The characateristics? Incoming radiation should not be reflected, but absorbed. Having the panels black (non glossy) helps greatly. The panels should automatically dumped of water when freezing temperatures are present. So this presents a problem, how can one collect heat in freezing days? Answer: the collector should be covered with a transparent (glass) which does not reflect radiation. Water should not be circulated when the temperature inside the collector is less than water temperature. So what I am suggesting, is that controls be automatic. Finally, the collector should be isolated from cold winds, but pointed directly at the Sun during the day. If possible, it can move with the sun's path, but generally, that is to difficult, so point it at the sun during mid afternoon.
heat gained: Area*solar flux*time
How much water? flow rate*time
ok but what is solar flux and should i assume that time is 24 hours?
You need to look up the solar radiation at that location. Then, look to see how many hours of radiation is supported. In june, one probably can get about 6 hours of effective radiation, but you will find tables for this. No, not 24 hours, you cant get radiation during the night. I have seen tables where solarflux*time is actually tabulized as a product, so you don't have to look up each.
I just found the following: I didn't find any time tables
I still need help
Solar radiation on Earth: As the Sun's energy spreads through space its spectral characteristics do not change because space contains almost no interfering matter. However the energy flux drops monotonically as the square of the distance from the Sun. Thus, when the radiation reaches the outer limit of the Earth's atmosphere, several hundred kilometers over the Earth's surface, the radiative flux is approximately 1360 W/m2