Alternative energy storage

Future hybrid cars may no longer need large batteries to store the kinetic energy created by braking with several new alternative technologies being developed in Britain.

Three UK firms were acknowledged at the Carbon Trust’s 2009 Innovation Awards for their alternative concepts for storing energy through hydraulic systems, flywheels and air tanks.

The use of air is being proposed by Ma Innovation. Its technology, which is still in the proof-of-concept stage, would take kinetic energy created by a braking vehicle to drive a supercharger that produces boost air. This boost air would then be stored in an air tank — located where the large electric hybrid vehicle battery would usually be — and later delivered to a downsized engine to help it cope with acceleration demands while the supercharger is switched off.

‘The engine only takes air at relatively low pressure at two bar,’ explained Jonathan Ma, the business development director of Ma Innovation. ‘So we would store the air at the same pressure the engine would want it at later.’

Ma compared the storage pressure to that of a bottle of coke. ‘So the walls of your tank don’t need to be particularly thick to store air at that pressure,’ he said, adding that the air tank could be made out of a single injection-moulded membrane piece.

Ma said the technology could be retrofitted to not only hybrid vehicles, but also diesel engines. The only prerequisite, he added, is the engine must be downsized — so it is designed for just cruising power — and it must be air charged with either a turbocharger or supercharger. 

The company estimated that depending on traffic conditions, driving a car equipped with this technology in the city could deliver a 25 per cent fuel saving compared to a standard turbo-diesel vehicle.

When the technology is fully commercialised, which Ma estimated will be in about two years, it will be initially targeted for retrofitting onto buses and vans. However, the ultimate goal for the company, he added, is to build the technology into new cars.

Another alternative for power storage is Williams Hybrid Power’s flywheel technology.

The Williams engineers, more accustomed to developing technology for Formula One, have developed this technology for the wider vehicle market.

The company said the electrically driven flywheel is like an electro-mechanical battery that could replace a conventional battery or ultra-capacitor pack in a hybrid system.

The distinctive, patented feature of the Williams Hybrid Power flywheel technology is its ‘magnetically loaded composite’. The company claims this feature makes it possible to produce a wholly composite flywheel that integrates the magnets of the electric motor into the composite.

Williams Hybrid Power points out that the flywheel system can be made significantly smaller and lighter than conventional flywheels. It also runs at efficiencies between 97 and 99 per cent.

A further alternative for energy storage involves a hydraulic system developed by Artemis Intelligent Power. Its technology removes the need for a battery and electric motor because power is stored by a hydraulic system that harnesses energy through regenerative braking.

Ma told The Engineer that any technology that aims to replace batteries in electric hybrid vehicles will bring added environmental benefits.

‘The amount of carbon dioxide you produce to create a battery is very high and the nasty chemicals in them make them very difficult to recycle,’ he said.

‘Also, batteries don’t last that long compared to the life of a car. You would need to change your battery within the lifespan of the car several times. So then you’ve got this issue seven times over where not only is the battery not particularly environmentally friendly to make or particularly environmentally friendly to recycle, but you have to have several batteries during the lifecycle of the car.’