US president elect Obama may have appointed a "green dream team" to help him govern, but it is far from obvious how they will tackle the thorny problem of how to make our energy use more sustainable. Yet we may already have seen the solutions, amongst the latest crop of innovations in green fuels. Here's a reminder of the discoveries from the past year that may revolutionise the way we power our lives. Greener gas Making cars greener does not require complex new ideas. Norwegian researchers reported that simply switching from gasoline to clean diesel could cut CO2 emissions by a quarter. Cleaning existing fuels more thoroughly before they reach cars could make a difference too. In October, came the announcement that a humble fungus can strip crude oil of the harmful sulphur and nitrogen compounds that cause air pollution and acid rain. And that's not the only fungus that could help cut drivers' carbon emissions. The following month a newly discovered Patagonian strain was shown to convert plant waste directly into diesel - a finding that could produce cheap biofuels without sacrificing arable farm land. Fuel and food The tricky problem of making sure that biofuels are not produced at the expense of food yields was addressed in other ways. Photosynthetic algae offer one plausible solution, because they can produce biofuels without impacting farm land at all. Meanwhile, the Holy Grail of biofuel production - cheap ethanol from waste plant material - received a boost in April, in the form of a self-digesting variety of genetically modified corn. After the cobs have been harvested, and the remainder of the plant crushed, enzymes produced by genes from a bacterium digest it from the inside out. This breaks down the cellulose-rich stems and leaves that are a waste product of so many crops. Even the lignin that gives woody material its toughness can now be converted into fuel. In July, researchers announced a new chemical reaction able to do just that, proving it worked by converting sawdust into the chemical precursors of biodiesel. Electric dreams Electric cars were also subject to feverish new developments, most focused on improving their range to make them more competitive with conventional vehicles. One approach is to replace batteries with ultracapacitors, which store power as electrical rather than chemical energy, and can be charged almost instantaneously. A new type, based on carbon nanotubes and manganese oxide "flowers", stores twice as much charge as existing ultracapacitors, and might power electric cars in the years to come. Batteries and ultracapacitors alone still look unlikely to cram quite as much mileage into the space of a fuel tank as a liquid fuel can. However, a novel design that is part fuel cell, part battery proved able to pack in energy twice as densely as petrol can. Hybrid vigour In the short term, hybrid systems that combine electric and internal combustion engines are likely to remain the most efficient, and most sustainable, way forward for road vehicles. The technology received a boost in October with news of a new "UltraBattery" that produces 50% more power than traditional lead-acid batteries while lasting four times as long. It doesn't become clogged with deposits during the repeated charging and discharging that occurs in a hybrid constantly switching from burning fuel to using electricity. Finally, although years of investment in hydrogen cars by the largest car manufacturers has yielded little more than a few prototypes, our in-depth report concluded it might be too early to sound the death knell for the hydrogen economy. Car makers continue to invest, despite diverting resources towards electric cars. And research into storing hydrogen more densely and safely continues. A novel spongy but tough material unveiled in October is capable of exceeding a target set by the US Department of Energy for hydrogen storage density. Were that technology to be developed into fully fledged fuel tanks, one obstacle preventing fuel cells revolutionising motor transport would have been removed. Before that happens, however, the cost of fuel cells needs to be reduced - they currently rely on expensive platinum catalysts. A low cost, precious metal-free fuel cell announced in late December could solve that problem