'Air hybrid' cars would be cheaper than electric hybrids, claims researcher

environmentresearchweb: Storing energy as compressed air rather than in batteries would reduce the cost of green hybrid cars, say researchers in Sweden

• On the road with the Airpod air-powered car

environmentresearchweb guardian.co.uk, Wednesday 2 March 2011 12.20 GMT
Electric cars and electric hybrid cars already make use of brake energy to power a generator that charges the batteries. However, according to Per Tunestål, a researcher in Combustion Engines at Lund University in Sweden, air hybrids, or pneumatic hybrids as they are also known, would be much cheaper to manufacture.

"The technology is fully realistic. I was recently contacted by a vehicle manufacturer in India which wanted to start making air hybrids," he says.

The technology is particularly attractive for jerky and slow driving, for example for buses in urban traffic.

"My simulations show that buses in cities could reduce their fuel consumption by 60%," says Sasa Trajkovic, a doctoral student in Combustion Engines at Lund University who recently defended a thesis on the subject.

Trajkovic also calculated that 48% of the brake energy, which is compressed and saved in a small air tank connected to the engine, could be reused later. This means that the degree of reuse for air hybrids could match that of today's electric hybrids. The engine does not require any expensive materials and is therefore cheap to manufacture. It also takes up much less space than an electric hybrid engine. The method works with petrol, natural gas and diesel.

The idea of air hybrids was initially hit upon by Ford in the 1990s, but the American car company quickly shelved the plans because it lacked the necessary technology to move forward with the project. Today, research on air hybrids is conducted at ETH in Switzerland, Orléans in France and Lund University in Sweden. One company that intends to invest in engines with air hybrid technology is the American Scuderi. However, their only results so far have been from simulations, not from experiments.

"This is the first time anyone has done experiments in an actual engine," says Trajkovic. "The research so far has only been theoretical. In addition, we have used data that means we get credible driving cycle results, for example data from the driving patterns of buses in New York."

The researchers in Lund hope that the next step will be to convert their research results from a single cylinder to a complete, multi-cylinder engine. They would thus be able to move the concept one step closer to a real vehicle.

Underwater kite-turbine may turn tides into green electricity

Swooping a turbine through the sea's currents could be a cheaper way to harness the power of the oceans

Minesto's device works like an underwater kite, tethered to the sea bed, which flies through the sea current carrying a turbine. Photograph: Minesto UK Ltd/Carbon Trust

As a surfer, I know the power of the sea and also that going with the flow is the only way to survive. And that's what I like about this underwater kite-turbine, being developed by Swedish company Minesto.

They will do the first sea trial in Strangford Lough in Northern Ireland this summer. The kite, which at full size will have a wingspan of 8-14 metres, carries a turbine below it. The kite is tethered by a cable to the sea floor and then "flies" in the tidal stream. It swoops round in a figure-of-eight shape to increase the speed of the water flowing through the turbine tenfold (see company video below), just as sailing boat cuts across the wind to go faster.

That manoeuvre means the kite can generate renewable electricity in tidal streams that would be too slow to drive the first-generation tidal devices, such as the SeaGen turbine also installed in Strangford Loch. The kite has neutral buoyancy, so doesn't sink as the tide turns and the turbine mouth is protected to stop fish flying through.

For those, like me, geeky enough to like the numbers, here they are. Ander Jansson, Minesto's managing director, tells me the kite should work in flows of 1-2.5 metres per second, while first-generation devices need over 2.5m/s. Depending on the location and size of the kites, each will have a capacity of between 150 and 800kW, and be deployed in waters 50-300m deep. The test will be at one tenth scale.

Other second-generation tidal devices include a floating turbine being developed by ScotRenewables in Orkney.

Stephen Wyatt, a marine energy expert at the Carbon Trust, says devices such as kites that exploit lower speed tidal currents would expand the UK's tidal resource by 16%, meaning it could supply about 1% of the UK's current total electricity needs. The Carbon Trust and Invest Northern Ireland will spend £350,000 funding the trials over the next 18 months.

What about the challenges ahead? Wyatt says installing the devices is one of the hardest steps. A boat has to get in to drill the foundations and deploy the kite during the short time while the tide is slack. Jansson says the key challenge will be getting the technology to commercial viability, where it can compete on cost with other ways of generating electricity. He suggests making and installing two turbines, with a joint capacity of 1MW, could cost £1.8-£2m, though he expects fleets of kites to be deployed to benefit from economies of scale.

"The sea is an extremely tough environment and I think this is why the sector has taken some time to develop," says Jansson, speaking from the RenewableUK Wave and Tidal conference. "But it is really starting to kick off now."

One per cent of the UK's electricity may not sound like much, but it's enough to power the city of Newcastle, and I think we need all the clean energy we can get.