  The XENON1T collaboration reported an excess of the low-energy electron
recoil events between 1 and 7 keV. We explore the possibility to explain such
an anomaly by the MeV-scale dark matter (DM) heated by the interior of the Sun
due to the same DM-electron interaction as in the detector. The kinetic
energies of heated DM particles can reach a few keV, and can potentially
account for the excess signals detected by XENON1T. We study different form
factors of the DM-electron interactions, $F(q)\propto q^i$ with $i=0,1,2$ and
$q$ being the momentum exchange, and find that for all these cases the
inclusion of the Sun-heated DM component improves the fit to the XENON1T data.
The inferred DM-electron scattering cross section (at $q=\alpha m_e$ where
$\alpha$ is the fine structure constant and $m_e$ is electron mass) is from
$\sim 10^{-38}$~cm$^2$ (for $i=0$) to $\sim 10^{-42}$~cm$^2$ (for $i=2$). We
also derive constraints on the DM-electron cross sections for different form
factors, which are stronger than previous results with similar assumptions. We
emphasize that the Sun-heated DM scenario relies on the minimum assumption on
DM models, which serves as a general explanation of the XENON1T anomaly via
DM-electron interaction. The spectrum of the Sun-heated DM is typically soft
comparing to other boosted DM, so the small recoil events are expected to be
abundant in this scenario. More sensitive direct detection experiments with
lower thresholds can possibly distinguish this scenario with other boosted DM
models or solar axion models.
