By Alistair Marsden
Commercial Director | Dulas
For years, meteorological (met) masts served as the wind-resource measurement instrument of choice for the wind-power industry. These free-standing towers come in different heights and hold the meteorological devices needed to measure important variables — such as temperature, and wind speed and direction — when siting wind farms. However, the introduction of SoDAR (sonic detection and ranging) and LiDAR (light detection and ranging) have given wind developers options.
Granted SoDAR, which uses sound to measure atmospheric conditions, has been used to assess wind conditions for several years and is typically deployed in addition to conventional anemometry. LiDAR is a comparatively newer option in the wind industry that applies light to measure atmospheric characteristics. There are many advantages to both of these remote-sensing devices, including fast and highly accurate data capture. However, these instruments come with a price point that may deter some developers.
So the question is: what device to choose?
Accurate wind data is critical for effective siting of new wind turbines and securing project financing — which is the backbone of a new wind farm. Failure to fully assess the merits of each measurement device (a met mast or remote sensing), or effectively deploy the selected technology, can lead to serious financial repercussions. In fact, data quality can make or break a project’s development.
Prior to selecting a measurement device, it is important to consider site-specific factors, such as:
- Landowner issues
- Site conditions, including weather and accessibility
- Onsite obstacles, such as complex terrain, trees, or pre-existing infrastructure
- Data requirements for financing and permitting, such as measurement location and heights
A bankable wind measurement campaign includes a high degree of quality data and thorough documentation, proper selection of measurement locations, and a reliable measurement instrument.
Most investors also require a minimum of one year of onsite wind data. Inaccurate or insufficient site information is one way to risk bankability. Therefore, it is important to choose a wind-resource measurement device wisely.
Remote-sensing units are becoming increasingly competitive. However, met masts retain a key advantage as the industry standard for data collection and assessing project bankability. Met masts have been the go-to measurement device since the early days of wind siting, and are well-recognized by financiers.
A strong second-hand market means these instruments provide a cost-effective choice, particularly compared to SoDAR or LiDAR devices. Previously owned or refurbished met masts may be passed on to new developers or reused repeatedly. However, these instruments have limitations and upfront cost is a poor deciding factor of successful siting (or financing).
Met masts typically require siting permits, which can take months to obtain. Their maximum height (about 160m or 525 ft.) and lack of versatility may present planning and operational challenges in the field. This is particularly true as developers choose taller towers to take advantage of stronger winds. Met masts’ measurement instruments (such as its cup anemometer used to measure wind speed) are also susceptible to mechanical failure and lightning strikes.
It is important to assess these risks, and consider the site conditions and location, before banking on met masts.
One compelling argument for choosing SoDAR or LiDAR units is the range of data captured compared to met masts.
By emitting a laser beam or sound pulses and measuring the return signals, LiDAR and SoDAR units provide information on numerous wind characteristics, such as wind speed, shear, and direction — and up to heights of 200m (656 ft.). These devices can also measure wind across the full sweep of a rotor blade, providing more bankable data.
What’s more is these remote sensors offer flexibility. They can be ground-based or mounted, and are easily transported at and between sites. But they will cost and can range up to more than double in price than a met mast. In addition, there is reluctance among some lenders to rely on remote-sensing data for project financing, but this is expected to change as the technology gains greater adoption and acceptance within the industry.
The right choice
One key to choosing the ideal method of data collection for a project is careful site evaluation. No two regions are alike, so assessing the physical and logistical features of a site is required.
For example, complex terrain such as that found in mountainous or forested regions is more likely to affect the reliability of remote-sensing data. Similarly, a boggy or overly firm ground can present challenges to erecting and installing met masts.
Local policies or restrictions may also vary between regions and countries, such as the ability to deploy a met mast above a certain height. In addition to practical considerations, there are financial ones. For example, it is important to ask: would an extensive range of data outweigh the upfront costs of investing in remote-sensing technologies? Or: are we dealing with an investor who has a track record of investing in data from met masts?
For some projects, co-location is the ideal choice, which means using remote sensing and a met mast. If time or data quality is a concern, the two instruments may provide quick access to a wider range of information at multiple locations (or wind sites). Co-location may also offer increased bankability because the data obtained from both devices can be compared and validated. While cost restrictions may apply, co-location is typically the most sensible and successful option for a reliable resource assessment.
There are many factors to consider when siting a new wind farm and securing financing. Developers will often seek advice from a consultancy that’s experienced in site assessments and wind measurement campaigns. Ultimately, developers and investors who consider a range of factors, rather than just what device was used for wind measurement, may derive the best value from these campaigns.
As a new report entitled, Enhanced Data and Enhanced Returns: Getting the best from wind monitoring technology, states: “The choice between met masts and remote sensing units is not a zero-sum game — both have a role to play in an integrated approach to wind resource assessment that factors the technology, site conditions and project timeline and resource budgets into the decision-making process.”