The solution in depth

Kitemill’s solution for generating renewable energy consists of three main parts: the kite, the tether, and the ground station. Together, they generate energy through a simple, yet effective principle.

1. The Kite

The kite is a specially designed aircraft composed of composite materials. It has a rigid structure and is designed for durability at high-power winds. It has a
form as a sailplane and 4 propellers only needed for taking off and landing. Once up in the air, the kite stays aloft by gliding seamlessly on air currents. The kite is designed to be able to move quickly and effortlessly while adding a high tractive force on the tether.

2. The tether

The kite is connected to the ground through a tether. This tether transforms the pull force from the kite to the ground-station generator. It is made of braided polyethene fibres chosen for their unique endurance capabilities. These in turn provide the lowest diameter for the tether; an important factor for extracting energy from kite turbines. The material of the tether is durable and can be exposed to varying environmental conditions such as moisture and UV light.

3. The ground station

The ground station converts the tractive force from the tether to electricity. This electricity is, in turn, fed into the power grid. A winch located in the ground station is connected to the generator which reels in and out the kite. The control system is also found in the ground station and makes sure all flights are conducted safely and efficiently. It ensures optimal energy production as it controls the kite and the winch. Sensors mounted on the aircraft provide data points for the control system to steer and balance the aircraft. The control system enables autonomous operation of Kitemill’s entire solution and the subsequent energy production.

Energy production

Production phase: flying in a helical pattern downwind pulling the tether (90% of the operational time)
Return phase: returning the kite and retracting the tether (10% of the time), before next production phase.

In the production phase, the kite flies in a circle downwind and builds up lifting force by pulling on the tether. In this phase, the tether ‘holds back’ the kite by releasing it with about ⅓ of the wind speed. The kite will then naturally act as a disruption to the wind that hits the kite and will glide in a helical form. This increases the contact area between the kite and the wind. When the max tether length of the production phase is reached, the kite automatically shifts position and is reeled in to begin its next production phase. This is done at great speed - increasing the energy created in the production phase and limiting the energy used in the return phase. The kites operate automatic, and due to the control system, they will always seek the optimal altitude and wind speed. In the event of severe weather conditions or low winds, they will automatically return and land at the ground station.