This simple hack save planet :D or maybe your wallet ....
- It is just small round piece of board
- micro USB for delivery power
- 3V regulator
- alligator clip holes for your multimeter to measure curent
- single board with micro usb is CR2016 =1.6mm + adapter is CR2032 = 3.2mm ... EASY ?????I
understand is not like real CR2032 but I believe that help with development battery operated devices.
You'll need to think beyond Joule thief as it isn't practical for that kind of wattage nor that voltage.
I am working on my project, but don't think it would deliver 4W. I am guessing 0.5W (or may be a bit higher) might be a realistic number. I don't have the answer until I try. 0.5V is not an easy voltage to work with as most common parts do not work on that natively.
I know only one chip http://www.analog.com/en/products/power-management/energy-harvesting/ltc3105.html#product-overview
0.5V is very low for everything