What will we do when the oil runs out? It's a finite resource, and since most scientists now seem to accept that by burning oil, then releasing the carbon dioxide generated into the atmosphere, we're altering the climate. Possibly with disastrous results.
Even if you're skeptical about climate change, or simply don't care about, it's hard to argue that petrol as we know it probably won't powering the motorcycles we'll be riding in fifty year's from now. As deposits of crude oil get used up, petrol will become scarcer, more expensive, and eventually run out altogether.
Among the options, one of the most promising – on the face of it – seems like electricity. Generate electricity from solar panels, wind turbines wave power, nuclear reactors or whatever other method you can, use it to charge up a battery in a motorcycle or car, then drive off. Perfect...
But it's not so easy. Petrol is actually an incredibly dense energy store, and petrol engines can output a lot of power. By comparison, batteries hold much less energy inside them. Battery technology is improving all the time – lithium batteries as used in mobile phones and laptops are much lighter and hold more energy than basic lead/acid batteries used to start your motorcycle. But even if a battery can be developed to hold as much energy as a tank of petrol, which will also fit on a motorcycle, charging is quickly is another matter. It's simply not possible to transfer and store electrical energy anywhere near as efficiently as petrol does.
So whatever the future holds for motorcycles – hydrogen-powered fuel cells, synthetic petrol, bio-diesel-fueled turbo-diesel engines or bio-ethanol, it seem unlikely that we'll ever be plugging in an electric sportsbike to the socket in the garage.
Stored hydrogen gas made from renewable electricity is converted back into electricity inside a fuel cell. It can store much more energy than ordinary batteries, but not as much as petrol. Hydrogen is dangerous (as it's highly flammable) and hard to store. But some motorcycle manufacturers have already build some concept motorcycles, and BMW has a 7-series model in production. Also, hydrogen is probably our best bet at the moment.
Ethanol can be used to power modified petrol engines. It can be made from fermenting plants and distilling the results – in the same way as Whisky and Vodka is made. In the USA and Brazil they already expending this, but it makes food more expensive and there isn't enough arable land in the world to provide enough fuel for all petrol vehicles.
Vegetable oil from rapeseed or similar plants can be converted into a diesel like substitute. But as with bio-ethanol, there isn't enough land to grow bio-fuels and food for everyone.