Renewable energy is doing well around the world - supplying around 22% of global electricity.

In 2013, the world achieved 1,560 gigawatts (GW) of renewable electricity generation capacity - almost five times more than the 331 GW of nuclear generation capacity. And where nuclear power supplied 11% of the world's electricity, renewables about twice as much.

Hydro is the biggest electricity supplying renewable, with around 1,000GW of generation capacity in place. Wind comes next at 318GW, while PV solar is at around 139GW globally. And on the heat side, along with biomass use, solar thermal is now at 326GW, much of it in China.

Will renewables continue to grow? Globally, the recession hit all investment, and total global investment in 'clean energy' of all sorts fell 9% in 2013 to $254bn, following a 9% drop in 2012, according to Bloomberg New Energy Finance.

Renewables take 72% share of new generating capacity

But within that, renewables have held up quite well. The REN21 group says 2013 marked the sixth consecutive year in which renewables had the majority share of new electricity generating capacity, with a 72% share in 2013.

REN21 may be seen as partisan, but the International Energy Association is surely not. Its 2013 Medium Term Renewable Energy Market report says that wind, solar, bio-energy and geothermal use may grow 40% by 2018, twice the 20% rate in 2011, supplying 25% of global electricity by 2018.

Longer term, its new Energy Technology Perpectives report notes that global nuclear capacity "is stagnating at this time" , while in its High Renewables Scenario, solar PV becomes the dominant electricity source by 2040, providing 26% of global generation by 2050'.

The similarly non-partisan World Energy Council (WEC), has a 2050 global energy market-led 'Jazz' scenario, in which the share of renewables in electricity generation is 31% and in a more policy-led 'Symphony' scenario, 48%.

In terms of the role that nuclear power may play, WEC said that while "the share of renewable energy sources will increase from around 15% in 2010 [of primary energy] to almost 20% in Jazz in 2050 and almost 30% in Symphony in 2050, nuclear energy will contribute approximately 4% of total primary energy supply in Jazz in 2050 and 11% in Symphony globally - compared to 6% in 2010."

Nuclear nations will remain a minority

Clearly, if they are right, some countries will still be using nuclear, but they will remain a minority. At present 30 or so countries, out of the 196 countries in the world, use nuclear at some level, whereas around 50 countries get most (over 50%) of their electricity from renewables (mainly hydro so far) some much more and for around a dozen of them near 100%.

And many more are joining them, while defections from nuclear continue: it seems to be stalled globally, with closures mostly wiping out new starts.

While that may allow more funding to flow to support renewables expansion, fossil fuels still dominate and receive a lot of subsides - the IEA says around six times more than do renewables. Unless that changes, and we also start cutting back on energy demand, there is a risk that, with weak carbon caps, fossil fuel use will continue to grow.

The IEA is keen to promote energy efficiency and clearly that should be a priority. Both Germany and France are now committed to cut demand by 50% by 2050. But however much you cut demand you will still need energy supplies.

How far can renewables expand?

If we want to avoid a retreat to nuclear and don't think fossil fuel CCS will help much, or should be relied on, then, if emissions are to be cut rapidly, renewables will have to expand even faster than they are already. Can they?

In the short term IRENA, the International Renewable Energy Agency, says that by 2030, renewables could supply 30-36% of global energy, depending on the level of energy saving - which is much more than the WEC envisages even by 2050.

Looking at some equally optimistic projections for 2050, there have been a series of scenarios published which go well beyond what the IEA and WEC envisage. Some suggest that, given proper support, by then, renewables could supply near 100% of the EU's electricity and perhaps even all of its energy by 2050.

Others go even further and says renewables could supply up to 100% of the whole world's electricity - and perhaps even all of its energy by around 2050.

More studies are emerging covering Korea, Japan, China, India, all saying roughly the same thing: up to 100% (of power and maybe of all energy) is possible by 2050 with balanced systems.

They may all be overstated. Not all countries would want to or be able to accelerate to 100% by 2050. But the quite cautious Global Energy Assessment (GEA), produced by an international team led by the International Institute for Applied Systems Analysis, noted that the share of renewable energy in global primary energy could increase "to between 30% to 75%, and in some regions exceed 90%, by 2050".

Nuclear uncertainties

There is perhaps some room in there for nuclear, which some countries may wish to keep and even expand (Russia for example). But GEA saw nuclear energy "as a choice, not a requirement".

Someone may eventually come up with a safe, technically and economically viable nuclear technology - but the most promoted technologies, such as the liquid fluoride thorium reactor (LFTR), or nuclear fusion, are surely half a century or more from commercial maturity.

And enormous technical hurdles remain to be overcome, for example the apparently simple question of what materials to build them with, capable of withstanding decades of intense neutron bombardment. Such investments are, shall we say, speculative and uncertain on any timescale.

By contrast renewables offer so much more and are nearly all much further advanced. That's not to say it will be easy to ramp them up fast. But their costs are falling rapidly, especially for PV, as rates of deployment rise.

Fossil fuels can be squeezed out by 2050

Given the political will, coupled with serious attention to energy saving, it should be possible to squeeze most fossil fuels out of the system in many places by around 2050, in some later and in some places earlier.

That still leaves fossil fuels playing a role for some time ahead - but as renewables and energy savings bite, it will be a diminishing one. Fossil fuel fired plants will be needed for a while for balancing grids as variable renewables expand.

Combined Heat and Power (CHP) plants can use fossil gas more efficiently and, linked to heat stores and district heating networks, can help with grid balancing. Gradually that role can taken over by green gas fired CHP plants, using biogas and gas produced from surplus wind and solar power, when production exceeds demand.

We will also need new energy storage systems and 'smart grid' demand side management measures, and the development of a continental-scale supergrid will allow countries to balance their electricity supply and demand, smoothing out local peaks of production and demand.

First, we must decide what to aim for

While fossil fuels are still used, CCS might help reduce some of the resultant emissions, although some see the development of biomass energy carbon capture and storage (BECCS) as a better bet, since that would be carbon negative. Assuming you are happy with using biomass!

There are of courses many other strategic issues to face like this: should we aim mainly for electrification or for green heat and gas as well? What's the right scale for projects? Can more of them be locally owned and controlled?

But the basic point is that we can head for a near 100% renewable future should we wish. The key questions are how quickly can, should or must we do that?

David Elliott is Emeritus Professor of Technology Policy at the Open University.

David's latest book, 'Renewables: a review of sustainable energy supply options' is available from the Institute of Physics and the Network for Alternative Technology and Technology Assessment.