Adams County discusses shadow flicker

Bobbi Maynes asked the Adams County Board of Supervisors Monday to delay any further action on the county’s wind and solar ordinances.

For weeks, the supervisors and residents have discussed revising the county’s wind ordinance. Some aspects of the regulations have been approved. Monday’s meeting included what is called shadow flicker.

Maynes stated that last week when she supported the change to not allowing shadow flicker on non-participant’s residences she thought the wind turbine operators could do that. She said she wants to talk to more experts as she said it is impossible for the wind turbines to avoid shadow flicker.

Shadow flicker is when the wind turbine tower and or rotating blades casting a shadow. According to the U.S. Department of Energy, shadow flicker becomes a concern when the flashing shadow from a rotating wind turbine casts across a building or home because it can cause the perception of a repeating flicker of alternating light and dark periods through windows.

Because of the sun angle and location of the turbine needed to cause the shadow, shadow flicker is rare. The Department of Energy claims its occurs.............

in limited locations and for only a few hours each year. When it does happen, it can potentially create a nuisance for residents close to turbines.

Debate over wind turbines includes how some people could have their health compromised because of shadow flicker. The “flickering” effect may concern individuals who suffer from photosensitive epilepsy (or seizures triggered by flashing lights or contrasting light and dark patterns). Modern wind turbines rotate at a maximum rate of 20 revolutions per minute (rpm) and have three blades, meaning shadow flicker would never be greater than 3 x 20 = 60 rpm (or 1 hertz). This is below the 120 flashes per minute threshold known to trigger epilepsy symptoms.

Wind turbines have been computer controlled. A technology called Supervisory Control and Data Acquisition (SCADA)monitors and controls almost all aspects of the turbine.

Wind turbine developers claim they create models of shadow flicker in order to make sure they comply with a common requirement of no more than 30 hours annually. These models produce a table for each turbine of exactly when a rotating turbine could cause shadow flicker on a residence. The tables can relatively easily be loaded into the computer that controls the turbine. Then set a parameter that during those periods the blades are feathered and the turbine stops. The actual stopping of the turbine is already a built-in process as it is used when employees enter the turbine, wind conditions exceed operation limits or emergencies.

It’s common for wind turbine ordinances to require a minimum setback distance for wind turbines from existing property boundaries or properties themselves. The setback distance is commonly determined by the size of the wind turbine. Shorter heights and smaller rotor diameters of small wind turbines create minimal shadow flicker.

In supervisor committee reports Scott Akin said he had a call from a citizen about a possible solar interest in the county. Maynes said she was aware of some solar easements that have been signed. Adams County has a moratorium on solar project until May 1, 2025.