Photovoltaic energy production

Solar radiation is not only the driving force behind the Earth’s weather phenomena, it also drives photovoltaic energy production. One day of solar energy received by the Earth exceeds the amount of worldwide energy consumption per year. Exploring this merely inexhaustible source of energy - either by direct transformation of radiant energy into electricity or by indirect energy production via wind, waves, etc. - seems to be the obvious way to go. In this context, solar radiation measurements are of primary interest for applications like site-specific solar resource assessments, PV performance evaluation, solar resource forecasting, and so on. However, as with most real-world measurement systems, the difficulties are in the details. Reliable and accurate radiation measurements need some knowledge and attention: think of environmental influences (wind, rain/snow, soling), re-calibration (bi-annually), not to mention data processing, spectral effects, etc. The remaining part of this article intends to give you some background information and best-practice recommendations.

Basically, accurate and precise solar radiation measurements are obtained using two components: a suitable pyranometer and an adequate data logger. In some cases, mostly for dedicated scientific research, reference cell can be used in parallel to pyranometers. But reference cells are also widely used to measure solar radiation as if it were broad band radiometers. For such a use, however, there remains an issue with the spectral selectivity of reference cells. A pyranometer having a flat broad-band spectral response measures the incoming solar radiation homogeneously but reference cells are confined to their band-gab specific sensitivity so that reference cells will not measure solar radiation equally and homogeneously like pyranometers.

As mentioned above, radiation sensors are physical instruments that provide accurate measurements if some basic recommendations are followed. Every user of radiation sensors needs a reasonable awareness of their measurement quality. By taking into account some simple rules the data product generated by the radiometer will fulfil its need for your application more than enough.

Key component of the PV evaluation system

To summarize, evaluation or monitoring of PV systems virtually always require accurate knowledge of the incident radiation. Therefore the radiation sensor is a key component of the PV evaluation system which directly reveals the efficiency of the entire PV installation. Radiation measurement equipment deserves therefore reasonable attention. Any type of radiation sensor has its legitimation as long as the purpose of it corresponds to the application and if it is maintained properly.