Importance of efficient heat transfer in straight solar energy collectors, where solar energy is converted into useable heat energy, has been ever increasing with demanding solar energy applications. In this study, thermal analysis of the absorber plate, where solar radiation energy is transferred to tie fluid carrying heat in the straight solar collector, have been performed. In the analytical formulation developed, the absorber plate has been treated as a one-dimensional fin. Radiation flux coming from the sun and heat loss to the environment are defined at the upper face of the absorber plate while the lower face is assumed to be ideally insulated. By solving the fin heat transfer equations analytically, relations giving temperature distribution on the absorber plate and heat transfer from the absorber plate to the working fluid have been derived. Effective parameters on temperature distribution and heat transfer are mainly: geometrical dimensions, fluid temperature, heat conduction coefficient of the absorber plate, radiation heat flux, environmental temperature, and total heat loss coefficient to the environment. Effects of these parameters are methodically investigated. One of the investigation results is that the absorber plate with high heat conduction coefficient yields increased temperature level and heat flux transferred to the working fluid. The achievable maximum fluid temperature at the practical working conditions, which quantifies the availability of useable heat energy obtained in the collector, has been determined as a function of incident solar radiation. Effects of the parameters dominating the collector efficiency have been investigated by evaluating all the analysis results.