The coal stockpile at the Laramie River Power Station in Wheatland, Wyoming, is so big that you can't really see beyond it. It is similar to standing on the beach and looking out over the ocean, except this is one is made of coal – 35 acres of it. That's enough to produce electricity for about one month.
As a source of power, coal is predictable, easy to store, and well understood. Renewables and natural gas share few of these characteristics and some see that as a huge problem.
As the Environmental Protection Agency puts the finishing touches its proposal to cut carbon dioxide emissions – known as the Clean Power Plan – warnings that the transition away from coal will impact grid reliability are getting louder.
Representative Ed Whitfield (R-KY), the Chairman of the Energy and Power Subcommittee is one of those voicing warnings.
"The president's plan could cause 50 million American homes to go dark - you cannot just shut down the nation's coal plants and still expect the lights to come on," he said, referring to an analysis by grid operator PJM Interconnection.
The American Coalition for Clean Coal Electricity, a coal advocacy group, has launched a campaign against the Clean Power Plan using the hashtag #coldandinthedark, insisting that the rule will lead to higher electricity costs and threaten grid reliability.
The Wall Street Journal ran an editorial with the headline, "The State Electricity Revolt," suggesting that states boycott the Clean Power Plan and that services disruptions would result from plan's adoption:
"Virtually everyone who understands the electric grid, from state utility commissions to the regional transmission operators, warns that the EPA's ambitions threaten reliability. These apolitical organizations think brownouts or cascading blackouts are possible."
The North American Electric Reliability Corporation is the nonprofit tasked with ensuring grid reliability. A November 2014 report [.pdf] released by NERC confirmed these concerns... sort of. It lists challenges like finding replacement generation for the coal-fired power plants that could go offline and in the building enough infrastructure to support new sources of electricity. But the report did not predict brownouts or cascading blackouts.
One of the authors of the report, John Moura, Director of Reliability Assessment at NERC, boiled down the report's overarching theme by saying, "there is a level of risk in having every utility going down that same path at the same time."
Here's the thing though, under the EPA's proposed plan, coal isn't necessarily going to disappear. States are able to choose how to comply through measures like retrofitting coal-fired power plants, energy efficiencies and adding more renewable sources.
"Well, can we have a reliable grid without the level of coal fired generation that we have right now? I think the answer is a resounding, yes, of course we can," Cheryl Roberto of the Environmental Defense Fund said.
We have been moving toward other fuel sources for a while. According to the U.S. Energy Information Administration, the total amount of coal-fired generation has decreased slightly since the 1990s, while natural gas capacity has been increasing since the 1980s. In 2014, one coal-fired power plant went online in the U.S. and 41 were retired. The same number of natural gas facilities went offline but 82 were added. Renewables win the 2014 tally, with over 300 new units and only a handful of retirements.
A good place to check out that trend is Southern California.
At around 34 percent, San Diego Gas and Electric has some of the highest renewable integration in the country. The rest of its power comes mostly from natural gas. SDG&E got rid of its small amount of coal-fired generation a few years ago. Over the past decade, SDG&E's reliability statistics have gone up and down but overall, haven't changed much.
Which is not to say that running off so much natural gas, wind, and solar is easy.
"The challenges are many," Dan Baerman, Director of Origination and Portfolio Design at SDG&E said, "One of the big ones that concerns us is its impact on rates for our customers. We try to minimize the impact as much as possible by getting renewables that are economical."
The simple facts of nature are another challenge as well.
"Wind and solar are intermittent resources so ... it makes it difficult to maintain grid reliability," Baerman said.
One of their solutions to that challenge are peaker plants; small, natural gas-fired facilities that can be powered up in minutes in times of high demand. SDG&E currently operates 24 of these units which Baerman described as "essentially air craft engines coupled with generators to make electricity."
Mike Florio, a commissioner with the California Public Utilities Commission, points to these existing peaker plants and a recently approved one for Carlsbad California as "critical insurance to get through the next 5, 10, 15 years."
"The absolutely worst thing that could happen if we have reliability problem and the whole world points and says look what happened to California, this clean energy stuff doesn't work," said Florio.
Inside Energy is a public media collaboration, based in Colorado, Wyoming and North Dakota, focusing on the energy industry and its impacts.