In May, the Brookings Institution published a working paper by economist and nonresident senior fellow Dr. Charles R. Frank Jr. claiming that solar and wind were far more expensive than previously thought.

Two weeks ago, that paper got a big and unwarranted boost when The Economist featured its conclusions in a full-page article.

There was just one problem: the paper’s conclusions were wrong.

Dr. Frank’s paper examined technology options for reducing carbon emissions by burning less fossil fuel for electricity generation. He evaluated five coal-saving options -- wind, solar photovoltaics (PV), hydro, nuclear and gas combined-cycle -- ranking them from the most to the least cost-effective carbon-savers.

Substituting for coal-fired plants, his analysis placed PV and wind last and next-to-last, respectively (while omitting efficiency, widely recognized as what would have been the most economical of the bunch), while gas and nuclear headed the pack.

Gas and nuclear advocates read Frank’s paper or the Economist article and probably thought, “We told you so." And renewable energy advocates were largely aghast. Readers deeply embedded in the electricity sector simply knew better. Some of them, in fact, have responded with their own critiques. Three are cited in a detailed rebuttal recently published by Rocky Mountain Institute.

Pick your metric: levelized cost of energy, saved carbon, cash flow profile, financial return, annual and cumulative installed capacity or global investment. By any meaningful set of accurate data and recent trends, renewables such as PV and wind are making rapid and accelerating inroads against incumbent fossil fuels -- precisely because they’re proving themselves increasingly economical, not because they’re supposedly swimming against the economic tide.

How did Dr. Frank reach a conclusion so counter to market reality? Simple: his analysis relied on outdated or otherwise incorrect data. 

For example, he assumed wind and PV are twice as costly and half as productive as they actually are, relying on old data in an industry where the landscape shifts dramatically each year, if not each month. At the same time, Dr. Frank overstated by double the actual productivity of gas combined-cycle plants, while overlooking both natural gas’ fuel price volatility and the impact of methane leakage.

He understated nuclear power’s total cost and construction time by twofold and its operating cost by fivefold. Finally, he assumed that PV is scarcely more productive at the grid’s peak hours (typically on sunny afternoons) than year-round; in fact, their output coincides well with system peak loads, creating much of their economic value.

In other words, he assumed solar and wind to be more expensive and less productive than they actually are, and conversely assumed nuclear and gas combined-cycle to be less expensive and (for gas) more productive than they actually are. All knobs got turned in exactly the wrong directions.

Using Dr. Frank’s methodology -- flawed as it is -- but swapping in accurate numbers for the nine key data points mentioned in the previous paragraph reverses his conclusion. Wind and solar become the most economical options while gas and nuclear become the least economical.

This is consistent with real-world observations, such as when utility Xcel Energy proposed adding 550 megawatts of wind capacity to its system last year -- not due to environmental motivations or state renewable-energy mandates, but because new wind power was the cheapest supply option from a list that included gas combined-cycle. Solar and wind similarly beat new gas plants in California electricity auctions.

Further confirming this, the near-future forecasts of the most respected industry analysts, including Bloomberg New Energy Finance, predict that unsubsidized solar power will beat retail prices more or less globally by 2025 (as they already do in favorable places, even though renewables receive smaller, temporary subsidies while fossil fuels enjoy well-documented larger, permanent ones).

And contrary to Dr. Frank’s assumption that wind and solar can’t contribute much reliable supply without a breakthrough in affordable bulk storage of electricity, four European countries already supply about half their electricity consumption from renewables, with superior reliability but without adding any bulk storage.

The electricity sector’s Transform scenario in Rocky Mountain Institute’s detailed 2011 analysis Reinventing Fire showed how, with investments first in efficiency and then in renewables such as solar and wind, we could build an electricity system to meet 2050 electric demand with 80 percent renewables. Half of those systems could be distributed on homeowners’ rooftops for essentially the same net present cost as simply maintaining today’s carbon-intensive grid -- while reducing electric sector carbon emissions by more than 80 percent below 2000 levels and making big, cascading blackouts virtually impossible.

This is not Pollyanna-ish wishful thinking, but rather an unfolding reality that's proving itself on a daily basis. The “ripped from the headlines” data and recent real-world trajectories of renewables show a low-carbon electricity future based on solar and wind is being built as fast as or faster than RMI’s analysis predicted it could. That’s not because renewables are defying economics (as Dr. Frank’s defective analysis would suggest they are), but because their ever-more-competitive economics reinforce their expanding gains against incumbent power stations.

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Amory B. Lovins is a physicist and chief scientist at the Rocky Mountain Institute. He has written 500 papers and 31 books, taught at ten universities, redesigned numerous buildings, vehicles and factories, and advised industry for more than 40 years in 50 countries.