Hello All! This is my 'grande finale' post in the Energy Harvesting Solutions Roadtest Challenge! It's been a nice challenge, with a lot of technical, well, ehm... challenges!
First, I'd like to element14 for organizing this challenge. After that, I'd like to thank Wuerth both for the Energy Harvesting Solutions To Go kit, and for helping me to get a PCB in time, and of course Linear Technology (how do you get a converter started at 50mV?) and EnergyMicro (thanks for the great documentation, and your very clear goal of making each microjoule count). It's been really nice to have a go at energy harvesting with you!
Another thank you goes out to Compact and Gelmi. The 'challenge' started out with 7 elected participants, for whatever reasons it's only you guys that stuck to it until the end. Every time a new blog post came out I was full of anticipation what you had come up with this time. Thanks for the shared enthousiasm!
At the start of this challenge, I was a bit overoptimistic on the possibilities of energy harvesting. I thought I could make a LED light out of the vibration of a bike, which wasn't possible because piezos give microwatts, not milliwatts. Then I thought of a submersible peltier harvester, where I had forgotten that a TEG element has a very low thermal resistance, and thus needs to be in a path of constant heat flow. When I had my prototype running I was very happy with the result. Getting that design on a self-designed PCB posed a new problem, that the amount of energy at the start of a harvesting process is quite low, and special precautions have to be taken to get the complete design going. All in all, designing a harvesting solution is not something that can be done in an afternoon while having a drink with your friends. On the other hand it's not that impossible either; now that I have got a working harvesting product, I can see how much energy is available from a pan with heated water (my application runs an hour after I've put the fire down). It makes me realize how much energy is wasted by throwing away boiling water, or showering. Will we -one day- have battery chargers in our house that run off wasted energy? I don't know...
One thing I've learned is that when designing a harvesting application, you have to take a lot of factors into account. How much energy is available? How long is that energy available? With what efficiency can you harvest it? How long will it take to start up, and how fast will you drain energy you've harvested before? A complete product has to take into account both the power source, the power consumption, and the expected usage by the 'end-user'.
The products in this RoadTest Challenge help enormously in these designs; we've seen the efficient WE-EHPI transformers, the Linear converters (storing excess energy as backup as built-in feature for the LTC3108, and the LTC3105 that makes it possible to match the impedance of your converter to your source...) and the GiantGecko that has power saving in every peripheral in an architecture made for low power.
In my presentation I've mentioned that this design uses digital technology where analog couldn't have done it with less power. This is mostly due to the power of doing a complex calculation at a very high speed, and going into a deep sleep using almost zero energy after that. Possibly, the sensing part of an application could be done in analog electronics. But the lower the sample rate (i.e. the processor can stay 'off' longer), the better the microcontroller will compare. And that's only the sensing. With only a few milliwatt I've got an LCD running, and I'm doing exponential operations on floating points! Coming from a background where float operations take lots of milliseconds and microcontrollers use at least 10-20mA, I had great fun in seeing that this was possible at all.
To me, this is exciting technology. Especially now that energy storage is getting cheaper, remote sensing networks are being deployed more and more, and new materials are developed (electro-active polymers, better solar cells,...) this could take a flight. Let's hope that long-term visions on economy, sustainability and (consumer)electronics will gradually change the way we think about using and yielding energy.
We're getting ready for a future of harvesting!