one state to another has it’s own capabilities, let’s see how much energy can generate different parts of the body:
- Breathing exhalation 1W
- Blood pressure 0.93 W
- Keyboard typing around 19 mW.
- Foot pedal 40 W.
- Crank hand 7 W.
Doing some calculations:
Let’s consider the Crank hand device(that generates 7W turning the crank 2 times in a second), connected to a USB(5V) that powers a battery of 3000mAh on a mobile phone. The user does the following task:
- 5 minutes moving the mechanism, 10 minutes resting.
- Repeats the previously step 4 times(1 hour in total)
- The total energy generated by the user is: 2.3 W in one hour.
- The energy needed for charging the battery completely is around 3Ah*5V = 15W per hour
So the user has to perform that task for around 6 hours and a half to charge the phone completely.
If you are thinking on using bio-mechanical energy *for* or *as* a product, you must consider the energetic limitations of the human body. A hand crank might be good for emergencies but it’s hard to use for the daily life.
Doubt from any product or idea that generates a reasonable amount of energy with no effort. There is a growing number of devices such as micro-controllers and sensors that are able to process information using small amounts of energy. Those devices can implement energetic schedules for keeping the consumption as low as possible, and only using power when it’s really need it. Are you thinking on using bio-mechanical energy harvesting for a product?
Then go for low power conpsumption!!