Brass body solar system heating

Working principle:
Solar vacuum tube was evacuated into the tank, the coating inside of tube can absorb more than 92% heat energy from sunshine.
The cold water in water tank flows into the tube and become hot, because of different density between cold and hot, there will be a natural circulation in the tube. Hot water will float back to tank.
The polyurethane heat insulation layer can keep the water warm about 2 days without any sunshine.
Consumer can enjoy comfortable bathe anytime.