The Difference Between Hydroelectric Generator And Wwind Turbine

First of all, it is necessary to clarify what is the definition of the efficiency of the two types of machinery: hydroelectric generator and wind turbine.

The efficiency of the hydro-generator set is the kinetic energy of the high-level water flow + the proportion of the total energy that can be captured in the potential energy. It is not the efficiency of the turbulent impeller system alone to capture the kinetic energy of free flow. The impeller of the hydraulic turbine operates in a closed system, and the conversion efficiency of the convective flow energy is not restricted by the Betz theory.

The efficiency of wind turbines, if not to mention the efficiency of mechanical and power electronic systems, refers to the impeller's ability to capture the kinetic energy of free flow. The upper limit of efficiency (~0.59) is determined by Betz theory, and the optimal Cp of modern wind turbines can reach ~0.50.

In fact, potential energy accounts for a large part of the energy of high-level water flow. After the water flow passes through the turbine, the speed or kinetic energy does not change significantly, and the main potential energy is converted, so it has such high efficiency.

Another question is, does the density of water and the resulting high energy density help? I think obviously there is. Wind turbines and hydraulic turbines are directly converted from mechanical energy to mechanical energy at the front end of power generation. A dense fluid can drive a heavy machine more efficiently: the machine itself can be made smaller, the fluid itself is viscous, and the small contact area can be reduced Small friction loss; large-scale fan blades have significant aerodynamic resistance such as blade tip induced resistance; the friction loss of the machine itself accounts for a smaller proportion of captured energy, and so on.

The density of water is large, but the difference between air density and water is three orders of magnitude. The upstream of the turbine is the high water level of the dam, and there is a lot of potential energy that can be used to transform the water; while the wind turbine is facing free flow, in other words, the kinetic energy of the air needs to be captured. Due to the density gap, this energy gap is very large, and wind energy can be said to be relatively thin.

Most importantly, the operation of the hydroelectric generator is in a closed system, which can maintain the pressure of the incoming flow, and the blades of the wind turbine are operated in the open system. The theoretical efficiency is high.