Step 1: Background
Our search for a key to future energy development can be found in wind energy. As the sun warms the earth’s surface, the atmosphere is warmed also. Warm air weighs less than cold air, which make it rise. The cool air then moves in to replace the warm air. This movement of air is what causes wind. In the 1st century, a Greek man named Heron of Alexandria created the first windmill. A wind generator attempts to convert the motion of air into electricity or in some cases, mechanical power. It is one of the oldest forms of renewable power generation in human history.
The quest for creating a revolutionary wind generator that has the potential to compete with fossil fuels starts with the wind. Modern wind turbines like the Enercon E-126 is highly engineered. Standard tower to turbine systems, no matter how highly engineered they are, have limitations. First, they cannot rise above 500 feet. They are tied to the constraints of a tower. They are heavy and extremely difficult to transport. They are expensive, and not cost effective enough. They do not produce enough power to be competitive with fossil fuels. Modern wind turbines are getting larger and larger, it seems they have reached their height limitations. Some say “the wind turbine,” is the most efficient design for converting the motion of the wind into mechanical or electrical power. I am here to tell you, it is not.
A man named Miles L. Loyd from Livermore, California wrote a seminal paper titled, “Crosswind Kite Power.” This paper describes a concept for large-scale wind power production by means of aerodynamically efficient kites. By using the same principles as airplane construction, these kites can transverse the wind at very fast speeds. The methodology used in Mr. Loyd’s paper lays the foundation for the study of power-producing kites. Mr. Loyd writes, “Recent development of large wind turbines has led to a high degree of refinement in their design. These turbines are near optimum for available materials and processes but the single-unit power output in limited to a few megawatts.” Through the years thermal and electric power have replaced windmills in many applications. Windmills, in recent years, have only gained recognition due to their connection with alternative energy. Kites have barely been considered.
A kites’ surface converts the motion of the wind into lift or motion of the kite. Conventional methods for power generation using a kite have involved mounting turbine to the kite. Moreover, some methods include the kite pulling its tether which in turn pulls on a generator producing power. In this project an entirely new perspective on Airborne Wind Turbines (AWT) will show the potential of kite based wind energy.
Up until now, airborne wind turbines have been stationary, only to face the wind, like the Magenn Air Rotor System featured on the right. A system like this is not only unimaginative, but it lacks the size and area of a ground based wind turbine. The only advantage Magenn delivers is that it functions at higher altitudes, soon. A kite system, as proposed in this project would not simply face the wind like the Magenn air rotor system, but such a kite would fly in a predetermined path downwind from the tether point and the kite motion would b e redirected to transverse the wind. The kite would fly in an orbital axis, is the same sense that a wind turbine’s blade flies transverse to the wind. The wind would not only be supporting the kite in this system, but it would also be generating usable electricity. The kite in this case, would mimic the rotational movement of the tip of the wind turbine. The tip of the wind turbine is one of the most efficient parts of the mill which constitutes the last 25% of the blade. In some cases, the tip of the wind turbine produces 75% of the power generated. The tip is rotating at the highest velocity due to the fact that it is sweeping the largest part of any of the blade.
In this brief talk, Saul Griffith unveils the invention his new company Makani Power has been working on: giant kite turbines that create surprising amounts of clean, renewable energy.