  Extreme precision radial velocity (EPRV) measurements contend with internal
noise (instrumental systematics) and external noise (intrinsic stellar
variability) on the road to 10 cm/s "exo-Earth" sensitivity. Both of these
noise sources are well-probed using "Sun-as-a-star" RVs and cross-instrument
comparisons. We built the Solar Calibrator (SoCal), an autonomous system that
feeds stable, disc-integrated sunlight to the recently commissioned Keck Planet
Finder (KPF) at the W. M. Keck Observatory. With SoCal, KPF acquires
signal-to-noise ~1200, R = ~98,000 optical (445--870 nm) spectra of the Sun in
5~sec exposures at unprecedented cadence for an EPRV facility using KPF's fast
readout mode (<16 sec between exposures). Daily autonomous operation is
achieved by defining an operations loop using state machine logic. Data
affected by clouds are automatically flagged using a reliable quality control
metric derived from simultaneous irradiance measurements. Comparing solar data
across the growing global network of EPRV spectrographs with solar feeds will
allow EPRV teams to disentangle internal and external noise sources and
benchmark spectrograph performance. To facilitate this, all SoCal data products
are immediately available to the public on the Keck Observatory Archive. We
compared SoCal RVs to contemporaneous RVs from NEID, the only other immediately
public EPRV solar dataset. We find agreement at the 30-40 cm/s level on
timescales of several hours, which is comparable to the combined photon-limited
precision. Data from SoCal were also used to assess a detector problem and
wavelength calibration inaccuracies associated with KPF during early
operations. Long-term SoCal operations will collect upwards of 1,000 solar
spectra per six-hour day using KPF's fast readout mode, enabling stellar
activity studies at high signal-to-noise on our nearest solar-type star.
