The best on-shore wind power sites in Massachusetts are along the coast and on top of ridgelines in the western and central parts of the state. Wind maps of the state can be used to identify areas of high annual wind, (although its worth noting that local terrain effects can overestimate wind speed) — and also create good sites in other areas of the state that may not be identiﬁed in wind maps. That’s why, if cost effective to do so, one should measure the wind at each specific site.
Why Assess Wind Resource?
The amount of power in the wind is very dependent on the speed of the wind. Because the power in the wind is proportional to the cube of the wind speed, small differences in the wind speed make a big difference in the power one can derive from it. A 10% difference in speed makes about a 33% change in power. This is the primary reason for wind resource assessment. In order to more accurately predict the potential beneﬁts of a wind power installation, wind speeds, and other characteristics of a site’s wind regime must be accurately understood.
Wind Maps — computer models can be used to predict annual average wind speed and maps created by these programs, like AWS TrueWind’s Wind Navigator maps and 3Tier's Firstlook, are useful as a screening tool for potential wind power sites. However, these maps do not eliminate the need for more precise and thorough wind data collection.
There are also important technical reasons for studying a site’s wind characteristics. Wind speeds, wind shear, turbulence, and gust intensity all need to be speciﬁed when procuring a wind turbine, designing its foundation, etc. Typically, wind is measured at a height of 50 meters (164’) or 60 meters (197’) for a year or more. Equipment designed speciﬁcally for wind power is used — weather stations are not sufficient.
Anemometers on a Tower — Meteorological towers, or “met towers” are the most common and cost effective method. The required height of the met tower depends on the topography and nearby trees.
SODAR — a Sonic Detection And Ranging device produces detailed proﬁles of wind speeds and directions up to hundreds of feet above ground, which is useful, for instance, for understanding wind shear, i.e. how wind speeds vary with height.
LIDAR — a laser-based Light Detection and Ranging system also provides detailed proﬁles of wind speeds and directions up to hundreds of feet above the ground.
Because of their expense, SODAR and LIDAR are generally not used for a full year at a single proposed wind site. Instead, when needed, they can be used for a shorter time and compared with longer term data from nearby anemometers.
Ideally, wind is measured at the exact spot and hub height of the proposed wind turbine. Realistically, this precision is not usually possible. First, wind characteristics measured via met towers are sensed at a different height, because most turbine towers are taller than standard met towers. Second, met towers have different siting requirements than turbines, so they may not be able to ﬁt in the same area. In practice, the data will need some amount of extrapolation. If sufﬁcient data are available, computer models that consider terrain can be used to extrapolate wind speeds measured at the met tower in one place, to a nearby turbine location.