What is an energy supply?

Energy is the capacity to do work. Your supply will do work for you when it supplies you with electrical energy.

What is electrical energy?

It is caused by the movement of electrons from one place to another and is the work done by the moving streams of the electrons or charges. The commercial or practical unit of energy is the kilowatt-hour (kWh).

How is electrical energy supplied?

Sources are:

1. objects: hot, moving, charged, sprung, radioactive 
2. fossil fuels: heat engines; turbogenerators
3. renewable energy technologies
   

How well do different technologies convert input energy to electricity?

See table