With 3 bottle caps and a few drops of hand sanitizer in each one (65% ethyl alcohol). An altoids tin filled with slush was used as the cooler. Peak output was 3.8V @ ~550mA for a total of 2.09 watts. All that from about 12 drops of hand sanitizer. This peak output only lasted approximately 10 seconds, but more nominal outputs of 2.5V @ ~300mA could probably be sustained for longer. The goal here is to use something that burns longer than a bottle cap of ethyl alcohol in combination with a DC/DC booster to smooth the output to 5VDC. If I can get it to run long enough, I can conceivably use it to charge USB devices.
I think it will also work better with a bigger cooler than an altoids tin. At the temperatures involved, the amount of water in a tin that size is going to heat up way too fast.I’m also considering some kind of passive radiator.