HIGH ALTITUDE WIND POWER GENERATION

INTRODUCTION

The problem of sustainable energy generation is one of the most urgent challenges that mankind is facing today. On the one hand, the world energy consumption is projected to grow by 50% from 2005 to 2030. Fossil fuels actually cover about 80% of the global primary energy demand and they are supplied by few producer countries, which own limited reservoirs. The cost of energy from fossil sources is continuously increasing due to increasing demand. Moreover, the negative effects of energy generation from fossil sources on global warming and climate change are recognized worldwide and lead to additional indirect costs. One of the key points to solve these issues is the use of a sustainable combination of alternative renewable energy sources. Some concise considerations are reported about wind energy to better motivate the presented research.

Wind power actually supplies about 0.3% of the global energy demand, with an average global growth of installed capacity of about 27% in 2007. It is interesting to note that recent studies showed by exploiting 20% of the global land sites of class 3 or more (i.e. with average wind speed greater than 6.9 m/s at 80m above the ground), the entire world’s energy demand could be supplied. However such potential cannot be harvested with competitive costs by the actual wind technology, based on wind towers, which require heavy foundations and huge blades, with massive investments.

Such a break through in wind energy generation can be realized by capturing high altitude wind power.The basic idea is to use tethered airfoils, linked to ground with cables which are employed to control their flight and to convert the aero dynamical forces into mechanical and electric power.

HIGH ALTITUDE WIND POWER ENERGY

The high-altitude wind of the troposphere represents an untapped energy source that is larger than the world's current energy needs. The key idea of Kitenergy is to harvest high-altitude wind energy with the minimal effort in terms of generator structure, cost and land occupation. In the actual wind towers, the outermost 30% of the blade surface contributes for about 80% of the generated power.

To understand the concept of Kitenergy, one can imagine removing all bulky structure of a wind tower and just keeping the outer part of the blades, which becomes a much lighter airfoil flying fast in crosswind conditions, connected to the ground only by the two cables. The cables are rolled around two drums, linked to two electric drives that are able to act either as generators or as motors. Thus, the rotor and the tower of the present wind technology are replaced in Kitenergy technology by the airfoil and its cables, realizing a wind generator which is largely lighter and cheaper.

TECHNOLOGY USED

The concept of Kitenergy is to use airfoils or power kites, similar to those used for surfing or sailing, linked to the ground by two cables, to reach altitudes of about 600-1000 m above the ground. At such elevations, winds are stronger and more constant compared to the elevation where actual wind towers operate. The flight of the airfoils is tracked using on-board wireless instrumentation and it is suitably driven by an automatic control unit, able to differentially pull the lines to influence the wing motion.

Electricity is generated at ground level by converting the traction forces acting on the airfoil lines into electrical power, using suitable rotating mechanisms and electric generators placed on the ground. An electronic control system can drive the kite flight by differently pulling the cables. The kite flight is tracked and controlled using on board wireless instrumentation as well as ground sensors to measure the airfoil speed and position, the power output, the cable force and speed, and the wind speed and direction.

The system composed by the electric drives, the drums, the on-board sensors and all the hardware needed to control a single kite is denoted as Kite Steering Unit (KSU) and it is the core of the Kitenergy technology.

Thus, high- altitude wind power generation may contribute to a significant reduction of the global dependence on the fossil sources in a relatively short time. Indeed, industrialization of this technology may require from 3 to 5 years, since no break through is actually needed in any of the involved engineering fields to apply this technology, but rather the fusion of advanced competencies, already existing in each field, in order to increase the efficiency and reliability of the system. Indeed, substantial new technological innovations, for example in the field of high efficiency airfoils, may lead to further great performance improvements.