Properties of nine composts obtained from perennial grasses for their potential use as an energy source were assessed in this study. The majority of grasses displayed high-moisture, hemicellulose, Na, K, Cl, and N contents, but low lignin content. The effect of composting was pronounced in (i) enhancement of lignin to 461.29%, fixed carbon to 49.46%, and cellulose to 35.05%; and (ii) reduction of Na to 98.77%, moisture to 93.49%, hemicellulose to 89.15%, K to 88.21%, N to 84.43%, Cl to 23.15%, and volatile matter to 12.57%. Subsequently, an increase in higher heating value to 13.90% was observed.