Based on the difference between local latitude and the latitude of the sun's direct point, the best angle for local direct sun is the winter solstice, when the sun hits the Tropic of Capricorn directly at 23 degrees 26 minutes latitude south< /p>
The latitude of Hefei is 39.9N, so the angle between the solar water heater and the ground should be 39.9 degrees - 23.26 degrees = 16.64 degrees p>
I hope to adopt it