Future fuels: What will power tomorrow's cars?

With air pollution getting worse and oil production declining, car manufacturers are looking to alternative fuels. But what will power tomorrow's cars?

Fly into any major city around the world and you will be greeted with a familiar sight: a sheen of brown smog that floats over the city. This smog comes mostly from cars.

Along with this smog comes carbon dioxide, the gas that's principally responsible for climate change. The steady increase in pollution has caused governments around the world to create legislation that will limit the volume of greenhouse gases that we can put into the atmosphere. The Australian Government has committed to reducing our greenhouse gas emissions by between five and 15 per cent below year 2000 levels by 2020.

In addition to reducing pollution, many nations, such as the United States, have talked about energy independence. That is, being able to generate energy, especially renewable energy, domestically without having to rely on imported oil either from unstable regions of the world or from regimes deemed unfriendly.

Don't worry, the car will not disappear. Even as you read, today's scientists are researching tomorrow's fuels. Here are the three most promising candidates.

Hydrogen: the space age fuel

• Good: More energy rich per kilogram than petrol or battery-powered electric cars • Produces only water as exhaust • Refuels faster than electric cars
• Bad: Very expensive to produce • Difficult to store and transport • Incompatible with current infrastructure
• Bottom line: Although on paper it's an extremely promising fuel, high costs and problems with storage means that a lot needs to be done to make hydrogen the fuel of the future.

In many ways hydrogen is an ideal fuel. In fact, when scientists really needed a fuel that would go the distance, they turned to hydrogen to generate power on NASA's Apollo missions — hydrogen was used as a propellant for the Saturn V rockets, while hydrogen fuel cells were used to power the electronics inside the command modules — including the Apollo 11 mission that landed the first humans on the moon in 1969.

As hydrogen is gas under normal conditions, it's typically compressed under high pressure, in a similar manner to the liquid petroleum gas (LPG) that's commonly used in Aussie taxis and other high mileage vehicles. While taxis burn LPG instead of petrol in a normal internal combustion engine, hydrogen fuel cells are quite a different beast.

While fuel cells may sound fancy, they are actually quite similar to batteries. Like batteries, fuel cells generate electricity, meaning that any car that runs off a fuel cell is actually an electric car. Also like batteries, fuel cells mix two chemicals that react to produce an electric current.

However, the important difference with fuel cells is that, unlike batteries, they do not store energy internally. Rather, they have their "fuel" fed directly into the battery "cell", thus the term fuel cell. To simplify things, think of fuel cells as batteries that eat out, rather than bring their lunch.

In the case of a hydrogen fuel cell, the two chemicals that react together are stored hydrogen and atmospheric oxygen. When reacted together they produce water. So if you have a hydrogen car, you can drink its exhaust. Also fuel cells aren't limited to smaller vehicles, they can power buses and, even, tractors.

Fuel cells can be fed a range of material, including methanol and ethanol, but hydrogen is generally used as it is light, produces only water as exhaust and has a high energy density per weight.

Right up until now, this picture sounds pretty rosy. Unfortunately, hydrogen isn't all clean water and sunshine. As a fuel, it has a number of serious drawbacks. Firstly, there are no large natural sources of pure hydrogen on Earth. Unlike fossil fuels, it doesn't just well up out of the ground.

This means hydrogen must be manufactured from scratch. At this point one of hydrogen's major advantages becomes a drawback. As hydrogen stores a huge amount of energy per kilogram, it takes a huge amount of energy to produce. Despite some promising new technologies, in almost every conceivable industrial scenario today, the price of hydrogen exceeds that of petrol.

In addition, because hydrogen is a gas, it needs to be compressed at a very high pressure. This makes it difficult to transport and store. For example, in order to store a measly 5kg of hydrogen, the Honda FCX Clarity hydrogen fuel cell car needs a massive 171-litre tank, which compresses the gas at 340 times atmospheric pressure. Added to the weight of this massive tank is the weight of the fuel cell stack itself, which in the Clarity tips the scales at 67kg.

Finally, it's very difficult to compress a significant amount of hydrogen. Thus, a litre of hydrogen only typically contains about a third of the energy of petrol. This difference is highlighted by Ford's hydrogen-powered Focus, which has a maximum range of 250km off a single tank of hydrogen. A petrol manual Focus meanwhile will give as much as 700km on a single 55L tank.

Putting high-pressure gas into your vehicle also requires plenty of expensive new infrastructure. For starters, hydrogen filling stations cost around US$2 million each. Add to that the cost of transporting hydrogen, along with the facilities to produce it and you have a significant up-front investment.

