  Battery energy storage systems can be integrated with photovoltaic
(PV)-diesel microgrids, as an enabling technology to increase the penetration
of PV systems and aid microgrid stability by smoothing out the power
fluctuations of the PV systems. The aim of this paper is to derive correlations
between the optimal capacity of the smoothing batteries and variabilities in
daily solar irradiance. Two commonly used smoothing techniques of moving
average and ramp rate control are applied on a real solar irradiance dataset
with a 1-minute resolution for a full calendar year across 11 sites in
Australia. The paper then presents the developed empirical model, based on
linear regressions, to estimate the optimal capacity of the batteries without
requiring the use of detailed simulation studies. The performance of the
developed technique is validated by numerical simulation studies in MATLAB. The
study demonstrates that the empirical model provided reasonably accurate
estimates when using the moving average smoothing technique, but had limited
accuracy under the ramp rate control technique.
