Bitaxes powered by solar is the only use case for bitaxes in my opinion. Thats because they have the lowest power requirements. Otherwise I would suggest an s9 which gives out heat as a byproduct but will require more energy to run. That being said if you are looking for a return you are better just buying. Bitaxes and s9s only really serve the hobbyist. Pointing that minuscule amount of hash to a pool is only going to yield you ≈ 40 sats a day so you mine as well yolo to ckpool