Solar Panel Performance Terms You Should Know

Written by Anita Alvarez
Updated December 1, 2016
solar panels on home's roof
A contractor installed this 20-panel, 5,500 kilowatt rooftop solar system on this New England house. (Photo courtesy of Angie's List member David L.)

Considering a solar power system? Learning a few key solar energy terms will help.

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Your return on investment in solar panels can increase or decrease depending on their performance ratings. Not all manufacturers use top-quality, durable materials to produce solar photovoltaic cells in panels or modules. It pays to invest in higher quality components to get a higher return through the years. 

Navigating the language of solar energy can be confusing. Here's a look at the key efficiency terms you'll need to know.

Solar power system efficiency terms

AMPM standard: As the name suggests, this rating indicates how solar panels perform throughout a day, from peak sunlight hours to nonpeak sunlight hours. It generally offers the most realistic view of how a panel will perform and takes into account light variations during the day, ambient temperatures and factors related to air mass that affect solar energy potential.

Normal operating cell temperature (NOCT) rating: This rating gives consumers a fairly accurate picture of a solar power system's potential to withstand factors that affect efficiency. The calculation uses peak sunshine during the assessment.

Peak watt rating: This number reflects testing in laboratory conditions and shows how much energy in peak watts (Wp) a solar module generates. It’s not very useful to consumers because your photovoltaic system will be installed and used in real life, where factors such as solar panel installation and weather can affect performance.

Solar energy performance terms

Current at maximum power (Im) rates the solar panel's production of electricity after inverting solar power into DC power.

Current-voltage (IV) ratings compare the differences in terms of output when insolation (the amount of light that falls on a panel) and temperature vary. This rating is useful for learning how a solar panel will perform as the temperature changes and sunlight potential decreases on a cloudy day, for instance.

Nominal voltage (Vn) shows the voltage the solar panels can work with. This often ranges from six to 24 volts, but it can be 48 volts and even more.

Rated power indicates the solar panel's ability to sustain power output throughout the day, based on the power of the sunlight that hits the panel. Presume this rating shows the panel's peak capacity.

Temperature at rated power is a standard that manufacturers use to rate solar panels' performance at a specific temperature, which is useful for comparison purposes. Generally, most manufacturers design their panels to deliver maximum power output around 77 degrees. As temperatures decrease and increase, the power output will vary.

Voltage at peak power (Vp) offers a glimpse of the panel's maximum output in terms of voltage when it's producing electricity at its highest rate.

Find out more about solar energy and how to select high-performance solar panels by contacting your local trusted solar contractor. 

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