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  • Author Author: vsluiter
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The EHG, and why it wouldn't work

vsluiter

I wish I could be more positive in my blog posts, and I think I will be towards the end of this design challenge. However, at this point I meet the REAL challenges of power harvesting; that it isn't as simple as I thought it would be. I recently wrote about my turnaround from harvesting from motion toward harvesting from temperature difference. The thing I had in mind for some time now was the 'Energy Harvesting Gadget' (EHG), which in my mind would be an egg shaped device that would harvest energy from the heat of the water surrounding it to generate energy.

The cool thing would be to use the power of the EFM32 to calculate the time needed to cook an egg, some very interesting formulae are available.

 

Now towards the design, the sketch below shows what I had in mind:

image

 

The peltier element would harvest the energy from the temperature difference between water (rising to 100 degrees Celsius) and the insulating foam which would start out at room temperature. Inside the foam a PCB would be placed that would sense the water temperature, and an EFM32 would be able to calculate the 'hardness' of the egg.

 

Why it won't work

Nice idea, ey? Unfortunately it will not be able to harvest energy for a long time. I started reading a few days ago, and found a great article on the subject of energy harvesting wilt thermo-electric generators - [pdf] from the AHG University in Poland. One of the things I hadn't realized is that Peltier elements are also very good thermal conductors. Which is in a way very logical since they're supposed to be heat pumps, I just hadn't realized it would mess up this application / idea. When you're heating up the water, both sides of the peltier will very soon have the same temperature, and no energy can be harvested anymore. Bummer. Back to the drawing board.

 

What I can do

I'll try to look for a way to use the difference in temperature between inside and outside of the pan. A bit tricky, because the outside air might be hotter if you're using it over a large flame. Back to the drawing board. At least the concept starts settling with me: energy harvesting is a VERY tricky business!

  • in reply to DAB

    I dont't think Peltier is a dead end, I think the way I wanted to use it was not unitable with physics image

     

    I think peltier, solar and vibration are good ways to harvest energy, but at this point in time I see them more as a way to get 'eternal-low-power' at remote sites, than as a way to 'go green'. The amount of materials used for energy harvesting will ecologically only be justifyable for products that are used a long time; COMPACTs idea about powering a remote control is very good, I think, as this will certainly reduce the amount of chemical waiste. Unfortunately I don't think remote control manufacturers will very soon shell out $10 for a harvesting circuit on a $1 remote control....

    Energy harvesting is actually more 'energy scavenging'. You're looking for by-products, otherwise waisted energy. This means that you have to look where process efficiency is low to get a maximum of by-products, and then you have to find a way to reliably 'scavenge' that energy. And now the hardest part for me: think of a useful application of using that energy....

  • Hi Victor,

     

    You just confirmed the reason why alternative energy has not taken over the world.  Its Tuff to do.

     

    I know everyone is wanting to go green and escape from the hydrocarbon fuel cycle, but you just cannot beat them for energy produced for amount of fuel used.

     

    That said, that does not mean that we have exhausted all potential sources of alternative energy.  Having you verified that some sources are dead ends helps others think about what to try next.

     

    Keep up the good work.

    DAB