  Production of dark photons inside the Sun forms the basis for the most
sensitive probes of such particles over a wide mass range. A small fraction of
dark photons is emitted into gravitationally bound orbits, building up a "Solar
basin" population that survives for astrophysically long times. We show that
this population could lead to signals in existing and proposed dark matter
detection experiments, opening up significant new parameter space independent
of whether dark photons make up the dark matter. Even with conservative
assumptions, results from current dark matter experiments already constrain new
parameter space; with fiducial assumptions, a Solar basin population of dark
photons could be responsible for excess events seen in XENON1T. Future
low-threshold experiments could be sensitive to these Solar-System-bound dark
photons down to sub-eV masses, at couplings orders of magnitude below current
constraints.
