Energy

Greener, safer flow battery could store renewable energy on the cheap

Greener, safer flow battery co...
A new flow battery developed at Harvard University uses only Earth-abundant materials, making it cheaper, safer and greener than previous designs
A new flow battery developed at Harvard University uses only Earth-abundant materials, making it cheaper, safer and greener than previous designs
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Design if the flow battery
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Design if the flow battery
A new flow battery developed at Harvard University uses only Earth-abundant materials, making it cheaper, safer and greener than previous designs
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A new flow battery developed at Harvard University uses only Earth-abundant materials, making it cheaper, safer and greener than previous designs
Flow batteries pump electrolytes to a membrane that exchanges ions to store or release power
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Flow batteries pump electrolytes to a membrane that exchanges ions to store or release power
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Improving on their previous design, scientists at Harvard University have developed a cheap and highly adaptable flow battery that could prove ideal for storing renewable energy throughout the day. The battery is made using Earth-abundant materials, is much safer than previous designs, and could reach the market in as little as three years.

Lithium-ion batteries are great for smartphones and electric SUVs, but they may not be the best solution to handle the stresses that solar and wind power put on the electric grid. To get the most out of renewables, we need something more flexible, scalable, and most importantly, cheaper than a solid-state battery (Elon Musk would have you use lithium-ion cells for home storage too, but his entry-level Powerwall goes for US$3,000).

So-called flow batteries could be the perfect solution. Such devices store energy in liquid form, in external tanks, and collect or release power by having those liquids exchange ions through a special membrane. This makes flow batteries extremely flexible: their capacity can be tweaked by modifying the size of the tanks, and their power output can be changed by adjusting the area of the membrane. Flow batteries can also remain idle for long periods of time without losing charge and are not affected by temperature extremes.

Prof. Michael Aziz and team have now built on previous work to design a safer and greener flow battery. Their device relies on cheap and abundant elements like carbon, iron and potassium to form compounds that are nontoxic, fire-resistant and generally safer. As such, the battery might find a place in our homes to store the intermittent energy produced by solar panels (or portable wind turbine, if you've got one).

Flow batteries are a relatively new technology and, to put it mildly, their first generation didn't feature the best choice of materials. Such batteries have commonly used vanadium and bromine dissolved in acid as their electrolytes (energy-carrying liquids). Though effective, this combination is expensive, dangerous and even toxic.

Flow batteries pump electrolytes to a membrane that exchanges ions to store or release power
Flow batteries pump electrolytes to a membrane that exchanges ions to store or release power

In last year's development Aziz and his team designed a flow battery that dropped the vanadium for the more environmentally friendly quinones naturally occurring chemicals involved in photosynthesis. Their latest battery improves on this by replacing bromine with ferrocyanide, which is commonly added to kitchen salt as an anticaking agent.

The new battery also works in an alkaline, not acidic, solution. The higher pH is less corrosive, allowing the tanks to be built out of plastic instead of heavier and more expensive metals. An alkaline environment creates more electrical resistance in the membrane, but this was compensated by increasing the battery's voltage.

According to the team, the cell's current efficiency exceeded 99 percent, while round-trip efficiency was measured at 84 percent. The data also suggests that the battery will have a lifetime of at least 1,900 cycles, which is much longer than a lithium-ion battery.

The Achilles' heel of the technology appears to be its low energy density, or amount of energy that can be stored inside the battery per unit volume. The researchers achieved 19 Wh per liter in their published study, and slightly higher figures using methods they've developed since.

This falls well short of lithium-ion batteries, which are closer to the 300 Wh/L mark. That could make a home-use flow battery out of the question for some (you'll most likely need a roomy basement). But for large-scale applications at the grid level, where space isn't such a concern and cost is the primary issue, these cheap, highly adaptable cells could prove to be the perfect solution.

The scientists are now working on improvements to increase cycle life and reduce the cost of the membrane. They tell us the battery could become commercially available in about three years' time.

A paper describing the advance appears in the latest edition of the journal Science.

