Tag Archives: green tech

A battery that you can ‘refuel’ instantly: the vanadium flow battery

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This post is part of an ongoing series of energy storage posts by intern Brett Szmajda.

Walking into the Castle Hill stores of the Powerhouse Museum is like walking into the prop warehouse of a Hollywood movie studio. You enter through a nondescript door in a modest, unassuming looking set of buildings, and when you turn around you encounter a cornucopia of steam engines, Mardi Gras floats, flywheels the size of a Mini Cooper, and exotic old X-ray machines that could be used for set dressing in a Frankenstein remake. The air is crisp and clean from the climate control system; the objects are neatly ordered and tagged, on stacks as high as a giraffe. We round a corner, and we come across an object that looks as if a drawer full of hanging files got intimate with the plumbing section at Bunnings.

“Take a look at this.” says Debbie.
“What is it?” I say.
“It’s one of the most promising battery technologies of the last 20 years,” she begins.

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The vanadium flow battery.

The vanadium flow battery is a brilliant archetype of the trials and triumphs that accompany research and development. Throughout the development, led by Professor Maria Skyllas-Kazacos at the University of New South Wales in Sydney, research momentum was maintained by the phenomenal theoretical promise of the battery. Imagine a fully electric car that you could ‘recharge’ in a matter of minutes. Imagine a battery that would let small businesses and power companies store cheap energy generated at night, and use that power during the day, when energy is expensive.

A typical rechargeable battery contains two electrodes of differing material, immersed in a liquid electrolyte; chemical reactions occur between the differing metals of the electrodes, mediated by the electrolyte. But in a flow battery, like the vanadium battery, the principal chemical reactions instead occur between two liquid electrolytes. These electrolytes are pumped past one another (hence the name flow battery) in separate chambers that are separated by a thin membrane. As the two electrolytes flow past one another, they exchange ions (charged molecules) across the membrane, and this generates current.

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Close-up of the exterior of the vanadium battery cells, where the electrolytes interact with each other.

To understand the difficulty in designing a flow battery, consider how your lungs extract oxygen from the air, and remove waste carbon dioxide from your body. Inhaling causes thin-walled sacs in your lungs (called alveoli) to inflate. Alveoli are surrounded by clusters of blood vessels; oxygen diffuses across the thin alveolar membrane, into the blood. Simultaneously, carbon dioxide diffuses from your blood into your lungs, to be exhaled. It’s critically important that the blood and air are kept in separate compartments (failure to do so would of course be fatal), and only selected molecules — oxygen and carbon dioxide — are allowed to pass through. Analogously, the challenge of designing a flow battery is making a membrane that will allow current to flow between the different electrolytes, but that doesn’t let the two electrolytes mix. The vanadium battery wasn’t the first flow battery, but it was the first to use the same metal in both electrolyte solutions, thus neatly eliminating the problem of electrolytes mixing across the membrane.

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Golfcart powered by vanadium battery, used as a prototype during battery development.

The unique strengths of the vanadium battery are a short recharge time and the ability to store charge efficiently for long periods. The vanadium battery can be quickly recharged at high voltages; or — perhaps most attractively — it can be instantly recharged by replacing the electrolyte with fresh, charged electrolyte. Second, by pumping the electrolytes out of the ‘cells’ (where the reactions take place) and into storage vats, the vanadium battery can sit for many hours, with no self-discharge. These two attributes suggested potential commercial applications. For the consumer, there could be electric cars that you refilled with vanadium ‘fuel’ instead of gasoline; and for the business customer, the vanadium battery could be used as energy storage for the electric grid, allowing arbitrage (charge batteries when electricity is cheap, use battery power when electricity is expensive) and providing stability during intermittent drops in power supply.

Vanadium batteries have found a home providing energy storage for power stations, with several stations world-wide trialling the technology. Unfortunately, the harsh light of reality intruded on the dream of vanadium-fuelled cars — vanadium batteries are expensive to manufacture, have problems operating at low temperatures, and no battery to date has an energy density (that is, power per unit weight) that can compete with the fantastic energy density of petrol. But research continues: scientists have recently boasted numerous improvements to the energy density and temperature tolerance of vanadium batteries. Don’t give up on the dreams of the vanadium car.

A hot topic: Solar Thermal Power

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This post is part of an ongoing series of energy storage posts by intern Brett Szmajda.

When I say ‘solar power’, most people conjure up images of the thin, iridescent blue panels that make a patchwork quilt out of the roofs of suburban houses. But photovoltaic solar power — converting the sun’s rays directly to electricity — is a youngster in the field of solar energy. Its great, great grandfather is solar thermal power; and with the looming threat of climate change, heat from the sun could be a significant part of Australia’s renewable energy transformation.

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Solar Heater by Lawence Hargrave

The principle behind solar thermal power should be familiar to anyone who has ignited dry leaves with a magnifying glass. Solar thermal power utilises the heat from the sun’s rays to do useful work. This object from the collection, invented by Lawrence Hargrave, illustrates the Australian inventor’s early attempts to heat water using the sun’s heat. Sunlight is focused by the conical dish onto the central pipe, which is closed at one end so it can hold a small volume of water. As best as we can tell, this was a hobby or proof-of-concept by Hargrave, who was also making small steam engines. However, around the same time as Hargrave was toying with solar, inventors on the other side of the world were patenting larger solar water heaters that could heat water for a household.

