SCADA Versus Web-Based Monitoring

Clients often ask PV system integrators and consulting engineers for recommendations on how best to monitor their assets and manage their portfolios. The variety of platforms available differ in cost and technical capabilities. However, most fall into two broad categories: supervisory control and data acquisition (SCADA) systems and web-based monitoring systems. Here we briefly consider the differences between these two platforms within the context of megawatt-scale PV systems. We also present 10 key questions to consider when selecting a platform.

Differences between Platforms

Many in the industry tend to use the terms SCADA and web-based monitoring interchangeably. However, there are important differences. On one hand, the traditional power sector has been using SCADA systems since the late 1980s, long before high-speed Internet connectivity became ubiquitous, and they provide active plant control. On the other, web-based monitoring systems are relatively new and generally focus more on data acquisition than on plant control and operation.

SCADA systems. Utility-scale power plants require not only large-scale data collection, but also a means of control. For example, a utility or independent system operator (ISO) may require a PV power plant to operate according to a contractually mandated schedule. In other cases, the utility or ISO may send commands directly to the on-site SCADA system via an energy control network. Traditionally, plant operators use SCADA systems with an on-board network historian server to meet plant control and data collection requirements like these.

SCADA platforms typically include software that is purchased up front. The purchaser owns the software licenses and the data collected. Providers generally do not sell SCADA packages as a service, but they do make annual updates available for a fee. The main difference between SCADA and web-based monitoring is that SCADA packages are typically designed to communicate with industrial automation controllers and provide enhanced control capabilities. As a result, the operator interface allows not only for monitoring and data collection, but also for direct control of plant operations, either locally or remotely.

Commercial plant operation requires such a high level of reliability that a firmware-based device—such as a programmable logic controller (PLC) or a similar type of smart relay—is necessary for plant control. Unlike a computer server, which is constantly executing many programs that are subject to interruption, a PLC runs only one application.

Web-based monitoring. The rapid growth of the solar industry over the last decade has spawned a multitude of companies that sell web-based PV monitoring software and services. Although some equipment manufacturers and system integrators offer their own monitoring platforms, lending institutions often impose independent monitoring requirements. Therefore, third-party companies typically provide data collection software and services optimized for PV applications. AlsoEnergy, Draker, Locus Energy and Solar-Log are a few of the vendors in this category. Providers typically sell web-based monitoring according to a software-as-a-service delivery model. The client pays up front for the site communications software and then pays a monthly fee for data storage and maintenance.

Choosing the Right Platform

When deciding between SCADA and web-based monitoring platforms, consider the following ten questions.

What is the size of your project? For projects of more than 10 MW in capacity, which typically have control requirements mandated by the utility or ISO, we recommend looking into a SCADA system. A web-based monitoring platform is good for individual projects of less than 10 MW in capacity and also for distributed generation sites.

What is the size of the overall portfolio? Some web-based monitoring systems are sufficient for site-level monitoring but do not manage multiple-site portfolios. In other cases, the client may have different monitoring platforms at different sites and may be looking to consolidate. If the client has a multiple-vendor portfolio, we recommend consolidating at a corporate level rather than changing equipment at the site level.

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