Energy Assessment for a 300-MW wind farm in mountainous area

Energy assessment studies in a pre-construction phase are a key step in the development of a wind farm. In recent years, the growth of big project located in always more complex environments makes this energy assessment... [ view full abstract ]

Energy assessment studies in a pre-construction phase are a key step in the development of a wind farm. In recent years, the growth of big project located in always more complex environments makes this energy assessment becoming a challenge. In this context, North-Eastern Brazil is a region where a very good wind resource is available at several sites, with mean wind speeds above 9 m/s at 80-100 m. Many of the most promising areas are located in complex terrain, i.e. mountains with high steepness or at the top of elevated plateaux.

In this study, the energy assessment of a wind project located in one of such areas in North-Eastern Brazil is presented (Figure 1). The project consists of 131 turbines totaling 303 MW of installed power.

For the energy assessment, a total of 18 meteorological masts were installed over an area of around 20 x 20 km (Figure 2).

Mast data with a recording period between 6 months and 6 years were validated and long-term adjusted using a re-analysis dataset. A wind map of the area was generated using numerical wind flow model, in this case the Sitewind system: a method developed by AWS Truepower which combines meso-scale and micro-scale scale modelling. The resulting wind resource map, which is adjusted to mast measurements, gives information about mean wind speeds, wind rose and sectorial wind speed distribution on a grid with 50 m spacing (Figure 2).

This map is used as input to calculate the production of the wind project. In order to obtain the net production losses were also assessed, such as wakes, availability, electrical, turbine performance, environmental and curtailment losses. The total energy uncertainty of this assessment was finally estimated according to industry standards.

The pre-construction production estimation of 34 turbines (shown as circles in Figure 2) was compared with the one obtained using production data after 1 year of operation, which has a much lower uncertainty. The comparison shows a very good agreement between pre-construction and operational assessments (Table 1), thus confirming the high reliability of the energy assessment.