Victorian Urban Wind Resource Assessment September 2008 March 2009 Melbourne Presented by Mike Bagot
Outline ATA wind project origin and objectives Resource assessment sites Measurement equipment What is a wind resource assessment and why is it undertaken? Key measurement results A simple model for direct turbine energy yield Turbulence findings Key findings of this project
Project origins ATA 2007 desktop study The Viability of Domestic Wind Turbines for Urban Melbourne Micro Wind Turbine (MWT) technology focused. The main findings of this report included: Recommendations to gather representative wind data from urban locations as a prelude to any MWT installation. The requirement for verification of turbine power curves with field testing.
Urban Wind Resource Assessment Objectives Produce a portrait of wind characteristics at a variety of urban sites around Melbourne s CBD based on at least 3 months of wind speed and direction data from each site. Coastal areas Typical built-up urban areas Hilly areas Investigate differences in wind behavior at likely MWT mounting locations: Pitched and flat roofs (building mounted turbines) Open yard areas (pole mounted turbines)
Urban Wind Resource Assessment Objectives The essential role of a wind resource assessment is to allow for quantification of available wind energy Measure levels of wind turbulence at these sites. Correlate ATA data from sites with BOM station data. All wind resource assessments are wholly specific to the site where measurements are gathered
Measurement Sites Ten Measurement sites in total: Five sites with a roof mounted anemometer and a 10m pole mounted anemometer in an open yard area. Three pitched roofed dwellings. Two flat roofed dwellings. Four of the remaining sites hosted a single anemometer. Two flat roofed dwellings. One open coastal area. One open suburban yard area. The single remaining site was a prominent high rise CBD building that hosted a single ultrasonic anemometer at a height of approx 10m above the roof surface.
Measurement Sites http://maps.google.com.au/)
Edithvale
Anemometers and Masts
ATA Anemometer at Manningham
Measurement equipment and duration Min 3 months of 2-D anemometer data from all sites except the CBD site, consisting of 10 minute averages of wind direction and horizontal wind speed. An additional minimum of 2 weeks of high speed (10hz) averaged ultrasonic anemometer data from most sites. High speed data is necessary for examining rapid changes in wind flow character
Anemometers APRS World Cup Anemometer & data logger Gill Windmaster Ultrasonic Anemometer
Why should we gather this data? We want to model energy availability. P wind =½.ρ.A.v 3 [P wind ]= W=Js -1 ρ = Air density(kgm -3 ) (also a function of temperature, relative humidity and pressure) A = Area perpendicular to flow (m 2 ) v = Flow velocity (ms -1 ) We are interested in power density [ Wm -2 ] available for turbines to harness. Velocity is the most important variable in determining available wind power.
Theoretical Wind Power Density How do we get to energy estimates from power?
Power, energy and probability Power has units of energy per second. Integrate power with respect to time gives us an estimate of available energy. If we observe wind conditions for long enough we can build a model of the likelihood of different wind speeds. If we understand how velocity changes with time at a site, we can understand how energy availability changes with time at the site. How do we model wind probability?
The Weibull Distribution We can fit a statistical distribution to our observations.
What makes a suitable MWT site? Energy production. Low turbulence levels. Sites suited for grid connected MWT installation are generally considered in the wind industry to require an average horizontal wind speed of 5 ms -1. Apart from deriving estimates of wind speed probability at all sites, what did ATA s Study reveal?
Summary of Results
Confused? All this probability and statistics can be hard to grasp. How about combining the Weibull curves with turbine power curves (which relate available power to wind speed) and estimating energy yield? Then we can just compare single numbers from site to site. For some context we can compare this to how a common 1kW rooftop PV system would perform. This is not intended as a model of actual end user energy yield.
A simple model for direct turbine energy yield PV Array modelled using ANU PV performance simulator: http://solar.anu.edu.au/eduresources/applets/pvpanel/_pvpanel.php
Conclusions so far Only the Williamstown and CBD site can be considered as potential MWT sites if turbines were to be installed at the measurement heights. The remaining sites are likely to operate at low capacity factors and suffer extended or indefinite financial and energy payback periods. Most typical urban sites around Melbourne are likely to fall into this category- there simply is not sufficient available energy density for MWT installation to be attractive. They are highly unlikely to be able to compete with PV arrays as an embedded generation technology.
Turbulence Wind turbulence can be described as chaotic, highly variable and unpredictable air movement. It is typically characterised by Turbulence Intensity, a dimensionless quantity which expresses the relative change in wind conditions in a time interval. High levels of turbulence reduce the ability of a turbine to harness energy from a wind flow, reduce infrastructure life spans and increase maintenance requirements. High levels of Turbulence Intensity are undesirable for turbine installation sites especially when they occur at high wind speeds.
Turbulence Intensity vs. Wind Speed
Turbulence and Turbine Performance There are no established standards for the formulation of MWT power curves to incorporate TI. We know that turbulence reduces effectiveness of turbines, but without standardisation we cannot say by how much.
Comment on Project Objectives Only open areas situated on the coast and high rise buildings appear promising for MWT installation. Most sites in built up urban areas appear to be situated within the turbulent urban boundary layer of wind flow, significantly reducing the quality of the wind resource. No clear differences in wind energy abundance were observed at pitched and flat roofs and open areas in yards. Vertical velocity components were not found to be significant at all sites. BOM data suggests study covers a windy period. These findings match those of similar studies performed elsewhere.
Conclusions Successfully deploying turbines at sites like the CBD site, with high levels of turbulence and only modest available wind energy represent the true challenge of urban wind technology. The Williamstown site lies on the boundary of the urban realm and represents wind conditions more akin to those found at commercial-scale wind farms rather than other built up domestic sites. A wind resource assessment is a vital prelude to installation of a MWT in an urban area. The wind resource is and will always be site specific. There is no substitute for gathering real data from a site of interest.
Most gracious thanks to all site owners, ATA members and ATA employees who helped out with this project.