8.5 Resolution of solar data
Integration studies for high penetration scenarios of solar will require projections of variability from a large amount of solar power generation for both distributed and large utility-scale solar plants. Currently, solar data is only available with low time resolution. In Australia, very limited detailed solar information is available to study the impacts of solar intermittency on the stability of the grid. Solar data covering a large spatial extent is available from satellite data, which has an issue of compounding errors, and very limited data can be obtained from ground stations. The only source of long-term insolation data is the Bureau of Meteorology (BOM) which provides daily averages, but this source is currently being phased out as more reliance is being given to satellite data. Global insolation data from the BOM has 7% mean bias error on sunny days and 20% on cloudy days. The Department of Resources, Energy and Tourism (RET) reported they are currently working on improving the satellite system capability to obtain 10-second solar data.
A number of key industry experts stated that much higher resolution solar data than is currently available is needed to study the impacts of solar variability on the stability of the grid. High resolution solar data from both large numbers of small-scale solar systems aggregated and large-scale solar systems is required to investigate the effects of a range of temporal variances on the Australian electricity network. The impacts of intermittency are very different at different locations in the grid and utilities expressed a major concern over the rural edge of network scenario.
It was widely claimed that solar data resolution of sub-second to ten seconds is required to investigate power quality issues and to study the dynamic response of the power system to solar intermittency. Sudden shadows due to passing clouds appear to produce more rapid flicker than sudden wind changes. The time it takes for a passing cloud to shade an entire solar system depends on the size of the installation, cloud speed, cloud height, and other factors. Different intermittency time-scales are associated with different impacts, management strategies and costs. General issues important for different time scales when operating power systems with intermittent generation, as reported by industry experts are:
- dynamic response of the system, power quality (e.g. voltage flicker), frequency stability - sub-second to 10 seconds
- market specific ancillary service product - seconds to five minutes
- load following - minutes to hours
- generation dispatch - beyond five minutes.
Due to the lack of inertia in most solar power systems, industry experts agreed that the higher ramp rates of solar systems, compared to other renewable generation, is a major concern. Information on different ramp rates and time-frames of intermittency is necessary to determine how quicklysystems have to respond. In order to determine both the ramp up and ramp down rates of solar systems, solar data with high resolution is required for both small-scale and large-scale solar installations. High resolution data, at least 1-second data, is also required to investigate how often solar output will significantly impact the grid for any given plant and location.