So, Toyota is planning to take hydrogen cars into the mainstream. But is the world ready for hydrogen fuel cell cars? And even if it is, will fuel cells live up to the low-carbon hype?

First, let's tackle the readiness issue. The big problem is infrastructure. Hydrogen fuel cell cars offer major advantages over conventional battery-electric cars like the Nissan Leaf and BMW i3 when it comes to charging times and range.

They can essentially be refueled just like a petrol or diesel powered car. But that assumes the availability of filling stations, which are largely non existent currently.

Toyota has spoken of its plans to build a network of hydrogen outlets in preparation for the 2015 launch of its fuel cell car. But the $200 million price it quoted to set up just 20 stations in California gives you an idea of the massive investment needed to shift the world's fuelling infrastructure from diesel and petrol to hydrogen. It will be massively expensive and it will take years and years.

Toyota's building, will anyone come?

And that's just part of the infrastructure problem. Production of hydrogen would also have to be massively ramped up to supply all those filling stations and in turn fuel the cars. More money, more time.

Of course, you could say that's an argument against any kind of change. In reality, that half of the hydrogen question comes down to will. If the world wants it enough, it will happen.

So the real question is whether it ought to be happening and whether the advantages of hydrogen fuel cells are all they're cracked up to be.

Toyota fuel cell
20 years in the making: Toyota's fuel cell tech

Certainly, fuel cells have immediate upsides in terms of local emissions. All you get out of a fuel cell is harmless water vapour. Win.

However, deriving the hydrogen fuel out of seawater is energy intensive stuff. And right now, the world's energy production is largely fossil fuel-based.

Time and space

In other words, if the world shifted from fossil-fuelled to hydrogen cars overnight, actual emissions wouldn't improve. They'd just be shifting in space and time from cars to the power stations providing the energy.

Well, it's actually even more complicated as that as, for instance, the UK grid doesn't have the spare capacity to suddenly cope with charging a significant proportion of the car fleet.

That said, cars fueled by grid-produced hydrogen wouldn't be any worse regards emissions than conventional cars. And they'd have the advantage of immediately benefitting from any improvement to the renewable balance in the grid's production mix.

Even better, there's no reason why you couldn't produce hydrogen from purely renewable energy sources. As the Middle East runs out of fossil fuels, it's easy to imagine the creation of solar-powered water-cracking and hydrogen production facilities.

When the wind blows

In colder climates like the UK, you could produce hydrogen using wind or tidal power. And unlike the problems that beset wind power for general electricity production, hydrogen production would be a case of when-the-wind-blows. A constant supply of wind power wouldn't be so critical.

BMW i3
Battery-electric cars like the BMW i3 are zero emissions but short on practicality

All of which means hydrogen offers an awful lot of promise. Then again, so do other options. Just as you can produce hydrogen from renewable power sources, pretty much any petrochemical can be synthesised using renewable energy.

Take water from the ocean, pull C02 from the atmosphere, add some energy and know-how and you can create carbon-neutral petrol. The really clever part of that solution is that you don't need to build new fuel stations or even make new cars.

What about synthetic fossil fuels?

Of course, synthesised carbon neutral fuels would have some local emissions. But modern petrol engines are actually very clean bar the CO2. And any CO2 emitted would be that previously pulled from the atmosphere to make the fuel in the first place.

Whatever happens, over the next 20 years or so it will be fascinating to observe how the various energy sources compete to power our cars.