Radiation is the energy transfer in the light from space from the sun to the solar collector.
Step-by-step explanation:
On the earth itself the solar collector is situated, here energy must travel from sun to the Earth through vacuum, but energy cannot be transmitted through vacuum by either conduction like molecular collision or convection like fluid movement due to difference in densities, as both of the process need medium. Thus energy from sun to the Earth is traveled through radiation carrying electromagnetic waves, many of these are light waves. Thus energy transfer in the light from space from the sun to the solar collector is processed through radiation.