In the past few years, the Sudbury Neutrino Observatory has demonstrated that the total active flux of neutrinos observed is consistent with the standard solar model prediction although there is a suppression in the number of electron neutrinos observed from the sun. The Mikheev-Smirnov-Wolfenstein model, which is used to describe the observed electron neutrino suppression, also predicts a distortion in the neutrino energy spectrum and/or a difference in electron neutrino survival probability day versus night. Neither of these outcomes has been observed. Additionally, certain models of non-standard interactions also predict a distortion of the neutrino energy spectrum. This talk discusses the physics potential of a spectral measurement to test these predictions and focuses on the experimental challenge of lowering the analysis energy threshold in SNO in order to be more sensitive to observing spectral distortions.