Que: What is the purpose of an on-site wind or solar measurement campaign for 1 year?

Ans: Most important for any wind or solar resource measurement campaign at the highest quality, is to reduce the uncertainty in the energy yield estimation for a considered wind farm or solar power plant during the development phase. The goal of the measurement campaign’ is to raise top precise information on the site's long- term resource that allows for better assessment of the energy yield to be generated.

Therefore, it is essential that at least one complete climatologic cycle is measured. that means 1 year.

Que: What is the procedure of such a wind or solar measurement campaign?

Ans: The measurement campaign includes:

Selection of a suitable location to set up the measurement equipment. Diverse criteria are to be considered and taken into account, relating to the precedent norms and standards representing best practice.

Installation and maintenance of the measurement equipment

Executing the measurement campaign and maintaining permanent data monitoring by remote access (modem) warranting data authenticity and data integrity per pertinent technical bankability standards.

Interim and final supervision, evaluation and analysis of measurement data

Compilation of interim and final reports, according to international standards

As a result of a well-designed measurement campaign, the wind or solar resource for the entire project area is assessed at a precise, bankable level.

Que: What are the recent technical challenges for the measurement campaign for wind projects?

Ans: As wind turbines get taller and the blades get longer, it is important to measure the wind speed at the wind turbine hub height, as well as the vertical profile of the whole portion of the blades. Failure to obtain adequate wind measurements could affect in several ways:

over- or underestimation of the wind resource

acquiring wind turbines for the project site with the wrong certification under IEC

problems in executing any rights or titles regarding product warranty or performance guarantees

In the end, a non-optimal wind measurement campaign can quickly result in the financial bankruptcy of a wind project in multiple terms.

Que: What does the term “bankable” for wind projects?

Ans: The wind measurement can be considered as “bankable” if a project’s estimated energy yield production and financial performance are acceptable to a bank, i.e. lenders. The entire financial performance of a project is built upon projections of “how much energy the turbines will generate”, which depends on the quality of the wind resource and its assessment. Wind measurements are the initial stage to assess the site’s resource potential, deriving the financial viability for developing a wind farm. So if there is descending in wind measurements then the whole estimation will be erroneous and misleading.

To reach bankability, best practices need to be applied and internationally developed or accepted standards and norms need to be considered and followed.

Thereby the correct choice of wind measurement equipment is very important. To save a few dollars by using lower-cost, low-quality sensors leads to low data quality and greater uncertainty in the results of the measurement campaign, which results in significantly higher financial costs. Often the negative effects on the financing and project RoI are several thousand times higher than the small amount saved on measurement devices in the initial stage. Besides: warranty rights and titles for project performance cannot be executed using low budget measurement sensors. An example to prove this is: wind turbine OEMs do perform their in-house power performance measurements for their wind turbine datasheets only with very particular high-class anemometers, e.g. from Thies, Vaisala, Vector Instruments or Windsensor. No other models are used, for very good reasons. Another example is: many banks only finance wind projects, if the resource measurements were executed at the highest quality, considering very particular high-class anemometers, e.g. from Thies, Vaisala, Vector Instruments or Windsensor.

We aim to deliver high-quality wind measurement campaigns to reduce uncertainties in estimation for energy yield and helps to get wind farm projects on better financing and to avoid any wrong WT selection, technical or financial risks.
ProfEC Ventus provides all necessary instruments for wind resource measurements and helps our client in setting up MEASNET and IEC (ilac/MRA)-accredit- ed (i.e. NABL complaint) wind measurement campaigns, which helps our client to get financed for their projects easily,

Que: What precisely needs to be done to make wind measurements bankable?

Ans: There are several factors to be considered for designing the measurement setup for wind resource assessments. The amount of met masts needed should be based on the local terrain conditions. Rules of thumb based on our practical experience often lead to the following picture:

If it’s a small wind farm with a capacity of 10 MW - 20 MW and it is flat terrain, one mast in many cases is enough to entirely comply with the pertinent standards and best practices.

If it’s a medium-sized wind farm with a capacity of above 20 MW and it is a complex terrain, mostly two met mast is needed.
If it is a larger wind farm with a capacity of 100 MW and it is a complex terrain with a forest area, more no. of masts is recommended under pertinent standards and best practices. In such circumstances, discussion with the analyst responsible for assessing the wind resource assessment at the site is recommended at the early stage, so costs can be kept low and quality can be kept high. Different eligible measurement strategies can be employed and realized.

