Hi!

Now I need to solve a flat solar water heater. For solving it I use only solar radiation from general settings without other heat sources.

Model of flat heater construction from figure. My collector composed of 5 parts: pipes (brown), two collectors (brass), absorber (blue), case and glass wool isolation. Transparent screens didn`t use because Flow Simulation doesn't have a special glass used in solar collectors.

Task is time-dependent, 10 hours with time step 60 seconds. Scenario of starting it at 9 AM and work to evening.

The result of solving is the delta of temperature between in and out of the water, which is equal to 25-30 degrees. This so lit I think for a heater with a 0.73 m2 work area.

I choose radiative surfaces respectively for absorber, case and collectors. Brass in solid materials using for collectors because cooper is default material. Default temperature for water - 20 degrees. Consumption of water - 30 liters per hour. 

Where I did a mistake in this solution or all right?