Renewable energy sources are available free of cost and they don't produce pollution while using them for generating electricity.Solar energy is an over lasting source of energy.
Plants use it to make food .it maintains the temperature of our planet suitable for survival of life on it.
We can use it to generate electricity through solar panels.
Flowing water in rivers and wind in the coastal areas are free of cost sources of kinetic energy that can be converted into electricity using turbines, windmills and electric generators.