PV Meter Reading

For batteryless, grid-tied systems, inverter meters are the system watchdogs, telling you how much power and energy is being generated, and alerting you to problems-if you know how to interpret what they're saying.

Today's inverter meters make it easy to keep tabs on your PV system.

Today's inverter meters make it easy to keep tabs on your PV system.

Output Power (Watts)

This is an instantaneous reading of how much AC power the system is producing and back-feeding into the AC load center. Because this value is the final output of the system, inefficiencies and variables, such as module temperature, irradiance, dust, and inverter efficiency, have already been accounted for. At midday, with clear and sunny skies, this value should be 70% to 80% of the array's STC rating.

Energy Produced (Kilowatt-Hours)

This value tells us how much energy has been produced so far that day. Cumulative energy production may also be reported. Although the daily kWh produced depends on several factors, including array size, site location, time of day, time of year, and cloud cover, at the end of a sunny spring or fall day, you should see the average kilowatt-hours per day your system was designed for. For example, if your system was designed to annually produce 2,500 kWh, at the close of an average solar day, your meter should read close to 6.8 kWh.

Troubleshooting tips: If output power (W) or energy (kWh) values are significantly lower than expected, visually inspect the array and look for shading (perhaps trimmed hedges have grown back) and dirty PV modules, and check for blown series string fuses.

PV Array DC Voltage (Volts)

Array input voltage can be interesting to observe, especially during hot or cold weather. Voltage decreases as PV cells heat up and increases as the cells get colder. Array voltage should remain within the inverter's voltage input specifications under all temperatures experienced at your site.

PV Array DC Current (Amps)

As solar irradiance increases or decreases, this value fluctuates. For example, as clouds roll in and block the sun, the current reading (and the output power) of the system will be reduced. This is normal, and you will see these numbers rise again when the cloud-cover disappears.

Some inverter meters include other readings, such as utility AC voltage, amperage, and frequency; pounds of carbon dioxide offset; historical maximum system output (watts and volts); and total inverter operating hours. Inverter meters also have an error menu that can be accessed and used for troubleshooting.

—Justine Sanchez

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