  Due to increased penetration of renewable resources in the distribution grid,
the distribution system operator (DSO) faces increased challenges to maintain
security and quality of supply. Since, a large proportion of renewables are
intermittent generations, maintaining production and consumption balance of the
electric system is at stake. The DSO needs to procure flexibilities not only
from large resources, but also small-scale resources connected to the LV grid.
Therefore, there is a need to estimate the aggregate flexibility at the
secondary substation available from the LV grids. The flexibility estimation
can only be achieved through monitoring of LV grid and the distributed energy
resources (DERs) connected at the LV level. Moreover, the variability of
intermittent resources affects the flexibility estimation methodology, and the
DSO operation must be robust to the changes in generation or demand outputs.
Furthermore, the up-to-date and accurate model of the LV grid is difficult to
access. This paper demonstrates a methodology of estimating flexibility by
sensitivity coefficients and thus, eliminating the need to have an up-to-date
LV grid model. It further presents a robust optimisation based methodology for
grid operation to address the impact of forecast uncertainties associated with
the variable DER output. The methodologies illustrate the value of grid
monitoring with a monitoring equipment. It has been validated on a real network
of a Swiss DSO with several grid monitoring devices.
