We show that the Deep Underground Neutrino Experiment (DUNE), with significant but feasible new efforts, has the potential to deliver world-leading results in solar neutrinos. With a $100\mathrm{kton}\text{−}\mathrm{yr}$ exposure, DUNE could detect $\gtrsim {10}^5$ signal events above 5 MeV electron energy. Separate precision measurements of neutrino-mixing parameters and the ${}^{8}B$ flux could be made using two detection channels (${\nu }_e+{}^{40}\mathrm{Ar}$ and ${\nu }_{e,\mu ,\tau }+e^{-}$) and the day-night effect ($>10\sigma$). New particle physics may be revealed through the comparison of solar neutrinos (with matter effects) and reactor neutrinos (without), which is discrepant by $\sim 2\sigma$ (and could become $5.6\sigma$). New astrophysics may be revealed through the most precise measurement of the ${}^{8}B$ flux (to 2.5%) and the first detection of the hep flux (to 11%). DUNE is required: No other experiment, even proposed, has been shown capable of fully realizing these discovery opportunities.