Is grid-scale energy storage the key to a renewable energy future? Brookings fellow John Banks, an adjunct professor at Johns Hopkins and Georgetown, says no.

The Brookings Institution has stepped up efforts to better understand renewable energy policy and trends in Germany and Japan in its newly released report, “Transforming the Electricity Portfolio,” which was launched at a September 19 event in Washington, D.C.

The research touched on a number of favorite themes of Energiewende fans and detractors in the United States. Perhaps most notably, the panelists disagreed on the importance of energy storage.

“When we spoke to transmission system operators in Germany, the bottom line was that storage is still too expensive, and that transmission is a lower-cost option, so that was what they were focusing on.”

Ron Binz, another Brookings fellow, former Colorado utility commissioner, and rejected nominee to run FERC, cited a 2013 Citigroup report that analyzed market opportunities for storage technologies in Germany.

“Citigroup reasoned that when renewables double to 45 percent to 50 percent, [Germany] would have an over-generation problem midday, which calls for storage,” he said. At that point, storage would allow solar output to be spread out from midday, reducing conflict with baseload plants. Germany got 28 percent of its power from renewables on average in the first half of 2014.

A recent study by Berlin-based think tank Agora Energiewende confirms this finding -- and suggests the renewables milestone is even higher.

“For the next fifteen to twenty years -- that is, up to a 60 percent share of renewable energies -- we have plenty of other, better flexibility technologies available," said Patrick Graichen, director of the think tank.

“New power storage is expensive,” he noted, citing the few niches in which it is currently cost-effective. “But this can change quickly. Storage must have equal access to the markets now.”

But panel moderator Lisa Wood, executive director of the Institute for Electric Innovation at the Edison Electric Institute, disagreed. “From my perspective, the big issue is storage,” she said. “Storage is going to make a huge difference for renewable energy. Grid-scale storage is going to be the game-changer for how we run the electric grid.”

Meanwhile, the widespread perception that Germany is using more coal due to its decision to phase out nuclear power was reiterated by an audience member, a former director of operations at the World Bank. “Whatever Germany did, did not reduce the carbon footprint, it increased it. That seems to have been driven by political motives rather than a proper assessment of technological options.”

This conventional wisdom is echoed in many places, such as the most recent edition of the PricewaterhouseCoopers low carbon economy index. “Germany has, since 2011, been reducing its reliance on nuclear, but at the cost of rising fossil fuel use, causing carbon intensity to rise in the last two years,” the firm writes.

But Banks dismissed this perception. “There are a number of market factors that have nothing to do with the phase-out of nuclear,” he said, citing low-cost coal imports from the U.S. and high-cost European natural gas.

“Right now, there isn’t any serious plan to add more coal. The German government would say this is a blip.”

Blogger and journalist Christian Roseland has drawn from Fraunhofer Institute data to assert that the numbers simply don’t add up to support the nuclear-to-coal-shift hypothesis.

“There is a much stronger correlation between falling gas use and rising coal use,” Roseland points out. He attributes the shift from natural gas to coal to high gas prices, low coal prices, and demand for low-cost power exports to other European countries.

The alleged “de-industrialization” of Germany was also scrutinized. “Can anybody show me a company that has left Germany due to high prices?” Banks asked. “Industry buys 20 percent of the power, but pays only 3 percent of the surcharge” that funds renewable energy.

Reliability was another red herring addressed at the Brookings event.

“I think there has been a lot of Germany-bashing on this side of the Atlantic,” said Banks, adding that it has often focused on reliability impacts from renewables.

In contrast, he cited the recent reliability report by the German grid agency BNA, which measures reliability through the System Average Interruption Duration Index (SAIDI). Germany averaged 15 minutes of interruption per customer per year, “the lowest in Europe, and it’s coming down. In the U.S., it’s over several hundred minutes.”

“The head of BNA said point-blank that the Energiewende is not threatening system stability,” he said. “When we talk to the transmission system operators, they say…'We can handle that. What we need is more transmission capacity.'”

There was less discussion about Japan’s experience with renewables. Energy policy in that country has been in flux since the earthquake, tsunami and nuclear meltdown at Fukushima in 2011.

Charles Ebinger, director of the Energy Security Initiative at Brookings, pointed out that “Japan has always been greatly concerned about energy security” due to its near total reliance on imports. This has been a major driver of interest in nuclear power since the 1970s.

In response to the Fukushima disaster, the government of prime minister Naoto Kan published the “Revolutionary Energy and Environment Strategy,” recommending a phase-out of nuclear power by 2040 (also called the “zero option”).

But business interests were strongly opposed, and the election of pro-business prime minister Shinzo Abe put an end to the plan.

What did survive was Kan’s adoption of a national feed-in tariff for renewables in 2012. At the time, Japan had 20 gigawatts of total renewables capacity (including hydro). Renewables have grown 43 percent since then, nearly half of that coming from solar, and there are 20 gigawatts of solar in the development pipeline.

Grid integration is perhaps more vexing in Japan, which continues to have a bifurcated grid, with one half operating on 50 Hz and the other on 60 Hz. This is a legacy from the earliest days of the grid, when Tokyo power companies bought 50-cycle generators from Germany, while their counterparts in Osaka bought 60-cycle equipment from the United States. “The result is a national grid whose two halves cannot directly exchange AC power,” according to the IEEE.