Photosynthesis is what converts lightenergy from the sun into chemical energy for plants.
Currently, most biofuel is burned to release its stored chemical energy.
Another branch, related to energetics, is concerned with the transformation of chemical energy into other forms of energy - heat, light, electricity.
The main energy used to power the vehicle or other device is from the chemical energy of the battery.
Combustion is a familiar example of the transformation of chemical energy into heat and light; the quantitative measures of heat evolution or absorption (heat of combustion or combination), and the deductions therefrom, are treated in the article Thermochemistry.
