Vertical Axis Wind Turbines Options appraisal

The wind speed profile will determine the choice for a wind turbine generator, while the supply of wind influences the relative dimensions of the rotor, generator and shaft height.
In poor wind conditions then a high shaft height and relative large rotor are necessary.
The selection process was mainly based on the evaluation of the rated power and rated wind speed, cut-in and cut-out speed and finally the power generation capacity. The larger the nominal power the better in terms of cost (€) per KW.

Rated power and rated wind speed. The rated power is usually defined as the maximum power output and the rated wind speed is the wind speed at witch the turbine reaches the rated power output. A combination of high rated power and low rated wind speed (it is advantage for wind turbines to reach their rated power at the lowest wind speed possible) is favorable.
Cut-in & cut-out wind speed. The cut-in speed is the lowest speed at witch a turbine will start to generate electricity. Practically the speed is around 3 to 4 m/s. Lower start up speed has the advantage in terms of total energy production. The cut out speed is the speed at which a wind turbine will stop producing electricity. Many VAWTs can withstand extremely high wind speeds and are designed in such a way that they do not shut down at any wind speed.

The vibrations and the noise effects that the turbine may cause were not considered as a first priority issues and this is mainly due to the fact that the turbines will be placed along a highway with no residents nearby. Thus, it is feasible to make use of a vertical axis wind turbines (VAWTs) farm in lower mountain areas in which – because of various reasons, the most prominent of which are the visual appearance and the noise production – the use of large installations is not justified.
Below is presented a comparison list of the available  vertical axis wind turbines (VAWT) turbines based on the basic specification as they are provided from the catalogue of European Urban Wind Turbines Manufactures.

NOTICE: all calculations made were based on energy curve wind data provided by the product suppliers under the same site conditions.

Annual renewable energy delivered

Based on capital cost and assuming comparable installation and maintenance cost the WRE.030 and Turby 2.5 provide the same annual savings and comparable capital cost and payback period. The cost per KW installed for the WRE.030 is approximately half the cost of Turby 2.5.

Also one of the basic reasons why the Ropatec was chosen is the fact that the turbine practically has no cut out speed.
Considering the fact that Greek drivers very often drive over the speed limit (in highways it is between 100-120Km/h, or 33,3m/s) the lack of upper limit can leave the turbine produce energy for additional period of time.

In contrast, the Turby 2,5 kW although has approximately the same capital cost and provides the same annual savings was rejected due to the limited cut – out speed limit.