A push from some U.S. lawmakers and presidential candidates to transition the U.S. entirely to renewable or zero-emission electric power poses a bigger challenge for some states than others. But proposals in Congress for utilities to gradually raise sales from renewable or carbon-free sources may offer a more measured path for states to boost clean generation, supporters say.

Concerns over climate change's risks to public health, food supply, infrastructure and the creditworthiness of cities have prompted some policymakers to promote 100% nationwide clean power targets.

In 2019, 13 members of the U.S. Senate and 95 lawmakers in the U.S. House of Representatives — nearly all of them Democrats — have backed a resolution saying the federal government should form a Green New Deal that includes working toward meeting 100% of the country's electricity demand with renewable, clean or zero-emission energy.

Moreover, of the 20 candidates participating in the first two rounds of Democratic primary debates in the 2020 U.S. presidential election, at least 14 have either supported the Green New Deal or laid out climate plans that include a full transition to clean energy by mid-century or sooner.

For now, however, federal legislation to hit the ambitious target is unlikely to clear the current Congress, and President Donald Trump has fought to revive the struggling coal industry, making him almost certain to reject any measure that would further decrease coal consumption.

In addition, most states are far from obtaining all their power from emissions-free sources. Only 13 states had renewable and/or nuclear plants generate more than half their electricity during 2018, according to U.S. Energy Information Administration data. And while a handful of states, including California, New York and Washington, have 100% clean energy targets, most others have set mandates and goals far below that threshold, according to information gathered by S&P Global Market Intelligence.

Despite those hurdles, renewable power experts say a 100% emissions-free grid is doable from an engineering perspective, even if the policy landscape is less straightforward.

"The declining cost of [solar photovoltaic generation], of wind, of batteries, has made it really possible to kind of envision a future where you're getting 70-80% or so of the nation's electricity from renewable resources," said Paul Denholm, a principal energy analyst at the U.S. Department of Energy's National Renewable Energy Laboratory, or NREL.

At that level, renewable energy paired with existing nuclear resources could get the U.S. very close to a 100% emissions-free grid. But reaching that share of renewable generation, which NREL has said the U.S. could achieve by 2050, would depend on adding more transmission capacity to move electricity from wind-rich areas like the Midwest to demand centers in other parts of the country, Denholm said. The pace of the transition would also hinge on how quickly the industry can raise capital for new factories to produce solar PV panels and other equipment.

"We are continually learning what we can do with the power grid," Denholm said. "It was really only about 15 years ago when I think there was a general consensus among the utilities that maybe 10, 15, 20% was about as far as you could go with wind and solar... As we've studied the grid, as we've deployed these technologies, we keep moving that [goal post] forward."

Clean energy standards bills offer easier path

While a full transition to renewable or zero-emissions power may be far off, legislation in Congress to establish national clean energy standards could be more achievable in the near term. Federal clean energy standard proposals have drawn the attention of major electric utilities, with Duke Energy Corp., Southern Co., American Electric Power Co. Inc. and Exelon Corp. among the generators that met with lawmakers and congressional staff on the topic during the second quarter, according to federal lobbying disclosures.

In May, U.S. Sen. Tina Smith, D-Minn., introduced a bill directing U.S. retail electricity suppliers to raise the amount of power they supply each year from clean sources, with the goal of achieving zero net carbon dioxide emissions from the power sector by 2050. Smith's bill, the Clean Energy Standard Act of 2019, defined clean energy to include renewable resources (including certain biomass facilities); hydropower, nuclear and waste energy facilities; and facilities that can capture their carbon emissions.

And in June, U.S. Sen. Tom Udall, D-N.M., a long-time advocate of a federal renewable portfolio standard, introduced a bill to require utilities generating over 1 million MWh of electricity annually to gradually raise the amount of power they sell every year from renewable sources. The legislation would put the U.S. on track to get at least half its electricity from renewable sources by 2035, nearly triple the current share of around 18%, Udall estimated.

Under both bills, electricity suppliers that cannot meet their clean energy targets can purchase credits to satisfy their obligations or, in the case of Smith's bill, make alternative compliance payments. Smith's bill would also help existing nuclear plants and other clean energy facilities by allowing them to generate compliance credits, although Udall's measure would require credits to largely come from new facilities.

By mandating uniform increases in clean generation, the bills do not disadvantage states based on their current power mix, supporters say. The proposals can also make room for existing state RPS or clean energy goals and voluntary markets.

"Both bills are easily implemented," said Robert Cowin, director of government affairs for the Union of Concerned Scientists' climate and clean energy program.

The Union of Concerned Scientists analyzed Udall's bill and found that it would cut the power sector's greenhouse gas emissions by 46% by 2035 and result in $34 billion of cumulative net energy bill savings for consumers between 2020 and 2035. The cost savings would stem from lower annual natural gas bills that would offset increases in annual electricity bills, the analysis concluded.

Cowin admitted that Udall's and Smith's bills, neither of which have Republican co-sponsors, face slim odds of passage in the current Congress. But a broad federal clean energy standard has polled "much better" with voters than alternative climate policies such as a carbon tax, he said, and a change of leadership in Congress and the White House in 2020 could help such legislation become law.

"This is probably going to be… in the mix as part of either a suite of policies or a package that would be a 'climate package,'" Cowin said. "It's too valuable of a policy not to be part of that mix."

Smith is discussing her legislation with lawmakers from both parties, including members of the Senate Committee on Energy and Natural Resources, of which she is a member. U.S. Sen. Lisa Murkowski, R-Alaska, who chairs the committee, has said she hopes to move bipartisan energy measures to the Senate floor sometime after Congress reconvenes from its August break, creating a narrow but possible opening for her bill.

"Clean energy standard legislation has a bipartisan history in the Senate, and several states have recently adopted clean energy standards," Smith told S&P Global Market Intelligence. "Of course I'd like to pass my bill sooner rather than later because I want the United States to lead, but getting a menu of proposals out there and having these critical discussions is a long game."