The University of Porto
Airborne Wind Energy
Research Project

In search for innovative solutions to generate power from renewable sources, namely to extract wind energy at high altitudes, the University of Porto started the project UPWIND in the area of Airborne Wind Energy Systems.

Our Research

At UPWIND, we are focused on developing the airborne wind energy technology, with an innovative method for harnessing the power of the wind using advanced airborne systems. Our research covers a wide range of topics, from path-planning optimization and path-following control of the kite, to the optimization of kite farms. More recently, we started tackling the automatic take-off and launch of our kite, along with the prototype assembling and test.

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The Motivation

Wind is one of the main renewable energy sources for large scale electrical energy production nowadays. Wind energy is mainly extracted on-shore at low heights by wind turbines mounted on towers with a few dozen meters (50-300 m) and, despite the significant number, still growing, of wind farms, most of the existing wind energy remains unexploited since it is available at high altitudes and off-shore.

100 m

250 m

source: Makani Power

The wind at high altitudes has higher speed when compared against the wind near the ground and, more importantly, it is more stable and consistent. Continuing to increase the height of the towers and the dimensions of the blades of wind turbines is not a viable solution since building such towers entails unsustainable costs. Thus, there is an urge to develop more efficient solutions that enable wind energy extraction at high altitudes and offshore, without increasing instalation and operation costs, making wind power a cost-effective and eco-friendly solution.

The Concept

One of the most promising proposals within AWES projects involves a kite, i.e. an aircraft connected to a generator on the ground through a tether. As the kite rises by the wind, the tether is reeled-out producing power. The tether is reeled-in when it reaches its maximum length and then the process restarts over again.

For efficiency reasons, it is desirable that the kite follows a pre-defined path in space. Knowing the maximum power that can be extracted from the wind is obtained when the kite moves in a perpendicular direction, the optimal trajectory is periodic and it follows a pre-defined path.

Reel–out/traction phase: Energy is generated when tether is unwinding.
Reel–in/retraction phase: A small amount of energy is consumed when coiling back the tether.

source: Airborne Wind Europe