Dear Mehedi

Try this: Article Determination of optimum tilt angles for solar collectors in...

The angle changes with the seasions because the solar radiation also changes. If you want to see the effect of changing on a solar still. see this: Article Seasonal effect on solar distillation in the El-Oued region ...

depends on what tracking you planning to do

optimally it should equal the sun altitude angle at every instance

- annualy it should equal the local latitude

- seasonally there is models that finds the optimum tilt that gives maximum cosine of incidence angle theta for range of months

- daily tilt= latitude- declination angle

There are several formula that you can use through a data sheet (Excel, for example). However I suggest to use a specific software (PVSyst) that can calculate the exact solar path for your location.

Dear Mehedi

Try this: Article Determination of optimum tilt angles for solar collectors in...

The angle changes with the seasions because the solar radiation also changes. If you want to see the effect of changing on a solar still. see this: Article Seasonal effect on solar distillation in the El-Oued region ...

dear sir,

i attached a file may be it is useful answer for your question about how to calculate the tilt angle.