modules clean. In many areas, a periodic rainfall can do the job. But if it’s been a long time since the last rain and you notice a fine layer of dirt or dust building up, you will boost your system’s energy production with a little cleaning.
System owners should periodically inspect their PV system and check performance to make sure all is functioning correctly. Physically inspect for broken modules and potential shading issues (for example, a growing tree). For checking performance, most grid-connected inverters have a meter that displays the amount of power (W) being produced and how much energy (KWH) has been produced that day and over the lifetime of the inverter.
Some systems may incorporate data-monitoring to remotely check the power and energy production. (See HP121, “The Whole Picture: Computer-Based Solutions for PV System Monitoring.”) Metering is helpful for a quick check on power production—but if it seems that the system is not performing as well as it should, more information will be needed. Irradiance and temperature, which are not typically a function of standard inverter metering, are constantly fluctuating and can significantly affect system performance; they need to be measured for accurate system assessment.
Other system losses (such as line loss, module mismatch, inverter efficiency, etc.) can also be estimated. PV professionals have basic tools to get a fairly accurate assessment of system performance, such as a hand-held solar irradiance meter and an infrared temperature reader. With irradiance and module temperature known, installers can calculate how much power the system should be producing (see Calculating Array Output sidebar) and compare that value to the inverter’s meter or a reading on a clamp-on multimeter on the output circuit. If the two values vary significantly, there may be a problem to troubleshoot—perhaps a faulty module, a blown fuse, or poor inverter MPPT performance.
With the significant cost of PV systems and the need to maximize output for production-based incentives, wringing as many KWH as possible out of your system makes economic and environmental sense. Paying attention to installation details and monitoring a system’s output over its lifetime will give you the most value from your investment.
Jeremy Taylor is a NABCEP-certified industry veteran, residing in southern California. He began his solar career in 2002, learning from the roof down from PV projects on-grid and off, ranging from 5 W to 1 MW. His focus is primarily on system design and performance monitoring.
PVWatts • http://www.nrel.gov/rredc/pvwatts/
Go Solar California • www.gosolarcalifornia.org • List of inverters & their weighted efficiencies
Dunlop, Ewan D. “Lifetime Performance of Crystalline Silicon PV Modules.” Proceedings of 3rd World Conference on Photovoltaic Energy Conversion, Volume 3, May 12–16, 2003: 2,927–2,930.