It is technically and economically feasible to run the US economy entirely on renewable energy, and to do so by 2050. That is the conclusion of a study last year in the journal Energy & Environmental Science, authored by Stanford scholar Mark Z. Jacobson and nine colleagues.

Jacobson is well-known for his ambitious and controversial work on renewable energy. In 2011 he published, with Mark A. Delucchi, a two-part paper (one, two) on "providing all global energy with wind, water, and solar power." In 2013 he published a feasibility study on moving New York state entirely to renewables, and in 2014 he created a road map for California to do the same.

His team's 2015 paper contains 50 such road maps, one for every state, with detailed modeling on how to get to a US energy system entirely powered by wind, water, and solar (WWS). That means no oil and coal. It also means no natural gas, no nuclear power, no carbon capture and sequestration, and no biofuels.

Why exclude those sources? And what does that do to costs? More on that in a minute.

The road maps show how 80 to 85 percent of existing energy could be replaced by wind, water, and solar by 2030, with 100 percent by 2050. The result is a substantial savings relative to the status quo baseline, in terms of energy costs, health costs, and climate costs alike. The resulting land footprint of energy is manageable, grid reliability is maintained, and more jobs will be created in renewables than destroyed in fossil fuels.

Here's how it looks:

Sounds pretty great! So how should we feel about this?

Remember when I discussed scenarios that showed humanity limiting global warming to 2 degrees Celsius? I made a point of saying that the scenarios demonstrated technical and economic feasibility, but represented enormous, heroic assumptions about social and political change. (Which is another way of saying that purely as a matter of laying odds, they were unlikely.)

Well, the same goes here. No one can say any longer, at least not without argument, that moving the US quickly and entirely to renewables is impossible. Here is a way to do it, mapped out in some detail. But it is extremely ambitious. Let's take a look at some of what's required.

Electrify everything

The core of the plan is to electrify everything, including sectors that currently run partially or entirely on liquid fossil fuels. That means shifting transportation, heating/cooling, and industry to run on electric power.

Electrifying everything produces an enormous drop in projected demand, since the energy-to-work conversion of electric motors is much more efficient than combustion motors, which lose a ton of energy to heat. So the amount of energy necessary to meet projected demand drops by a third just from the conversion. With some additional, relatively modest efficiency measures, total demand relative to BAU drops 39.3 percent. That's a much lower target for WWS to meet.

Switching from liquid fuels to renewable electricity would also virtually eliminate air pollution, thus avoiding health costs to the tune of $600 billion a year by 2050. Meanwhile, moving everything to carbon-free electricity would avoid about $3.3 trillion a year in global climate change costs of US emissions by 2050. Estimating health and climate damages is notoriously difficult, of course, involving a number of assumptions about discount rates, the value of human lives, and second-order effects of better health. These figures are averages drawn from very wide ranges of estimates.

Still, the potential health and climate gains of a WWS-based system are one of the big stories here: they are enormous, enough that in and of themselves they "pay for" a clean-energy transition.

So how could the economy be electrified on this ambitious timeline? Brace yourself:

Heating, drying, and cooking in the residential and commercial sectors: by 2020, all new devices and machines are powered by electricity. ... Large-scale waterborne freight transport: by 2020–2025, all new ships are electrified and/or use electrolytic hydrogen, all new port operations are electrified, and port retro- electrification is well underway. ... Rail and bus transport: by 2025, all new trains and buses are electrified. ... Off-road transport, small-scale marine: by 2025 to 2030, all new production is electrified. ... Heavy-duty truck transport: by 2025 to 2030, all new vehicles are electrified or use electrolytic hydrogen. ... Light-duty on-road transport: by 2025–2030, all new vehicles are electrified. ... Short-haul aircraft: by 2035, all new small, short-range planes are battery- or electrolytic-hydrogen powered. ... Long-haul aircraft: by 2040, all remaining new aircraft are electrolytic cryogenic hydrogen ... with electricity power for idling, taxiing, and internal power. ...

Like I said: ambitious.

Build lots and lots (and lots) of new power plants

Here's what the paper says:

Power plants: by 2020, no more construction of new coal, nuclear, natural gas, or biomass fired power plants; all new power plants built are WWS.

One of the big challenges here is that wind and solar power plants have a much lower "capacity factor" than plants that run on fuel. A fuel-based plant can run around the clock (with breaks for maintenance), while wind and solar plants produce energy only when the wind is blowing or sun is shining. Although a nuclear plant and a wind farm might have the same "nameplate capacity" of 1 gigawatt, you'd actually need three or four wind farms that size to produce the same number of MWh as the nuclear plant. (EIA info on US capacity factors here; nuclear is highest, producing around 90 percent of the time, while solar PV is lowest, at around 20 percent.)

The upshot of this is that to meet most energy demand with wind and solar, you have to radically overbuild electrical generation capacity. To wit: the authors estimate that total US energy demand in 2050 will average 2.6 terawatts. To produce that much energy, they propose building power plants with a total of 6.5 TW of capacity. By way of comparison, the US currently has about 1.2 TW of installed electric generation capacity, so this plan would involve expanding generation capacity fivefold in 35 years.

Here's what that would require:

... 328,000 new onshore 5 MW wind turbines (providing 30.9% of U.S. energy for all purposes), 156,200 off-shore 5 MW wind turbines (19.1%), 46,480 50 MW new utility-scale solar-PV power plants (30.7%), 2,273 100 MW utility-scale CSP power plants (7.3%), 75.2 million 5 kW residential rooftop PV systems (3.98%), 2.75 million 100 kW commercial/government rooftop systems (3.2%), 208 100 MW geothermal plants (1.23%), 36,050 0.75 MW wave devices (0.37%), 8,800 1 MW tidal turbines (0.14%), and 3 new hydroelectric power plants (all in Alaska).

