Please try to check the following papers:

http://www.sci.sdsu.edu/SOCOL/FortranJournalArt.doc

http://www.powerfromthesun.net/Book/chapter05/chapter05.html

http://elth.ucv.ro/fisiere/anale/2006/4_22.pdf

http://www.iitj.ac.in/CSP/material/scan0001.pdf

* You didn't mention which type of solar collector in your question?

you might look at my lecture. you can calculate the temperature by using the equations in the slides

Thanks a lot! I will take a look inside the papers and slides. I will give you feedback.

*I want to use the equation for flat plate collectors and evacuated tube collectors...

you can use utilizability equations to estimate the temperature of solar collector.

kindly do through " solar engineering of thermal processes": Duffie and Beckman - utilizabity of flat plate solar collector. 

you may get some idea regrading  what are the controlling variable in a solar collector and ways to maximize the performance of solar collector.

Most solar collectons available on the market are tested according to ISO standard ISO 9806:2013 Solar energy -- Solar thermal collectors -- Test methods. Such tests provide thermal characteristics of the colector, namely its absorption coefficient a or efficiency at ambient temperature, a heat loss coefficient U and a non-linearity coefficient. Neglecting the latest, the heat flow rate delivered by the collector is the absorbed solar energy a·I (I being the irradiance) minus the heat losses U*(temperature difference between absorber and ambient).

On the other end, this heat flow rate delivered by the collector is the fluid flow rate multiplied by its heat capacity and the temperature difference between input and output. Assuming that the absorber temperature is the average of input and output temperatures, equating the two expression of the heat flow rate delivered by the collector allows getting the absorber temperature, providing that ambient and input temperatures are known, in addition to solar irradiance and collector characteristics.

I also recommend the book of Duffie and Beckman : "Solar energy, thermal processes" edited by John Wiley in 1974, but still valid!