After the solar collector tube is filled with water, the water temperature begins to rise under the sun's rays, causing the water volume to increase, so that the return pipe returns the water . If the water keeps coming back, it definitely means that the water supply valve is not closed properly (if the sensitivity of the water meter is low, the water return meter will not turn on) - it is recommended to change the water valve.
Whether it is hot or cold water depends on the amount of solar radiation and the duration of the radiation. In short, it is the amount of heat absorbed by the solar water heater. Solar energy is heated. The tube shape is easy to heat and transfers heat to the water, causing the water temperature to rise. There is a distance between the solar water storage location and your faucet outlet, and the water in this section is cold.
The fact that the water is hot ou no depends on whether the sun is shining that day and how long the sun is in the sun. For example, the water temperature in my home's solar system peaks at 86° in the summer, and it gets hot after prolonged exposure to the sun