9.5 Comparison of ramp events for 196kW and 22kW PV system

Variations in output power of the 196kW PV plant at DKASC and the 22kW PV installation at CSIRO Energy Centre were compared for various timescales. Note that the data from DKASC was for a one-year period whereas only two weeks of data was able to be analysed for the 22kW PV system. The plots in Figure 129 show percentage variations in output power of the two PV plants over 10-second periods. The graphs with the blue bars represent the 196kW DKASC system while the ones with the green bars represent the 22kW CSIRO PV system. A similar trend can be seen for the variations in both the plants and the number of variations with higher ramp rates is significantly higher for the 22kW PV system considering the difference in the duration for which data was available for the two plants, i.e. two weeks for the CSIRO system versus a year for the DKASC system. The time it takes for a cloud cover spread to shade a smaller PV plant is smaller than for a larger PV plant, and therefore more rapid variations in output power with larger magnitude are more likely to occur in the 22kW plant compared with the 196kW plant.

Figure 129 Comparison of output power 10-second ramp events for 196kW and 22kW PV system

Similar comparisons were made for 20-second and 50-second periods, results of which are shown in Figure 130 and Figure 131 respectively. It can be seen that both PV systems experience high ramp rate events over short timeframes. The rate of occurrence of high ramp rate events is significantly higher for the 22kW PV system, as it is more likely that a larger proportion of the smaller PV plant will be shaded by a cloud cover spread than the larger 196kW PV system at DKASC. It is also more likely that the PV system at CSIRO’s coastal location will be shaded by intermittent clouds than the inland system at DKASC. Ramp events for the UQ 1.22MV PV plant were not included in this comparison study as high-resolution data below 1-minute was not available.

Figure 131 Comparison of output power 50-second ramp events for 196kW and 22kW PV system