THINKING ENERGY
Wind modelling, made simple
Wind and Solar

Written by Joe Wyndam

Senior Data Scientist | BEng UTS (Civil) | MSc Eng (Renewable Energy)

August 29, 2022

The new energy system will be made up of lots of variable renewable energy generation from wind and solar, balanced with energy storage and demand flexibility.

Gridcognition enables all of these resources to be integrated together for everything from utility-scale front-of-meter projects, to microgrids and multi-site behind-the meter projects.

If you’re wondering “does wind make sense for my project?”, Gridcognition’s new Wind Asset feature makes it super easy to assess projects that integrate wind generation with battery storage, flexible loads, hydrogen electrolyers, vehicle and fleet charging, solar generation, and traditional thermal gensets.

In this post we’ll explain how we model wind and then show you how you can create your first Wind Asset in your Gridcog project. 

The basics of wind generation modelling

Calculating Power – Turning wind into kW

We use power curves to relate wind speed and power output. Power curves are a standard of the wind industry – manufacturers publish power curves for each turbine they sell.

Power curves show us some useful performance characteristics of a turbine:

  • Rated power: the maximum power output of the turbine under ideal conditions
  • Cut-in speed: the wind speed below which the turbine generates no power
  • Rated output speed: the wind speed above which the turbine generates its maximum rated power.
  • Cut-out speed: the wind speed above which the turbine shuts down generation to prevent unsafe operation and damage.

We don’t expect that you know what wind turbine will best suit your project, so our wind asset model uses generic power curves that represent typical modern turbines that suit non-extreme conditions.

Wind speed extrapolation – Getting your data off the ground

The wind speed data we use with our power curves is specific to your site’s location. Our meteorological data gives wind speed at 10 meters above the ground, but our turbine power curves consider wind speeds at hub height, which could be anywhere from 40 to 160 meters off the ground, where wind speeds are higher. We therefore extrapolate to determine wind speed at turbine hub height.

The reason wind is slower near the ground is because of drag caused by the landscape and its features – trees, slopes, buildings, and more. How we extrapolate therefore depends on the amount of drag caused by the landscape at your site.

For this we need you to provide a wind shear exponent. Don’t worry if this sounds technical, just select the most appropriate value for common landscape types from the table below.

Losses

Power curves are based on ideal conditions, but under real operating conditions many factors reduce the total power generation of a wind farm. We refer to these as losses, and express them as a percentage reduction of total generation. Common loss factors for wind farms include:

  • turbine availability (2 – 5%)
  • electrical losses (2 – 3.5%)
  • wake effects (0 – 10%)
  • turbine control and performance (1 – 3%)
  • environmental losses (1 – 7%)
  • curtailment (1 – 4%)

Our Wind Asset rolls these factors into a single Losses parameter, which is applied to the total generation at each time interval in your project. We set losses to a default of 17.25%, but you can change this to whatever value is appropriate for your project.

Degradation

Degradation refers to a reduction in power output of each turbine in a farm due to asset ageing. Therefore, degradation is applied at an annual rate and is compounding. The default value for the Degradation Per Year parameter is 1.6%

Creating your first Wind Asset

You will find the Wind Asset in the same place as other resources; simply click New Asset in your project. You should think of your wind asset as a wind farm with one or more turbines.

Step 1) Enter the total wind farm size in Wind Size (kW). As always, you can enter more than one variation here to allow you to quickly assess multiple wind farm sizes. 

Step 2) Enter the number of turbines that will make up your farm’s total capacity. Note that by specifying a greater number of turbines, their individual capacity and hub height will be automatically set to lower values.

Step 3) Enter the wind shear for your site. The table above provides some common numbers, and remember that a lower number will usually provide more conservative outputs.

Step 4) Add your resource costs in the same way as other resources.

Step 5) If you want to use your own values for losses and degradation, enter them in Advanced.

If you run into any problems with these steps, check out the docs for help, or check in with our customer team.

Refining your wind modelling

As your project progresses, perhaps to on-site collection of wind resource data and engineering design with specific wind turbines, you can use specialised wind modelling software with specific turbine power curves and wind resource data to simulate the expected output from your system and upload the results into Gridcognition.

You can then continue to co-optimise your wind assets with other assets and loads, and model project economics in Gridcognition.

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