Despite all these complications, a number of car manufacturers have produced prototype hydrogen fuel cell cars including Fiat, Volkswagen and BMW, while Peugeot-Citroen has even produced a hydrogen-powered quad-bike.

However, the big car manufacturer that is arguably pushing hydrogen hardest is Honda. The company's FCX Clarity is one of the most advanced hydrogen fuel cell cars, and is currently available for lease in the US and Japan.

Despite Honda's enthusiasm, not everyone is on the bandwagon. Toyota to date has mostly focussed on hybrid cars. Ford has generally shied away from hydrogen cars, pinning its hopes instead on a very different type of car, the electric car.

Batteries: high voltage dreaming

• Good: No tail-pipe exhaust • Almost silent • Utilises current electricity grid • Batteries already produced en masse
• Bad: Terrible range • Batteries are heavy • Long charge times • Most of Australia's electricity comes from burning coal
• Bottom line: The electric car has long been an inventor's dream. With the right government and industry support, it might just come true.

There are a lot of conspiracy theories about what killed the electric car. But any story about electric cars needs to start with a discussion of batteries.

Battery technology has come a long way in the last 20 years. The current industry's golden child, the lithium-ion battery, is a remarkable piece of technology. It's substantially lighter, holds more energy and is more efficient than the long history of batteries that precede it. You don't need an introduction to the lithium-ion battery though, as it powers almost all of today's consumer electronics.

Yet, even today's very best batteries hold substantially less energy than either hydrogen or petrol. To give you a rough idea, the battery pack in one of today's most promising cars, the Chevy Volt, has a lithium-ion battery pack weighing 170kg that produces an electric-only range of roughly 60km. Ouch. That's why, despite the fact that its wheels are driven by an electric motor, there's also a petrol engine on-board to generate electricity should you wander out of that 60km range.

Pure electric cars have managed to push their range out a little further. For example, the Mini E manages a range of 240km on a single charge. Though, closer inspection shows that the Mini E is a tiny car with a massive battery. In fact, its 35kWh battery weighs more than 300kg and is so massive that the designers were forced to take out the back seats to fit it in.

By comparison, Honda's hydrogen powered FCX Clarity has range of approximately 460km, giving it seven times the range of the Volt and almost double the range of the Mini E. Then again, an average petrol-powered Japanese road warrior, like a Toyota Corolla, can travel up to 750km on a single 55L tank.

Along with the terrible range of battery-powered electric cars, there is another unfortunate drawback. As our everyday experience with rechargeable batteries has taught us: they're very slow to charge.

A typical wall outlet in Australia delivers 240 volts at 10 amps, meaning that it supplies 2400 joules per second (watts). The battery on the Chevrolet Volt stores 57.6 million joules (16kWh). Doing the maths, this means it would take about seven hours to recharge the battery on the Volt from a wall outlet and around 14 hours to charge the Mini E. In both cases, it will only take you five minutes to cry over your power bill.

However, there are also a number of great technological innovations that are leaping up to meet the engineering challenges posed by electric cars. Rather than go for a fancy technical solution, Israeli company Better Place is planning to set up a network of recharge stations throughout Australia, where drivers of compatible electric cars can have their depleted battery pack swapped out and replaced with a fully charged set.

Other solutions include creating fast charging batteries and high voltage charge stations, where charge times can be brought down to two hours. It is also technologically possible to charge special batteries in as little as 10 seconds using very high voltages. Keep in mind that these high voltages have the ability to blow your arms off if something goes wrong. This is perhaps a good reason not to let consumers handle them at recharging stations.

Put together, these engineering challenges killed the first "mass produced" electric car, GM's EV1. However, what killed the electric car may also resurrect it. While batteries are an awful way to store energy compared to petrol, electric cars produce no exhaust. This reason alone pushed GM into making the Volt a production car by 2010. In addition, companies like BMW have pushed ahead with cars like the Mini E. While not currently commercially available in Australia, the Mini E is available for lease in limited numbers in the US and UK.

Of course, compared to both batteries and fuel cells, the humble tank of petrol remains king in terms of energy storage, safety and price. This leads one to ask, what if there was a pollution-free way to make petrol?

Biofuels: Mother Nature to the rescue

• Good: No new delivery infrastructure needed • Renewable • Can be carbon neutral • Already in production and use
• Bad: May damage bikes and older cars • Competes with food production • Massive amounts of biomass required to meet the world's fuel needs
• Bottom line: Biofuels are already in use today. With further technological refinement and increased production, they're potentially unstoppable.

