Dick Ahlstrom, Science Editor, looks at the alternatives to fossil fuels
There is a constant and ongoing search for alternatives to petrol and diesel as a way to keep the cost of private motoring down and also forestall the day when hydrocarbon fuels run out. The motor manufacturers are of course involved, but so too are research teams in the universities and government-run labs around the world.
Despite years of effort, very few commercial alternatives to these traditional fuels have arisen. Most alternative fuels and power sources suffer from being impractical, inefficient compared to hydrocarbon fuels or just unworkable.
Here are some of the alternatives that have been studied intensively, with observations on their suitability from mechanical engineer, Dr Will Smith, programme director of Formula Student at University College Dublin:
HYBRID COMBINATION OF PETROL/DIESEL ENGINE AND AN ELECTRIC MOTOR POWERED BY A HYDROGEN FUEL CELL
This approach is strongly promoted by motor companies including BMW which plans to have a 7-Series model out in two years. The conventional engine is backed up by an electric motor driven by a fuel cell that burns hydrogen and air to produce electricity. Hybrids switch back and forth between electric and petrol/diesel as appropriate to driving conditions, in the same way that Toyoto's Prius combines conventional fuel with electric motors powered by battery.
The fuel cell produces a constant supply of electricity so battery storage is not necessary, but a major drawback is access to hydrogen fuel. Hydrogen gas is costly to produce and store. Most importantly, there is no network for the supply of hydrogen gas, the cleanest way to power a fuel cell.
It is possible to use other hydrocarbon fuels including natural gas and even petrol, but then the car must also have an onboard chemical plant to strip off the hydrogen, leaving waste carbon behind.
Despite the immediate difficulties with hydrogen supply, fuel cell technology is well developed, having been used for decades in international space programmes. Fuel cell powered cars and buses are already on the road and if hydrogen supply can be sorted out this alternative fuel source will probably come into widespread use.
ELECTRIC CAR POWERED ENTIRELY BY HYDROGEN FUEL CELL
The use of hybrid petrol/diesel and fuel cell combinations is seen as a logical stepping-stone towards an electric car powered by fuel cell alone. Fuel cells work at a theoretical 80 per cent efficiency compared to 30 or 40 per cent for petrol so it is an effective power source. Hydrogen would be the preferred fuel as it burns with air to produce water and no pollutants, but again access to hydrogen gas is the problem.
Even if hydrogen gas was readily available at any petrol station, a pressurised storage tank the same size as a conventional petrol tank would only hold enough hydrogen for 70 to 100 miles, compared to the 300 mile range if using petrol. Using larger hydrogen tanks or tanks at higher pressures would improve this but hydrogen is explosively flammable. Motorists may be hesitant to carry such a fuel supply around, much as they are with LPG.
BATTERY POWERED ELECTRIC CARS
While battery-powered motors look like a clean alternative energy source for private motoring, distances that can be travelled are unacceptably short. The benefit of using clean electricity is lost with the need to carry huge numbers of heavy batteries to achieve a decent range.
The difficulty is not overcome by having convenient recharging sockets at every parking space. Battery recharging produces a significant drain on electricity systems that would have to be beefed up to accommodate large numbers of electric cars.
The hours required to recharge heavy batteries is an issue. A petrol pump puts a litre or two of petrol in your tank per second and a fill-up takes just a couple of minutes. A full tank holds a potential energy of about 10 to 15 megawatts, equivalent to the peak power output from a small power station.
SOLAR CELL ELECTRIC CARS
Solar cell technology works but the watts delivered per square centimetre of solar cell is low. Unless you live in the California desert you may not get enough power to take off.
Batteries are the usual supplement for cloudy weather or night journeys, but then the need to carry lots of battery weight works against efficiency and carrying capacity.
Range is also an issue because you might be only part way through your journey before clouds roll in to spoil the fun and your backup batteries might not have the juice needed to get you to your destination.
BIODIESEL AND ETHANOL SUPPLEMENTED PETROL
One argument holds that we can grow all the fuel we need to keep our cars on the road. Plants that produce large amounts of oil including rape seed and olives can be grown to deliver a fuel crop provided the diesel vehicle they are destined for can burn vegetable oil. Only minor adjustments are needed to allow most diesels to burn vegetable oil. VW promotes biodiesel engines.
Equally, any sugar producing crop including sugar beet and sugar cane but also starches including maize and even potatoes, can be grown for later fermentation and distillation to produce ethanol. This is added to ordinary petrol to reduce dependence on the refined product.
While these approaches look promising as a way to stretch oil reserves, there are problems, none of them associated with the engineering. Estimates suggest that if Ireland were to meet its current diesel requirements entirely with vegetable oils about 25 per cent of the island would have to be given over to oil crops. This would be unworkable given only 13 per cent of our lands are currently in agriculture for cultivated crops.
LIQUEFIED PETROLEUM GAS AND LIQUEFIED NATURAL GAS
LPG and LNG are both in relatively plentiful supply, but only LPG is currently available here for road use. Both meet consumer resistance, however, given the fact that they must be kept under pressure in onboard tanks. Many motorists don't like the idea that a highly flammable gas sits in a compressed state only a few metres behind them given the possibility of accidents. While the tanks are designed to take hard knocks, there is a heightened perception of risk.
Liquefying hydrogen can increase the range achievable by hybrids or fuel cell electric cars, but this demands a large amount of energy and then exceptional insulation measures are required to keep it liquid at ambient temperatures. This would not be an option in a mass production car.