You’re pretty sure your grid-tied PV system is working—but how well? And how can you tell? Here’s how to keep tabs on your system to ensure optimal performance.
The first place most system owners look to assess their grid-tied PV system’s performance is their electricity bill. But examining bills won’t give you the big picture. Since most electric companies offer net metering, you’ll only be provided with the information they measure: how much electricity you import from the grid and, depending on the utility meter, how much your system exports to the grid. Because your bill won’t typically show how much PV-generated energy the home consumed, you won’t be able to determine how much energy your PV system produced overall by using the bill as your only guide. But you can get your hands on this information with data-monitoring solutions from inverter manufacturers and third-party providers.
For some, an inverter’s basic display is informative enough. It is easy to access—right on the front of the inverter—and provides a basic level of monitoring, which often includes instantaneous power output, daily energy production, and total to-date energy production. Depending upon the inverter, readings may also include voltage characteristics of the utility grid and PV array voltages. Some inverters will even translate the PV system’s production (in kilowatt-hours) to pounds of carbon dioxide (CO2) offset to give homeowners insight on how their systems are shrinking their carbon footprints. System owners can view this information at will, just by checking the inverter display.
Remote display options offered with some inverters can provide the same basic system performance information in a portable device, allowing homeowners to be armchair data-junkies. An example of wireless onsite monitoring is the Fronius Personal Display. Simple graphics illustrate the data, such as instantaneous watts; DC and AC volts and amps; daily, yearly, and total kWh; the dollar value of the energy produced; and pounds of CO2 saved.
If you wish to compare daily outputs without recording this information by hand, most inverter manufacturers offer data-monitoring software that can run on your personal computer. Typically, a cable is connected between the inverter and the PC to collect system data, which can be formatted and accessed at your convenience. This strategy offers a relatively inexpensive data-collection solution, but it requires that the PC be connected and running anytime you want to collect data.
Inverter manufacturers also provide data logging solutions that can store performance data without a PC and some even offer online data monitoring using network-savvy portals. System owners, installers, and equipment manufacturers can track system performance from any Internet-connected computer. Some packages can even send automated e-mails to the installer and the system owner in the event of a system fault. If the system has multiple inverters or string-level monitoring, you also may be able receive warnings of discrepancies in energy outputs.
For this convenient and sophisticated data-collection approach, additional data logging and communications hardware is required, which ranges in price from $400 to $1,300. This hardware is installed internally to the inverter or simply connected to the inverter via cabling. These enhanced data-management systems often offer add-ons, such as sensors for measuring irradiance, module temperature, and wind data. This information can also be accessed via the Internet. This level of data monitoring is rarely needed for small-scale systems, but solar geeks, data junkies, and owners of large PV systems will appreciate having this capability to fully assess system performance.