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An excerpt from Taming the SunInnovations to Harness Solar Energy and Power the Planet by Varun Sivaram

Stashing the Sun

In early 2012, the Japanese automaker Toyota found itself at a crossroads. A year before, it had been sitting pretty, having sold more new cars than any competitor. But the 2011 Fukushima disaster was a blow to business. The price of electricity to run Toyota’s factories surged after Japan shut down its fleet of nuclear reactors; domestic suppliers couldn’t deliver parts on time; and the yen spiked, raising the price of Toyota’s exports to the rest of the world. The firm’s net profits plunged by half, and it watched helplessly as the U.S. automaker General Motors and the German car company Volkswagen raced ahead of it in sales.

Yoshikazu Tanaka, a senior Toyota engineer, recalls fretting, “There is only extinction ahead if no action is taken.” At the time, Tanaka was in charge of the Toyota Prius plug-in hybrid, a variant on the original, high-mileage Prius that launched the hybrid revolution. Toyota had sold more than a million Prius cars in each of the U.S. and Japanese markets, and Tanaka’s plug-in hybrid Prius gave customers the new option of charging up with electricity at home in addition to refueling with gasoline at a gas station. Despite its present woes, Toyota still owned the greenest brand in the industry, and it was poised to take a big next step to capitalize on that lead.

Presumably that step would be to launch a fully electric vehicle (EV) with no gas tank. All electric seemed to be the way of the future globally. In 2008, U.S. president Barack Obama had announced a splashy goal: put 1 million EVs on the road by 2015. China upped the ante in 2012, pledging to introduce 5 million EVs by 2020. The same year, Tesla launched its Model S sedan to critical acclaim, breaking the ratings scale of the venerable Consumer Reports magazine. Electric cars looked as if they might finally break petroleum’s stranglehold as the fuel of choice for passenger vehicles.

Imagine Tanaka’s surprise when his executives assigned him to lead the design of a brand-new, ecofriendly car with nowhere to store petroleum, but also nowhere to plug into the power grid, either. Instead, he was asked to bring to market the Toyota Mirai—whose name literally means “future” in Japanese—a car that would run on hydrogen as its fuel, and to accomplish the job on a shoestring budget. Tanaka—a mild-mannered, bespectacled engineer with a gently receding hairline—began running 5 kilometers a day right before lunch just to cope with the stress.

Elon Musk, Tesla’s founder, would deride Toyota’s bet on hydrogen, sneering, “If you’re going to pick an energy source mechanism, hydrogen is an incredibly dumb one to pick.” But by 2015, when Toyota unveiled the Mirai, EVs had lost some of their luster. A plunge in oil prices in 2014 from a high of over $100 to less than $50 per barrel had juiced consumer demand for gas-guzzlers and undercut the case for EVs. Promptly, EVs fell as a share of new vehicles, dropping from 3.5 percent to 2.9 percent in the United States. The United States missed President Obama’s million-EV target by a whopping 60 percent. As of 2017, China, too, was on track to substantially miss its 2020 target, especially once it ratcheted back EV subsidies. Toyota was not alone in seeking to forge an alternative path—the Japanese govern- ment was behind its champion automaker. Prime Minister Shinzo Abe later declared, “a hydrogen society of the future is about to begin here in Japan.”

In 2015, with Toyota having regained its crown as the world’s biggest automaker, Tanaka argued that the Mirai, rather than the EV, was the logi- cal descendant of the Prius. Indeed, he had repurposed many of the same components from the Prius—including its electric motor, which was pow- ered by using hydrogen fuel to generate electricity—for the Mirai. But more important, the Mirai retained a crucial design feature of the Prius that all-electric cars had abandoned: the ability to fuel up (with hydrogen) in under five minutes. That feature, coupled with a 340-mile range on a single tank, would make owning a Mirai similar to owning a conventional gasoline-fueled vehicle. Toyota was betting that most consumers would be reluctant to buy an EV with a limited range and long recharging time.

Toyota could be right that EVs may be slow to take off and challenge conventional vehicles, which have a massive head start. In 2016, global annual sales of petroleum-fueled vehicles grew more than 3 percent, to nearly 90 million. New EV releases—such as Chevy’s Bolt and Tesla’s Model 3, each of which can travel more than 200 miles on a single charge—might increase the rate of EV adoption. Many more all-electric models are on the way; Volvo announced in 2017 that it would only make electric or hybrid vehicles beginning in 2019. But EVs are starting way behind conventional vehicles, having accounted for less than 1 percent of total vehicle sales in 2016.

The market challenges faced by EVs point to an even bigger challenge. If the planet is going to decarbonize, the task will not be accomplished solely by eliminating fossil fuels from electricity generation and powering on- road vehicles with electricity instead of oil derivatives. Most of the world’s energy demand is not met by electricity but by burning other fuels, the most prevalent of which is oil. So, decarbonization will require replacing oil—the most widely-used energy source on the planet—with storable fuels that have no carbon footprint.

