Rethinking internal combustion engines

It may seem dirty and outdated compared with the batteries that power electric vehicles, but the internal combustion engine is set for a makeover that could halve its greenhouse gas emissions.

Today's engines are pretty inefficient, converting only around a quarter of the energy contained in fuel into motion; the remaining three-quarters is lost as heat. So efforts are under way to recover some of this lost energy in the hope of reducing fuel consumption and emissions.

Up to 40 per cent of an engine's potential output is lost in its exhaust, says Guy Morris, engineering director at Controlled Power Technologies based in Laindon, UK. The company plans to recover some of this energy by fitting a turbine inside the tailpipe: the fast-moving exhaust gases coming straight from the engine drive the turbine, generating electricity.

A prototype device fitted to a large family car harvests up to 6 kilowatts of energy in track tests, says Morris. This could be fed back into the car's battery to power its onboard electrical systems, reducing fuel consumption by up to 15 per cent, he claims.

Super fly

Elsewhere, designers are looking to capture the energy that most cars lose in braking. Putting that kinetic energy to work would reduce the load on the engine.

Hybrid cars that have both an electric motor and an internal combustion engine already have regenerative brakes that generate electricity when they are applied. But a team led by car maker Jaguar is cutting out the electric middleman with a system that simply stores unwanted kinetic energy for later.

They are developing a hybrid car equipped with a kinetic-energy-recovery system similar to those used in last year's Formula 1 season. The prototype car, which is due to hit the test track in June, has a flywheel linked to its gears. When the driver wants to slow down, the flywheel can be used to recover the rotational energy of the wheels and store it as kinetic energy. When more power is needed the system works in reverse, drawing energy from the flywheel and feeding it back to the driveshaft through the gears. The system reacts automatically to gas and brake pedal movements, thus storing power without needing control from the driver.

Like the Formula 1 version, the mechanism is built by Flybrid Systems based near the British Grand Prix race circuit in Silverstone.

Chris Brockbank of project partner Torotrak, based in Leyland, UK, says over 70 per cent of the energy recovered by the system can be converted into motive force to drive the car. This makes it more than twice as efficient as conventional hybrid cars, which can only recover about 30 per cent of the braking energy, he says.

The team claim the system will reduce fuel consumption and greenhouse gas emissions by more than 30 per cent compared with conventional gasoline engines. What's more, unlike batteries, the flywheel will not need regular replacement, says Brockbank.

Shape-shifting engine

But perhaps the biggest efficiency savings could be made by changing the shape of the engine itself. The traditional cylinder-piston design used in engines means that only the piston head itself produces motive force, as it is pushed up and down by the expansion of the burning fuel-and-air mixture. The remaining 75 per cent of the cylinder's surface area – the chamber walls – absorb energy from the burning fuel in the form of heat, reducing the amount that is available to produce motive force.

This has prompted IRIS Engines, based in Washington DC, to design a combustion chamber called the internally radiating impulse structure (IRIS). The walls of the hexagonal chamber would be overlapping, hinged panels; as the burning mixture in the chamber expanded it would push the panels outward, forcing them to rotate on their hinges and so provide motive force. This means that more of the engine's surface area would be used to produce motion, says Iris's CEO Levi Tillemann-Dick.

Computer simulations of the IRIS design by automotive research and development consultants AVL, based in Graz, Austria, suggest the it should have a fuel efficiency of up to 45 per cent, he says. "Our goal is to prototype and license an engine that will allow vehicle manufacturers to double the efficiency of their vehicles and so halve their emissions."

Green machine: Power from the people

At the end of a hard day it can sometimes feel like gadgets such as phones and computers are sapping our energy. But now they are set to do it literally, and we should be pleased.

Technologies that harvest energy from movement could see your every move charge a mobile device, or even a building. Such people power could provide an alternative to mains charging of electronic gadgets, reducing energy consumption and greenhouse gas emissions.

Crowdsourced energy

London-based architectural research firm Facility: Innovate is developing an energy harvester for crowded areas such as sports arenas and shopping centres.

The technology will be invisible to the people it feeds on: they will simply walk over what looks like a normal floor tile. But their steps will push down on a pneumatic device that drives air through a turbine to generate electricity, says managing director Oliver Schneider. People will feel only a slight movement at most, like stepping on an entrance mat, he says.

"We're looking to generate around 1 kilowatt-hour of electricity [from each device]per day. That's enough to charge around 300 phones per day," he says. The power will be fed to phone-charging stations, or to lighting and electronic advertising. The system generates a direct current, so using it to power DC devices locally is more efficient than switching to the alternating current needed to feed it back to the grid.

The company plans to install its first device later this year in a US shopping centre, with a UK site to follow soon after. "Ticket barriers at sports stadiums are also a good spot, anywhere people are funnelled through a small area," Schneider says.

Unlike existing energy-generating paving slabs such as those developed by London-based Pavegen Systems, the technology can be installed under conventional flooring, allowing it to be used in a wide range of settings without altering a building's appearance, claims Schneider.

Strain gain

But Zhong Lin Wang at the Georgia Institute of Technology in Atlanta wants to generate electricity from footsteps without ripping up the flooring at all. He hopes to produce devices such as shoe pads that harvest energy from the pressure of their wearer's feet within the next five years, using piezoelectric nanowire generators that produce an alternating current when squeezed.

Just last month Wang published the results of experiments on a device about 5 centimetres across that when flexed can produce 1.3 volts, enough to charge an AA battery.

Meanwhile Chieh Chang at the University of California, Berkeley, and colleagues have developed a technique to "print" nanowires that generate energy in the same way. They are made with a process known as electrospinning, in which a charged solution is drawn through an electrically charged needle onto an electrically grounded surface.

That method can print nanogenerators on all kinds of surfaces, including textiles, raising the possibility of clothes that power electronic devices as the wearer moves.

World's third-largest dam gets the go-ahead

A decades-long tug of war between environmental and indigenous groups on one hand and the Brazilian government on the other came to a close yesterday when a Brazilian energy consortium won the right to build what will become the world's third-largest dam.

The controversial Belo Monte dam on the Xingu river in the Brazilian Amazon, a tributary of the Amazon, could power as many as 23 million homes. But since its proposal 20 years ago, it has been the subject of a vitriolic dispute with the government on one side and indigenous people and green groups on the other.
The latter say it would flood 500 square kilometres of farms and rainforest and prevent the migration of fish that are a major food source for 800 indigenous communities.

During the rainy season, the power plant should churn out 11233 megawatts, but that only accounts for three months of the year. Output is expected fall to as little as one-tenth of that during the dry season, leaving the plant with an annual efficiency of around 39 per cent, according to the charity Amazon Watch.

Injunctions galore

"In the dry season, portions of the river will dry out entirely and in other areas there will be standing water with little movement that will serve as a breeding ground for mosquitoes, spreading malaria, dengue fever and other disease," says Atossa Soltani of Amazon Watch.

Contractors bid for the project in an auction on Tuesday, which had been suspended by an injunction late on Monday. Then, at the very last minute, the injunction was lifted and the auction went ahead. Monday's injunction was the last in a series of attempts to halt the auction. A similar one had been issued, then lifted, last week.

The Belo Monte dam is set to become the world's third largest, after the Three Gorges dam on the Yangtze river in China and Itaipu, on the Parana river, on the border between Brazil and Paraguay.

Hacking the planet: who decides?

Plans are taking shape for the day when a global coalition may have to "hack the planet" in a bid to reverse the ravages of global warming.

Proposals to cool the Earth by deploying sunshades or sucking carbon dioxide from the atmosphere were considered fanciful just a few years ago, but are now being considered by politicians in the US and UK. At a gathering of key scientists and policy experts held in Asilomar, California, last week, detailed debates began over who should control the development of a planetary rescue plan.

The sense at the meeting was that drastic emissions cuts are the best way to limit the catastrophic droughts and sea-level rises that global warming is expected to cause. But the failure of December's summit in Copenhagen, Denmark, and the relentless rise in global CO2 emissions have persuaded many to reluctantly consider geoengineering solutions (see diagram)

Artificial trees

Few argue against "artificial trees" that could suck CO2 directly from the atmosphere (see "Artificial trees on the way" below). But more controversial proposals – to bounce solar energy back out into space, for instance – split the conference, with policy experts warning climate scientists that there would be a public backlash.

Oliver Wingenter at the New Mexico Institute of Mining and Technology in Socorro presented details of an ambitious plan to shift westerly winds. Temperature and pressure changes over the Southern Ocean are thought to have pushed these westerlies 3 to 4 degrees south over the last 50 years. This shift strengthens the ocean currents that bring warm, salty water to the surface, where it accelerates the melting of Antarctic ice.

Wingenter proposes seeding the Southern Ocean with particles of iron to boost phytoplankton growth. Plankton release a chemical called dimethyl sulphide into the atmosphere which helps cloud droplets form. More droplets mean whiter clouds that bounce more solar energy away from Earth. Wingenter calculates that it would be possible to cool regional temperatures by 0.5 ˚C, which could push the westerlies back towards their original position.

