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TURN on the nearest switch. You won鈥檛 notice anything different; that is kind of the point. Yet in many places, there is a better chance than ever that the electricity coming out of the socket was generated by clean, renewable sources such as solar panels and wind turbines.

That is progress, of a sort. In most countries, however, most electricity still comes from climate-polluting, fossil-fuel sources. Your heating, too, almost undoubtedly uses fossil fuels, as does your car, if you have one. Most goods you buy require fossil fuels to make them and transport them to the shop or to your front door. And if this is the world you live in, you are a lucky one: access to affordable, reliable, convenient energy of any sort is far from a given in many parts of the globe.

That is the background for an energy revolution that needs to happen over the next three decades if we are to hit net-zero carbon emissions, and limit global warming to a 鈥渟afe鈥� 1.5掳C. 鈥淭he scale and speed of the efforts demanded by this critical and formidable goal make this perhaps the greatest challenge humankind has ever faced,鈥� said Fatih Birol, the head of the International Energy Agency (IEA), in May, as he unveiled the agency鈥檚 landmark report .

That report contained few surprises about what we need to do. The big two questions remaining are whether we will actually do it, and what sort of world we end up making in the process.

Stories about renewable energy鈥檚 rise can make it seem as if we were already doing brilliantly at boosting its use. Not so, sadly. Back in the 1960s, 6 per cent of global energy came from low-carbon sources, mainly nuclear energy. By 1994, this was 14 per cent, but since then, growth has largely stalled. In 2019, the last year for which we have good figures, fossil fuels supplied 84 per cent of the world鈥檚 total energy, once 鈥渢raditional鈥� biomass 鈥� wood used for cooking and so on 鈥� is excluded. Of the remaining 16 per cent, hydroelectricity supplied 6 per cent, with nuclear on 4 per cent. Wind and solar supply less than 4 per cent of global energy.

Meanwhile, global energy demand has been growing steadily, from 40,000 terawatt-hours (TWh) in 1965 to 160,000 TWh today. Installed renewables capacity isn鈥檛 growing fast enough to cover this rising demand.

Fourfold challenge

Yet there are grounds for optimism. Not that long ago, many people doubted whether wind and solar power could ever supply a sizeable amount of energy at a reasonable cost. No longer. 鈥淚t鈥檚 clear that renewables have massively outperformed most people鈥檚 expectations and continue to do so on a regular basis,鈥� says Simon Evans at , a UK website specialising in climate analysis. 鈥淲e are getting closer to the point where renewables are going to genuinely cut into fossil fuels.鈥�

The transition to a net-zero energy system requires four things to happen. First, electricity generation needs to switch to renewables, replacing all that is generated using fossil fuels. Second, everything that can run on electricity, must: cars, trains, heating systems and industrial processes such as making steel. Third, we need to find truly sustainable ways to power planes, ships and sectors that cannot be easily electrified, for instance by removing carbon directly from the atmosphere and using renewable power to turn it into fuel.

All this will require a lot more electricity. The Net Zero By 2050 report envisages global electricity generation rising from what it is currently, 27,000 TWh a year, representing a sixth of all the energy we consume, to more than 50,000 TWh by 2050, representing nearly half. For that to compute, a fourth thing needs to happen: a huge increase in energy efficiency.

Some countries have made strides with the first challenge. In the UK, for instance, the proportion of low-carbon electricity has soared from a fifth to over half in the past decade, thanks largely to growing wind power capacity. But globally, a decline in nuclear power means that the proportion of electricity derived from low-carbon sources in 2019, 37 per cent, has hardly budged since the 1980s.

Nuclear energy could play a big part in replacing fossil fuels, but the costs, long construction times and lack of public and political support in many countries 鈥� not helped by the 2011 Fukushima disaster in Japan 鈥� mean it isn鈥檛 likely to. The IEA envisages only a 25 per cent rise in nuclear power capacity by 2030, driven mainly by new plants in China and extensions to the operational lives of existing plants. Meanwhile, nuclear fusion reactors, which aim to mimic the sun鈥檚 power-generation processes, are still decades from playing any practical part 鈥� if they ever will.