That will meet average demand. Then you need 1,364 additional new CSP plants and 9,380 50 MW solar-thermal collection systems ("for heat storage in soil") "to produce peaking power, to account for additional loads due to losses in and out of storage, and to ensure reliability of the grid."

"This," the authors note, "is just one possible mix of generators." But no matter what mix you pick, if you're confining yourself to WWS, you're going to be building a huge amount of generation capacity.

Would this power be reliable?

One common criticism of renewables is that because they are variable, they are not reliable. There will be times, critics say, when there's no sun shining and no wind blowing. Then we'll all be shivering in the dark!

Jacobson and colleagues, however, say that the grid they propose will be not only reliable, but more reliable than today's grid. They've got a detailed grid modeling and reliability study coming soon that makes the case in more detail, but the short story is that reliability is assured through three measures.

First, there's some nonvariable generation involved, namely hydro, geothermal, and CSP with storage. Those sources are "always on" and can be ramped up and down to "firm" variable power.

Second, there's energy storage. Interestingly, the authors mostly eschew stationary batteries, which they dismiss as too expensive (though they include electric vehicle batteries). Instead they prioritize "storage for excess heat (in soil and water) and electricity (in ice, water, phase-change materials tied to CSP, pumped hydro, and hydrogen)."

Third, there's "demand response," which refers to shifting energy demand to times of high production and away from times of low production.

There's also a concern about frequency regulation on the grid, which is too nerdy to get deep into, but:

Frequency regulation of the grid is proposed to be provided by ramping up/down hydroelectric, stored CSP or pumped hydro; ramping down other WWS generators and storing the electricity in heat, cold, or hydrogen instead of curtailment; and using demand response.

How to get there from here

What sorts of policies could produce these enormous shifts in energy technology and practice? Helpfully, the authors list a few. And by "a few," I mean 28. Here are the recommendations just for the transportation sector:

* Promote more public transit by increasing its availability and providing compensation to commuters for not purchasing parking passes. * Increase safe biking and walking infrastructure, such as 5 dedicated bike lanes, sidewalks, crosswalks, timed walk signals, etc. * Adopt legislation mandating BEVs [battery-electric vehicles] for short- and medium-distance government transportation and use incentives and rebates to encourage the transition of commercial and personal vehicles to BEVS. * Use incentives or mandates to stimulate the growth of fleets of electric and/or hydrogen fuel cell/electric hybrid buses starting with a few and gradually growing the fleets. Electric or hydrogen fuel cell ferries, riverboats, and other local shipping should be incentivized as well. * Ease the permitting process for the installation of electric charging stations in public parking lots, hotels, suburban metro stations, on streets, and in residential and commercial garages. * Set up time-of-use electricity rates to encourage charging at night. * Incentivize the electrification of freight rail and shift freight from trucks to rail.

These recommendations — indeed, all 28 — would require coordinated action from Congress, federal agencies, state legislatures, and local officials. Together, they represent an unprecedented level of government activism, a skein of incentives, mandates, standards, and laws unmatched in US history.

Much of that government activism is scheduled for the next five to 10 years, while Republicans, who fervently oppose nearly every one of these goals, are expected to control the House of Representative and well over half of the 50 state legislatures.

Is that realistic?

Uh, no. No it isn't. The authors inadvertently give away the game:

We do not believe a technical or economic barrier exists to ramping up production of WWS technologies, as history suggests that rapid ramp-ups of production can occur given strong enough political will. For example during World War II, aircraft production increased from nearly zero to 330,000 over five years.

The phrase "given strong enough political will" is open-ended enough to allow virtually anything through. But what would create this political will, equal to what gripped the US in the wake of the Pearl Harbor attack? The authors don't say much about it, other than a hopeful note at the end that their quantification of the benefits of such a transition "should reduce social and political barriers to implementing the roadmaps."

Hm. Maybe a paper can help kick-start a WWII-scale mobilization. But it's probably going to take a whole lot more than that.

Is it wise?

This is, in many ways, the more interesting question. Assuming we could conjure up the political will for this kind of wholesale transformation to WWS ... would we want to?

The authors make the case that the resultant total-system costs would be lower than the business-as-usual scenario. Which is great, since BAU sucks, as most everyone agrees (except the people profiting from BAU). What they don't try to show is that the resultant system is the optimal system, i.e., the optimal balance of costs and benefits.

Insisting on 100 percent WWS — excluding nuclear, biomass, cogeneration, natural gas, etc. — almost certainly raises the total-system costs relative to a broader portfolio of low-carbon options. Just a little bit of nuclear or biomass power, for instance, would reduce the amount of power-plant overbuild necessary.

Lots of people are extremely skeptical of Jacobson's work for just this reason. They say, Why not accept a little bit of asthma, or some nuclear waste, in exchange for a cheaper system?

But I think that misses the point. Jacobson has set out to create a benchmark: this is what we could do if we aimed to create an entirely sustainable, pollution-free energy system. After all, the cost-benefit trade-offs of less sustainable systems almost always mean higher benefits for the already privileged and more costs for the already less privileged.

Jacobson's approach is more like political philosopher John Rawls's famous "veil of ignorance" approach. What kind of power system would you choose for society if you had no idea where you might be placed in that society? If you didn't know whether you'd be rich or poor, living in a gated suburb or right next to a power plant or waste dump? You'd probably design a system that is equitable and healthy for everyone.

That's our highest aspiration, and the one Jacobson's work speaks to. Whether we pursue our highest aspirations is up to us.