A source of power.
What are the types of energy?
There are electric energy, kenetic energy, themal energy, potential energy and chemical energy.
There are heat energy,water energy,and wind energy.
Heat energy is from the sun to transferred to keep us warm, wind energy comes from windmills to give us electricity, chemical energy is from bonds of chemical compond used for batteries, nature gas, and coal are examples of stored chemical energy.
Energy cannot be destroyed nor created, for example when you turn on the kettle the water will turn into gas and when people burn coal there will be gas that turns into energy.
Well in my opinion I think that we will still have enough coal in the future to make enough energy for us.