The large-scale solar industry is still relatively new in Australia, with only a handful of installations online, most notably the Nyngan (102 MW), Moree (56 MW), and Broken Hill (53 MW) solar farms. Many more utility-scale solar systems have been approved, and an indication of the boom to come is ARENA‘s release of 22 large-scale solar projects invited to apply for ARENA funding.
The existing large-scale solar proposals will form part of the solar development Australia sees in the short term, as the major energy players clamber to meet the Renewable Energy Target requirement by 2020. Failure to meet this target will attract a penalty, which will then be passed onto energy consumers as an increase in electricity price.
The expansion of large-scale PV systems across Australia will create a resource demand for the construction, operation and maintenance of these sites. To respond to this demand, the solar industry needs to develop a sound understanding of what utility solar entails.
Utility-scale solar PV systems differ from residential and commercial systems not only in scale, but also in the additional monitoring and control components on site. Operation and maintenance is a focus of large-scale PV systems: any downtime or loss in power production is associated with potential financial losses incurred as the system’s operation fails to capture high energy price events on the National Electricity Market (NEM), or fails to meet the requirements of a Power Purchase Agreement.
Utility-scale PV plants can be broadly divided into two components: the power generation component and the monitoring and control component. The power generation component consists of solar PV modules connected in series and parallel combinations. The monitoring and control component contains monitoring equipment, the Supervisory Control and Data Acquisition (SCADA) system, as well as a power plant controller. This component monitors commands from the control centre or grid operator and operates the plant equipment appropriately based on monitored data.
In addition, the system may also incorporate energy storage devices (e.g. batteries) and/or power generating sources (e.g. fuel, wind, hydropower) to form a hybrid system with backup supply.
Operation and maintenance procedure
Utility-scale PV system owners will often contract the services of an O&M specialist, whose roles may include normal operational procedures, executing the maintenance program, maintaining security around the site, overseeing the environmental protection plan, and other responsibilities as required by the system owner.
The maintenance actions carried out at a utility-scale system can be divided into preventative maintenance, corrective maintenance, or condition based maintenance.
Preventative maintenance includes scheduled activities carried out to prevent system equipment impacts and failures that may lead to reduction in performance and loss of revenue. Actions which fall under this category include vegetation management, regular checking of balance of system components, checking arrays for hotspots and anomalies, and inverter inspections.
Corrective maintenance is performed in the event of failures within the system. The speed of response and duration of repair will be determined by the problem identified, the amount of information available regarding the problem, and the relative impact this failure has on the system’s performance. For example, given that the solar system will have a regular maintenance schedule, on some occasions it makes better economic sense to correct the identified problem at the same time as the standard maintenance visit. Corrective maintenance can include rectifying inverter faults, replacing damaged components, and rectifying SCADA faults.
Condition based maintenance comprises scheduled O&M activities that are carried out when deemed necessary based on the monitored data. It is a strategy that uses the monitoring systems present to reduce the need for regular preventative maintenance. The activities carried out during condition based maintenance would depend on the level of monitoring that exists at site, as well as the data itself.
Monitoring at site
Weather monitoring and system monitoring are essential in order to evaluate and predict the PV plant’s performance throughout its lifetime.
Weather monitoring provides adjustment factors for the evaluation of system performance. Weather data is also essential to analyse weather patterns and be able to extrapolate future power generation trends. A ground based meteorological station is typically installed with a range of components including but not limited to: pyranometer, anemometer, relative humidity sensor, temperature probe, dust monitor, and rain gauge.
System monitoring involves remote monitoring of all the major components of the PV plant to allow for easy troubleshooting and fast and cost-effective repairs.
Monitoring should include both array-side performance and grid-side status. Array-side monitoring would produce typical PV data such as array voltage, current and power, as well as system communication status and array output comparison. Grid-side monitoring may include line voltage, frequency, power factors, and other information needed for the plant’s participation on the NEM.
Supervisory Control and Data Acquisition (SCADA) System
The SCADA system describes a range of data acquisition and control equipment required by a utility-scale system, as well as the communication network that connects them all.
The SCADA system brings in field information from the weather station, string monitoring, inverters, step-up transformers, switch gear, site security system, and so on. The SCADA system will present the information in real time to ensure the system is operating as expected and will trigger alarms if it is not.
The SCADA system may be able to respond to monitored data by using automatic controls or it may need operator input and use a human machine interface (HMI).
With the energy sector in Australia looking to solar, the industry needs to be prepared not only for the onset of the construction of utility-scale solar power plants, but also for the opportunities that exist in the ongoing operation and maintenance of these plants.