Why is there steam in the solar bucket?

This steam is really not caused by the temperature difference between inside and outside.

There is an insulating layer between the liner and the outer shell of the water tank. This insulating layer is quite good in industry, so the steam should be ejected from the exhaust or overflow hole of the water tank. . When steam encounters condensation may drip onto the outer body of the water tank.

The water temperature in the water tank is high. In summer, the ambient temperature is relatively high and usually no vapor is visible, just like breathing. However, in winter, the ambient temperature is relatively low. and when the solar water temperature is high, steam appears.

Or please ask.