Yet oil is so popular, especially in the transportation and industrial sec- tors, because it and fuels derived from it are remarkably convenient. For example, gasoline packs eighty times as much energy into the same volume as taken up by the lithium-ion batteries that power electronics and EVs. In fact, a single gallon of gasoline has enough energy to charge your iPhone every day for 20 years. And transporting oil around the globe in massive tankers adds just a few cents to the cost of that gallon of gasoline.

What is more, many forms of transportation—including heavy-duty trucking, shipping, and aviation—depend on the high energy density, portability, and reliability of fossil fuels. (Indeed, when a solar-powered plane finally circumnavigated the globe for the first time ever, the trip took more than a year because bad weather kept grounding the plane.) Applications that cannot be electrified readily, if at all, account for 40 percent of global transportation energy demand.

The challenges for electrification don’t end there. Global industrial energy use, which is twice that of transportation and accounts for half of the world’s energy demand, relies on electricity for less than 15 percent of its needs. It is often cheaper to burn fossil fuels for heat to run industrial processes than it is to pay for electricity to produce the same heat.

If electricity serves only a minority of the world’s energy demand, then how can humanity possibly harness the sun’s energy to power a majority of its needs sometime this century? Rapid financial and technological innovation in the field of solar photovoltaics (PV) alone cannot resolve this quandary. In addition, innovation is needed to develop and commercialize alternative technologies that stash sunshine by converting it into convenient stores of energy that can be used where PV can’t.

The production of hydrogen fuel from sunlight is one of those tech- nologies. The Toyota Mirai is just the tip of the iceberg when it comes to the potential for hydrogen to replace fossil fuels. In addition to fueling cars, hydrogen could fuel trucks and provide heat for industrial uses. And solar-produced hydrogen would solve that pesky problem of intermittent sunlight, acting as a store of energy that can be used on demand, in contrast to solar PV, which produces power only when the sun is shining.

Scientists seeking inspiration for converting sunlight into fuel have found it all around them—in the form of plants, which harness solar energy to produce fuel through photosynthesis, a process that includes splitting water to make hydrogen. Plants are an imperfect model, because photo- synthesis is a highly inefficient method of energy conversion. So, scientists have copied some of the basic principles but ditched many of the details in a quest to produce an artificial leaf that will exploit sunlight to generate hydrogen fuel from water. In 2015, researchers developed a prototype device that produced hydrogen with respectable efficiency and the potential for low cost once the technology is improved and reaches manufacturing scale. Just as important, the device neither broke down immediately nor exploded. Although this breakthrough still leaves plenty of challenges on the road to commercialization, it is an encouraging sign of progress.

Yet hydrogen is far from a shoo-in as oil’s replacement. In the realm of cars, for instance, consumers will not switch to hydrogen vehicles en masse unless they have convenient access to hydrogen-refueling stations, which don’t yet exist. If stations did exist, supplies of cheap hydrogen would need to be generated and transported to them at a scale rivaling that of today’s massive petroleum sector. Recognizing this reality, Toyota is hedging its bets. It announced in 2017 that it hoped within five years to commercialize a new type of battery (known as an “all-solid-state battery”) that would enable an EV to charge up in a few minutes and travel farther than today’s EVs on a single charge.

In light of the drawbacks of hydrogen, scientists have embarked on a much tougher quest: cost-effectively converting sunlight into liquid fuels that can substitute readily for today’s fossil fuels. If such a process were to use as a raw material carbon dioxide from power plant exhausts, or even from the atmosphere, as an input, then burning the output fuel to produce energy would be carbon-neutral. But the chemistry involved in producing convenient, carbon-based fuels is far more complex than the comparatively simpler task of splitting water to produce hydrogen. Still, researchers are undeterred, and a breakthrough in 2016 harnessed the complex metabolisms of bacteria to do the hard work of producing usable fuel.

Technologies to convert sunlight to fuels could store intermittent solar energy one day, something that solar PV cannot do. Another way to crack the storage nut is to convert the sun’s energy into storable heat. Already, some concentrated solar power (CSP) plants on the market can store energy throughout the night and generate electricity hours after the sun has set. Yet CSP growth has stalled owing to its high cost compared with solar PV. To drive down the cost of CSP plants equipped with storage, researchers are attempting to concentrate sunlight to realize previously unreachable high temperatures. Greater efficiency combined with cheap and long-lasting thermal storage could boost the profits of these plants and enable them to stabilize the power grid in response to rising PV penetration, storing excess energy produced at sunny times of the day and making it available when needed later on.

To reach solar’s potential, all these non-PV technologies—including convenient solar-generated fuels and CSP plants that generate electricity 24/7—will need to advance dramatically. And it won’t do to wait to make the requisite investments until an urgent need for them arises. Technology development can take decades, and even pumping gobs of money into innovation at the last minute will compress those timelines to just a limited extent. Only with long-term planning and a willingness to incur costs up front can countries around the world reap the massive rewards of innovation down the road.

For its part, Toyota is probably crossing its fingers that the artificial leaf can graduate from the lab bench to a commercial scale. Aside from betting big on hydrogen, the automaker has pledged to slash emissions from its cars in 2050 by 90 percent. And without a way to generate hydrogen or liquid fuels from a clean source like sunlight, its advertised zero-emission Mirai would be just a mirage.