Ridge Technology

Davis Wind specializes in hilltop and ridge wind sites.

Like politics, all wind is local. The problem with ridges and hilly sites is that they are physically difficult to survey and later difficult to develop.

Ridges have very local weather so, once initial survey data comes in, the data is applicable at the measured location but hard to apply to adjacent sites on nearby hills and ridges. These sites are also difficult to model and in relation to other reference sites such as nearby airport weather stations.

In hilly and ridge environments such as exist in Northern California and Nevada, it is necessary to carefully measure or estimate the winds at the point on the ridges where the turbines will be installed. If a hub height meteorological tower is not possible or economical, careful modeling and a SODAR campaign is recommended. This is because the wind shear (how winds vary with elevation) is a very complex function of topography, and also of micro climatological effects that are hard to model as they vary over time.

The difficulty of accurately estimating wind shear for all winds and the similar difficulty of correlating wind measures at one point with winds at a second point makes the wind resource estimation difficult to develop using conventional technology.

To address these problems, Davis Wind is focusing on a two pronged approach:

• developing extensive SODAR capability to augment meteorological tower data, and
• working with smaller manufacturers to produce turbines designed for mountainous locations.

The Meteorological Problem Discussion

Hills and ridges create turbulence and air flow that is hard to measure. For example, if you place a single anemometer on a 20 meter tower you gather data on the horizontal components and direction of wind at that site, however you do not obtain:

• an understanding of the angle of the wind coming up a hill,
• more than a summary understanding of the turbulence,
• any data on how the wind speed varies above and below that point, and most importantly,
• an understanding of how all these factors vary with mesoscale meteorology such as season, time-of-day, and local solar thermal effects around the site.

On marginal sites, all of these factors are important. Clearly, a single anemometer does give an idea of the wind available. If winds were observed close to the rotor center, and there was very little wind, the site can be abandoned. Likewise if there is a huge amount of wind, further work is warranted; perhaps not as much to assess the energy resource as to assess the mechanical requirements of the turbines. The important point is that on hills and ridges, winds vary a lot, especially in time and with height, and these sites have to be studied more intensively than sites in open plains.

To meet the challenge of hilly and ridge sites, Davis Wind is working on turbine adaptations and proprietary new geophysical equipment for wind assessment applicable to these types of sites. Specifically, Davis Wind is working with a new group Down East Wind, LLC who are designing new proprietary types of SODAR survey equipment, currently under development for these difficult conditions.

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