Utility companies have taken these basic small-scale ideas and supercharged them, creating solar thermal power stations to yoke the sun’s heat and turn it into electricity. (There are many alternative designs; most involve a lot of mirrors). For example, ‘power tower’ solar thermal power plants use several hundred mirrors to concentrate the sun’s rays on a central tower containing a column of water; this causes the water to boil, producing steam that drives a turbo-generator.

A 'power tower' solar thermal station. Image by Flickr user afloresm, reproduced under Creative Commons licence.

A 'power tower' solar thermal station. Image by Flickr user afloresm, reproduced under Creative Commons licence.

The big problem for solar thermal power generation is that sunlight isn’t constant — a solar thermal plant must contend with clouds, inclement weather, and of course, nightfall. The Solar Tres power plant (a ‘power tower’ design) in Andalusia, Spain has overcome this using a novel form of energy storage: molten salt. Instead of heating water directly, sunlight is concentrated onto a column containing a mix of 60% sodium nitrate and 40% potassium nitrate. The heat from the molten salt boils water and turns a turbine, as usual. The advantage of this additional step is that the molten salt can store the accumulated heat (for the electronics junkies in the audience, it’s almost like a ‘heat capacitor’). So when the sun goes behind the clouds or night falls, the heat from the molten salt continues to boil water, turning the turbine and keeping the power flowing. The simple addition of molten salt to the system allows 15 hours of heat storage, meaning that Solar Tres can run around the clock.

Solar thermal plants have been rolled out in a number of locations world-wide, but the uptake in Australia has been limited to two small plants: a 1.5 MW demonstration solar thermal plant has been added to the coal-fired Liddell Power station, and CSIRO has a 0.5 MW solar thermal power station in Mayfield. The biggest recent development was in June 2011, when a 250 MW solar thermal/gas hybrid plant (Solar Dawn) was given 464 million dollars of government funding as part of the Australian Government’s Solar Flagships program. Solar power is a natural fit to the Australian climate, so I’d expect some considerable growth in this sector. Until then, we’re left to wonder why Germany has invested more in solar infrastructure than Australia, when the majority of Australia has more sunshine hours per day than the German average.

How do you bottle the wind?

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Image: Powerhouse Museum

“The final perfection of the storage battery, which I believe has been accomplished, will in my opinion bring about a multitude of changes and improvements in our business and social economy.”
— Thomas Edison
North American Review, 1902

The Clean Energy Act recently passed into law. This carbon pricing legislation heralds a broad transformation in the electricity industry in Australia: increased investment in renewable energy will prompt a revision of our energy infrastructure, and a key focus of this restructuring will involve adding energy storage to the electrical grid.

Energy storage is exactly as the name implies: you take energy, usually electricity, and convert it to another form to save it for later use. The electronics industry has been revolutionised by innovations in energy storage: iPhones, portable GPS, and ultra-slim laptops would not exist without batteries that efficiently convert electricity into chemical energy, and back again. You might expect that the electrical grid, which brings power to homes and industry, has been similarly transformed by these innovations in energy storage. The reality is a very different matter. Bill Gates wonderfully summarised this in a 2010 talk: if we connected all the batteries in the world, including all batteries from the consumer electronic devices I mentioned above, this monumental collection of batteries would be able to store — wait for it — ten minutes of the world’s energy demands.

Given the ubiquity of batteries in our everyday lives, it may seem odd that we do so little grid-scale energy storage. The reason for this is historical: the technology for generating energy outpaced the technology for storing it efficiently. As a result, today’s electricity grid is the ultimate ‘just in time’ system: electricity supply is generated to match demand, as perfectly as possible, as demand varies across each day and season. To facilitate this, some power stations (coal or nuclear) generate continuously 365 days a year, while others switch on and off as demand fluctuates (natural gas or hydroelectric power stations). 

As we transition to renewable forms of power generation — e.g. solar and wind — the design of our electricity grid hits a roadblock, because most renewable power plants are intermittent generators. The sun doesn’t shine all the time, and the wind doesn’t blow all the time; and the times when these renewable plants are generating lots of electricity might not correspond to times when we, the electricity-consuming public, are demanding more power. As a result, renewable power plants can’t be on all the time (and compete with coal power) and can’t be switched on and off at will (and compete with demand-following power plants like natural gas). This limits the market uptake of renewable power technologies, and makes the energy they generate more expensive than energy from other sources.

The answer to both these problems? Energy storage. First and most obviously, storing energy when it is in surplus lets renewable power plants deliver power to consumers when the sun isn’t shining and the wind isn’t blowing. With energy storage, renewable power plants can compete with continuously operating power stations like coal power plants. Secondly, integrating energy storage into renewable power stations allows the owners of these plants to engage in arbitrage: producing energy when a station can generate it most cheaply, and selling it at a premium when customers demand it. With energy storage, renewable power plants can also compete effectively with demand-following plants like natural gas power plants.

Improving competitiveness in both these ways will mean that renewable power plants are a more attractive investment, and it will drive down the cost of the energy they produce. This is a good thing for both the environment and your wallet.

There are many more benefits to grid-scale energy storage, but I hope I’ve sold you on at least two reasons why storing electricity is a good idea. (Those interested in other applications of grid-scale energy storage should see Appendix C of this 2002 Sandia report — be forewarned that it’s a little dry and technical). In the coming weeks, I’ll be writing a number of blog posts about various forms of energy storage that we might see commercialised within the next ten years. Batteries are just the starting point: ultracapacitors, flywheels, molten metal, compressed air, and even hydrogen are all forms of grid-scale energy storage that are being considered by utility companies worldwide. Bottling the wind will soon be something that we rely on every day.

This piece was written by Brett Szmajda, intern at the Powerhouse Museum.