Hydro turbines, the oldest and the most commonly used renewable energy source, have the highest efficient of all power conversion process. The potential head of water is available right next to the turbine, so there are no energy conversion losses, only the mechanical and copper losses in the turbine and generator and the tail end loss. The efficiency is in the range of 85 to 90 %.
Wind turbines have an overall conversion efficiency of 30 % to 45 %.
These two renewable sources, though efficient, are dependent on availability of the energy source.
Solar thermal systems can achieve efficiency up to 20 %. The moving path of the sun and the weather conditions drastically alter the incident solar radiation. The efficiency on an annual basis, around 12 %, is considerably less than on a daily basis.
Geo thermal systems, on the other hand, also use the Rankine cycle with steam temperatures at saturation point. Since there is no other conversion loss, this plant can achieve efficiencies in the range of 35 %.