Pyranometers are used during various phases of a solar installation. During the pre-construction stage of a project, they are needed to evaluate the location of the site by measuring the irradiance of the sun at a certain point. The irradiance is a measure of how much light hits a particular surface, usually expressed in watts per square meter, which is important in determining how much power a project could potentially harvest from the sun at a certain site. During post-construction of an installation, pyranometers are placed next to the PV panels to determine whether they are working properly, said Rodney Esposito, sales office director at Kipp & Zonen. These assessments are oftentimes used in conjunction with temperature measurements to obtain an accurate analysis of the module’s output, added Thomas Enzendorfer, president of Soligent.
There are two types of pyranometers: thermopile pyranometers and semiconductor pyranometers. A thermopile pyranometer measures the total amount of radiation on a surface using a thermopile detector, a device that converts thermal energy into electrical energy. A thermopile pyranometer has a horiztonal surface coated with a light-absorbing black paint that consumes radiation from the sun. A temperature difference is created between the black surface and the body of the instrument, resulting in a small voltage that is measured in watts per square meter.
A semiconductor pyranometer measures radiation using a photodiode, a device that converts light into a current. An electrical signal is created from the solar radiation being absorbed. Semiconductor pyranometers are typically less reliable than thermopile pyranometers because they cannot capture the sun’s entire spectrum, resulting in measurement errors.
Pyranometers are mainly used in large-scale projects rather than smaller installations to determine the efficiency of the panels, explained Esposito. However, Enzendorfer said that all projects, despite their size, should use pyranometers to verify expected performance and ensure the installation will operate at its full potential.
Solar installers and project developers more prevalently use pyranometers, but anyone commissioning a system or troubleshooting to resolve issues with system production should use these measurement tools to obtain the most accurate analyses possible.