S_eff(E) and the 7Be(p,gamma)8B reaction

We explore approximations to the effective $S$ factor for the $^7Be(p,\gamma)^8B$ reaction using different approximation for the integral over the Gamov peak. In the temperature range of interest for solar neutrino production, $S_{eff}(E)$ may be determined to within 0.5% from S(20) with no direct information on the derivatives of S(E).