The energy source is the bond energy released by the breaking of chemical bonds among carbon, hydrogen and oxygen.

The main components of candles are n-docosane (C22H46) and n-octacosane (C28H58).

Compared with alcohol (C2H6O), the number of chemical bonds is more than ten times.

In addition, the ratio of derivative bond to σ bond in chemical bond also affects the energy.

That's all I know. I hope it helps you.