THE LAST PERCENT:

[O]ver the past 20 years, amid a growing sense of urgency about combating climate change, all of New England's biggest coal plants have shut down. 

Some switched over to natural gas. Others were demolished. The site of one plant, razed in 2018, may one day host offshore wind infrastructure. Many coal plants just couldn't compete while paying for required environmental upgrades.

That's left three coal-fired power plants in the region. 

Two are in New Hampshire, owned by Granite Shore Power: Merrimack Station in Bow, and the much smaller Schiller Station in Newington, which also burns oil and woodchips. The third is Bridgeport Station in Connecticut, which is being replaced with natural gas and will retire by 2021.

2. The power plant now runs more rarely than ever - though "rare" is relative. 

Merrimack Station was built as a "baseload" plant - one that supplies a large, steady supply of power regardless of conditions on the grid. These days, it's become what's known as a "peaker" - a resource that only comes on when the grid is stressed and in need of extra electricity.

These days, New England's grid mostly runs on natural gas and nuclear power.  Merrimack Station is typically fired up only on the hottest days of the summer months - when air conditioning use drives up energy demand - and on the coldest days of winter - when natural gas supplies are put toward heating demand, and the electric grid needs a boost.  

To put that in context: Twenty years ago, when bigger coal plants were still online, New England burned several million tons of coal a year to meet nearly a fifth of its total electric demand. 

Last year, that was down to about half a million tons of coal burned to meet about 1 percent of total electric demand.

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