¿Qué energías alternativas existen? ¿Qué tan contaminantes son? ¿Qué ventajas y desventajas tienen?

Solar, hydroelectric, eolic and thermal are alternative sources of energy.

Explanation:

- Solar energy is the direct utilization of the energy obtained from the sun.

- Eolic energy uses the energy obtained from the winds.  

- Hydroelectric energy uses the energy obtained from natural and artificial water masses including oceans, lakes, rivers, etc.

- Thermal energy is produced by Earth's heat.

These types of energy are critical sources to obtain clean energy, this means that they do not produce greenhouse atmospheric gases such as carbon dioxide, which is an important advantage considering the global warming.

The main limitation of alternative sources of energy is that they are expensive compared with conventional energies, especially those derived from petroleum.