Bat curtailment

General concept and requirements

Yield losses due to bat curtailments are calculated with the module LOSS & UNCERTAINTY or directly via the times series based PARK calculation at tab Curtailment.

Requirements:

• Information on the curtailment criteria (period, wind speed, temperature, time of day). These criteria are site- and species-specific and are usually defined by the authorities.
• a PARK calculation for the site which defines the energy yield conditions.
• Information about the time variation of production (as METEO time series or WTI file). The time variation data should also contain information on the variation of the temperature, if it is one of the criteria for the bat curtailment.

Curtailment conditions for wind turbines can be defined

• Identical for all WTG
• Identical for all WTG on a particular layer
• Individually for each WTG

If several, but not all wind turbines are affected by the curtailment, affected WTG should be placed on a separate layer before the PARK calculation. Otherwise, the curtailment would have to be assigned to each WTG individually.

Operation in LOSS & UNCERTAINTY

1. The calculation of bat curtailments requires the option Use advanced loss calculation tools based on time variation data (module LOSS & UNCERTAINTY | tab Main)
2. The sub-module for bat curtailment is in LOSS & UNCERTAINTY on the tab Loss in Group 6: curtailment.
3. Check the box in the Calculate column and click on the Edit button. If there is no checkbox in the Calculate column, the Advanced loss calculation tools (point 1) is not selected.

Selection of curtailment criteria

In the Parameters used list (top right of window), set the checkboxes according to the required switch-off criteria. Usually, for bat curtailment, these criteria are used:

• The period(s) of the year in which the curtailment is relevant: Date
• Switch-on and -off times during the day: Mostly Sun rise / Sunset, sometimes Time
• Mean wind speed, because bats do not fly at high wind speeds
• Temperature, because bats do not fly at low temperatures.

Use the checkbox Allow individual settings (center left of window) to assign switch-off criteria to individual WTGs; otherwise, assign them layer wise.

Select a WTG or a group of WTGs (Layer) in the bottom part of the window; then add lines to the table in the upper part (Add line).

• For each separate switch-off period (eg spring and autumn), a separate line is required
• A line can only include either sun rise or sun set conditions. If a curtailment relating to both is required, two lines must be used. This is also true if a curtailment for the whole night is required!
• Exception to this rule is Curtailment from sunrise to sunset

Filling in the table

The table contains two columns for each switch-off criteria, one for the beginning and one for the end. For the temperature, these are for example:

• Temperature (from)
• Temperature (to)

For sunrise, it's:

• Sunrise (from hours before)
• Sunrise (to hours after)

• etc.

If several termination criteria are selected, all criteria in a line must be fulfilled for the curtailment to become effective.

Example:

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)	Mean wind speed (from)	Mean wind speed (to)	Temperature (from)	Temperature (to)
30.06.2007	31.08.2007	2.0	1.0	-	7	10	-

This will shut down the WTG between June 30 and August 31 between 2 hours before sunrise to one hour after sunrise, when the wind speed is <7 m/s and the temperature is above 10° C.

Note that the year value has no meaning.

Examples and special cases

Curtailment one hour before and after sunrise and sunset

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)	Sunset (from hours before)	Sunset (to hours after)
30.06.2007	31.08.2007	1.0	1.0	-	-
30.06.2007	31.08.2007	-	-	1.0	1.0

The criteria "sunrise" and "sunset" must not be used in the same line in this case!

Curtailment from sunset to one hour after sunset

Date (from)	Date (to)	Sunset (from hours before)	Sunset (to hours after)
30.06.2007	31.08.2007	0.0	1.0

Note that in column "Sunset (from hours before)", a zero must be entered. If instead, you enter nothing, the condition is met for all time stamps before "one hour after sunset", which applies to most of the day!

Curtailment 2 hours before sunrise to one hour before sunrise

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)
30.06.2007	31.08.2007	2.0	-1.0

The entry under "Sunrise (to hours after)" is indeed confusing, but logical - a negative time after sunrise corresponds to a time before sunrise.

Curtailment all night (from sunset to sunrise)

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)	Sunset (from hours before)	Sunset (to hours after)
30.06.2007	31.08.2007	-	-	0.0	-
30.06.2007	31.08.2007	-	0.0	-	-

The first line is true for all time stamps after "0 hours before sunset" (which is from sunset to midnight). The second line is true for all time stamps before "0 hours after sunrise" (which is from midnight to sunrise).

It is not possible to define a curtailment for the whole night in one line!

Curtailment for the night, from 1 hour after sunset until 1 hour before sunrise

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)	Sunset (from hours before)	Sunset (to hours after)
30.06.2007	31.08.2007	-	-	-1.0	-
30.06.2007	31.08.2007	-	-1.0	-	-

For details see the two previous example cases.

Curtailment all day (from sunrise to sunset)

Date (from)	Date (to)	Sunrise (from hours before)	Sunrise (to hours after)	Sunset (from hours before)	Sunset (to hours after)
30.06.2007	31.08.2007	0.0			0.0

The period is defined as "Zero hours before sunrise to zero hours after sunset".