HOW TO MEASURE SOLAR RADIATION AT YOUR SITE?
The amount of irradiation is measured for both DNI and GHI. The device that is used to measure Global Horizontal Irradiation is Pyranometer and Pyrheliometer is the device used to measure Direct (beam) Normal Irradiation. There is another device that tracks the movement of sun throughout the day i.e., Sunshine recorder.
Silicon sensors are the other land based measuring device. These are cheaper than Pyranometers and consist of a PV cell, often using crystalline silicon. The current delivered is proportional to the irradiance. Temperature compensation can be used to increase accuracy but its scope is limited by the spectral sensitivity of the cell. Some wavelengths (for example long wavelength IR) may not be accurately measured, resulting in a lower irradiance measurement of up to 5% compared to thermal pyranometers.
Silicon Irradiance Sensor
The doubt may arise, where do we get these irradiation data from? Here, is the answer to your question. There are huge databases of different data providers. Among them, two data providers are taken into consideration. They are NASA POWER (NASA Prediction of Worldwide Energy Resources) and Meteonorm worldwide irradiation data. This data provider’s gives all the data related to the selected location. These are the satellite derived data’s. Satellite-derived data can offer a wide geographical coverage and can often be obtained retrospectively for historical periods in which no ground-based measurements were taken. This is especially useful for assessing long term averages. One advantage of satellite resource assessment is that data is not susceptible to maintenance and calibration discontinuities. The same sensor is used to assess locations over a wide area. This can be particularly useful in comparing and ranking sites as bias errors are consistent.