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Monday, April 27, 2015

Liquid Batteries for Solar and Wind Power - NYT

Liquid Batteries for Solar and Wind Power

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An engineer checks a power module during production at UniEnergy Technologies in Washington. The batteries, also called flow batteries, use large tanks of liquid. They are durable and can provide energy steadily over time UniEnergy Technologies
In an industrial park on the outskirts of Pullman, Wash., 10 white storage trailers sit side by side, neatly arranged in two rows.
These are no ordinary storage units. Arranged on racks inside are the guts of a large rechargeable battery, the kind of device that can store and release utility-scale amounts of electricity.
But this is no ordinary storage battery, either. In contrast with the typical lead-acid batteries used to start car engines or the lithium-ion cells that power electric vehicles — both of which are largely solid — this battery is mostly liquid.
The chemicals that react to produce electricity are dissolved in water and circulated into and out of the heart of each cell, where the reaction occurs. For that reason, it is called a flow battery, and the one in Pullman, a demonstration project that will be tested over the next year and a half, is one of the largest in the world. It can store about 3.2 megawatt-hours of energy and discharge a megawatt of power for over three to four hours — enough to keep 500 average homes going for an afternoon.
Flow batteries are not new (and they are similar, in some ways, to fuel cells), but they have never really caught on. They were invented in France in the 19th century and studied by NASA in the 1970s as potential power sources in space or on the moon.
Now, flow batteries are being viewed as a possible way to help the electrical grid handle greater amounts of renewable energy, and they are being developed further by companies like UniEnergy Technologies, the maker of the Pullman battery, and academic and government researchers.
Because solar panels and wind turbines produce varying amounts of electricity during the day, utilities and system operators must work harder to integrate the renewable sources into the grid. Batteries are one way to do this, by storing excess electricity from solar panels during the middle of the day, for example, and releasing it in the evening.
Such batteries are being used mostly for purposes other than integrating renewables into the grid — for example, by providing short infusions of electricity to keep the grid stable. Only 60 megawatts of storage were in use in the United States last year. But storage is expected to grow rapidly as prices of batteries and related control equipment fall.
Other battery technologies — notably lithium ion, by virtue of its widespread use by Tesla Motors and other electric-car makers — have a head start in the market.
Experts say, however, that flow batteries have some advantages that make them well suited to grid storage.
“I see flow batteries as being increasingly important,” said Imre Gyuk, who manages an Energy Department program to help develop technologies for utility-scale electricity storage.
Lithium-ion and lead-acid batteries pack more power for their size, which makes them especially useful for tasks like turning over a gasoline engine or getting an electric car moving from a full stop. And watt per watt they are smaller than flow batteries, which have tanks for the liquid chemicals and equipment to pump them into the cells.
But on the grid, batteries do not need to supply a lot of power at once; instead, they need to provide energy steadily over time. And compact size is not as important.
“A smaller footprint is not as useful in a stationary battery,” Dr. Gyuk said.
Because the electricity-producing reactions take place in the liquids, increasing the size of the tanks allows flow batteries to store larger amounts of electricity. While there are practical and economic limits to their capacity, flow batteries are seen as having potential for situations where a battery system has to discharge a large amount of electricity for more than a few hours.
“If you’re talking six-hour batteries, you’re probably going to be looking at flow batteries,” said Matt Roberts, executive director of the Energy Storage Association, an industry group.
Rick Winter, chief operating officer of UniEnergy Technologies, which is based in Mukilteo, Wash., said flow batteries had other advantages as well. Compared with other batteries, which lose capacity as they go through many charge-discharge cycles and must eventually be replaced, flow batteries have much longer life — the company warrants the battery for 20 years and unlimited cycles. Flow batteries can also be completely discharged — something that is not recommended for lithium-ion and other types because it affects their longevity.
“There’s no physical mechanism for degrading the system,” Mr. Winter said. “It’s going to have the same power and energy rating no matter how many times you cycle it.”
The Pullman battery uses vanadium salts for its energy-producing reactions, a chemistry that was developed at the Pacific Northwest National Laboratory. (At a White House business forum four years ago, President Obama mentioned the vanadium process and commented, “That’s one of the coolest things I’ve ever said out loud.”)
The demonstration project, which cost $7 million, was paid for by the region’s utility, Avista, and a grant from a state clean energy fund. It will be used to add electricity to the grid in times of peak demand, but because it is on the campus of a large electrical engineering company — a big user of electricity — it will also be tested as a large uninterruptible power supply. It will kick in nearly instantaneously in a power failure to keep the company’s sensitive digital equipment running.
“It will be fast enough that the equipment won’t notice the outage,” Mr. Winter said.
Correction: April 27, 2015 
An article on Thursday about the development of flow batteries for use with the electrical grid described incorrectly the capacity of a large rechargeable battery, in Pullman, Wash. The battery can store about 3.2 megawatt-hours of energy, and can release about a megawatt of power over three to four hours. It does not store a megawatt of electricity; storage is measured in megawatt-hours.
A version of this article appears in print on April 23, 2015, on page F5 of the New York edition with the headline: Liquid Batteries for Solar and Wind Power. Order Reprints| Today's Paper|Subscribe
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Saturday, April 18, 2015

