Think of renewable energy and you probably focus on wind and solar power, or perhaps hydropower, biomass and anaerobic digestion. But there are exciting innovations emerging in the sector which seem to be even more futuristic.

Underground liquid magma is being researched in Iceland, taking geothermal to a new level by accessing 1,000 degree C magma located deep underneath the surface of the Earth. This could produce ten times the heat and electricity of standard geothermal.

Trees are being assessed for wind energy because of the way that they sway in stormy wind conditions. Tree vibrations have already been found to be suitable for energy conversion, and the concept has been proven on a tiny test basis to date. The next stage is to take the concept to real tree conditions in a forest in a working piezoelectric electricity array.

Meanwhile, bacteria are being looked at for battery power. Some strains of bacteria are known to produce energy, and Harvard University researchers are developing a battery that is powered by dirt. The technology is being developed with off-grid developing-country regions in mind, as the batteries would be very cheap to make if they could be produced effectively.

And Sweden is looking at waste management and aiming to divert 99pc of its rubbish away from landfill and instead towards waste to energy plants. Already half of the country's domestic waste goes to these EfW plants, which takes energy from incinerator steam. The country is so good at it that it already imports over 800,000 tonnes of rubbish every year for its 32 processing plants.

But the prize for futuristic green energy has to go to Las Vegas and its kinetic streetlights, which are now being powered by footsteps thanks to kinetic energy pads that are housed in the city's walkways.