Keep your scepticism close at hand if you plan to dip into the volatile debate on biofuels. While biofuels have a lot of promise, their environmental impact is the subject of an intense discussion.

Before we get into that, let's get back to basics. A biofuel is any fuel that is derived from biological materials such as wood chips, sugar or vegetable oil. While regular fossil fuels are also a result of biological material, biofuels differ in two important ways.

When we dig up and burn fossil fuels we are adding carbon to the atmosphere that has long been buried. On the other hand, biofuels are made from newly grown plant materials that have already taken carbon dioxide out of the atmosphere through photosynthesis. Therefore, as biofuels merely recycle the existing atmospheric carbon, they are technically considered carbon neutral. That is, they don't add new carbon dioxide to the atmosphere and so aren't helping to speed up climate change. In addition, because biofuels come from virgin plant material, they are renewable.

Yet, there are a couple of environmental hiccups in this otherwise sunny picture. A production process is needed to turn the biological material, known as biomass, into biofuels. This production process requires energy and unless this energy comes from a renewable source, biofuel production causes pollution.

The second problem is that replacing the world's fossil fuels with biofuels requires growing a huge amount of new biomass. This may mean eating into the world's food supplies as, traditionally, biofuels (like ethanol) have been made from foodstuffs, such as corn. There are non-food biofuel sources, for example, palm oil, but these often entail chopping down virgin forests to grow new palm trees.

The good news is that a diverse range of fuels can be made from biological material. These include fuels ranging from natural gas (methane) and LPG, to the common fuel additives, like ethanol, right up to heavier fuels, like diesel.

Biofuels are the subject of intense scientific research and have received a considerable amount of government subsidies in Australia and overseas. Much of this is because they can be used with existing internal combustion engines, thus requiring no new infrastructure and no new cars, just a new fuel production process.

More recent efforts from ethanol producers have focussed on making ethanol from cellulose, the non-edible parts of plants. Cellulose has two advantages. Firstly, using cellulose means biofuels don't compete with food production. Secondly, cellulose is the most abundant biological material on Earth.

Of all the renewable fuels, biofuels are the most commercially ready. In fact, many of you are likely already using it in your cars. In Australia, ethanol is combined in a 10 per cent blend with regular unleaded petrol, commonly known as E10.

Almost all cars made after 1986 can safely run on E10, while most cars made before 1986 cannot. The Australian Federal Chamber for Automotive Industries (FCAI) maintains a list of cars and bikes that can safely run on E10.

Watch out if you own a motorcycle though, because even recent bikes, particularly those from Honda, Kawasaki, Suzuki and Yamaha, aren't designed to run on E10. In unsuitable engines, ethanol will cause long-term damage, such as the rusting of fuel lines.

Along with ethanol, another alternative fuel you may have come across is biodiesel. Just like ethanol, biodiesel is typically blended together with standard fuel in low concentrations. Similar to ethanol, fuel that contains 10 per cent biodiesel is called B10.

Biodiesel isn't that common in many parts of Australia, but you'll find it being served at Western Australia and Queensland. The FCAI recommends a blend no stronger than B5, with Caltex stating that most original manufacturers agree that B5 can be used in place of regular diesel. If you plan to use blends stronger than B5, it's worth checking your vehicle's manual first.

What will be the fuel of the future?

If fossil fuels are to be phased out, the cheapest and fastest alternative to get to market will win.

Judging by this criteria, biofuels currently lead the race. They are on sale today, broadly used and are yet to feel the full price drop that accompanies significant economies of scale. In some cases, they are sold today at a cheaper price than the equivalent fossil fuel.

Electric cars come a close second, with many car makers trialling or leasing electric cars. Though, the ones already on sale, such as the Tesla Roadster, and the ones due for sale shortly, like the Mitsubishi i MiEV, are a tad on the expensive side. Hydrogen cars languish in last place as, outside certain parts of California, the infrastructure to support them simply doesn't exist.

Of course, the story that has not been told here is that of hybrid cars. If run off a combination of biofuels and renewable electricity, they are pollution free. Judging from consumers' reactions to cars like the Toyota Prius, the hype surrounding the Chevy Volt, along with the US Government's commitment to put one million hybrids on the road by 2015, these will be the cars of the near future.

Then again, a sudden technological breakthrough might change the game, such as a cheap way to store large amounts of hydrogen. Who knows what the future holds.