Ocean, wind and others are sources or alternative energy.
Alternative energy is often referenced as: any energy source that is an alternative to fossil fuel. These alternatives are intended to address concerns about such fossil fuels. It causes less pollution too.
The nature of what constitutes an alternative energy source has changed considerably over time, as have controversies regarding energy use. Today, because of the variety of energy choices and differing goals of their advocates, defining some energy types as "alternative" is highly controversial.
In a general sense, alternative energy as it is currently conceived, is that which is produced or recovered without the undesirable consequences inherent in fossil fuel use, particularly high carbon dioxide emissions (greenhouse gas), an important factor in global warming.
Historians of economies have examined the key transitions to alternative energies and regard the transitions as pivotal in bringing about significant economic change. Prior to the shift to an alternative energy, supplies of the dominant energy type became erratic, accompanied by rapid increases in energy prices.