High Quality Wind Resource in Brazil measured by 230 Met Mast Campaigns

Introduction

Since the advent of wind energy market in Brazil, it is not unusual to find articles talking about exceptional capacity factors that are expected in this country due to the quality of wind resource: high and constant wind speeds, and unidirectional wind flows. However, published information is usually qualitative, inducing people to question validity of these characteristics, rarely seen worldwide. Due to this fact, Casa dos Ventos (CdV) has thought about giving some statistical analyses to those characteristics, increasing international credibility on Brazilian wind resource.

Approach

In order to measure and understand the characteristics of Brazilian wind resource, CdV has conducted around 750 wind measurement campaigns since 2008. So, this work proposes to present a quantitative analysis of the data collected over the last year, based on high quality continuous measurements using first class anemometers and respecting the IEC standards and the best wind measurement guidelines. To accomplish this objective, CdV defined a period of analysis that maximizes the number of masts with at least 1 year of concurrent data, resulting in 230 masts (all 230 with continuous measurement, starting and ending at the same days, and measuring the same height above ground). These 230 points covers almost 17GW of CdV wind projects in different phases of development at a maximum distance of 5Km of each wind turbine and its closest measurement point.

The analyzed masts are very representative of the Northeast inland part of Brazil, covering 631 CdV projects of around 30MW each, where 314 of these projects already have public registration in ANEEL (National Agency of Electrical Energy). As can be assumed, this study represents the official wind measure of near 40% of all the Northeast inland projects registered by the National Agency.

After proper treatment of each mast data, CdV conducted an analysis of the usual wind parameters, such as Weibull, Shear and Wind Direction, providing representative statistics about Brazil’s wind resource and its overall quality. All parameters refer to 80m, as this is the common measurement height for all types of masts. Moreover, this is the typical hub height that manufacturers offer in Brazil (66% of in-operation projects use wind turbines at a hub height between 75m and 85m).

Main body of abstract

As a result, 80% of all masts have:

Mean Weibull shape parameter between 2.7 and 4.4 (k =3.6 and σ=0.7).
Mean Weibull scale parameter between 8.2 m/s and 10.2 m/s (c =9.2 m/s and σ=0.8 m/s).
Mean power law shear parameter between 0.086 and 0.243 (α =0.165 and σ=0.048).

In terms of directional scatter, 80% of all masts have a standard deviation of the mean direction lower than 33°, indicating that at least 80% of all direction measurements from those masts do not differ from the mean direction more than 43° in terms of absolute difference.

In order to analyze the energetic potential of the resource measured by those masts, their Weibull parameters were associated with Gamesa G114 2.1MW power curve at 80m hub height. The assumed values for air density, aerodynamic losses and other losses are the average values from all CdV projects: 1.1 kg/m3, 5% and 10%.

As a result, 80% of all masts have a mean Liquid Capacity Factor (LCF) between 48% and 63% (LCF =55% and σ=6%), evidencing the expected LCF value of 55% for the Brazilian wind resource.

Conclusion

These results show that Brazilian Northeast inland wind resource characteristics are indeed consistent and of high quality. The analyses evidence that wind speeds are high and constant (c =9.2 m/s and k =3.6), and that wind flows most part of the year from a narrow range of directions.


Learning objectives
Many of the emerging wind markets present wind resource characteristics that differ a lot from the main European windy countries.