What's greener - hybrid or diesel? Japanese and European makers are in hot debate over the merits of their 'green' programmes, says Daniel Attwood
With Vehicle Registration Tax expected to be replaced, eventually, by an emissions-based tax, the importance of a car's emissions is becoming more relevant to Irish motorists, and so is the debate over what's greener - diesels or hybrids.
Hybrid cars already receive a 50 per cent VRT rebate in Ireland because, as their Japanese manufacturers contend, such cars are the greenest available.
But some European manufacturers are hitting back, claiming that the latest generation diesel engines offer almost the same green advantages as hybrids but at a much lower initial cost.
Toyota has earned thousands of green Brownie points for its hybrid Prius, and Honda has just rejoined the green revolution with a hybrid version of the new Civic.
But Renault is claiming that its Megane dCi diesel engine matches all the low-emission and fuel consumption claims made for hybrid cars, but costs substantially less.
The five-door Megane dCi86 costs €24,350, while Toyota's Prius, even with its VRT rebate, costs €29,495.
Hybrid cars work by offering two power units - one petrol and one electric. Petrol engines are less efficient than diesel engines, so by mating a small electric motor to a petrol engine the environmental performance of the car is improved.
But European manufacturers who have concentrated on developing diesel engines claim that new turbo charger and common-rail injection technology have improved engine efficiency to the point where a petrol/electric hybrid offers little or no advantage, but costs significantly more to buy.
Renault says that its Megane dCi86 produces CO2 emissions of 120g/km compared to 109g/km for the Honda hybrid and 104g/km for the Toyota hybrid.
In addition, Renault says the Megane's official combined fuel economy is 4.5 litres per 100km, compared to 4.6 for the Civic and 4.3 for the Prius. "Hybrids are an interesting novelty but don't achieve anything that a dCi-engined Renault can't achieve," claims Renault.
Hybrids do offer the advantage of switching to zero-emission battery power during stop/start city traffic, but on the open road both engine and battery power are used, resulting in lower fuel economy and higher emissions. For many, the hybrid sums just don't add up, says Renault, and motorists should consider the type of driving they do before jumping on the hybrid bandwagon. While hybrids get better mileage in the city, diesel cars consume less fuel in all driving conditions, says the French manufacturer.
It is not just Renault which is championing diesel technology. Daimler Chrysler, Volkswagen, BMW, Fiat and Peugeot are all committed to developing cleaner diesel technology. However, it should be remembered that both Toyota and Honda also produce the latest generation diesel engines. After all, Toyota is not saying hybrid is better than diesel, it is just saying it is another option.
Saab is taking things one step further. Its BioPower Hybrid Concept combines bioethanol fuel and electric power generation for the first time.
Packing formidable pulling power from its 260bhp 2.0-litre turbo engine and 53kW electric motors, the BioPower Hybrid Concept can briefly generate torque values three times greater than its petrol-only equivalent.
"This project allows us to evaluate and explore the potential of hybrid technology in combination with our existing and already-proven BioPower technology," explains Jan Åke Jonsson, Saab Managing Director. "Although the exact hybrid application shown in this concept does not currently figure in our production plans, it shows how we could develop the sporty performance associated with Saab while using only renewable resources and saving energy overall."
Meanwhile, Peugeot Citroën has unveiled what is perhaps the best of both worlds, with diesel-electric hybrid versions of its 207 and 307 cars.
Average diesel consumption for the two cars fitted with these new hybrids is just 3.4 litres per 100km, with just 90 grams of CO2 emitted per kilometre, which is some 25 per cent better than the current petrol hybrid cars, or as much as one litre per 100km in combined urban and motorway driving.
The French manufacturer's hybrid technology is basically a 1.6-litre diesel engine, a 'stop & start' system and an electric motor. It enables the vehicles to start and drive using only the HDi diesel engine, even when the high-voltage battery pack is totally flat.
The company says it could market its Hybride HDi vehicles as early as 2010. However, it needs to bring the price of the technology down.
Currently, the price gap between a Hybrid HDi model and a comparable diesel HDi model is still too wide and would have to be halved to make diesel hybrid vehicles competitive.
Meanwhile, Toyota has hit back at Renault's claims, saying it "acknowledges that there are many alternative routes to achieving the ultimate eco-car". But forcing "customers into an either/or decision between diesel and hybrid power, using confusing messages to weight the argument in their favour is not helping".
However, this hasn't stopped the Japanese manufacturer taking a swipe back at Renault.
Toyota points out that its Prius is faster from zero to 100km/h than both the Mégane dCi86 and the dCi106. Toyota says the Prius has a further advantage during urban driving, where pollution and fuel economy are a bigger issue. Around town, official urban consumption for the Prius is 5 litres per 100km, compared to 5.5 litres per 100km for the Renault.
And, says Toyota, the Prius is the master of slow-moving traffic, being able to run on electric motor power alone, with zero emissions and maximum fuel efficiency.