Side effects

Little is known about the side effects, however. Cooling a small region by 0.5 ˚C could dramatically change rain patterns. The impact of plankton blooms on ocean life is also poorly understood. Computer models can go some way to filling in these blanks, and Wingenter foresees at least 10 years of computer studies before field tests could kick off. Other solutions could be field-tested sooner, raising the delicate question of whether such experiments should be allowed in the first place, and what forms they could take.

Modelling has already shown that stratospheric clouds of sulphate particles could rapidly cool the planet. David Keith of the University of Calgary, Canada, has submitted a paper to Nature in which he outlines a proposal to release about a tonne of sulphate particles from a NASA plane at an altitude of 20 kilometres. The results would help researchers refine their models, and the number of particles released would be far short of the number required to produce a significant cooling effect.

Silver Lining, a non-profit organisation founded by Kelly Wanser, an entrepreneur based in San Francisco, California, has a team of 35 scientists working on a cooling process in which a flotilla of boats fire particles of sea-salt into the atmosphere, where they would whiten clouds.

Salt solution

The group is seeking funds for pilot research involving 10 ships and 10,000 square kilometres of ocean. Kelly Wanser says it could take place in three to four years. This study would not use enough particles to create a noticeable cooling effect. Many climate scientists in Asilomar thought regulations that govern other oceanographic experiments would probably provide sufficient oversight of this project.

Wanser also argued extra regulation would create potentially dangerous delays, as governments might later be forced to deploy a technology that had not been properly tested. That view split delegates at Asilomar. Social scientists and policy experts took issue with the view that trials did not need further oversight.

They warned of a popular backlash unless would-be geoengineers consult with the public before running such studies. Just running tests sends a signal that scientists are interested in a future for geoengineering, says Shobita Parthasarathy at the University of Michigan, Ann Arbor. "The intention is to expand the process. The path will have been set."

Global perspective

If experiments progress to a larger scale, a second problem arises: which nations should decide whether a proposal has proved safe enough to implement? Most agreed that as some solutions could have a global impact, they could only be deployed after global talks, led by the United Nations, for instance. Talks would have to include plans to compensate people whose livelihoods could be damaged by side effects. Others argued that global negotiations could become impossible to manage, and cited UN-led climate talks as an example of how all-inclusive efforts can fail to solve problems requiring decisive action.

Richard Benedick, president of the US National Council for Science and the Environment and a former US government negotiator, circulated a document in which he argued that the principles governing geoengineering research should be developed by a group of 14 nations, including the US, several European nations, India and China. His proposal garnered some interest, but at least one person New Scientist spoke to was disapproving. "I cannot imagine a few countries making a decision for everybody," says Pablo Suarez, who studies climate and humanitarian disasters at Boston University. "Participation is difficult, but that is not an excuse for not doing it."

A lack of consultation could fuel campaigns against geoengineering similar to those that have derailed the use of genetically modified crops in Europe, Parthasarathy warns. Such protests seem to be taking off already. While delegates were talking in Asilomar, a body of over 70 environmental, health and social groups published an open letter attacking the meeting. "Such a discussion cannot happen without the participation of the full membership of the United Nations," it reads. "Determining guidelines for geoengineering research and testing in the absence of that debate is premature and irresponsible."

Artificial trees on the way


There is one geoengineering solution that almost everyone would like to see work. If carbon dioxide can be removed from the air and stored safely underground, we might be able to stave off the worse effects of climate change.

The big problem is that sucking CO2 out of the atmosphere is expensive: many estimates put the cost at close to $1000 for each tonne captured.

It might, however, turn out to be a lot cheaper than that. In October 2009, David Keith, a climate and energy researcher, founded Carbon Engineering in Calgary, Alberta, Canada. The firm aims to build a device to captureCO2 at economically viable prices. He claims his device will draw down a tonne for US$100 to $250.

He did not release details of the device at the Asilomar conference, but said that it involves scaling up existing processes for capturing CO2, which involve passing the gas over a substance such as sodium hydroxide. The gas combines with the chemical and can then be removed and stored underground.

Keith says Bill Gates has invested in Carbon Engineering, which plans to spend $3 million over the next five years building a prototype device.

Skip the hard cell: Flexible solar power is on its way

ELECTRICITY from sunlight: bright hope for the future, or false dawn? Solar power has its share of detractors who'd go for the latter. Photovoltaic cells are too expensive, they say, requiring huge amounts of material and energy to make. And they are inefficient, too, converting at best about 20 per cent of the incoming solar radiation into usable power.

So, the sceptics say, solar cells are only ever likely to be a small, disproportionately expensive part of our future energy mix. In the temperate, oft-cloudy climes of much of Europe and North America, satisfying the population's electricity needs with photovoltaics alone would mean plastering something like 5 to 15 per cent of the land surface with them.

Such criticisms might be tempered by a new generation of solar cells about to flop off the production line. Slim, bendy and versatile, they consume just a fraction of the materials - and costs - of a traditional photovoltaic device. They could be just the fillip solar power needs, opening the way to a host of new applications: solar-charged cellphones and laptops, say, or slimline generators that sit almost invisibly on a building's curved surfaces or even its windows.

Photovoltaic cells have traditionally presented renewable-energy enthusiasts with an unenviable choice. If low cost and flexibility are the watchwords, inefficiency is the price to pay: the best flexible solar cells, made from thin films of amorphous silicon or organic polymers, convert barely 10 per cent of solar radiation into power. That makes them unsuitable for all but low-power gizmos such as solar cells for backpacks. For higher efficiency, you need crystalline silicon, which absorbs light less readily than its amorphous cousin, but does so over a much broader range of wavelengths. Making a solar cell that is 20 per cent efficient takes thick, expensive slabs of the stuff, as seen in today's rooftop solar cells.

Marrying efficiency with low cost requires thinking outside the box, or at least outside the plane. Traditionally, solar cells consist of a single flat layer of a light-absorbing semiconductor. An alternative currently being explored is to replace this layer with a film of vertically grown nanoscale semiconductor wires (Nano Research, vol 2, p 829). Light gets trapped in this forest of nanotrees, bouncing between the individual nanowire trunks (see diagram). "That optimises light absorption," says Ali Javey, who is pioneering these new materials at the University of California, Berkeley.

Absorption alone is not enough: the light must be converted into charge carriers such as electrons, to be extracted from the wires and fed into a power grid. Here, the internal crystal structure of the nanowires is crucial. Any imperfections form "potholes" into which electrons fall, impeding their movement and limiting the cell's overall efficiency. The silicon of normal solar cells is particularly prone to imperfections, so Javey and his colleagues have been experimenting with an alternative semiconductor, cadmium telluride. The resulting cells are economical in their use of material, but, much like amorphous silicon cells, convert only about 6 per cent of the solar radiation into usable power.

That low conversion is partly due to a weak point in the vertical design: the tips of the wires cover only a few per cent of the cell's sun-facing surface, so much of the light hitting the cell passes through unabsorbed. In February this year, Harry Atwater and his colleagues at the California Institute of Technology in Pasadena reported a solution to this problem. They used microscale silicon rods slightly thicker than Javey's nanowires, and poured a polymer containing light-reflecting nanoparticles into the spaces between them. The polymer scatters unabsorbed light back onto the rods and this, combined with a silver reflecting layer at the bottom of the device, allows the cells to absorb up to 85 per cent of incoming light. Still, losses - chiefly from imperfections in the crystal structure of the microrods - drive the overall efficiency below the 20 per cent achieved by the best crystalline silicon cells (Nature Materials, vol 9, p 239).

So why the fuss, if these devices are no more efficient than what went before? The key is that although these cells are merely as efficient as conventional devices, they use only about a hundredth of the material. What's more, they are highly flexible: grown on a bed of silicon, Atwater's microrod arrays can simply be peeled off and stuck pretty much wherever you want. "They could even be integrated into buildings, as components that match the shape of roof tiles," says Atwater. He has started up a company, Alta Devices, to do just that, and has recently received research funding from the US Department of Energy.

John Rogers and his colleagues at the University of Illinois at Urbana-Champaign are at a similar stage. They make solar cells by using a rubber stamp to pick up a conventional cell structure etched onto a silicon substrate and imprint it onto a flexible polymer surface (Nature Materials, vol 7, p 907). The efficiency of the resulting cells is a respectable 12 per cent, although Rogers thinks they can do markedly better with tweaks such as adding fluorescent molecules to capture the light coming through the sides of the device. His cells also have a unique selling point: by spacing cell features more widely on the polymer substrate, the cells can be made virtually transparent. That makes power-generating windows a distinct possibility.

Rogers, too, has set up a company, Semprius, to commercialise his technology, and has installed about a dozen modules for power-generation companies across the world to test their long-term performance. Another target in the works is vehicle-top cells that generate electricity for music systems, GPS or even air conditioning - lending a whole new meaning to the word "sunroof". The US Department of Defense is also supplying funds for Rogers' work, with a view to equipping special operations troops with lightweight, efficient solar cells.

