In certain wind parks in Europe, there are environmental laws that have the goal to save wildlife around the wind park. One of the most frequent restrictions is the protection of bats. These are the most common bats in Germany: List of mammals of Germany.
Bats usually start hunting and flying under certain conditions during the day. These conditions depend highly on the site of the wind park, its individual bat population, the time of the year and day, as well as the weather conditions.
Historically, the turbines needed to be shut down during between one hour to sunset and one hour after sunrise during the summer. The timing of sunsets and sunrises varies throughout the year and it also depends on where the windpark is situated. This is why Turbit needs the exact geo-position of the turbines in order to make this module work. This rule was a rather conservative rule that led to a lot of unnecessary downtime of the turbines during which no bats were flying.
The next step was to add the condition of rainfall: If there is rain, bats are not flying.
Another specification was that only during certain temperatures during the summer, bats are flying. Bats want to have at least some warmth like 10°C outside temperature to get out of their homes.
These temperature conditions do vary over the year, which is why for each month there are different temperature conditions.
Also bats don’t like to get out if there is too much wind, e.g. more wind than 6 m/s. The conditions of windspeed vary throughout the year but also throughout the night, which is why the night is split into 10 parts (night percentiles) to get more granularity in the rules of the wind speed. Because the length of the night depends on the time of the year, the time when certain conditions apply is never the same and it needs to be calculated for each night individually.
The last addition to the bat rules was that all of these conditions need to be present for some time, e.g. at least for 30 minutes so that bats start to fly. But also if bats are already flying because conditions are met, the conditions need to be bad for a certain time until they stop flying. This is most commonly called hysteresis. Depending on whether the bats were not flying or are already flying the conditions of the windspeed change a little bit. The thresholds of windspeed change either to lower values (e.g. minus 0.5 m/s) if the bats were not flying and to higher values if the bats were already flying. These hysteresis rules, if applied correctly, lead to fewer start and stop events of the turbine and, as a consequence, to less wear and tear on the turbine.
These very complex rules are applied to the control system of the turbine. If e.g. a sensor for the measurement of the outside temperature is broken or malfunctioning, this can lead to a lot of unnecessary downtime or uptime that is not conform with the law.
It is therefore strongly recommended to monitor the correct functioning of these bat protection control systems.
Turbit has a module to monitor all of these described rules, given that all data is provided. If a rule is not correctly applied, Turbit sends an automatic alarm. These alarms can either be “Turbine operates although it should not” or “Turbine does not operate although it should”.
Mostly Turbit receives only data for 10 min. average values, but the bat control system is working on 1 min average values or higher. This leads to some uncertainties in the calculations of Turbit if bat rules should apply or not. Turbit is therefore only sending out events if a wildlife bat event is longer than 40 minutes.