insolation
Concise Oxford English Dictionary © 2008 Oxford University Press:
insolation /ˌɪnsəˈleɪʃ(ə)n/
▶noun technical exposure to the sun's rays.
■ the amount of solar radiation reaching a given area.
– origin C17: from L. insolatio(n-), from insolare, from in- ‘towards’ + sol ‘sun’.
'insolation' also found in these Oxford entries:

