Paying our respects at a CO2 graveyard

It doesn't look like much, but this facility is testing the future of CO₂

THERE are more cows than people here in Nirranda South, three hours south-west of Melbourne, making it the perfect spot to test a technology that remains hugely controversial.

I am at a facility run by Australia's Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC). If anyone can convince the public that carbon capture and storage can reliably reduce carbon dioxide emissions it's these guys. Even Friends of the Earth, Australia - which opposes the approach - has grudging respect for the research done here.

Wherever permeable and porous rock is capped by an impermeable layer, a natural gas store may form. Such stores can trap gas for tens of millions of years, making spent oil and gas fields a logical choice for industrial CO₂storage.

But these spent fields are small, and can store only so much CO₂ - up to 900 gigatonnes worldwide, according to the Intergovernmental Panel on Climate Change. A more common type of subterranean structure - deep saline aquifers - has the potential to store up to 100,000 gigatonnes. The problem? It is not clear that these aquifers, which naturally house salty water, can keep hold of CO₂. "It's very difficult to predict how the gas will move underground," says Peter Cook, a hydrologist at Flinders University in Adelaide. That's where the Nirranda South facility comes in.

Above ground, the facility is just a few shipping containers, a series of pipes that snake around the muddy floor, and a large white container filled with CO₂. But beneath my feet, some 1500 metres down, is a saline aquifer.

At the end of June, two tracer gases - krypton and xenon - were injected into the saline aquifer, says Josie McInerney, the community liaison officer for CO2CRC. When I arrived last week, hydrologist Allison Hortle and colleagues were busy sucking up salty water samples every hour over a four day period to track how the tracers travelled through the aquifer. The results will help predict how CO₂ is likely to behave under similar circumstances, Hortle says.

Or so it is hoped. Matthias Raab, the programme manager of the site, tells me, euphemistically, that using the tracers "is highly experimental" - in other words, it is not clear that noble gases behave as CO₂ does. So this week the team will inject 150 tonnes of CO₂ into the aquifer, and compare its movements with the tracers.

It's this slow-and-steady testing approach that has garnered respect from Friends of the Earth, Australia. "We have trust in the monitoring regimes of CO2CRC," says Cam Walker, a spokesperson for the organisation. "But it's sucking up a lot of the money that should be going to renewables."

Australia is spending A$1.6 billion over five years on carbon capture and storage technology. According to Walker, that cash could buy three large solar power stations.

Raab points out that solar power is not yet ready to fully replace fossil fuels, though. "Carbon capture cannot be the only solution to reducing carbon emissions, but it is has to be part of it," he says.

Polymer sandwich harvests electricity from waste heat

So much going to waste 

when he heated a black crystalline rock called tourmaline, it would suddenly attract ash and bits of straw. He had observed what we now call pyroelectricity - the ability of certain crystals to produce a voltage briefly when heated or cooled. Now the same phenomenon is being used to convert waste heat into electricity.

Nearly 55 per cent of all the energy generated in the US in 2009 was lost as waste heat, according to research by the Lawrence Livermore National Laboratory in California. There have been many attempts at using this waste heat to generate electricity, so far with only limited success.

Pyroelectricity could be the key, say Scott Hunter and colleagues at Oak Ridge National Laboratory in Tennessee. They have built an energy harvester that sandwiches a layer of pyroelectric polymer between two electrodes made from different metals. Just a few millimetres long, the device is deployed by wedging it between a hot surface and a cold surface - between a computer chip and a fan inside a laptop, for example. Crucially, the device is anchored to the hot surface alone and so acts as a cantilever - a beam supported at one end.

As the device warms, the polymer expands more than the electrode close to the cold surface, and the whole device bends like the bimetallic strip in a thermostat. It droops toward the cold surface, where it cools and then springs back toward the hot surface, warming up again. Soon the cantilever is thrumming between the hot and cold surfaces like the hammer of a wind-up alarm clock. Each time it is heated, the polymer generates a small amount of electricity which is stored in a capacitor 

Previous attempts at using pyroelectric materials to recycle waste heat have only managed to turn 2 per cent of the heat into electricity. Hunter believes his device could achieve an efficiency of between 10 and 30 per cent.

Hunter says the device can also convert heat in exhaust gases into electricity. It might even be used to capture the energy that solar cells lose as heat, he says. Energy generation aside, he adds that the devices could soak up enough heat to play a significant role in cooling laptops and data centres.

Laurent Pilon of the University of California, Los Angeles, who also studies pyroelectric energy harvesting, says he likes the compactness of the device and its relative simplicity, but has some doubts about the potential efficiency. "I think some of their expectations are a little exaggerated," he says. "They are relying on conduction to heat the device, which is a slow process." He and other groups have used fluids to heat or chill a pyroelectric material. This is much quicker, though the need to pump the fluid around does consume some of the energy generated.

Twice the height of the Empire State - EnviroMission plans massive solar tower for Arizona

An ambitious solar energy project on a massive scale is about to get underway in the Arizona desert. EnviroMission is undergoing land acquisition and site-specific engineering to build its first full-scale solar tower - and when we say full-scale, we mean it! The mammoth 800-plus meter (2625 ft) tall tower will instantly become one of the world's tallest buildings. Its 200-megawatt power generation capacity will reliably feed the grid with enough power for 150,000 US homes, and once it's built, it can be expected to more or less sit there producing clean, renewable power with virtually no maintenance until it's more than 80 years old. In the video after the jump, EnviroMission CEO Roger Davey explains the solar tower technology, the Arizona project and why he couldn't get it built at home in Australia.

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How Solar Towers Work

Enviromission's solar tower is a simple idea taken to gigantic proportions. The sun beats down on a large covered greenhouse area at the bottom, warming the air underneath it. Hot air wants to rise, so there's a central point for it to rush towards and escape; the tower in the middle. And there's a bunch of turbines at the base of the tower that generate electricity from that natural updraft.

It's hard to envisage that sort of system working effectively until you tweak the temperature variables and scale the whole thing up. Put this tower in a hot desert area, where the daytime surface temperature sits at around 40 degrees Celsius (104 F), and add in the greenhouse effect and you've got a temperature under your collector somewhere around 80-90 degrees (176-194 F). Scale your collector greenhouse out to a several hundred-meter radius around the tower, and you're generating a substantial volume of hot air.

Then, raise that tower up so that it's hundreds of meters in the air - because for every hundred metres you go up from the surface, the ambient temperature drops by about 1 degree. The greater the temperature differential, the harder the tower sucks up that hot air at the bottom - and the more energy you can generate through the turbines.

The advantages of this kind of power source are clear:
• Because it works on temperature differential, not absolute temperature, it works in any weather;
• Because the heat of the day warms the ground up so much, it continues working at night;
• Because you want large tracts of hot, dry land for best results, you can build it on more or less useless land in the desert;
• It requires virtually no maintenance - apart from a bit of turbine servicing now and then, the tower "just works" once it's going, and lasts as long as its structure stays standing;
• It uses no 'feed stock' - no coal, no uranium, nothing but air and sunlight;
• It emits absolutely no pollution - the only emission is warm air at the top of the tower. In fact, because you're creating a greenhouse underneath, it actually turns out to be remarkably good for growing vegetation under there.

The Arizona Project

While this is not the first solar tower that has been built (a small-scale test rig in Spain proved the technology more than a decade ago) EnviroMission has chosen to build its first full-scale power plant in the deserts of Arizona, USA.

The Arizona tower will be a staggering 800 metres or so tall - just 30 meters shorter than the colossal Burj Khalifa in Dubai, the world's tallest man-made structure. To put that in context - it will stand more than double the height of the Empire State building in New York City, and it'll be as much as 130 meters in diameter at the top. Truly a gigantic structure.

Currently undergoing site-specific engineering and land acquisition, EnviroMission estimates the tower will cost around US$750 million to build. It will generate a peak of 200 megawatts, and run at an efficiency of around 60% - vastly more efficient and reliable than other renewable energy sources.

The output has already been pre-sold - the Southern California Public Power Authority recently signed a 30-year power purchase agreement with EnviroMission that will effectively allow the tower to provide enough energy for an estimated 150,000 US homes. Financial modelling projects that the tower will pay off its purchase price in just 11 years - and the engineering team are shooting for a structure that will stand for 80 years or more.

Considering that a large city like Los Angeles requires total power in the region of 7,200 megawatts, you'd have to build a few dozen solar towers up to the same size as the Arizona project if you wanted to completely replace the existing, primarily coal-based energy supply for that city's 3.7 million-odd residents. So it's not an instant solution - but then, its short projected payback period and virtually zero operating costs make it a very sound economic proposition that competes favorably against other renewable sources.

Under the terms of the pre-purchase agreement, the Arizona tower is due to begin delivering power at the start of 2015. Watch this space!