Commercial PV System Data Monitoring, Part Two

In Part One of this article (October/November 2011, SolarPro magazine), we discussed the value of monitoring commercial PV systems and the benefits to investors, integrators, system owners and operators. We also discussed the options and components involved in the selection of a monitoring system.

In Part Two, we concentrate on the best practices for successful integration, including predesign planning with the monitoring provider, site-specific considerations and conduit routing. We provide a case study showing the financial effects of system downtime, which potentially can be alleviated via sufficient data monitoring. We also explore the trend toward inverter-integrated monitoring and its advantages and disadvantages compared to third-party monitoring.

MONITORING SYSTEM SELECTION AND SPECIFICATION

According to the subject matter experts we interviewed for this article, the most common mistakes made when specifying and implementing PV monitoring systems are generally traceable to a lack of planning, foresight or communication. Planning for a monitoring system after the PV system is built has obvious flaws. It may also be problematic to add a monitoring system after the PV system is quoted, let alone sold.

“The most common mistake integrators make is waiting too long to decide upon and implement a monitoring solution,” observes Robert Smith, director of marketing at ArgusON, a provider of site monitoring and management services. This often adds costs that could have been avoided. “When the monitoring platform is the last item to be selected on a commercial PV site,” he says, “expenses can rise substantially due to an inefficient system design.”

Fortunately, there is general agreement on how to avoid these problems: Plan ahead, do your homework, and communicate with the customer and the monitoring solutions provider early and often.

Customer needs ultimately determine the best data monitoring system configuration specific to each project. According to Benjamin Compton, COO at meteocontrol North America, which provides solar management solutions to large PV power assets: “In any measurement and verification program, a balance must be struck between the level of detail required for an accurate evaluation and the associated costs relative to the overall energy generation value.”

Site survey. Once you have determined that a commercial system will be monitored, the conceptual design must be tailored to meet the needs of the customer, system operator or both. The best way to make sure that you are asking the right questions and getting the right answers is to complete a monitoring installation site-survey form as early in the sales or design process as possible.

Typically, PV monitoring companies provide a site-survey document to their customers upon request. Site-survey responses are useful for specifying the right equipment, optimizing the system design and providing an estimated price for the goods and services. A site-survey form seeks to answer as many basic questions as possible about the site and desired functionality of the monitoring system. Typical questions include:

  • What data do you plan to collect?
  • Who will be using the web portal and how?
  • How will Internet access be achieved?
  • How will you power components that need a dedicated power supply?
  • What are the conduit and cable requirements?
  • Where will major monitoring system components be located?

The other major component of the monitoring site survey is a one-line electrical drawing. If this is provided along with an approximate or to-scale site layout, the monitoring provider can use this information to create a customized site-specific single-line drawing, showing the location of power and communication connections to the monitoring equipment. Sharing the system design with the monitoring provider also helps verify that all components are compatible, including inverters and meters.

Gathering this information during the planning stage of the project is crucial. The addition of a monitoring system inserts another layer of electrical equipment to the design, including power supply circuits, communication circuits, meters and IT equipment that must be located, sized and considered in advance to be fully incorporated into the PV plan set. The predesign process for determining the monitoring system should be considered just as important as sizing the correct inverter or choosing a racking system.

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