so·lar 
(sōlər)
(sōlər)adj.
1. Of, relating to, or proceeding from the sun: solar rays; solar physics.
2. Using or operated by energy derived from the sun: a solar heating system.
3. Determined or measured in reference to the sun: the solar year.
[Middle English, from Latin sōlāris, from sōl, sun; see sāwel- in the Appendix of Indo-European roots.]