In general, technologies such as nuclear and tidal energy that involve massive, hugely expensive projects probably won鈥檛 play a big part in the energy transition, says energy researcher at the University of Oxford. Thanks to huge efficiency improvements and falling prices, it is a different story with wind turbines and solar panels, which can be mass-produced and positioned where needed. 鈥淧hotovoltaic panels have improved out of all recognition, but a nuclear power station looks much the same,鈥� says Eyre. The IEA anticipates wind and solar alone supplying nearly half of global electricity by 2050, with a third coming from nuclear, hydropower and other renewables, and fossil fuels supplying just a fifth.

More might be possible. Not everyone thinks that 100 per cent renewables generation is achievable, but many agree that we can get much closer to it than we once thought. 鈥淥ver time, the perceived limit has gone up and up,鈥� says Evans.

The main stumbling block is the seasonal variability of wind and solar power. Batteries are great for storing power and smoothing out variations over hours or days, says Jenny Chase, head of solar analysis at BloombergNEF, but sometimes there is no wind and little sun for weeks. 鈥淏uilding a battery for that would be incredibly expensive,鈥� she says.

If people switch to electricity for heating, there will also be much bigger surges in electricity demand during cold snaps. Grids must be designed to avoid incidents like the power crisis in Texas this past February, when widespread outages led to shortages of water, food and heat, and to the deaths of at least 150 people. Some politicians blamed this on renewables, but it was, in fact, due to gas plants failing to cope with freezing conditions.

There are ways round the seasonal variability problem. One is to maintain or build more nuclear and hydropower plants to supply 鈥渂aseline鈥� power. Another is to create continent-wide supergrids: the sun is always shining or the wind blowing somewhere. Conventional alternating current power lines lose a lot of energy over large distances, but hooking up distant regions using high-voltage direct current lines greatly reduces these losses. The longest of these lines to date, completed in 2019, carries electricity in the Brazilian Amazon to Rio de Janeiro.

More energy storage will also be vital. Pumped hydroelectric plants, which use excess energy to shunt water uphill into reservoirs, from where it can be released for powering turbines when needed, have long existed. Similar concepts include pumping compressed air into old mines. Then there is using excess electricity to split water to produce hydrogen, large quantities of which can be stored cheaply. Which will we end up using? 鈥淚 think it鈥檚 probably all of the above,鈥� says Chase.

Electrify, electrify, electrify

All of the above will become all the more important as we tackle the second challenge, electrifying as much energy consumption as possible. Again, in some areas, we have made a start. Electric cars are gaining market share in many countries, helped by plans to ban the sale of petrol and diesel cars. 鈥淎 few years ago, if you had said that by 2021 a very large number of the world鈥檚 leading car companies would be planning an all-electric future, I鈥檓 not sure I would have believed you,鈥� says Evans. 鈥淭hat鈥檚 quite a remarkable turnaround.鈥� Yet there is a very long road to travel and very little time. The IEA鈥檚 net-zero road map says 60 per cent of cars sold globally need to be electric by 2030. In 2020, the figure had reached just 5 per cent.

When it comes to switching heating to run on electricity, the challenge is even greater. About a quarter of all global energy demand is for heating and cooling the spaces we live, work and play in. A few countries, such as Sweden, have greened their heating systems, but most still rely heavily on fossil fuels. In the UK, for instance, 85 per cent of homes have gas boilers, although the government is reportedly considering a ban on their sale from 2035.

Many gas companies are promoting a switch to hydrogen boilers, but that isn鈥檛 a green option as things stand. Although 鈥済reen鈥� hydrogen can be made by splitting water using clean electricity, currently more than 95 per cent of hydrogen we use is derived from fossil fuels, releasing carbon dioxide in the process.

Using renewable electricity directly rather than employing it to produce hydrogen is a lot more efficient, in any case. Heat pumps, which extract heat from the air, water or ground to produce three times as much heat energy as they consume in electrical energy, are seen as the best solution by many, including Eyre. But they aren鈥檛 a straight swap for gas boilers. They are bulkier, more expensive for now, sometimes require radiators to be replaced and work best in well-insulated houses. They should save people money in the long run, however, and many can operate in reverse to cool houses in summer. The UK鈥檚 official climate adviser, the Climate Change Committee (CCC), is recommending hybrid systems that switch to using hydrogen or natural gas on very cold days.

