The study evaluated the capability of current thermal generation to back-up variation generation from solar energy penetration into the Nigerian power grid from a system operation perspective using security constraint unit commitment model. This provides an empirical evidence of the impacts that can tip the balance towards a sustainable future low carbon electricity mix. Through 10 and 20% solar energy penetration scenarios, greenhouse reduction of 1975.70 and 3590.03 lb/day, respectively, can be achieved. However, daily peak-valley net demand difference to be supplied by the thermal plants will increase from 702.5 to 857.5 and 1607.5 MW, numbers of daily start-up will increase from 23 to 30 and 25, daily system spinning reserve will increase from 723 to 757 and 815 MW and daily idle hours of the thermal plants will increase from 52 to 71 and 72 h, in a 10 and 20% solar energy integrated system, respectively. The daily operational revenue of the thermal plants will also reduce by 5.5 and 7.9% in a 10 and 20% solar energy integrated system, respectively. These are useful data in developing policy framework for the future electricity market as the country diversify her energy source and mitigate greenhouse effect.