The answers you got are excellent but a short response might just say you don't start with just X energy. In a sense it's no more mysterious (conservation of e

The answers you got are excellent but a short response might just say you don't start with just X energy. In a sense it's no more mysterious (conservation of energy-wise) than adding the energy of a spark results in the energy of the wood fire. i.e. energy is transformed, not created as you quite accurately write.