Blog

Multi-Height WRGs

October 31, 2014

This is some of what has been keeping us busy over the summer. For a while, the WRB format has been capable of handling multi-hub-height WRGs but Openwind has not supported this kind of compound object. With the next release this will all change. From now on all WRGs are time-queryable, multi-height objects with the standard single height annual WRG being merely a special case. This should allow us to simplify the setup of openWind workbooks considerably as well as allowing users to model wake effects of external projects with multiple hub-heights in an easy and convenient way. You can use one or more multi-height met masts to run adjust to masts on these objects and if they are time-queryable then the met mast data will be filtered by the same set of time-queries that are defined in the compound WRG. A lot to take in in one go I know but I will be posting more on this in the coming weeks and months. For now, here is a simple demo on how to start using the new functionality.


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Turbulence Intensity Adjustment

January 29, 2014

Turbulence intensity, in the form of the standard deviation of the wind speed over the measurement period, can impact turbine performance.

In general, TI can be thought of as a standard distribution of wind speeds around the ten minute mean

At the lower end or ankle of the power curve, deviations above the mean give more energy than deviations below the mean lose.

At the upper end or knee of the power curve then deviations above the mean do not compensate for deviations below.

Now some level of TI is assumed in the power curve supplied by the manufacturer. More TI than this assumed level will result in more power at the ankle and less power around the knee.

Less TI than the assumed level will result in the opposite.

This complicated only slightly by whether the turbine manufacturer specifies a power curve at 10% TI to mean 10% across all wind speeds or whether they mean 10% TI at 15m/s and assuming a normal turbulence model as described in the IEC standard

At present openWind has two ways of dealing with the effects of TI on energy production:

1)      Is to switch between power curves defined by the manufacturer at different TI values

2)      Is to modify the given power curve according to the consensus method of the power curve working group.

The following video shows the basic functionality from a user perspective:


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