8.4 Large-scale versus small-scale solar systems

Respondents indicated the need to investigate the impacts of large numbers of small-scale solar systems in the distribution network and large-scale solar systems in the transmission network separately. Large-scale solar systems are often located in remote areas, where the environmental conditions are noticeably different from urban areas in Australia, where majority of the small-scale solar systems are located. The urban areas are located in coastal regions of the country where cloud movements are more prominent and the grid is also relatively stronger than in remote areas, meaning the impacts on the electricity network are likely to be different. Small-scale solar systems are also more inverter operation dependent. Therefore, it was emphasised that the impacts of small-scale and large-scale solar systems need to be studied separately.

The likely impacts of intermittency from large-scale solar systems listed by workshop participants include:

  • larger system voltage and frequency variations mainly due to their location being remote areas with relatively weaker grids
  • high electricity price volatility due to uncertainty
  • increased uncertainty in the operational position of the conventional plant in the system which might lead to increased frequency variations if the additional control duty is not provided
  • increased need for the quantity of ancillary services
  • the need for reactive power considerations to maintain stability due to transients in the section of the power system
  • network security is also a critical factor in the successful implementation of large-scale intermittent renewables as they create higher levels of uncertainty. Energy supply is an essential service, which if denied leads to societal breakdown.

These impacts are important as they affect the viable penetration levels of solar systems. Displacement of conventional plant by highly variable solar/wind plant output has the potential to create load-generation imbalances, leading to frequency and voltage excursions. The extent of the impacts of intermittency from large-scale solar systems is not known at present, and more data and research are required to get a better idea. Accurate predictive tools will also help to minimise the impacts of intermittency from large-scale solar systems on the electricity network.

The likely impacts on the electricity network due to intermittency from small-scale solar systems are expected to be more localised. They include:

  • voltage and power fluctuations in close proximity to connection points of the solar systems
  • adverse power quality which has the potential of causing equipment failure
  • shutdown of inverters as a result of poor voltage regulation if not controlled
  • impact on spinning reserve to maintain frequency.

These impacts are important and need to be addressed, as they will limit the penetration of small-scale solar (mainly PV) systems. Small-scale solar systems are mainly inverter-operation dependent and the limited controllability and protection capability of existing inverters might not be sufficient to help mitigate the adverse impacts of intermittency on the electricity network.

Workshop participants believed aggregation of many small-scale solar systems will not only reduce variability but allow for better/smarter control to provide a dispatchable energy source. This allows the renewable source to be offered to energy markets, and either used for ancillary services, or matched with controllable loads to cancel out the variable energy source in terms of overall system impact. This will require forecasting tool improvements and good data collection on the penetration and performance from the distribution businesses.