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NREL Model Improves Predictions of Shade Effects on Solar PV

Using microinverters instead of typical string inverters can improve solar panels’ performance in shade by more than 12 percent, according to a new National Renewable Energy Laboratory test procedure, which the lab says greatly improves the accuracy of predictions about shade effects.

Shade hinders photovoltaic performance, which is why solar installers consider it in PV system design. The effects of shade can vary depending on the configuration of the PV modules, the extent of the shade and the use of shade-mitigating power electronics in the system. However, the industry currently lacks representative, repeatable test procedures for evaluating the annual effect of shade on different PV systems equipped with different shade mitigation devices.

NREL’s report, “Photovoltaic (PV) Shading Testbed for Module-level Power Electronics,” details a repeatable test procedure for simulating shaded operation of a PV system and an analysis model for converting these measurements into annual performance forecasts.

NREL measured shade from more than 60 residential installations, which were analyzed for three typical shade scenarios: light, moderate and heavy shading. Engineers compared the relative performance of a system using shade mitigation devices against an identical system equipped with a reference string inverter for these three shade scenarios, providing an annual performance improvement score.

PV Evolution Labs conducted an initial application of the test protocol, which showed the shaded performance benefit of microinverters compared with a typical string inverter on identical 8-kW solar arrays. According to the test, the microinverter increased system production by 3.7 percent under light shading, 7.8 percent under moderate shading, and 12.3 percent under heavy shading, relative to the reference string inverter case.

The annual shade improvement score can help performance modeling software such as PV Watts and System Advisor Model better predict annual performance for PV systems that use shade mitigating power electronics, NREL says. It also allows an accurate comparison between different devices.

Also this week, Clean Power Research launched the latest version of its SolarAnywhere solar prediction tool, Greentech Media reports. The tool predicts rooftop installations’ minute-by-minute power output using a combination of satellite imagery, solar installation data and patented methods to predict how the systems will act when hard data isn’t available, Jeff Ressler, the company’s president of software services, said.

In April, the EPA launched a tool to test vacant and contaminated land for solar and wind energy potential.

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