Commercial PV System Data Monitoring, Part Two: Page 5 of 6
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Location. For best results, show the locations of datalogger enclosures, energy meters, weather sensors and other monitoring system components in your site plans and elevation drawings. Once again, not including these items in the plans leads to wasted time and money. Sometimes inverter rooms or pads are small, and the designer must plan for the additional wall or pad space needed for the datalogger or external revenue-grade meter.
Distance considerations between components must also be taken into account for data accuracy. For example, the distance between the energy meter(s) and the datalogger may have limitations depending on the communication protocol and bus drivers used. Weather sensors have limits on how far they can be located from the datalogger or analogto- digital converter. RS-485 cable should not be run farther than 4,000 feet from the first device to the last.
Just as the power system equipment is sensitive to environmental conditions, so is the monitoring equipment. Although most systems are housed in NEMA 3 or better enclosures, the equipment should be kept out of direct sun.
Other considerations. When evaluating monitoring services providers, consider whether their product features enable you to successfully operate your plant today and provide the flexibility to meet your needs tomorrow. Besides applicationspecific criteria, consider long-term compatibility. Here are some questions to ask:
- Is automatic REC-compliance reporting an option?
- What are the configurations for downloadable system performance reports, including time periods available and data views?
- How can you troubleshoot the data monitoring system?
- What service contracts and warranties are available, and at what cost?
- What kinds of support services are available?
- How confident are you that the monitoring company will still be around in 20 or 25 years?
Some criteria, like product features, are relatively self-evident; others, like level of customer support, are more nuanced. Support services might include any or all of the following: predesign support, installation support, commissioning support, predelivery system testing, host customer training and preconfigured equipment.
Because PV systems have such long service life expectancies, choosing data monitoring components and service providers is a significant exercise. “Convince yourself that your data monitoring partner will still be around in 25 years and supporting its equipment with boots on the ground,” advises Solectria’s Zuercher-Martinson.
INVERTER INTEGRATED OR THIRD PARTY?
For a decade or more following the inception of the gridconnected PV industry, inverter manufacturers generally provided minimal inverter-integrated faceplate data— usually just ac energy, ac power, and dc and ac volts and amps. When installers and system owners wanted verifiable in-depth data reporting, they relied upon specialized hardware and software from providers of third-party data monitoring solutions.
In recent years, central inverter manufacturers have increasingly begun to offer more sophisticated inverter-integrated data acquisition systems. The latest inverterintegrated monitoring systems have a much wider ability than those of the past to track, log and display PV system data and error alerts. Revenue-grade metering and reporting is generally an option.
This trend toward more sophisticated inverter-integrated monitoring is likely to continue. As an example, Power-One— which is currently the second largest solar inverter manufacturer in the world—purchased the assets of Fat Spaniel Technologies, a leading US provider of PV monitoring solutions, in October 2010. Subsequently, Power-One acquired monitoring business assets from National Semiconductor, which included solutions developed by Energy Recommerce.