means:

Transform light energy to thermal energy (Solar Water Heater) or light energy to electric energy (Photovoltaik). The light energy is mesured in solar radiation that is proportional to the sunshine duration and to the sun elevation. Therefor the solar radiation in South Thailand is about double the radiation in central Europe. Thats all about solarpower!

The solar radiation is measured by satellites. Here you can see the global radiation for an average may and for an average december. These are maps from the NASA, blue color means "no sun", while red color means "a lot of sunny hours":

In Thailand the annual radiation is about 1.800 kW/m². Although just a fraction of about 10 % can be transformed to energy: A surface of 30 m² is theoretically sufficient to power an average household.