According to the wind turbine size it’s always needed to measure the wind speed and wind directions at several heights. Also, the right and most appropriate sensors need to be carefully selected, based on the environmental condition.

For some systems, particularly in cold climates, the measurement of temperature is important to assist with the detection of icing and to take into account the variation in air density. In such circumstances the use of heated or “ice-free” anemometers is essential, nevertheless to keep the lubrication of the sensor bearings in tolerated margins. The whole measurement station should include sensors, power supply, and a data logger that have the brilliant operational working condition to run the measurement uninterruptedly, yielding data availability >99% per year.

If it is a complex terrain due to the wind inflow angle the anemometers won’t respond to the correct wind sometimes it measures low and sometimes it over-estimate the wind. So have to check the classification of the anemometers matches to the site condition and the anemometers are checked and classified in the wind tunnel concerning the tilt angle.

If it is highly complex terrain, then an ultrasonic anemometer or propeller anemometer can be additionally installed to calculate the inflow angle of the wind.

Que: What role do remote sensing devices (RSD) play and do they comply with bankable approaches for a wind measurement campaign?

Ans: Remote sensing devices are being used nowadays to measure wind speed and wind direction in places where met mast cannot be transported and installed, such as high mountain areas and in offshore, which can measure wind speeds at a range of heights without the need for a conventional mast. Also, the combination of masts and RSD is used, in case several locations need to be measured (i.e. large wind farm area), since an RSD can change position after 4-6 months and hence replace the need for several wind masts. Important in complex terrain is, that always at least one wind mast is taking measurements in parallel, so a transfer function between the mast and the RSD can be derived.

Que: What remote sensing devices are most frequently used?

Ans: Principally there are two types of devices:

SoDAR (Sound Detection and Ranging), which emits and receives sound and from this infers the wind speed at different heights using the Doppler Shift principle;

LiDAR (Light Detection and Ranging), which also uses the Doppler Shift principle but emits and receives light from a laser.

The minimum parameters for the wind measurement campaigns are mean and standard deviation of wind speed at least two heights, mean wind direction, mean temperature, mean pressure and humidity to derive site-specific air density. These parameters are continually measured in the frequency of 1 Hz recorded with a sampling rate of every 10 – mins the data acquisition is to meet with the above requirement and the data can be stored locally in the device and also can be transferred via GSM/GPRS to the protected cloud server. The measurements should have a minimum term of 12 months to take any seasonal effects in the account.

Using the mathematical calculation result the following, the frequency distribution and average wind speeds at all measured heights, wind shear/height exponents from the measured wind speeds, turbulence intensity at the site and diurnal variation. By incorporating the surface roughness (topography), ground-level (orography) and neighboring obstacles in the surroundings of the proposed installation site the wind conditions of the site will be determined by using statistical and CFD modeling based computer programs. Hence these evaluations shall be done by an independent neutral accredited testing laboratory to estimate the energy yield to ensure the bankability project.

Que: Could you quickly summarise the most important standards to be considered for wind measurements?

Ans: Best practices for bankable wind resource assessment is to follow these standards and guidelines:

IEC 61400-12

IEC 61400-12-1 Ed.1 (2005)

IEC 61400-12-1 Ed.2 (03-2017)

IEC 61400-12-2

IEC 61400-1 Ed. 2, Ed. 3, Ed. 3.1

IEC 61400-2 Ed. 2

FGW TR6

FGW TR2

MEASNET Power Performance Measurement Procedure

MEASNET Evaluation of Site-Specific Wind Conditions

MEASNET Anemometer Calibration Procedure

ProfEC Ventus is accredited as Testing Laboratory as well as Calibration Laboratory following ISO/IEC 17025 for the following services:

Anemometer Calibration

Wind Vane Calibration

Measurement of Wind Turbine Power Performance

Wind Resource (incl. Wind Mapping) and Energy Yield Assessment of Wind Turbines (incl. Assessment of Losses following TR6 Rev.9)

Installation and Evaluation of Wind Measurements with Anemometers

Site Classification of Wind Turbines

During all our services we comply with the above-mentioned standards to warrant bankability.