Pyranometers are expensive and not easily available. Therefore in order to measure the global solar irradiation a solar cell can be used.
It is known fact that the current output of solar cells is a linear function of solar irradiation. Also, the current output of solar cell does not depend strongly on the temperature of the solar cell. Therefore solar cell current can be used as a measure of solar irradiation at a given time.

Cell current Solar Irradiation —Solar Irradiation or
Solar Irradiation (W/m2) = K * Cell current (Amp)

Here K is the proportionality constant.
Normally solar cells in short circuit mode are used for measurement of solar irradiation. A calibrated solar cell (Figure 5) is provided with the laboratory kit of ‘1000 teachers training program’. This solar cell is calibrated against the Pyranometer.