Solar power will soon be as cheap as coal

Solar power will soon be as cheap as coal
Thanks to this wafer-thin technology. (AP Photo/Mike Groll)
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WRITTEN BY
Phil McKenna
8 hours ago
This post originally appeared at Ensia. http://ensia.com/republished.php?title=Look%20what%E2%80%99s%20cooking%20in%20the%20world%20of%20renewable%20energy
http://qz.com/386261/solar-power-will-soon-be-as-cheap-as-coal/

Inside a sprawling single-story office building in Bedford, Massachusetts, in a secret room known as the Growth Hall, the future of solar power is cooking at more than 2,500 °F. Behind closed doors and downturned blinds, custom-built ovens with ambitious names like “Fearless” and “Intrepid” are helping to perfect a new technique of making silicon wafers, the workhorse of today’s solar panels. If all goes well, the new method could cut the cost of solar power by more than 20% in the next few years.
“This humble wafer will allow solar to be as cheap as coal and will drastically change the way we consume energy,” says Frank van Mierlo, CEO of 1366 Technologies, the company behind the new method of wafer fabrication.
Secret rooms or not, these are exciting times in the world of renewable energy. Thanks to technological advances and a ramp-up in production over the decade, grid parity—the point at which sources of renewable energy such as solar and wind cost the same as electricity derived from burning fossil fuels—is quickly approaching. In some cases it has already been achieved, and additional innovations waiting in the wings hold huge promise for driving costs even lower, ushering in an entirely new era for renewables.
Solar surprise
In Jan. 2015, Saudi Arabian company ACWA Power surprised industry analysts when it won a bid to build a 200-megawatt solar power plant in Dubai that will be able to produce electricity for 6 cents per kilowatt-hour. The price was less than the cost of electricity from natural gas or coal power plants, a first for a solar installation. Electricity from new natural gas and coal plants would cost an estimated 6.4 cents and 9.6 cents per kilowatt-hour, respectively, according to the US Energy Information Agency.
Technological advances, including photovoltaics that can convert higher percentages of sunlight into energy, have made solar panels more efficient. At the same time economies of scale have driven down their costs.
For much of the early 2000s, the price of a solar panel or module hovered around $4 per watt. At the time Martin Green, one of the world’s leading photovoltaic researchers, calculated the cost of every component, including the polycrystalline silicon ingots used in making silicon wafers, the protective glass on the outside of the module, and the silver used in the module’s wiring. Green famously declared that so long as we rely on crystalline silicon for solar power, the price would likely never drop below $1/watt.
The future, Green and nearly everyone else in the field believed, was with thin films, solar modules that relied on materials other than silicon that required a fraction of the raw materials.
Then, from 2007 to 2014, the price of crystalline silicon modules dropped from $4 per watt to $0.50 per watt, all but ending the development of thin films.
The dramatic reduction in cost came from a wide number of incremental gains, says Mark Barineau, a solar analyst with Lux Research. Factors include a new, low-cost process for making polycrystalline silicon; thinner silicon wafers; thinner wires on the front of the module that block less sunlight and use less silver; less-expensive plastics instead of glass; and greater automation in manufacturing.
“There is a tenth of a percent of an efficiency gain here and cost reductions there that have added up to make solar very competitive,” Barineau says.
25 cents per watt
“Getting below $1 [per watt] has exceeded my expectations,” Green says. “But now, I think it can get even lower.”
One likely candidate to get it there is 1366’s new method of wafer fabrication. The silicon wafers behind today’s solar panels are cut from large ingots of polycrystalline silicon. The process is extremely inefficient, turning as much as half of the initial ingot into sawdust. 1366 takes a different approach, melting the silicon in specially built ovens and recasting it into thin wafers for less than half the cost per wafer or a 20% drop in the overall cost of a crystalline silicon module. 1366 hopes to begin mass production in 2016, according to van Mierlo.
Meanwhile, thin films, once thought to be the future of solar power, then crushed by low-cost crystalline silicon, could experience a renaissance. The recent record-setting low-cost bid for solar power in Dubai harnesses thin-film cadmium telluride solar modules made by USmanufacturer First Solar. The company not only hung on as the vast majority of thin film companies folded, but has consistently produced some of the least expensive modules by increasing the efficiency of their solar cells while scaling up production. The company now says it can manufacture solar modules for less than 40 cents per watt and anticipates further price reductions in coming years.
