As environmental concerns drive power companies away from using coal, natural gas has emerged as the nation’s No. 1 power source. Plentiful and relatively inexpensive as a result of the nation’s fracking boom, it has been portrayed as a bridge to an era in which alternative energy would take primacy.

But technology and economics have carved a different, shorter pathway that has bypassed the broad need for some fossil-fuel plants. And that has put proponents of natural gas on the defensive.

Some utility companies have scrapped plans for new natural-gas plants in favor of wind and solar sources that have become cheaper and easier to install. Existing gas plants are being shut because their economics are no longer attractive. And regulators are increasingly challenging the plans of companies determined to move forward with new natural-gas plants.

“It’s a very different world that we’re arriving at very quickly,” said Robert McCullough, an energy consultant in Portland, Ore. “That wind farm can literally be put on a train and brought online within a year. It is moving so fast that even critics of the old path like myself have been taken by surprise.”

The Arizona Corporation Commission, which regulates the state’s investor-owned utilities, recently refused to endorse plans by three power companies that included more natural-gas facilities. Commissioners directed them to make greater use of energy storage and plants that produce zero emissions.

“It’s very erratic what we’re now doing with power,” said Andrew M. Tobin, an Arizona commissioner who led efforts to block new gas plants. “I am so nervous that we will end up building a lot of capital plant that doesn’t stand the test of time.”

Some feel the push to get beyond natural gas may be too much, too soon. Officials at Arizona Public Service, the largest utility in the state, said they needed to include new natural-gas development as part of an overall mix, partly because of the state’s round-the-clock air-conditioning demands.

“Our needs are different than other utilities,” said Greg Bernosky, the utility’s director of state regulation and compliance. “We need resources that can have a long duration when our load is high, well after the sun has set. Natural gas resources provide that flexibility.”
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Natural gas isn’t likely to be unseated as the country’s primary source of electricity generation anytime soon. In fact, utility companies plan to add more natural-gas plants than any other source, including all alternative energy sources, like solar, wind and hydropower, combined.

But the calculus is rapidly shifting as the prices of wind and solar power continue to fall. According to the Department of Energy, power generated by natural gas declined 7.7 percent in 2017.

And the latest report by Lazard, the financial advisory and management firm, found that the cost of power from utility-scale solar farms was now on a par with natural-gas generation — and that wind farms were less expensive still.

Lazard calculated the unsubsidized cost of wind power at 3 cents a kilowatt-hour, while natural gas and solar energy were a little more than 4 cents. The typical American household pays 12.5 cents a kilowatt-hour for electricity, according to the United States Energy Information Administration. (The cost beyond generation reflects transmission, taxes, and other utility expenses and profits.)

Two years ago, Kansas repealed a law requiring that 20 percent of the state’s electric power come from renewable sources by 2020, seemingly a step backward on energy in a deeply conservative state.

Yet by the time the law was scrapped, it had become largely irrelevant. Kansas blew past that 20 percent target in 2014, and last year generated more than 30 percent of its power from wind. The state may be the first in the country to hit 50 percent wind generation in a year or two, unless Iowa gets there first.

Some of the fastest progress on clean energy is occurring in states led by Republican governors and legislators, and states carried by Donald J. Trump in the presidential election.

The five states that get the largest percentage of their power from wind turbines — Iowa, Kansas, South Dakota, Oklahoma and North Dakota — all voted for Mr. Trump. So did Texas, which produces the most wind power in absolute terms. In fact, 69 percent of the wind power produced in the country comes from states that Mr. Trump carried in November.

These red states are not motivated by a sudden desire to reduce greenhouse gas emissions. Nor are they joining solidly Democratic New York, Washington and California in defending the Paris climate agreement that President Trump walked away from last week. Instead, their leaders see tapping the wind, and to a lesser degree the sun, as an economic strategy.

The clean energy push allows their utilities to lock in low power prices for decades, creates manufacturing jobs, puts steady money in the hands of farmers who host wind turbines and lures big employers who want renewable power.

“We export lots of things, and in our future, I want us to export a lot of wind power,” Kansas’ conservative Republican governor, Sam Brownback, said in a speech in 2011. “We need more of it, and we need more of it now.”

Mr. Brownback got what he wanted: Since he spoke, wind power production in Kansas has nearly tripled, and the state is now an exporter of clean electricity.

Whatever the motives, the push in the red states does help to lower emissions, which means their goals tacitly align with those of blue states worried about climate change.

When Charles Patton joined American Electric Power in 2000, around 90 percent of the company’s electricity production came from coal. Since then, AEP’s executive vice president of external affairs says things have changed dramatically.

“I will confess, there was a time I wouldn’t have publicly stated — although in the last few years I have publicly stated that I was wrong — that you would be able to [interconnect] renewables to the extent that we’ve been able to,” said Patton, speaking Tuesday at Greentech Media’s inaugural Power & Renewables Summit in Austin, Texas. “If you were a utility guy…that wasn’t something you necessarily believed was possible to the degree it is today.”

AEP isn’t traditionally thought of as the most environmentally friendly utility, but that reputation is changing — marking arguably one of the most significant endorsements of clean energy technologies to date.

In 2005, coal made up 70 percent of AEP’s generation capacity — which is how the utility measures its electricity mix today. Since then, coal’s share of capacity has dropped to 47 percent. At the same time, AEP’s natural gas capacity increased from 19 percent in 2005 to 27 percent today, and renewables entered the scene in a meaningful way, growing from 4 percent in 2005 to 13 percent today.

Renewable energy is now slated to make up the vast majority of AEP’s planned generation additions over the next decade. In AEP’s third-quarter 2017 earnings report, the utility said it plans to add another 8,360 megawatts of wind andsolarthrough 2030 across its regulated and deregulated businesses — and that doesn’t even include the 2,000-megawatt Wind Catcher project, which could become the largest wind project in North America.

AEP currently operates more than 224,000 miles of distribution lines in 11 states that deliver power to nearly 5.4 million regulated customers. It has approximately 33 gigawatts of generating capacity, 4.2 gigawatts of which is renewable energy.

Taking India as an example, BNEF is now showing benchmark LCOEs for onshore wind of just $39 per MWh, down 46% on a year ago, and for solar PV at $41, down 45%. By comparison, coal comes in at $68 per MWh, and combined-cycle gas at $93. Wind-plus-battery and solar-plus-battery systems in India have wide cost ranges, of $34-208 per MWh and $47-308 per MWh respectively, depending on project characteristics, but the center of those ranges is falling fast.

Seb Henbest, head of Europe, Middle East and Africa for BNEF, said: “Competitive auctions for new renewable energy capacity have forced developers, equipment providers and financiers to bear down on all the different costs of establishing wind and solar projects.

“Thanks to this and to progressively more efficient technology, we are seeing record-low prices being set for wind and solar, and then those records being broken again and again on a regular basis. This is having a powerful effect – it is changing perceptions.”

BNEF has been analyzing the numbers on levelized costs of electricity for the different technologies since 2009, based on its database of project financings and work by its analyst teams on the cost dynamics in different sectors.

In that nine-year period, the global benchmark LCOE for solar PV without tracking has tumbled by 77%, and that for onshore wind by 38%. LCOEs for older established sources, such as coal, gas, nuclear and large hydro, have seen only very modest reductions, at best, in that time – and in some countries, they have actually increased. BNEF’s lithium-ion battery price index shows a fall from $1,000 per kWh in 2010 to $209 per kWh in 2017.