Complex sentence: The stimulus package doesn't address one big obstacle for green energy buildings: the comparatively cheap cost of burning coal to make electricity renewable energy advocates are trying to persuade Congress to put a carbon price on carbon-heavy fossil fuels that contribute to global warming.
Split into simpler sentences: The stimulus package doesn't address one big obstacle for green energy building, the cheap cost of burning coal. To make electricity renewable energy advocates are trying to persuade Congress to put a carbon price on carbon-heavy fossil fuels that contribute to global warming.