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Solar and wind power sound like great, environmentally clean ways to generate electricity, don't they?

But what happens when the sun doesn't shine and the wind doesn't blow? It's a question often posed by skeptics.

The answer, according to a local environmental group, is compressed air storage: When excess electricity is generated, it is used to pump compressed air into underground caverns. When electricity is needed, the air is released, heated and used to drive generators.

"It's like charging a huge battery," Christopher Thomas, policy director for HEAL (Healthy Environment Alliance) Utah, told a group of about 40 people attending Westminster College's annual Bioneers program.

Compressed air storage is the centerpiece of HEAL's plan for generating all of Utah's electrical needs with renewable energy sources by the year 2050.

Thomas said the so-called eUtah study is the result of months of research, coordination with experts and meetings with key energy players.

The complete study, three years in the making, will be presented at 6:30 p.m. on Dec. 14 at the Jewish Community Center, 2 N. Medical Drive, Salt Lake City.

Without revealing details, Thomas said the study included a year-long study of wind and sun availability, which was plotted against the electricity demands for most of Utah. The study also predicts how much sun and wind are needed to supply a compressed air storage facility, and how much storage volume is needed to meet electricity demand.

Thomas called the plan by HEAL — which he said has about 5,000 members — "a visionary study, a totally new way of looking at electricity." But he added that feedback from an advisory board, which includes people from consumer affairs and public utilities, helped "keep it practical."

Thomas said compressed air storage has been used in conjunction with a German nuclear power plant since 1978. And an Alabama power plant, which has been operating since 1991, uses an underground salt dome for air storage. Thomas said 75 percent of the stored energy can be regenerated.

He said Utah has "good" solar and wind resources, as well as the geology needed for large-scale compressed air storage. He said the Magnum Gas Storage company, with an eye toward compressed air storage, had acquired a lease for an underground salt bed in Utah, which he called "the largest salt bed in the American West."

A draft report from Gov. Gary Herbert's energy task force does not envision building any new coal-fueled power plants in the next 10 years, according to Thomas, who added that Utah's coal reserves are expected to run out in about a decade. The draft report also does not view nuclear power as a viable option, Thomas said.

The final report from the task force is to be presented to the governor on Dec. 22. A public hearing regarding the report will be held from 5 to 7 p.m. on Wednesday at the Senate Building (state Capitol complex east building), Room 215.

Thomas urged those in his Westminster audience to go and be heard on the subject. Thomas said he would like renewable energy to be a "cornerstone" of the report.

Thomas, who for the past four years has worked to keep depleted uranium out of Utah, said it was "exciting to be working on the green grid of tomorrow."

He said he would love to see Utah become a national leader in creating "a clean, green energy grid, with no need for the dirty energy we rely on today."