A good idea of the numbers regarding various energy sources can be found in David MacKay’s excellent book Sustainable Energy Without The Hot Air. His intentionally rough, but very informative estimates give the physical scale on which renewables such as wind and solar energy need to operate to be effective. Consider a bar of an electric fire which uses energy at a rate of about a kilowatt (1000 Watts). The rate at which sunlight supplies energy in space is about 1.3 kilowatts per square metre.  By the time this energy finds its way down to us here in the UK we get in the order of a few (wind) to tens (solar) of Watts per square metre. This means we need to use a lot of area to capture this energy - we in the ‘developed world’ use about 5-10 kilowatts each, so think football pitches per person.

In some cases geography ‘funnels’ the energy into a smaller area for us to collect, which is why in the case of tidal energy a barrage is being proposed to harness the energy of the Severn estuary bore, with all the accompanying concerns about impact on wildlife. Or we can go to the places on the planet where the supply is richest, so for solar, a nice desert nearer to the equator would gain us a good factor of ten. Of course there are still some losses getting the energy back home.

There is the additional problem of how we get this energy into our cars. Biofuels give up to about a Watt per square metre of field for sugar cane grown in sunny Brazil; less for sugar beet in the UK (this doesn’t include the energy needed for fertilizers and production).  Land planted for biofuel is then not available for food production and again, the area of farmland needed to make a significant impact on our energy needs is substantial.

It is highly unlikely that we will significantly reduce our energy needs - ‘significantly’ meaning getting by on maybe 10% of what we use now. There are of course good things that can be done, and relatively cheaply, by insulating our lofts properly and not needing as much ‘stuff’ in our lives or as much meat in our diets (those who make a living manufacturing and selling us this stuff might not be happy with this). Also one might hope that our global society strives to do the right thing and give decent living conditions - electricity, clean water, adequate housing, access to healthcare and education - to everyone, not just to the ‘developed world’. Currently ‘developing’ countries use on average about a tenth of the energy per person as we do in the developed world.

We can, of course, carry on burning fossil fuels for the time being, but even setting aside concerns for climate change, these resources are good for one or two more generations - estimates vary widely. If the link between fossil fuel burning and global warming is real, and there is considerable evidence to support it, then clearly we need to switch from fossil fuels now. If things are as bad as many models suggest, we will still also need geo-engineering solutions. These include controlled global dimming to reduce the amount of sunlight falling on the planet, the creation of algal blooms and other means of carbon bio-capture, and we can try to ‘sequester’ carbon by storing it underground in old oil wells.  More work is needed here, as practically we are far from being able to predict the outcome of global scale experiments on our climate.

One now-term possibility for carbon neutral energy supply is nuclear fission. This is technology that is operational now, and could supply much of our energy needs. If we moved over to significant energy production from fission there is again a few generations worth of mined uranium (the first step – fuel) available, again, estimates vary. There is a lot more if we can efficiently extract it from seawater. There are of course issues here – not least the relationship between this technology and that needed for weapons development.

One future possibility for clean, carbon neutral energy is nuclear fusion, the process that drives the sun. Unlike fission, which splits heavy atoms and results in highly radioactive waste materials, fusion pushes together atoms of hydrogen, the lightest and most abundant element in the universe, to create helium, an inert element that most of us know as the gas which fills party balloons.  In doing so energy is released, but no unpleasant waste. The difficulty is that this reaction only happens at high temperatures and/or densities. The sun is large enough that it contains this hot reacting gas by its gravitational pull. For a much smaller reactor on earth, another method is needed- donut shaped tokamaks do this by trapping the hot charged (plasma) gas in magnetic fields. High powered lasers use the radiation pressure of light itself to compress and trap the reacting gas.

Although we are some way towards demonstrating the possibility of sustained fusion, we are still a long way from implementation in power stations. An analogy with 20th century technology might be that we’re in the age of the biplane when a London to Paris flight was front page news.  Where we need to be is in the jet age in which an airliner resists metal fatigue and corrosion to the point that it can be used safely for 20 years non stop and turned around at an airport in 30 minutes. What drove this scale of developments in avionics, electronics, airframe and propulsion is far beyond the straightforward operation of the commercial sector.

So where exactly are we with fusion? There is a road map in place to help take us from the biplane to the jet age, and it’s a road map that has been ‘bought into’ by a reassuring number of partners: China, the EU, India, Japan, Korea, Russia and the USA. ITER (Latin for ‘The Way’) is a ‘proof of concept’ tokomak (the device used for containing the incredibly hot fusion plasma within a powerful magnetic field) due to give us ‘first plasma’ in 2018 and in the subsequent 20 years of operation will demonstrate sustained fusion burning of plasma. This will be followed by DEMO which will be the first demonstration power plant that generates fusion energy.

If ITER and its successors are successful, our world will enter the long heralded and much awaited Age of Fusion - an age when mankind will finally start to generate a significant part of its energy needs from an inexhaustible, environmentally benign, and universally available resource.

Will it happen that way? Cost overruns and budget issues in the current economic climate, as well as technological hurdles may combine to delay things, but as the ‘opportunity cost’ of not getting fusion power into the grid gets higher and higher, so will the political will to make it happen.

Sandra Chapman is primarily a plasma astrophysicist. She is currently Professor of Physics and Director of the Centre for Fusion, Space and Astrophysics at the University of Warwick. She also a core member of Warwick’s Complexity Complex.