Mitch Leslie

Senior Technology Writer

Since 2011,a total of 121 pow er plants in the United States have stopped burning coal and sw itched to burning natural gas[1],w hich produces about 50%less carbon dioxide(CO2)per megaw att-hour of electricity generated than does burning coal[2,3].If current plans come to fruition,more than 170 new gas-f ired generating plants could join them by the mid-2030s[4].These actions may reduce greenhouse gas emissions,but they w ere triggered less by concerns for the climate and more by the availability of cheap natural gas.

Unleashed by hydraulic fracturing and other drilling technologies,plentiful gas supplies have transformed USpow er production,w ith the cost of gas-generated electricity falling by more than 40%betw een 2010 and 2019[5].Partly as a result,the percentage of US electricity obtained from coal-f ired plants has declined over the last 20 years from 52%to 23%,w hereas the share from gas has vaulted from 16%to 38%[6,7].The USEnergy Information Agency now projects that gas w ill furnish about the same percentage of the energy mix—a little under 40%—through 2050[8].

Natural gas provides a cleaner prof ile than coal,but the climate effects of the surge in natural gas use remain unclear.A 2020 study estimated that new gas-f ired pow er plants in the United States resulted in a 24%drop in CO2emissions from electricity generation betw een 2000 and 2018[9].Yet the reduction over the next several decades w ill only be half as much,the researchers projected,because utilities often replaced old coal-f ired plants that w ere close to retirement w ith gas-f ired plants that w ill continue to release CO2—albeit at low er levels—for an average of 50 years[3,9].Given the rapid decline in costs for renew able energy generation[10,11],and especially if these declines continue,some experts argue that adding gas-f ired pow er plants w ill burden consumers w ith higher prices for those 50 years w hile still harming the environment[12].

The falling costs for renew ables are setting up another energy battle.Natural gas w on the battle against coal,but the next struggle w ill pit cheap natural gas against sources such as solar and w ind.Natural gas advocates often tout it as a bridge betw een fossil fuels and new renew able technologies.But others w orry that the fuel’s affordability could impede a transition to cleaner energy sources and slow US progress tow ard climate goals[13-15].For example,even if no new gas-f ired pow er plants w ere to come online,existing facilities w ould have to slash their capacity by tw o-thirds by 2050 to meet targets the United States assented to under the 2016 Paris Agreement[9].Although the Trump administration pulled out of the accord,US president-elect Joseph Biden has pledged to rejoin it.If the current energy mix remains about the same,w ith gas continuing to play a major role in electricity generation,a 2020 report concludes that USCO2emissions w ould decline less than 10%over the next 15 years,much below the 50%decrease by 2030 called for by the United Nations Intergovernmental Panel on Climate Change[16].To meet the goal of converting US electrical pow er generation to 90%renew able sources by 2035,w hich w ould cut CO2emissions by 88%,‘‘The role of natural gas has to be signif icantly reduced,”said Amol Phadke,a staff scientist at the Law rence Berkeley National Laboratory in Berkeley,CA,USA and a co-author on the report.‘‘Gas can play a limited role in terms of providing backup w hen renew ables are not available,”he said,supplying about 10%of electric pow er until it is phased out after 2035.

The economic arguments for sticking w ith gas for electricity generation typically cite cost and intermittency,or the ability to deliver pow er no matter the time of day or w eather[14].Natural gas has set a low price bar that renew able sources w ill have to slip under,and‘‘nobody expects cheap gas to go aw ay anytime soon,”said Sheila Olmstead,an economist and professor of public policy at the University of Texas at Austin.But over the last decade,‘‘The cost of renew able electricity decreased much faster than anyone anticipated,”said Tom Konrad,a Stone Ridge,New York-based investment analyst w ho tracks clean energy stocks.

The latest f igures suggest that renew ables are beating gas on price(Fig.1).A respected annual analysis sponsored by Lazard,a f inancial advisory company based in Bermuda,estimates the levelized cost—the amount pow er companies need to charge to recoup construction and lifetime operating costs—of different energy sources[17].The 2020 f igures calculate a levelized cost per megaw att-hour for utility-scale crystalline silicon solar panels,the most common photovoltaic technology,of betw een 31 and 42 USD,w ith thin-f ilm solar panels,a new er and more eff icient alternative,coming in at 29-38 USD[18].Meanw hile,costs for so-called peaker gas-f ired plants,w hich sw itch on only w hen the grid is short of energy,range from 151 to 198 USD.Estimates for gas combined cycle plants,w hich operate steadily,run from 44 to 73 USD.

Fig.1.The cost of generating electricity w ith renew able sources,such as the solar energy captured by the immense Topaz Solar Farm in San Luis Obispo County,CA,USA,has fallen below the cost of using natural gas.The facility covers 25.6 km2 and generates 550 MW of energy w ith nine million thin-f ilm cadmium telluride panels.Credit:Sarah Sw enty/USFWS(CCBY 2.0).

Renew ables are also making some headw ay on intermittency,Konrad said.Lithium-ion battery storage that can compensate for dips in pow er production over several hours has become much cheaper in recent years,he said.For short term storage,‘‘Gas peaker plants are starting to be less cost-effective than large batteries,”but for middle-term storage of days,w eeks,and months,how ever,gas still has the advantage.

In addition,the largest component of natural gas,methane,is some 80 times more potent as a greenhouse gas than CO2over a 20-year time period.Thus,the impact of sw itching to natural gas depends on how much methane is intentionally vented or escapes during its production,transportation,and use[19],a number that has proven diff icult to pin dow n[20].Recent estimates suggest that leaks and venting could reduce or even eliminate the potential climate change benef its of the sw itch from coal to gas[9,21].

The prices for natural gas w ould be higher if they ref lected the environmental impact of its associated greenhouse emissions,Phadke and Olmstead noted.‘‘Because gas does not pay for its climate costs,w hich are signif icant,it is not a fair competition,”said Phadke.How ever,there are signif icant negative environmental impacts associated w ith solar panel production and disposal that are not factored into the cost of solar pow er as w ell[22].

How or if to price carbon to account for environmental damage remains a matter of debate in the United States[23].In one approach that w ould end up making fossil fuels more expensive,several states,cities,and counties have f iled law suits that w ould require major oil companies to pay for the costs of climate change[24].Another option,said Olmstead,could be requiring pow er plants to employ carbon-capture technology,w hich some facilities are now testing,and w hich w ould also increase the cost of electricity generated w ith gas[25].How ever,all carbon pricing strategies have an uncertain future.

Some analysts,pointing to cancellations of high-prof ile projects and record increases in renew able generation,claim that gas has already fallen out of favor w ith investors and decision-makers,dubbing it‘‘the new coal”for w ealthier countries[26].The economic calculations about w hich energy source to use are complex,how ever.Olmstead cautioned that the biggest obstacles to increased use of renew able energy may be factors other than fuel cost.Decisions about w hat type of plant to build include factors such as capital costs and the expense of adding transmission lines to distribute the generated pow er[27].Regulatory decisions also play a role,and currently tend to favor construction of gas plants in the United States,Konrad said.The bottom line is that w hether building a new gas plant makes sense‘‘depends on w hat it is replacing,”said Olmstead.‘‘Do w e w ant to use it instead of coal?Yes.”But if the choice is betw een a gas-fueled plant and a renew able facility,‘‘it depends on w hat you are doing about emissions.”