It is a crucial shift in human energy use and development from which society can expect thousands of years of a clean green future inreforestation, while natural renewable resources are used to produce power. Major functions of sustainable energy systems include taking energy from the sun home, wind substation, and water electric plants, as well as geothermal heating devices. Technological features range from photovoltaic solar panels and wind turbines to hydroelectric generators and heat pumps. These technologies transform raw renewable resources into useful energy, greatly reducing the need for us to depend on fossil fuels. Application goes from residential systems to commercial and industrial ones: they generate electricity, provide heat, even power public transport. Sustainable energy systems are designed to do very little harm to their environments. This has led to the present situation where a continuous supply of power can be assured without depleting resources or causing people unnecessary pollution.