Estimating the amount of energy a wind turbine will generate in a year is a key factor in determining the viability of any wind development project. To do that responsibly, it is important to understand wind characteristics, especially its variable nature. Equally important, however, is an understanding of site and operational issues that affect the ultimate, bottom-line net usable energy production from a wind turbine installation.
When it comes to generating electricity, the single most important characteristic of wind is its speed. A wind turbine turns kinetic energy, a function of mass and velocity, into electrical energy. The faster the wind, the more energy it contains. The denser the wind, the more energy it contains. In fact, the kinetic energy in the wind increases in relation to the cube of the wind speed. Doubling wind speed increases its energy by a factor of eight.
Wind speed distribution and estimating the speed of the wind are both important parameters that need to be considered.
Estimating Energy Production
In addition to the wind speed and distribution, the last bit of information necessary to estimate energy production from a wind turbine is the turbine’s power curve. The power curve describes the power (kW) the turbine generates at each wind speed. Manufacturers publish power curves for their products. It is important to understand the veracity of manufacturer-published power curves. Many are verified by independent third-party testing labs, as is true for the NPS 100 wind turbine. Many are not.
Other factors that must be considered are nominal energy production estimate and de-rating output. The elements of energy output derates include air density, turbine availability, site availability, and site losses.
For more information on these considerations and their various elements, please download the Engineering Bulletin:
This document outlines the issues and describes how we address them at Northern Power.
–Alan Axworthy, Director, Application Engineering