Data Acquisition System Installation and Commissioning
Inside this Article
With the increase in performance-based incentives, and system owners and financers paying closer attention to ROI, the demand for accurate and reliable performance data has increased. This has given rise to complex data collection systems with multiple monitoring points, energy meters and weather sensors. Despite this advancement, installation of the data acquisition system (DAS) is often relegated to the final stage of the project. Often installers must familiarize themselves with new DAS products and systems in the absence of design documentation, training and other preparation, causing unnecessary delays in the field.
It takes a significant amount of time and effort for installers to successfully integrate the associated components of a DAS and properly configure, commission and verify the system. We contacted several experts on DAS installation and commissioning to better understand current issues with implementation. In this article, we summarize their feedback and our own experience with installation and commissioning best practices.
THE IMPORTANCE OF DATA MONITORING
System performance data serve two main roles in the operation of PV arrays: recording and reporting.
First, the data recorded provide insight into how the system is performing. At the highest level, commissioning agents compare measured performance with expected values based on temperature and irradiance readings. This comparison identifies when and where underproduction occurs within the system and how much it is underperforming. For instance, if the measured production equals two-thirds of the expected levels, and three PV source circuits are feeding one inverter, it is likely the production issue stems from one of those circuits— perhaps a blown fuse in the combiner box. Recorded performance data may also identify underperformance due to soiling or shading. If losses are the same from one day to the next, soiling may be the culprit. Alternatively, shading is the likely source of losses that occur during certain times of the day or year. Ultimately, DAS data serve to uncover performance issues so the system owner can address them quickly.
Second, data monitoring systems play an important role in production metering and reporting. PPA contracts, feed-in-tariff incentive programs, and utility-owned and municipal projects utilize—and often require—a DAS to meter and report PV production for billing and crediting purposes, and sometimes for REC monitoring. For example, the California Solar Initiative, which requires performance monitoring and reporting, allows approved companies to serve as performance data providers or to provide performance monitoring and reporting services. These services rely on approved DAS solutions to accurately measure and report production on behalf of the clients.
DAS PLANNING AND DESIGN BEST PRACTICES
In “Commercial PV System Data Monitoring, Part One” (SolarPro magazine, October/November 2011), Kyra Moore and Rebekah Hren explore the value proposition of PV system monitoring, and identify and review the key components and concepts of a DAS. Given that PV monitoring systems consist of multiple subsystems—including communication networks, power supplies and weather stations—understanding the hardware requirements and interconnection protocols for each subsystem is essential to DAS planning and design. During our interviews, several DAS suppliers and end users attributed some of the frequent problems they encountered during the DAS installation and commissioning process to poor planning or lack of design. The following best practices can eliminate problems in the field.
Site visit. Conducting a site visit prior to specifying and designing a data monitoring solution reduces the amount of guesswork required during the DAS installation. With an understanding of the client’s monitoring goals and requirements, the designer can identify the challenges specific to the site. As Gabe Abbot, the director of business development at Locus Energy, says, “Performing a site survey prior to the design helps to determine network connection availability and security requirements, to identify the proper location for DAS equipment and to plan wiring and conduit runs.”
If the DAS will utilize an existing network, it is important to meet with the on-site IT administrator to understand network requirements and limitations. Make sure to obtain contact information for use if questions come up. This is the best time to determine how and where the DAS will connect to the local network. With this information you can identify the exact locations for the devices, determine the route and distance between devices and locate necessary power supplies and their potential tie-in points. This information will ensure that the designer specifies the appropriate components and installation details.