  We report the observations of the clear sky fraction at the Concordia station
during winter 2006, and derive from it the duty cycle for astronomical
observations. Performance in duty cycle and observation duration promotes Dome
C for efficient asteroseismic observations. This performance is analyzed and
compared to network observation. For network observations, simulations were run
considering the helioseismic network GONG as a reference. Observations with 1
site in Antarctica provide performance similar or better than with a 6-site
network, since the duty cycle limited by meteorology is as high as 92%. On
bright targets, a 100-day long time series with a duty cycle about 87% can be
observed, what network observation cannot.