Other teams are exploiting the bumper light-harvest that comes when solar cells are sprinkled with a little stardust. This takes the form of gold or silver nanoparticles that quiver with electronic resonances known as plasmons when light hits them, focusing it onto the absorbing semiconductor film (Nature Materials, vol 9, p 205).

Plasmonic nanostructures can also be designed to bend the incoming light so that it travels along the surface of a device, rather than through it. A slimline layer of silicon 100 nanometres deep can then attain a light-harvesting efficiency usually only achieved with cells several thousand times as thick. "Absorption in 100 nanometres of silicon is negligible, but if you turn the light by 90 degrees then it is a different story altogether," says Albert Polman at the Institute for Atomic and Molecular Physics in Amsterdam, the Netherlands, who designs such cells.

Material wants

Since the first modern photovoltaic cell was demonstrated in 1954, solar-cell efficiency has been increased mainly by slowly improving the purity of the materials used - a strategy with inevitably diminishing returns. Alternative materials often contain scarce elements such as tellurium, indium and selenium, so any technology that reduces the amount of material needed to harvest the sun's power has an obvious appeal. Driving costs down also makes the technology more accessible to developing economies, many of which boast abundant sunlight but limited cash.

It is crunch time for these new technologies as they start to be implemented in real-world applications. Taking small-scale designs up to the realm of square metres is not trivial, and big breakthroughs in solar power have been heralded before. Yet with their winning combination of economy, efficiency and flexibility, this latest generation of solar cells might allow proponents of solar technology to silence its critics at last.

Joerg Heber is an editor at Nature Materials

Big Ideas that Changed the World - Consumerism

UK water use 'worsening global crisis'

The amount of water used to produce food and goods imported to developed countries is worsening water shortages in the developing world, a report says.
The report, focusing on the UK, says two-thirds of the water used to make UK imports is used outside its borders.
The Engineering the Future alliance of professional engineering bodies says this is unsustainable, given population growth and climate change.
It says countries such as the UK must help poorer nations curb water use.
"We must take account of how our water footprint is impacting on the rest of the world," said Professor Roger Falconer, director of the Hydro-Environmental Research Centre at Cardiff University and a member of the report's steering committee.

"If we are to prevent the 'perfect storm', urgent action is necessary."

The term perfect storm was used last year by the UK government's chief scientist, Professor John Beddington, to describe future shortages of energy, food and water.
Forecasts suggest that when the world's population soars beyond 8bn in 20 years time, the global demand for food and energy will jump by 50%, with the need for fresh water rising by 30%.
But developing countries are already using significant proportions of their water to grow food and produce goods for consumption in the West, the report says.
"The burgeoning demand from developed countries is putting severe pressure on areas that are already short of water," said Professor Peter Guthrie, head of the Centre for Sustainable Development at Cambridge University, who chaired the steering group.

"If the water crisis becomes critical, it will pose a serious threat to the UK's future development because of the impact it would have on our access to vital resources."
Key to the report is the concept of "embedded water" - the water used to grow food and make things.
Embedded in a pint of beer, for example, is about 130 pints (74 litres) of water - the total amount needed to grow the ingredients and run all the processes that make the pint of beer.

A cup of coffee embeds about 140 litres (246 pints) of water, a cotton T-shirt about 2,000 litres, and a kilogram of steak 15,000 litres.
Using this methodology, UK consumers see only about 3% of the water usage they are responsible for.

The average UK consumer uses about 150 litres per day, the size of a large bath.
Ten times as much is embedded in the British-made goods bought by the average UK consumer; but that represents only about one-third of the total water embedded in all the average consumer's food and goods, with the remainder coming from imports.

The UK is not unique in this - the same pattern is seen in most developed countries.
The engineering institutions say it means nations such as the UK have a duty to help curb water use in the developing world, where about one billion people already do not have sufficient access to clean drinking water.
UK-funded aid projects should have water conservation as a central tenet, the report recommends, while companies should examine their supply chains and reduce the water used in them.

This could lead to difficult questions being asked, such as whether it is right for the UK to import beans and flowers from water-stressed countries such as Kenya.
While growing crops such as these uses water, selling them brings foreign exchange into poor nations.
In the West, the report suggests, concerns over water could eventually lead to goods carrying a label denoting their embedded water content, in the same way as electrical goods now sport information about their energy consumption.
The Engineering the Future alliance includes the Institution of Civil Engineers (ICE), the Royal Academy of Engineering (RAE) and the Chartered Institute of Water and Environmental Management (CIWEM).

For the full article with interactive diagrams click on the title to be taken to the BBC website.