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can be taken up without imposing extra costs. They may even deliver a system that is actually more economically viable than the present one. Moreover, renewables are now getting so cheap that their uptake may accelerate under market pressures, regardless of whether climate change or pollution is taken seriously (PEI 2018).

That opens up some interesting possibilities. Although the environmental and climate benefits are still obviously important, some renewable energy proponents have suggested that renewables no longer need to use climate change as a justification. They can now prosper on their own economic merits. Indeed, for many countries, it is claimed, the direct economic benefits, and their role in fuel-cost saving, have become, or will become, the main motivation for investment in renewables. Thus it has been argued that ‘renewable generation will stand on its own commercial feet and cutting down emissions will become a fortuitous side-effect’ (Swift-Hook 2016).

      That may be going too far, but it is certainly clear that the cost of renewables has fallen dramatically, in particular for PV solar (Lazard 2018a). According to the International Monetary Fund, ‘between 2009 and 2017, prices of solar photovoltaics and onshore wind turbines fell most rapidly, dropping by 76% and 34%, respectively – making these energy sources competitive alternatives to fossil fuels and more traditional low-carbon sources’ (IMF 2019).

      That trend also extends to offshore wind, initially seen as one of the most expensive renewable energy options, with ‘strike prices’ under the first round of the UK’s CfD capacity auction system in 2015 reaching nearly £120/MWh. In the 2019 CfD round, strike prices for some successful project bids fell to just under £40/MWh, around a third of the earlier figure (New Power 2019).

      These cost falls have been important in propelling renewable energy to the fore, and they are likely to continue. So it has become very hard for opponents to maintain resistance to what seems likely to be an unstoppable change dynamic. However, they do sometimes try. For example, it is ironic that the incumbent fossil and nuclear interests, which often initially dismissed the renewable energy options as totally irrelevant, now have to fight to protect their market shares as opposition to fossil fuel use mounts, nuclear costs rise (Portugal-Pereira et al. 2018) and renewables win out across the board. They already supply more than 26% of global electricity (REN21 2019), compared to nuclear power at around 10%, and are displacing fossil fuels in many markets.

Interestingly, under increasing pressure from renewables, some of the fossil and nuclear lobbies have therefore changed tack a little and are now arguing that renewables are still problematic since they cannot expand fast enough to deal with climate change (BP 2018a), with some climate change sceptics joining in (Lyman 2019), this after they have all resisted change and spent so long trying to stop renewables from getting started. Some of the incumbents may continue to resist, but over 185 companies so far have signed up to ‘100% by 2050’ renewable electricity targets (RE100 2019).

      As argued above, what has changed things is not a sudden extra concern about climate or air pollution (although, as noted, that has happened and has helped) or even what some see as a collapse of nuclear power as a future option (WNISR 2019) but the fact that the cost of renewables has fallen dramatically. Arguably, a new economic dynamic has, at least partially, taken over, with renewables well placed to become the dominant option.

      However, while the case for renewables does look strong, they are up against a set of well-established energy technologies, well entrenched in lucrative markets. The fossil fuel-based incumbents look to new carbon capture technology to allow them to stay in the game, and the nuclear lobby similarly looks to new technology to improve its economics. To set the scene, Box 1.2 provides a short summary of the main impacts of the options on offer, and I will be looking at the options, and at the issues raised by them, in more detail later.

       Box 1.2 The new energy options – a summary of impacts and issues

      The use of naturally and continuously replenished renewable energy flows, like the winds, waves, tides and solar heat/light, produces no direct carbon dioxide (CO₂) or other emissions. There will be indirect emissions due to the use of fossil fuel for the construction of the technologies and for the production of associated materials, but that is true, at present, for all energy technologies. Once built, renewable energy-based power plants, like wind turbines and solar farms, differ from the rest in not needing any fuel to run. However, they may have some local impacts, and some (but not all) produce variable power outputs.

Those issues apart, they are strong ‘clean energy’ contenders, arguably more so than nuclear plants, which, although they do not produce CO₂ in operation, rely on the use of fossil fuel to mine and process/enrich their fuel, a very energy-intensive process, thus incurring a carbon debt. There are also long-lived radioactive wastes to deal with, as well as the risk of leaks and unplanned release of radioactive material. Global fissile fuel reserves are also finite; they are not a renewed resource. Nuclear fusion, as opposed to fission, is still some way off as a practical option and may remain so but might have fewer fuel resource limitations, although there could still be risks and radiological implications.

      It is possible to capture and store the CO₂ produced by fossil fuel combustion plants, but, although that might allow us to continue to use fossil fuel, as I will be describing, there are operational and economic limitations to this arguably rather inelegant ‘end of pipe’ engineering approach to post-combustion ‘carbon capture and storage’. The environmental argument is that we should not be burning fossil fuel in the first place nor trying to find places to store the resultant CO₂ safely and indefinitely. The global fossil fuel resource is in any case finite, so using it is not a long-term option, even ignoring CO₂ and other emissions and impacts, for example in relation to air quality.

      The combustion of biomass (plants, wood and other bio-materials), and then the capture and storage of the CO₂ produced, is an option. In theory, since CO₂ is absorbed when biomass is grown, that process would be carbon negative, reducing net atmospheric CO₂ levels. However, to have a significant CO₂ impact, in addition to vast CO₂ storage requirements, very large amounts of biomass would have to be grown and burnt, with large land-use and ecological impacts.

      The capture and storage of CO₂ direct from the air is also possible, although that process would use energy rather than generate it. As an alternative, some of this CO₂, or the CO₂ from power plants, might be used to make new hydrocarbon fuels, if a source of hydrogen were available, for example produced using renewable energy. However, burning the resultant synthetic hydrocarbon fuels would release the CO₂ again. It might be better to use the ‘green’ hydrogen direct as a fuel since its combustion only produces water vapour.

      I will be coming back to these various options, issues and choices later, for example looking at costs, but from this short summary it does look as though, in terms of clean energy supply, renewables have the edge environmentally.

Can renewables deliver?

      While in general terms the prospects for the future of renewables may look positive, and the overall case for alternatives may look poor, the resistance of incumbents, and some of the arguments against renewables that they have adopted, do have to be faced. A central issue raised is the question of whether renewables can expand rapidly enough to meet global energy needs.

      This was met head on in a scenario published initially in 2009 in Scientific American (Jacobson and Delucchi 2009) and then more formally in 2011 (Jacobson and Delucchi 2011) and developed in their subsequent studies. It was suggested that a global target of obtaining 100% of all energy from renewables by 2050 was viable, at reasonable cost. That was ridiculed by critics as impossible, and there were debates over methodology (Clack et al. 2017). However, now, with several countries already above 50% and many dozens of further studies from around the world suggesting that very high renewables shares are possible (Stanford 2019), the debate is more about total-system costs and whether it will ‘only’ be 70%, or more than 80% (of electricity), globally by 2050 (IRENA 2017a), or how to do better

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