Smoothing of generation variability, i.e. reduction of variance in the aggregate generation is crucial
for grid integration of large-scale wind power plants. Prior studies of smoothing have focused on
geographical smoothing, based on distance. In contrast, we propose a novel concept ‘diurnal
smoothing’ that depends on spatial variations in the timing of seasonal-mean diurnal cycle peak.
Considering the case of India, which experiences a strong diurnal cycle of wind-speed, we show
how spatial heterogeneity in the wind diurnal cycle can be exploited to smooth wind power
variability over and above geographical smoothing. For any given separation distance between
sites, the hourly wind speed correlation is highly variable. Difference in timing of the diurnal cycle
peak is an important factor for explaining this variability and we define smoothing from differently
timed seasonal-mean diurnal cycle as ‘diurnal smoothing’. We show that apart from separation
distance, the diurnal cycle is crucial for correlation among sites separated by 200 km or more with
strong diurnal cycles (amplitude more than approximately 0.5 m s−1
). Thus, diurnal smoothing is
a vital factor in the aggregation of large wind power plants, and grid integration is benefited by
considering (in addition to distance) new wind plant sites with largely separated diurnal cycles,
especially those differing by roughly 12 h. Such diurnal smoothing is relevant for regions across the
world with strong wind speed diurnal cycles. Ultimately grid integration depends on variations in
total wind and solar generation and demand. Hence, their combined effects must be studied.