Wave power is the capture of energy of wind waves to do useful work - for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC). In this concern, wave power is distinct from tidal power, which captures the energy of the current caused by the gravitational pull of the sun and moon. Waves and tides are also distinct from ocean currents which are caused by other forces including breaking waves, wind, the Carioles effect, caballing, and differences in temperature and salinity. Wave-power generation is not a widely employed commercial technology compared to other established renewable energy sources such as wind power, hydropower and solar power. However, there have been attempts to use this source of energy since at least 1890 mainly due to its high power density.