Environmentalists have warned that Michigan will be stuck with more coal-fired power plants if lawmakers do not significantly change an energy plan that passed the state Senate last month.

Activists stood outside the state Capitol Tuesday with large inflatable smokestacks to depict the dangers of coal plants such as acid rain, mercury poisoning and global warming.

They said energy legislation approved June 27 "under the cover of night" by Senate Republicans is a "travesty."

A plan passed by the Democratic-led House would require that 10 percent of Michigan's power come from renewable sources such as wind by the end of 2015. It also would require utilities to save 1 percent of electricity through efficiency programs in 2012 and beyond.

The Senate voted to require that a combined 7 percent of power come from renewable sources, "clean" coal plants or be saved through energy efficiency by the end of 2015.

Environmentalists signaled out a sponsor of the Senate plan, Republican Patricia Birkholz of Saugatuck, by fastening a large "Smokestack Patty" puppet onto a protester.

Terry Miller, executive director of the Lone Tree Council and opponent of proposed coal-fired plants in Midland and outside Bay City, accused Birkholz and other GOP senators of "leading the charge to keep Michigan locked up in the energy dark ages."

Birkholz released a statement saying she supports renewable energy but adding that Michigan must adopt a plan "that minimizes the negative economic impact on our citizens."

Because legislators think green power is more expensive than power supplied from old coal plants - at least in the short run - residents would be charged up to $2 more a month over 20 years and be allowed an income tax credit to offset the costs under the Senate plan. The House set a $3 monthly cap for residents.

Smaller businesses would pay $11.05 more a month under the Senate plan and $15.83 under the House version; industrial businesses would pay $125 a month more vs. $187.50.

Environmentalists said building more coal plants instead of requiring cleaner power ultimately would cost customers more because the price of coal is rising along with construction costs, not to mention the potential that Congress will tax carbon emissions. They said Michigan would lose out on jobs and economic investment by passing a weak mandate for green energy.

There are eight proposed coal plants in Michigan, which environmental groups said is the most in the country.