4.4 Summary

Power output from both solar and wind generating sources are known to vary considerably with varying irradiance and wind speeds, respectively. Studies have shown the repeating daily production profile of solar generation correlates better with load and can be considered far more deterministic than wind generation. This reduced randomness in solar generation in comparison with wind should result in a reduced impact on the complexity of scheduling dispatchable generation.

Analysis of results illustrated in the studies carried out on wind and solar variability indicates that the output of individual wind turbines is similarly variable in nature in the second-to-second timeframe to individual solar arrays. When wind and solar output are taken in aggregate and analysed at time intervals of 1-minute to 10-minute, wind seems to benefit more from the smoothing effect associated with aggregation, showing less variability than solar. When behaviour is observed at 1-hour intervals, again in aggregate, wind is shown to be more variable. A Swedish study observed that the correlation between wind sites decreases with distance at a greater rate than for solar, suggesting the smoothing effect due to aggregation will be greater for wind than solar. It should be noted that the level of variability is highly dependent upon the number of sites and spatial diversity of the solar and wind sites.