Wind Assessment Basics

For Island InstituteFall 2013

by Mick Womersley

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Power curve for Northwind 100

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Wind speed in M/S

A misspent youth?

Essentials of Wind Assessment• Turbines are expensive and if you don’t put them in a good windy spot,

you can waste money: millions of dollars for a big turbine• Subjective assessment is not scientifically valid. You may think you

have the wind, but you don’t know• Wind maps are OK, but not great. (I’ll show you how to get a good-

enough one for free)• To really know, instrumental assessment is best. You need to put up an

anemometer and vane at the same height as the turbine, on the same site, or better yet, a bank of anemometers at different height intervals, with back-ups in case of failure

• Computer logging is best. No one can read an anemometer as often as a computer can

• The industry standard is to record wind speed in meters/second, averaged every ten seconds, over one or two years

• This is an expensive procedure, done only for the larger more expensive turbines. Smaller turbines can be simply put up on the basis of a wind map and the recommendation of a region-knowledgeable site analyst, monitored for performance (and moved/sold on if need be)

Maine has enough wind – in

some places

USDOE Maine wind resource

map

The majority of Maine is listed as

a Class 1 to 2 wind resource

area

Estimated average wind speed = 5.24 m/s

Frankfort/Prospect, Maine community wind power planning GISMick Womersley, Unity College, June 2011Base data from Maine GIS library, wind data from National Renewable Energy Lab 50 meter high resolution wind data set

Legend

50 meter AGL Wind Power Class (WPC) contours:First contour: Wind Power Class 1(0 to 5.6 meters/second)Second: Wind Power Class 2(5.6 to 6.4 meters/second)Third: Wind Power Class 3, (6.4 to 7 meters/second)Fourth: Wind Power Class 4, (7 to 7.5 meters/second)

20 foot USGS contours

Wetland zoning

Roads and tax parcels in black, tax parcels not available for some towns

Discussion:

This map uses basic mapping data and GIS software freely available for use. It was made in Q-GIS using basic data from the Maine GIS Library, free access online, as well as wind data from the NREL.It shows the terrain and basic planning features most pertinent to community discussion of wind power proposals in parts of the Maine towns of Frankfort and Prospect. Copies can be made by request for town or public use by calling or emailing the author at Unity College. Similar maps can be produced on request for other towns in Maine.

WPC 2

WPC 2WPC 2

WPC 3 WPC 4

Penobscot River (WPC 2)

Mount Waldo

Maine Wind Energy Potential• Sites so far (public data, Villeneuve, Womersley and FIW)

– Thorndike– Vinalhaven– Charleston– Oakland– UMPI– NMCC– Sedgewick– Mercer– Strong– Fayette– Auburn– Lewiston– Farmington– Old Orchard Beach– Peaks Island

What you need: PreliminariesA windy site where you expect a turbine is feasible and have completed preliminary surveys:

– There seems to be good wind– Ground is suitable or can be made so: trees, rocks, soils– Preliminary tests are done with hand-held equipment– Existing wind maps are consulted. A wind mapping

program such as WAsP is used to extrapolate potential wind speeds

– The site owner gives permission, and will likely allow a turbine in the future

– An idea of potential turbine scale and any siting difficulties to be planned for: neighbors/community objecting, noise, zoning, interference

– Preliminary cost assessment and funding potential –includes “free” federal and state money, rebates and offset costs

What you need: Logistics/training/equipment

• An appropriate anemometer rig, sized to match potential turbine, may have several sensors, custom or standard

• Computer logger and home base computers with software, etc• Trained safe work crew, up to ten strong backs• Safety knowledge and installation skills• Lift kit and tools, etc: Personal safety gear, winch, tool kit,

crew and freight vehicles, may need off-road• Workmen’s comp, liability, OSHA, etc

• Or (newly available), access to existing wind data from a nearby site and a LIDAR machine -- LIDAR and comparative data must run concurrently

Typical costs:• Equipment: up to $18,000 for 60-meter, six-sensor, two-

vane rig• Lift kit and special tools: up to $6,000• Three long days trained crew @ $15/20/hour: $3,000-

$6,000• Crew chief, check-ups, maintenance and analysis: $3,000-

$5,000• Vehicles, transport, mechanics tools etc: $1,000• Total expenses for one grid scale tower site: up to

$35,000 or $40,000 (without paying any commercial profit)

• Currently, Unity College can do one site/year for the variable costs only ($9,000-$10,000), for a community group or non-profit, and is seeking such a site. Federal grants may be available

Please don’t ask…

“Why do we have to have a large ugly turbine?”“Why can’t we have one/lots of those nice little turbines?”

Why not?Laws of physics: •square-cube law •the power law

Going up….

Coming down….

(A year later)

The basic system we used,in the testing phase

Data analysis• The primary data set, wind speed in ten-second averages, is converted

to 10 minute and 60 minute averages, filtered for errors, icing, etc, using NRG Wind Data Retriever

• NRG reports and charts are produced: Monthly averages, wind rose, etc, to explore the data

• .txt files are exported of 60 minute and frequency distribution data sets• Frequency distribution is matched to the power curve of a specific

wind turbine make and model, can be done in MS Excel• Adjustment is made for hub height, altitude, air density, etc.• Final report includes projections of annual production in WWH or

MWH, also possible economic analysis if important parameters are known:– Cost of money (interest rates) – Turbine costs, O & M, can be several turbines– Power sales earnings (¢/kwh)– “Free money”, offset costs, etc

• This is fairly technical work: graduate, or post-graduate training required

Mt View Site data:

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Percent Frequncy of occurance

Wind speed frequency intervals in mph

Refurbished Northwind 100 on the Mt View site:

KWH per wind speed frequency intervals

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Refurbished Vestas V17on the Mt View site:

KWH per wind speed frequency intervals

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Fox Islands Wind Farm (Photo Prairie Weather blog

Where we come in:• Wind assessment:

– scientifically measure the wind and assess the power production potential

– remove (most, not all) doubt as to the economics of a site

• Community wind mapping– Better data for planning, including noise and

planning not to have a turbine if that’s the best choice

• Time to get to work?

Wish-list! NRG Systems LIDAR