While having so much valuable answers to my question I have also done some further research about the topic. I have found an additional harvesting solution and also a great reference design about a wireless, solar energy powered sensor node, without using a battery. ---------- First the additional method from Texas Instruments, which is called [RF switch harvesting technique][1]. (The video is worth watching, the RF switch part starts at 2:29.) It is based on a magnetic switch which structure can be seen on the image below. [![enter image description here][2]][2] > On the drawing here in the red is the switch part the user will push. We have a magnet inside with the two poles. And this is creating a magnet field through this core back to the other pole. >When the user flips the switch, you can see the field changes. It goes the opposite direction through the core. And we know from Maxwell's equations that this change in magnetic field through these windings will produce a current. This is energy that we can harvest and make use of. The switch produces an AC current that needs to be converted to DC current which can charge a capacitor. Then the energy stored in the capacitor can be used to power a low-power wireless MCU. [![enter image description here][3]][3] TI has actually realized this and they were able to supply enough energy for 21 milliseconds for the wireless MCU. [![enter image description here][4]][4] ---------- The reference design is a [Solar Dice][5] which can wirelessly transmit an accelerometer's data to a smartphone. The solution does not use a battery and quite compact. Worth reading or browsing the provided [test data][6], schematics and other documents. [1]: https://training.ti.com/how-harvest-energy-nano-power-dcdc-solutions [2]: https://i.sstatic.net/MqMn7.png [3]: https://i.sstatic.net/ifkSU.png [4]: https://i.sstatic.net/qjnTb.jpg [5]: http://www.ti.com/tool/PMP9754#Technical%20Documents [6]: http://www.ti.com/lit/ug/tidu369/tidu369.pdf