hitting the cell in a range between 350 nm and 1150 nm. When invested by a luminous radiation in the mentioned range, it produces current as a consequence of the photovoltaic effect. Its sensitivity is not flat, but it is same as that of Silicon photovoltaic cell. See the Spectral Response graph. Design A photovoltaic pyranometer is essentially assembled with the following parts: A metallic container with a fixing staff A small photovoltaic cell Signal conditioning electronics Silicon sensors such as the photodiode and the photovoltaic cell vary the output in function of temperature. In the more recent models, the electronics compensate the signal with the temperature, therefore removing the influence of temperature out of the values of solar irradiance. Inside several models, the case houses a board for the amplification and conditioning of the signal. Usage Photovoltaic pyranometers are used in solar simulators and alongside photovoltaic systems for the calculation of photovoltaic module effective power and system performance. Because the spectral response of a photovoltaic pyranometer is similar to that of a photovoltaic module, it may also be used for preliminary diagnosis of malfunction in photovoltaic systems. Reference PV Cell or Solar Irradiance Sensor may have external inputs ensuring the connection of Module Temperature Sensor, Ambient Temperature Sensor and Wind speed sensor with only one Modbus RTU output connected directly to the Datalogger. These data are suitable for monitoring the Solar PV Plants. Standardization and calibration Both thermopile-type and photovoltaic pyranometers are manufactured according to standards. Thermopile pyranometers Thermopile pyranometers follow the ISO 9060 standard, which is also adopted by the World Meteorological Organization (WMO). This standard discriminates three classes. The latest version of ISO 9060, from 2018 uses the following classification: Class A for best performing, followed by Class B and Class C, while the older ISO 9060 standard from 1990 used ambiguous terms as "secondary standard", "first class" and "second class"., Differences in classes are due to a certain number of properties in the sensors: response time, thermal offsets, temperature dependence, directional error, non-stability, non-linearity, spectral selectivity and tilt response. These are all defined in ISO 9060. For a sensor to be classified in a certain category, it needs to fulfill all the minimum requirements for these properties. ‘Fast response’ and ‘spectrally flat’ are two sub-classifications, included in ISO 9060:2018. They help to further distinguish and categorise sensors. To gain the ‘fast response’ classification, the response time