Ten years from now we could easily see the cost of solar modules dropping to 25 cents per watt, or roughly half their current cost, Green says. To reduce costs beyond that, the conversion efficiency of sunlight into electricity will have to increase substantially. To get there, other semiconducting materials will have to be stacked on top of existing solar cells to convert a wider spectrum of sunlight into electricity.
“If you can stack something on top of a silicon wafer it will be pretty much unbeatable,” Green says.
Green and colleagues set a record for crystalline silicon solar module efficiency at 22.9% in 1996 that still holds today. Green doubts the efficiency of crystalline silicon alone will ever get much higher. With cell stacking, however, he says “the sky is the limit.”
A matter of size
While solar power is just starting to reach grid parity, wind energy is already there. In 2014, the average worldwide price of onshore wind energy was the same as electricity from natural gas, according toBloomberg New Energy Finance.
As with solar, the credit goes to technological advances and volume increases. For wind, however, innovation has mainly been a matter of size. From 1981 to 2015 the average length of a wind turbine rotor blade has increased more than sixfold, from 9 meters to 60 meters, as the cost of wind energy has dropped by a factor of 10.
“Increasing the rotor size means you are capturing more energy, and that is the single most import driver in reducing the cost of wind energy,” says D. Todd Griffith of Sandia National Laboratories in Albuquerque, New Mexico.
Griffith recently oversaw the design and testing of several 100-meter-long blade models at Sandia. His group didn’t actually build the blades, but created detailed designs that they subsequently tested in computer models. When the project started in 2009, the biggest blades in commercial operation were 60 meters long. Griffith and his colleagues wanted to see how far they could push the trend of ever-increasing blades before they ran into material limitations.
Their first design was an all-fiberglass blade that used a similar shape and materials as those found in relatively smaller commercial blades at the time. The result was a prohibitively heavy 126-ton blade that was so thin and long it would be susceptible to vibration in strong winds and gravitational strain.
The group made two subsequent designs employing stronger, lighter carbon fiber and a blade shape that was flat-backed instead of sharp-edged. The resulting 100-meter blade design was 60% lighter than the initial model.
Since the project began in 2009 the largest blades used in commercial offshore wind turbines have grown from 60 meters to roughly 80 meters with larger commercial prototypes now under development. “I fully expect to see 100 meter blades and beyond,” Griffith says.
As blades grow longer, the towers that elevate them are getting taller to catch more consistent, higher speed wind. And as towers grow taller, transportation costs are growing increasingly expensive. To counter the increased costs GE recently debuted a “space frame” tower, a steel lattice tower wrapped in fabric. The new towers use roughly 30% less steel than conventional tube towers of the same height and can be delivered entirely in standard-size shipping containers for on-site assembly. The company recently received a $3.7 million grant from the US Department of Energy to develop similar space frame blades.
Offshore innovation
Like crystalline silicon solar panels, however, existing wind technology will eventually run up against material limits. Another innovation on the horizon for wind is related instead to location. Wind farms are moving offshore in pursuit of greater wind resources and less land use conflict. The farther offshore they go, the deeper the water, making the current method of fixing turbines to the seafloor prohibitively expensive. If the industry moves instead to floating support structures, today’s top-heavy wind turbine design will likely prove too unwieldy.
One potential solution is a vertical axis turbine, one where the main rotor shaft is set vertically, like a merry go round, rather than horizontally like a conventional wind turbine. The generator for such a turbine could be placed at sea level, giving the device a much lower center of gravity.
“There is a very good chance that some other type of turbine technology, very well vertical axis, will be the most cost effective in deep water,” Griffith says.
The past decade has yielded remarkable innovations in solar and wind technology, bringing improvements in efficiency and cost that in some cases have exceeded the most optimistic expectations. What the coming decade will bring remains unclear, but if history is any guide, the future of renewables looks extremely positive.

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