Energy harvesting is charging your e-textile circuit with power from the sun, wind, muscle, body, piezo, or even more exotic sources.
In the e-textile world you have either to carry your own batteries or generate your own energy. If you succeed in harvesting energy while performing you save weight and gain independency.
For harvesting to be worthwhile you also have to minimize your energy consumption: the energy which we can get from non conventional sources is not big. But circuits nowadays consume less and less energy and the batteries (needed for storing anyway) are getting more efficient. Or could we even use these ultra capacitors?
To make this subject more clear the different subjects of energy harvesting have been given their own post.
The starting energy harvesting post is:
The rest of this post is the documentation kindly provided by Mika.
Documentation from the Workshop
The workshop was lead by 2 experts, Beam and Becky. They have already posted a lot of information above, so the workshop documentation goes over what we have done and what I (as a participants) took note in the workshop.
The first thing we tried is to hook up piezo element to multimeter and see how much energy it produces. When you tap the piezo element, you see some voltage produced (can go up to 20V!). But if you are careful, you notice it produces – voltage first, and then go to + voltage. Yes, it is producing AC, which is a bit of a problem if you are feeding this into DC circuit.
To avoid this, we inserted one diode to the circuit. This way, we only get the + voltage.. but this means we block the whole negative side voltage, meaning we are throwing away half the energy.
Now, another problem we face is that your energy source (piezo, solar cell.. so on) could produce sadden energy peak that is bigger than what you want to have for your harvesting circuit. You add voltage/current regulator to avoid this situation. The component is called LM317. We used 5kohm potentiometer and 220ohm resister to build the suggested circuit (the last drawing). The resistance over the potentiometer decides the regulating voltage on LM317. 220ohm resister is a protection for the pin.
When I tried this circuit, it looked like it did not work.. but actually it is working. The piezo gives out voltage for very short time, therefor you can not measure it with multimeter (it is too slow). When we hooked this circuit with Oscilloscope, we see the regulated voltage coming out.
Now, the last thing to consider is the MPP (Maximum Power Point). The Power (Watt) is calculated as W=IxV. So, you want to take highest voltage and current point to harvest. Now, as you can see in the above chart, Voltage drops as current goes up. So, you want to find the good valance point between voltage and current, regulate with LM317 to that exact point for harvesting.
You can add more than one energy harvesting devices to one circuit to harvest more energy. When you use solar cells, you connect them in series. If you are using many Piezo elements, you connect them in Parallel.
Beam brought in some funny Chinese gadget to hack. My favorite is the hat that cools your head off with solar energy. Well, if you wear it long, it actually cools your forehead so much that you can get even headache! hm, this can be in fashion next year in Paris?!