Standard analyses of solar collector thermal performance are based upon an energy balance in which the environments adjoining the front and rear of the collector are assumed to be at the same temperature. This assumption is inappropriate for some collector designs, particularly building-integrated collectors. An approach for analyzing such situations is presented based upon a new conceptual temperature termed the "equivalent ambient temperature." The concept is explained, the new temperature is defined, and the approach is applied to a typical collector geometry. The approach retains the convenience of the standard analysis while accounting for the unequal front/rear ambient temperatures and permits collector characterization in terms of the conventional parameters: plate efficiency factor, F' ; heat removal factor F-R; overall heat loss coefficient, U-L, and effective transmittance-absorptance product, (taualpha)(e).