Hybrid wind-turbine tower with braced foundations
Hybrid towers based on braced foundations allow for the highly efficient evolution of any conventional steel tower into a hybrid tower, with an increase in height of 8–10 metres. The resulting product is a truly hybrid tower, the first 8–10 m section of which from the ground up is made of concrete, followed by any existing conventional steel tower. The entrance, lift and ground-level equipment (cabinet, switching gear, etc.) can be positioned at ground level in the concrete part of the tower. The old T1 steel section is simplified as a result of eliminating the door, access ladder, platforms and other items. The cage bolts are shorter. This results in a notable saving in the bottom part of the steel tower (about 20,000 euros per tower).
The cost of building the concrete part of the tower and the foundation is slightly higher than the cost of building a conventional foundation with no height gain. The solution with braced foundations saves a significant amount of materials, but the building process is more complex for this solution than for a conventional foundation, although significant improvements have been made in recent projects. The prefabrication or specialisation of the building process may give rise to cost savings, but the cost difference for the foundation (positive or negative) is very small if we compare it to the value of the extra hub height and the saving in the tower’s bolt-cage section + T1.