A photothermal radiometer for concentrated sunlight intensity measurements

Attention is given to a radiometer based on the measurement of the time-varying surface temperature of a metal plate exposed to chopped concentrated sunlight. This periodic temperature is measured by a noncontacting pyroelectric infrared detector. At 1000 suns, for a chopping frequency of 30 Hz, the periodic surface temperature excursions are of the order of 2 C, so that convection and reradiation losses are minimal. For this arrangement the pyroelectric detector output is linear with sunlight intensity in the concentration range of 100-1000 suns. The radiometer has been used to measure the relation between short-circuit current and illumination of solar cells.