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Cambridge team rethinks solar-powered technology

The World Solar Challenge is a marathon race across Australia, from Darwin in the North to Adelaide in the South, that sees around 40 teams design and build solar-powered cars, each intent on getting to the finish line first.

Cambridge University student Keno Marioghae with the new and old solar car designsFor the last twelve years or so, since the arrival of BP’s Quiet Achiever, design for these continental cruisers has stagnated, with the now relatively common ‘table top’ style becoming dominant. The theory is simple; present a large area to place solar panels on and make the shape as aerodynamic as possible. More space equals more power, which then equals more speed.

Tables to tears

A team from Cambridge University followed convention in 2009 by entering their Endeavour table top design, before refining and improving the vehicle for an attack on the 2011 race. However, with the top teams on budgets measured in multiple millions, the small University team could not compete by following the same basic design. It was time for a change.

How the new Daphne solar car will look

Initially, a motorbike like design was drawn up, with the rider taking a recumbent position in an enclosed cockpit. However, a late rule change outlawed that option and the team returned to the drawing board.

Revealed this week, the vehicle that the Cambridge University Eco Racing team believe will take them to the title in 2013, codenamed Daphne, sees new thinking that could have an impact on road cars of the future.

Taking an aerodynamic tear drop shape, the team have actually gone against convention and reduced the size of the solar panels on the back of the car, using just three square metres of panelling. That’s around half the area of the traditional designs and means they will be producing around half the power.

There is clever thinking behind the design, though. Firstly, the shape is inherently extremely efficient, with a CdA figure of 0.075; to put that in to perspective, the slippery Bugatti Veyron has a CdA of 0.745.

Efficiency is key

Where the team really hope to steal a march on their competition is in the positioning of the solar cells. Lined up behind the driver, the cells can be angled to fully face the sun. As the sun moves from east to west, this can lead to an increase of up to 20 per cent in energy captured. The whole array is then encapsulated in a plastic cover to retain aerodynamic efficiency.

A model of the new Daphne solar carThe net result of the compact design means the team are facing a shortfall of up to 40 per cent in power compared to their competitors, but in a far more efficient and lightweight machine. Currently the vehicle weighs just 117 kg, but the target is to reduce that to 110 kg making it around 30 kg lighter than any other vehicle ever entered in to the race.

Whilst it’s clear that solar energy won’t be powering our own cars any time soon, as you would need a football field sized panel to push a family saloon along, the work going in to increasing efficiency, reducing weight and improving aerodynamics will be leading directly to developments on the road.

The 5 kWh battery pack can already propel Daphne for 500 miles, but new developments in battery technology will see cells that actually get cooler in use and therefore operate more effectively. Efficiency gains in the build process means that 98 per cent of the energy collected by the solar cells makes it to the battery pack.

A composite suspension system will see the spring and dampers found on a normal vehicle combined in to one single piece of carbon fibre in a form that can move easily over to road cars, while it is hoped that some carbon fibre wheels can be developed to further reduce weight.

An intelligent ‘cruise control;’ system is also in development that will plan energy use in advance depending on terrain, traffic conditions and energy available. It is easy to see how this development alone could benefit road cars, especially electric vehicles.

Solar-powered driving experience

At the launch of Daphne, which is still under development and not expected to turn its first wheel until 2013, its predecessor was on display. It would have been rude not to have a go in it.

The old Cambridge Endeavour design solar car on the road

Despite being designed for a waif-like driver less than five and half feet tall, I managed to squeeze my ample frame through the safety cage and slide in to the driving seat. Switching on and sliding the speed controller to maximum, I waited for the clicks and whirrs to translate to forward movement and was soon away, heading down the streets of Cambridge. I was driving a solar powered racing car.

Phil tries out the old-design Cambridge solar carA cool autumn day was not the ideal testing environment for a solar powered car, so my driving time was limited, but the old car felt nimble, smooth and surprisingly powerful, a constant surge of power increasing the speed continuously.

If the new car retains that sensation while removing weight, lowering resistance and increasing efficiency, there’s every chance that this team of students could take their £500,000 budget and upset the teams from Holland, America and Japan who are spending 20 times that amount.

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Phil Huff

Filed under: Solar

1 comment

AFAYOL

please, your below statement is FALSE: " solar energy won’t be powering our own cars any time soon, as you would need a football field sized panel to push a family saloon along". I drive, in France, a REVA with solar PV on its roof, and only need to add less than 5% wind&sun energy of my carpark place, based on the annual French average driver mileage.AndreF

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