SCADA’s Role in Utility-Scale PV Plants

Utility-scale power producers face a demanding and multifaceted mission: Meet contract commitments, operate safely, support grid stability and maximize profits. Supervisory control and data acquisition (SCADA) systems play an essential role in meeting these objectives. SCADA systems monitor and control a variety of devices at utility-scale PV sites, including inverters, meters, trackers, meteorological stations, storage systems and other smart devices. Properly designed SCADA systems provide total site control to optimize power generation, control voltage, maximize revenue, ensure accurate settlements and satisfy utility compliance requirements.

Here I look at the role of SCADA systems in utility-scale PV power plants for compliance, operations management, asset management and revenue optimization. I conclude with an overview of design and deployment considerations.

Compliance, Grid Support and Security

On the regulatory compliance front, power producers use SCADA technology to honor contracts, meet regulatory compliance or both. For example, a power-producing site may have either a contractual or a compliance requirement to operate at a certain production level, a condition that effectively requires SCADA capabilities. Plant operators need to have not only visibility into how the site is performing currently, but also foresight into how it will perform in the future. SCADA systems can be invaluable in reviewing historical performance and correlating past values to projected weather patterns. These systems enable operators to provide accurate forecasts to address operational and compliance requirements.

SCADA systems also enable utility-mandated grid support functionality. With the right technology, the site can not only react to and counter the impact of variations in voltage, frequency or reactive power, but also can ride through transient events to avoid exacerbating a grid disturbance. The SCADA system evaluates grid conditions in real time and can make grid-support decisions automatically.

Site security is another important consideration with compliance implications. Technology plays a vital role in protecting large-scale power generation sites from those who intend to do harm, from unwanted access and control, or from unintended human error. Although physical security systems can limit perimeter access, operators must also implement cybersecurity systems to limit access to sensitive information and control activities. For large sites, the North American Electric Reliability Corporation (NERC) explicitly outlines cybersecurity requirements for low-, medium- and high-impact sites in its critical infrastructure plan (CIP) standards. Even if regulators do not require that a site meet these NERC CIP levels, operators must still address cybersecurity, as it is essential to successful plant operations.

Operations, Performance and Safety

To optimize operational management activities, plant operators need accurate and timely information. SCADA systems collect, analyze and present site information clearly and concisely so operators know how to prepare for and react to site events. Operators can leverage this technology to automatically react to values that exceed defined thresholds by adjusting how the site operates, by raising alarms or both. For example, an on-site SCADA system can compare actual production to expected production and raise an alarm if the site is not performing optimally. This ensures that restricted performance does not negatively impact overall revenue and profitability.

Operators can use a well-designed SCADA system to establish key performance indicators (KPIs) with the goal of streamlining operational activities. These KPIs allow operators to focus quickly on the actionable information they need to operate the site rather than having to review thousands of pieces of information. For example, rather than rely on an arbitrary washing schedule, operators can use SCADA systems to calculate the soiling impacts, and then present these data as a metric that indicates when to schedule panel washing. Ideally, the SCADA system identifies any gaps or anomalies in the data and makes the adjustments necessary to ensure data integrity. A customized SCADA solution can provide this extra level of data analysis.

To improve operational safety, SCADA systems can proactively identify events that may affect a plant’s safe operation. If a power transformer shows signs of overheating, for instance, the SCADA system can raise an alarm so that the operator can dispatch a maintenance crew to investigate the problem. As an additional layer of protection, a well-implemented SCADA system can also vary plant behavior to compensate for this type of event before it becomes more serious and harmful. In the event of a transformer temperature alarm, for example, the SCADA system could automatically reduce or curtail the power flowing through the transformer to lessen or eliminate the risk of equipment damage.

Asset Management and Capital Planning

The focus of asset management, which is necessary to meet the project’s overall financial goals, is maximizing revenue from the site while minimizing operating costs. To support these business goals, operators can leverage SCADA systems to provide timely information about performance—not only in terms of kilowatt-hours but also in terms of dollars and cents. This revenue perspective is critical for determining maintenance priorities, as it allows operators to identify the items that have the largest returns.