Efforts to electrify industrial processes have even further to go. Swedish company SSAB, for instance, is building a pilot steel plant powered solely by electricity and hydrogen, but that is only emission-free if both the electricity and hydrogen come from renewable sources. This is the kind of thing we need to reserve truly green hydrogen for in the next few decades, the CCC says, rather than using it for heating, where there are alternatives.

For some things, electrification simply isn鈥檛 an option. The weight of the batteries needed to power a long-haul aeroplane, for example, is so great that it would never get off the ground. 鈥淭he energy density of batteries is just really, really low,鈥� says at the University of Erfurt in Germany.

So we are still probably going to need liquid fuels. The aviation industry thinks biofuels are a big part of the answer, but this cure could be worse than the disease. Biofuels can increase poverty by pushing up food prices, and harm biodiversity by boosting demand for farmland, driving deforestation. Accounting for such knock-on effects, many biofuels actually produce more CO₂ than conventional fuels: using palm oil-based biofuels triples emissions, for instance. A more sustainable solution could be capturing carbon from the air and using renewable electricity. As yet, such 鈥渘egative carbon鈥� solutions are barely off the drawing board.

None of these transitions is going to happen by itself, either. There are big upfront costs in building up wind and solar generation capacity, and much of what has happened so far has depended on subsidies. Record low interest rates, meaning a lot of cheap money available for investment, have also helped.

Once installed, wind and solar have become the 鈥� so much so that in some countries, particularly Spain, projects are going ahead without subsidies. But as the proportion of electricity coming from renewable sources rises, it gets harder to sell that electricity for a profit, because so much is produced when the weather conditions are right.

To achieve the huge increase in renewables required, strong state intervention will be needed, for example through carbon pricing 鈥� a tax on fossil fuels, essentially 鈥� or cutting the many fossil fuel subsidies that still exist. Simply banning the sale of tech such as combustion engines and gas boilers can work too. Whatever the policies, says Eyre, a clear, long-term strategy is vital to give investors the confidence to bet on renewables. 鈥淚 don鈥檛 think it鈥檚 a straightforward case of saying there should be more subsidies for solar any more,鈥� says Chase. 鈥淚t鈥檚 more about planning for a high solar future.鈥�

The challenge is even greater in some countries. Take Ghana, which set itself a target of 10 per cent renewables by 2020 and did offer some subsidies. It achieved just 0.5 per cent, says at the University of Ghana in Accra. The problem, replicated in many lower-income countries, is that many people still don鈥檛 have access to electricity at all, he says. Solar panels might be cheaper in the long run, but they generally cost more than fossil fuel generators upfront and only provide power during the day 鈥� batteries are a big additional cost. Officials with tight budgets still opt for fossil fuels.

鈥淲e want to transition to renewables because climate change is a big factor,鈥� says Afful-Dadzie. 鈥淏ut it鈥檚 very difficult.鈥� The world invested about $280 billion in renewables in 2019, of that was spent in the group of higher-income countries known as the OECD, along with China, India and Brazil, says Goldthau.

As part of international climate agreements, high-income countries are supposed to be providing $100 billion a year to help other nations cut emissions and adapt to climate change. But this target isn鈥檛 being met, and campaigners say much of the money that has been pledged is coming from existing aid budgets. At the COP26 climate summit in the UK in November, they want . The energy transition will require close cooperation between countries to share technology, align policies and provide financial assistance where needed, for example to allow lower-income countries to 鈥渓eapfrog鈥� to clean energy technologies. It is far from a given that this will happen 鈥� other, less happy geopolitical scenarios are very much imaginable.

A world powered mainly by renewables is certainly going to be a very different place. In many ways, it should be better: cleaner and healthier, and with far less air pollution. But we must get there first, and that isn鈥檛 just a technological challenge. 鈥淥ur pathway requires vast amounts of investment, innovation, skilful policy design and implementation, technology deployment, infrastructure building, international cooperation and efforts across many other areas,鈥� as the IEA road map towards net zero puts it.

鈥淲e鈥檝e seen exceptional levels of wind and solar expansion, and they are getting closer to cutting into fossil fuels,鈥� says Evans. But even that falls way, way short of what we need. Making the new energy world reality is going to take all we鈥檝e got.