Source: Harvard University

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10 comments
Kaiser Derden
solar and wind will never replace large central power plants ... better to develop thorium nukes or finally get fusion working ... I could see a use in current power plants to allow them to run more efficiently and store power from non peak times to be used during peak power spikes ... but solar and wind ? sorry just another rent seeking taxpayer funded Utopian dream ...
ikarus342000
Sorry Mr. Derden you are wrong. About 70% + of energy in Germany is generated by alternative sources. So to have flow batteries with this efficency would be a good solution for peak power needs.
Fretting Freddy the Ferret pressing the Fret
ikarus342000, I don't know where you got those numbers, but the primary energy generated by renewable sources in Germany is actually closer to 11% in 2014. Electricity generation by wind, bio and solar was about 30% that same year. *Peak* power generation from combined wind and solar however, reached +70% during its best day. The low-cost and scalability of this battery certainly makes it interesting to consider building a pilot plant and see how it performs in the field. Also, improving its energy density would be desirable.
StWils
Some years ago super flywheels were seen as a possible storage solution and safety concerns were answered by a design that used vertical concrete drainage pipes set just below the surface of a homeowners yard. A similar solution would work here for many, not all, but still many users. The storage system could be utility owned & managed and the user would effectively pay a monthly utility fee. When the cells aged out the utility would then open a below grade box and swap out the worn cells. Some variant of this approach would work well in many settings. Keep in mind that one design does Not have to work everywhere to be valid.
thingstodo
Lithium-Iron-Phosphate cells have been available for years (Brands CALB, Sky energy to name just 2) that reach 3000 cycles to 80% of capacity. It's not that they stop working after that, that's just - worst case - when their capacity drops below 80% of their original rated capacity. What is the rating for 1900 cycles of these flow batteries?
J4rH43d
Regarding the "higher pH" claim allowing plastic instead of metal for the tanks, that is the reverse if what pH does. Low pH is acidic and attacks metals and minerals. High pH attacks organic materials, such as plastics. Detergents have high pH for that very reason, to break down oils and soils.
zevulon
Energy density is relevant only at a far different scale for stationary applications in large power plants. you don't need high energy density relative to lithium ion. in fact you can have much much lower than lead acid and still succeed where lead acid has failed. the point isn't density------it's creating a CHEAP MASSIVELY SCALEABLE BATTERY TO STORE MEGAWATT HOURS OF CAPACITY . this can only be done with a flow or other usual batter types that get around the problems of the 'banking' strategy of conventional cell batteries by hopelessly aggregating them in large rooms when they will never ever work well enough to provide grid scale store-age for power stations. comparing these applications with home power storeage or a car battery or phone or laptop or powertool batteries is comparing apples and oranges.
Marcus Hicks
That is the biggest load of garbage, Kaiser. Solar & Wind are already price competitive with large central power plants for peak power.....& are threatening to do the same with base-load. They've managed this with only a fraction of the subsidies that have been enjoyed by both the fossil fuel & nuclear power industries. The only thing holding us back, in fact, is waiting for luddites to die off.
Grunchy
19 Wh = 68,400 Joules. If the specific gravity is equal to water (1 L = 1 kg) that's the same energy as if the litre were raised 6,840 metres above the ground (if g = 10 m/s^2). 19 Wh is also about 16.5 Calories, which is about the food energy of a couple potato chips!
Cuckoo
Kaiser Derden. Thorium is the ill-informed person's answer to green energy. There are many problems and a lot of misinformation about thorium. One of the more glaring problems is that thorium cannot reach critical-mass by itself, so it still requires a much heavier nuclear fuel to kickstart the reaction. So it will never be a clean source of energy. As far as fusion goes, we are a long long way from producing anything viable, there are major opstacles to overcome. Not the least of them is how do you contain a plasma that is 1,000,000C, without melting the reactor containing it? Your assertion that renewables can never replace power plants is equally misinformed. Not only is energy storage technology improving all the time, but energy capture is too. THe next generation of solar power technology will be far more powerful. There are also other promising technologies such as artifical photosynthasis.