Asset managers can use SCADA technologies to determine which preventative maintenance activities to schedule and when, so as to maximize revenue. With accurate forecasting, for example, the site operator can schedule inverter maintenance during lower power production periods, effectively minimizing the revenue impacts of taking equipment offline. It is also possible to use data analysis to make a business decision about when to repair nonproducing PV strings—either immediately or during the next scheduled maintenance visit.

Asset managers can also use SCADA solutions to optimize warranty activities. If an inverter fails while it is still under warranty, it is obviously to the asset manager’s advantage to have the installer or manufacturer replace or repair the inverter according to the warranty terms. SCADA systems with full-featured asset management functionality can track how long equipment has been in operation relative to the warranty period, which has a positive impact on the bottom line. In other scenarios, asset managers might use SCADA technologies to perform an accurate lost-energy analysis as part of a warranty claim resolution.

SCADA systems can even help asset managers get the most out of critical or costly components by controlling this equipment with lifespan or duty cycles in mind. A site might have 50 inverters that operators must actively control to regulate power based on compliance and operating requirements. During curtailment or regulation activities, SCADA technologies can intentionally limit the contributions of older inverters or run different inverters at different power levels based on their efficiency curves.

When asset managers use SCADA capabilities to extend the life of devices, they are saving money by deferring equipment replacement cost. Optimizing inverter efficiency, meanwhile, can increase revenue. SCADA technology can also support capital planning and investment decisions. To the extent that asset managers can determine predictively when trackers or inverters are likely to need replacement, they can manage their capital plan for replacement purchases more effectively.

Power Generation and Revenue

An important best practice for utility-scale power producers is to use SCADA technology to measure, monitor and control power production at the point of interconnection (POI). Everything that happens before the POI is about the resource; everything that happens on the other side of that POI is about the grid. You should base every decision that you make about the resource—from the monitoring to the controls—on the effect it will have on that interconnection point with the grid. Using SCADA technology to make decisions based on what actually is going on at the POI, rather than assuming what is happening, maximizes the effects of your actions.

Power regulation is a good example. Perhaps a developer built a site to produce as much as 60 MW, but from a contractual standpoint, it needs to limit power production to 54 MW. If the installation has 60 inverters, each rated for 1 MW, they certainly would not all be producing the same amount of power all the time—therefore it would not be prudent to simply reduce all of the inverters by 10%. By taking measurements at the POI and adjusting each inverter to its individual capability, plant operators can generate the maximum amount of power allowable without exceeding the contracted power limit. Additionally, if an inverter has an issue or is undergoing maintenance, operators can leverage technology to recognize the lost production and adjust the remaining inverters to make up the difference automatically. This approach allows the system to maximize revenue while still meeting both contractual and operational requirements.

Implementation Considerations

Deploying the right technology can make all the difference in terms of project success or failure. Here are some important considerations when leveraging monitoring and control technologies to operate and manage a utility-scale power plant.

Use job-appropriate technology. Do not implement a commercial monitoring system when the plant needs a full SCADA system. (See “SCADA Feature Checklist.”)

Keep the site secure. Layer security so that someone cannot damage the site intentionally or inadvertently. Make sure that information is accessible only to those who need it and not to unauthorized users.

Automate processes where possible. Automation ensures that people can focus on nonroutine, problem-solving knowledge work and not on mundane and tedious operational tasks. Automated controls can also eliminate unnecessary truck rolls to the site and reduce the labor expended on routine control activities.

 Design for interoperability. Usually various business systems need to communicate and operate with the site. These can include energy management systems, operational data management systems and surveillance systems. Selecting the right technology ensures that all these systems use standard communications protocols to ease integration and interoperation.

Plan in advance. Implementing and leveraging technology is much easier if you make it part of the plan from the start. Industry regulations and best practices are changing constantly. Designing the site technology to adapt and interoperate with changing conditions will help ensure that the site does not become obsolete before its end of life.

Diane McClelland / Trimark Associates / Folsom, CA / trimarkassoc.com

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