For this insight analysis, a statistically average day of hourly production for renewables in South Africa across all years (April 2012 – July 2017) and provinces was compiled. Furthermore, seasonal variations in hourly production were analysed.
While the interactive dashboard available on REDIS holds data for all renewables (wind, PV, CSP, hydro, biomass, landfill gas), the analysis here focuses on wind power and PV with and without tracking.
Average day of hourly production
The figure above illustrates that wind power output is relatively stable throughout an average day, observing a peak around 17:00-19:00 (5pm-7pm). The wind production peak correlates fairly well with the demand peak, which appears around 19:00 (7pm) in winter and 20:00 (8pm) in summer according to data from Eskom [Eskom, 2014].
In REDIS Update #3, it was shown that the average load factor for PV with single-axis tracking is 19% higher than the load factor for PV without tracking. However, when analysing the hourly variations, it is found that PV without tracking is performing 6% better than PV with single-axis tracking in the 3-hour period between 11:00 and 14:00 (11am - 2pm).
As illustrated above, PV with single-axis tracking produces more electricity than PV without tracking from 5:00 – 11:00 (5am – 11am) and again from 14:00 – 19:00 (2pm – 7pm). While this results in a higher overall load factor for PV with single-axis tracking, the load factor in the middle of the day is actually higher for PV without tracking.
In order to understand this phenomenon, it is necessary to understand that:
1. The performance of PV depends on the angle of incidence – the lower the angle, the higher the performance, and
2. That majority of PV installations with single-axis tracking in South Africa are so-called horizontal single-axis systems, which tracks the sun from east to west. An illustration of PV tracking systems is included in the notes below.
A horizontal single-axis system tracking from east to west is gradually tilting the panel to minimize the angle of incidence. However, at mid-day, the horizontal single-axis PV panel is horizontal to the ground. This results in a higher angle of incidence, and thus lower production, than that of a PV panel without tracking, which is fixed tilted north towards the sun.
A tilted single-axis tracking system would be able to match the fixed tilted PV without tracking at mid-day. However, tilted single-axis tracking systems are more expensive than horizontal single-axis tracking systems, mainly as they cast more shadow and therefore require more land-use.
Significant seasonal variations are observed. For example, while wind power output is virtually constant on an average winter day, the afternoon peak is double than that of the morning output on an average summer day.