  Electric field measurements of the Time Domain Sampler (TDS) receiver, a part
of the Radio and Plasma Waves (RPW) instrument on-board Solar Orbiter, often
exhibit very intense broadband wave emissions at frequencies below 20~kHz in
the spacecraft frame. During the first year of the mission, the RPW/TDS
instrument has been operating from the first perihelion in mid-June 2020 and
through the first flyby of Venus in late December 2020. In this paper, a
year-long study of electrostatic fluctuations observed in the solar wind at an
interval of heliocentric distances from 0.5 to 1~AU is shown. The on-board
processed properties of waveform snapshots that are continuously collected
allow mapping plasma waves at frequencies between 200~Hz and 20~kHz. For a
detailed spectral and polarization analysis, the triggered waveform snapshots
and a Doppler-shifted solution of the dispersion relation for wave mode
identification were used. The occurrence rate of low-frequency waves peaks
around perihelion at distances of 0.5~AU and decreases with increasing
distances, with only a few waves detected per day at 0.9~AU. A more detailed
analysis of more than ten thousand triggered waveform snapshots shows the
median wave frequency at about 2.3~kHz and wave amplitude about 1.1~mV/m. The
relative phase distribution between two components of E-field projected in the
Y-Z Spacecraft Reference Frame (SRF) plane shows a mostly linear wave
polarization. Electric field fluctuations are closely aligned with the
directions of the ambient field lines. The observed waves are interpreted as
the strongly Doppler-shifted electrostatic ion-acoustic mode generated by the
resonant interaction with ion beams or by the current-driven instability.
