 
 
8b   OPTIMIZE 
8b.1  Introduction .......................................................................................................................................... 2 
8b.1.1  Noise Curtailment vs. Layout Curtailment ............................................................................. 2 
8b.1.2  The GUI tree-structure ........................................................................................................... 2 
8b.1.3  Presentation of results ........................................................................................................... 9 
8b.1.4  Storing results ...................................................................................................................... 11 
8b.2  Optimization decisions ...................................................................................................................... 12 
8b.2.1  The noise model .................................................................................................................. 12 
8b.2.2  Noise receptors .................................................................................................................... 13 
8b.2.3  Wind resource model ........................................................................................................... 13 
8b.2.4  Strategy decisions ............................................................................................................... 14 
8b.3  Optimization algorithm ...................................................................................................................... 15 
8b.3.1  Noise curtailment optimization algorithm ............................................................................. 15 
8b.3.2  Turbine shutdowns .............................................................................................................. 15 
8b.3.3  Operation mode curtailment ................................................................................................ 15 
8b.4  References .......................................................................................................................................... 15 
 
   

Introduction 2

8b.1 Introduction

Wind farms must comply with noise regulations, and two approaches are being used to ensure compliant noise

immission levels at noise receptors emitted by wind turbines: control the turbine position (Cao et al. 2020) or

control the turbine operation modes (Nyborg et al. 2023). When wind turbines are already installed or the planned

positions are decided upon, the remaining option is, therefore, curtailing the operation modes of the turbines.

The curtailment of wind turbine modes comes with reduced noise emission but also reduced energy production

(Steurer et al. 2017). The purpose of noise curtailment optimization in the context of wind farm planning is to

satisfy acoustic constraints while maximizing the usual benefits, e.g., energy production or profit.

The Noise Curtailment Optimizer (NCO) adds such functionality to the Optimizer module in windPRO to the

Layout Optimizer. The objective of the NCO is to suggest a curtailment strategy for wind farms to comply with

noise receptor thresholds around the wind farm with the lowest production loss possible. If a noise curtailment

is insufficient to comply with defined noise regulations, the tool can also propose to shut turbines down for

specific conditions as a last resort.

The NCO facility in windPRO was developed as part of the Decowind project, supported by the Danish Innovation

Fund.

8b.1.1 Noise Curtailment vs. Layout Optimizer

The Noise Curtailment Optimizer is designed to resemble the Layout optimizer, and a lot of the structure of the

optimizer will look and feel similar. In both cases the objective is to maximize production output of a wind farm,

but the degrees of freedom are different. The Layout Optimizer reaches its objective by moving the turbines

within a set of constraints, while the NCO does the same through changing the operation mode on the turbines.

The constraints of the NCO are controlled by the noise code it must comply with and the possibilities the turbine

type offers. For these reasons, the GUI must diverge from that of the Layout Optimizer as described in the

following. The result of the NCO is not a new layout but a Noise Curtailment Matrix for each turbine.

8b.1.2 The GUI tree-structure

The GUI of the Noise Curtailment Optimizer uses a tree structure like that of the Layout Optimizer with three

levels: Site, Layout and Strategy (Figure 1).

Figure 1: The three hierarchy levels of the GUI tree: Site, Layout, and Strategy.

When the NCO is opened for the first time, a first Site will be available and set with default settings for the country

of the project. The optimizer allows creating several sites, where each site can contain several layouts, and a

layout can have several strategies. Each hierarchy level can be expanded or collapsed and if highlighted, the

options for the level become visible to the right.

New levels can be added, deleted or copied. Sites can be cloned by right-clicking on the Site level:

Introduction 3

Figure 2: Option to expand, collapse and clone sites.

There are some restrictions to the upper levels in the structure once lower levels have been added. These

restrictions can be lifted if the lower levels are removed. It is for example not possible to change the noise model

once a Strategy has been added but removing all strategies reenables noise model changes.

8b.1.2.1 Site

The Site level sets up fundamental decisions regarding the noise model and wind resource model. In principle,

the Site will include all the basic conditions of the location and would, ideally not need to be changed when

testing different options. There may be a need or an interest in changing fundamental conditions, such as the

selection of noise receptors, parameters in the noise model or details in the wind model. For such variations,

separate sites can be made. Selecting a Site in the left column enables the Setup & Run field on the right.

Figure 3: On the Site level, three components of the optimization are selected: the noise receptors, the noise

model, and the wind resource.

Noise receptors: On the Noise tab, the relevant receptors are selected by pointing out the layer in which the

receptors are located. As default all receptors in a layer are selected, but by removing the check in Use all

objects from selected layers, specific objects can be pointed out.

Introduction 4

Figure 4: Noise model configuration.

It is important that the noise receptors selected match the noise model used, see section 8b.2.2.

Noise model: The NCO gives access to both Decibel and NORD2000 from the Noise tab. To access either

requires a license for the module. The Noise model selection box provides quick access to one of the preset

models in either Decibel or NORD2000. The Edit model parameters button gives access to view or modify the

parameters in the noise model. DECIBEL and NORD2000 are described in detail in section 6 of the windPRO

Environmental manual. The model parameter details are also described in section 6 with additional information

in section 8b.2.1 where the optimizer provides additional or reduced options.

If a model needs to be customized, it is recommended to select the ISO 9613-2 General model from DECIBEL

or General from NORD2000.

It is not possible to use different noise models at the same site. The questions of how to combine multiple models,

e.g. one noise model for existing turbines ad one noise model for new turbines, has not been answered yet.

Introduction 5

Figure 5: Noise regulation specification selection.

Wind resource model: On the Energy tab, the wind resource model is selected. The wind resource model is

used to calculate the production loss inflicted by curtailments. The wind resource model can be based on time

series data or a wind resource map. A wind resource map is a precalculated map for the area that provides

Weibull parameters and direction frequencies in each grid cell. Wind resource maps are described in detail in

section 3 of the manual. For the NCO a wind resource map in either .rsf, .wrg or .siteres format can be used. It

is required that it covers the location of all wind turbines in the calculation as well as any reference points (for

the Wind speed inside Wind farm model). A very easy and simple access to a wind resource map is the GASP

data which are freely available world-wide from windPRO. A wind resource map can be used if the only two

dimensions used in the optimization are wind speed and wind direction.

Figure 6: Resource and wake model specification.

The Time series option sets up a time domain model as described in the Chapter 3 Energy. This includes a

Scaler and a time series and is entirely identical to the model in the PARK module. A full description of the Scaler

and selection of time series data can be found in Chapter 3 Energy.

The time series model has the advantage, compared to a wind resource map, that it is not limited to wind speed

and direction. The time domain nature of the model means that the time dimension can be used in the

optimization, i.e. calculation of day and night curtailments. If the time series includes temperature and humidity

data, it is possible to include these dimensions as well. If these dimensions are needed, but not available in the

time series used by the Scaler, time series with those data can be pointed out separately at the bottom of the

field. As the objective is to calculate and minimize curtailment losses, precision on the absolute wind speed is

not required and downscaled mesoscale data is an easy and suitable option for a time series wind model.