comparing remote sensing systems to met towers

Comparing Remote Sensing Systems to Met Towers What You Can Learn From Vaisala’s Recent Study Webinar, October 22, 2015

Lee Alnes Dr. Mark Stoelinga

#WindWebinar

q  This webinar will be available afterwards at www.windpowerengineering.com & email

q  Q&A at the end of the presentation q  Hashtag for this webinar: #WindWebinar

Before We Start

#WindWebinar

Michelle Froese Senior Editor - Moderator Windpower Engineering & Development

Lee Alnes Key Account Manager Vaisala

Dr. Mark Stoelinga Senior Scientist Vaisala

Comparing Remote Sensing Systems to Met Towers

Meet the Speakers…

Page © Vaisala | www.vaisala.com/energy

Why Remote Sensing? Higher height data

10/27/15 4


Why Remote Sensing? Additional advantages

10/27/15 5

•  Easy to install

•  No permitting delays

•  Easy to move, relocate, and service


Applications of Higher Height Data

10/27/15 6


Accuracy

10/27/15 7

The words accuracy and uncertainty are sometimes interchanged…

Accuracy of measurement [means] ‘the closeness of the agreement between the result of a measurement and a true value of the measurand’… Accuracy is a qualitative concept.’ It can be high or low for example but strictly it should not be used quantitatively.

In practice, though, it is often used quantitatively…this unofficial definition breaks down because it inherently assumes that a true value can be defined, known and realized perfectly.

… Uncertainty of measurement acknowledges that no measurements can be perfect and is defined as a '… parameter, associated with the result of a measurement, that characterizes the dispersion of values that could reasonably be attributed to the measurand.’ National Physical Laboratory (UK): http://www.npl.co.uk/reference/faqs/is-there-a-difference-between-'accuracy'-and-'uncertainty'-%28faq-length%29


Uncertainty

10/27/15 8


“P values” (P90, P50, . . .)

10/27/15 9

§ Probability of exceedance

§ P50 – median value § P90 – 90% chance of

achieving at least this value

P99 P90 P75 P50


Correlation: R and R2 R: correlation coefficient R2: correlation squared, a.k.a. coefficient of determination. It represents the fraction of variance in the y-variable “explained” by the linear fit to the x-variable.

10/27/15 10

Rem

ote

sens

or w

ind

spee

d (m

-1s)

Tower wind speed (m-1s)


Validation Studies

§ Who does them §  Wind developers and operators §  Remote sensing manufacturer §  Research organizations

§ What they measure §  Wind speed, direction, etc. à comparisons §  Data recovery, up-time, power consumption, …

§ Not to be confused with calibration

10/27/15 11


Ongoing Validation Studies

§ Triton® Wind Profiler has been independently evaluated and verified for accuracy by:

§ Studies in progress – 2015

10/27/15 12

China Hydroelectric Corporation


Our Main Question

§ How does Triton uncertainty compare to a met tower system, in actual commercial use?

10/27/15 13


Vaisala’s Unique Position

10/27/15 14

MANY DEPLOYMENTS HAD COLLOCATED TOWERS MANY LEADING CUSTOMERS VOLUNTEERED DATA FOR A GLOBAL STUDY IN-HOUSE WIND RESOURCE ASSESSMENT EXPERTISE

2500+ TRITON LOCATIONS

IN 30+ COUNTRIES


The Data Set §  30 Triton / Tower data sets included in the study:

§  Triton data came from 24 different units manufactured between 2008 and 2014 §  A total of 100 correlation pairs (heights) were used

–  Shortest tower measurement height was 34m –  Tallest tower measurement height was 120m –  Average tower to Triton distance was 134m –  Most Triton / tower elevation differences were less than 2m, and all were within 6m

§  18 of the data sets used Tritons with the original speaker array §  12 of the data sets used Tritons with an improved speaker array that was released

in 2013 §  All Tritons were deployed as they were shipped from the factory with no special

modifications or equipment

10/27/15 15


Geographic Distribution

§ Well distributed geographically

§ Exact locations not shown to preserve customer confidentiality

10/27/15 16


Key Take-aways § Certainty: Triton has the same uncertainty on mean wind speed as a

well designed met tower—about 1% RMSE. §  Not just in one experiment, but over 10’s of 1000’s of data-hours §  Measuring with Triton cuts met tower shear extrapolation error in half

§ Repeatability: You can expect continued, repeatable performance from one Triton to another

§ Longevity: Study included data collected over 6 years – with no degradation due to age of unit

10/27/15 17


But what is the “Truth”?

10/27/15 18

“TRUE” WIND SPEED ?

TOWER UNCERTAINTY SOURCES: CALIBRATION | TURBULENCE & OFF-HORIZONTAL FLOW | SENSOR DEGRADATION | TOWER FLOW DISTORTION | TO NAME A FEW!


Conclusion: Wind speed “When the mean wind speed differences at all 100 qualifying anemometer measurement heights within the 30 Triton/met tower pairs are aggregated, the average percent difference is +0.09%, and the percent root mean-square of the differences is 1.27%. This is consistent with an estimated uncertainty of the Triton of approximately 1%, if the met tower measurement uncertainty is assumed to be independent and approximately 1% as well, a reasonable assumption for a large set of met towers maintained by many different Triton users.”

10/27/15 19


Data Recovery “All Tritons (both original units and those with the upgraded speaker array, or “TPU” units) exhibit high data recovery (>=90%) up to 80m. Data recovery for the newer TPU units is considerably improved compared to that of original units at higher heights: •  17% higher at 100 m, •  47% higher at 140 m, and •  106% higher at 180 m.”

10/27/15 20


Reducing Shear Extrapolation Uncertainty When mean winds directly measured by Triton are compared with estimates sheared up from lower met tower heights, the Triton-measured mean wind speeds exhibit uncertainties less than half that of estimates sheared up from met towers.

10/27/15 21


Summary: Main Points

§ Remote sensing is in widespread use and will continue to grow

§ Accuracy, uncertainty, calibration, validation, correlation are frequently misunderstood or misused

§ Vaisala Triton has been shown to have equivalent uncertainty to met towers – all over the world

10/27/15 22

#WindWebinar

Michelle Froese Senior Editor - Moderator Windpower Engineering & Development @Windpower_Eng

Lee Alnes Key Account Manager Vaisala [email protected]

Dr. Mark Stoelinga Senior Scientist Vaisala [email protected]

Comparing Remote Sensing Systems to Met Towers

Questions?

#WindWebinar

Thank You q  This webinar will be available at

www.windpowerengineering.com & email

q  Tweet with hashtag #WindWebinar

q  Connect with Windpower Engineering & Development

q  Discuss this on EngineeringExchange.com