Hawaii’s largest wind farm has come up with a new proposal to offset, and hopefully reduce, killings of endangered Hawaiian hoary bats.

The renewable energy plant called Kawailoa Wind, with 30 turbines on Oahu’s North Shore, recently submitted a draft plan to the state Department of Land and Natural Resources to address higher-than-expected deaths in recent years.

The public may comment on the plan by Dec. 24, and DLNR will hold a public hearing on the plan at a date to be announced later.

Kawailoa Wind and four other Hawaii wind farms were listed in a DLNR report last year as having killed an estimated 146 Hawaiian hoary bats over six years despite a limit of 187 deaths over 20 years.

As the biggest wind farm in the state, Kawailoa Wind was the worst offender with 54 killings in less than five years — six deaths shy of its 20-year maximum.

Kawailoa Wind said in its plan that its original 60-death limit was based on the best available, but relatively poor, information leading up to when it began operating in November 2012.

“Risk to bats associated with wind energy development in Hawaii was largely unknown at the time,” the plan said.

The 155-page plan is a proposed amendment to a prior DLNR-approved “habitat conservation plan” that sets out measures to reduce bat deaths and offset the losses but also allow a higher death limit.

Kawailoa Wind is seeking a limit of 265 deaths. That equates to 13.25 a year, up from 10.8 a year in the first five years. However, Kawailoa Wind said it does not expect to reach the proposed higher limit because of adjustments to windmill operations.

“Considering the avoidance and minimization measures committed to by Kawailoa Wind, the total take rate may be as low as 5.75 bats per year,” the plan said.

Kawailoa Wind also said measures to increase the bat population should more than offset losses it causes.

The wind farm proposes spending more than $10 million to preserve bat habitat, mainly by contributing money to protect areas where the bats live. This would include $2.75 million to help The Trust for Public Land buy the nearly 2,900-acre Helemano Wilderness Area near Wahiawa.

“It is anticipated that the mitigation described in this (plan) will protect bat habitat in perpetuity and, based on a conservative mitigation acreage ratio, will fully offset the impact of the taking (deaths),” the plan said.

Kawailoa Wind also is committing to change wind farm operations in several ways with the expectation of reducing bat deaths.

These measures include determining the effectiveness of an ultrasonic acoustic bat deterrent installed in July at one turbine. Kawailoa Wind said that based on research elsewhere, it estimates that bat deterrents will be commercially available and installed on all 30 turbines by 2022.

Kawailoa Wind also will increase the minimum wind speed for running its turbines to 5.2 meters per second, and will pause turbines overnight during low wind speeds throughout the year, up from nine months originally and 11 months more recently.

Despite efforts to study variables from weather to geography that might help better understand and reduce bat deaths from wind farms, not a lot is known about the issue.

The bats can die in collisions with wind turbine towers or blades but also can suffer fatal organ damage due to barometric pressure changes from the spinning blades.

No credible population estimates for the Hawaiian hoary bat exist, according to research cited by Kawailoa Wind.

Calculating bat deaths from windmills also is somewhat imprecise. A U.S. Fish and Wildlife Service model takes data on dead bats found around turbines and estimates how many were likely killed but not found. There also is an addition of indirect deaths that factor in reproduction losses.

Kawailoa Wind’s plan also proposes to cover the endangered Hawaiian petrel seabird based on one death discovered last year. The wind farm operator is seeking a limit of 24 petrel deaths, which it said it would offset with $392,800 in habitat improvement measures for the species, estimated to have a population between 19,000 and 52,000 birds.

A copy of the plan and instructions for submitting comments are available at health.hawaii.gov/oeqc in the Tuesday edition of the Environmental Notice.

Kawailoa Wind farm’s plan also proposes to cover the endangered Hawaiian petrel seabird based on one death discovered last year. The wind farm operator is seeking a limit of 24 petrel deaths, which it said it would offset with $392,800 in habitat improvements.