How can we generate a hundred per cent renewable electricity?

Installing solar panels

Charlie Cook, a student on the first cohort of Imperial’s new MSc in Climate Change, Management and Finance, checks on the roadmap leading to a world with electricity generated from a hundred per cent renewable sources.

If you don’t know where you’re going, any road will take you there; Lewis Carroll’s Cheshire Cat points out to Alice.

The Paris Agreement has set our sights on a clear goal: a world where global temperature rise is limited to 1.5°C, or at the very most 2°C. If this is our destination, what does the map that will take us there look like?

At least part of the answer lies in how quickly we can do away with fossil fuels and generate a hundred per cent of our electricity from renewable sources, such as solar or wind power. To achieve this research institutions and policymakers must determine both what mix of energy sources are required, and how soon they need to be built.

The destination

Figure 1. 25 per cent of global emissions come from electricity and heat production, which could be reduced by building clean electricity grids (Intergovernmental Panel on Climate Change (IPCC), 2014)

What do the Paris targets mean in terms of reducing greenhouse gas emissions? The ‘Feasibility of limiting warming to 1.5°C and 2°C’ report by Climate Analytics concludes that “global energy and industry CO2 emissions must reach zero by around 2050” in order to limit global warming to 1.5˚C. Therefore the monumental challenge ahead is to build a carbon neutral society in just over 30 years.

Currently, the electricity and heating sector accounts for a quarter of global greenhouse gas emissions (Figure 1). Therefore, each new wind turbine, wave turbine and solar PV panel chips away at this large chunk of the pie, and the overall size of the pie itself .

Planning the route

Several models agree that electricity grids powered by a hundred percent renewable energy are capable of providing for national electricity demand day and night, 365 days a year and even during extreme circumstances (See Table 1).

Table 1. (Jacobson & Delucchi, 2009)

These models follow a common theme. By 2050, electrical power generation is derived from a combination of technologies including wind turbines, wave turbines and solar photovoltaic panels plus base load generation. In a traditional system, the baseload is a source of continuous electricity supply to the grid. The models typically suggest that base load is provided by biomass, biofuel, nuclear or carbon capture and storage (CCS).

In 2009, Jacobson and Delucchi proposed a scenario in which electricity is produced almost entirely by a combination of wind, water and sun (coined WWS) as early as 2030. The plan was published in 2010. This is one of the most optimistic forecasts, providing the cleanest energy mix imaginable, but it allows us to put the alternative models and scenarios into perspective.

According to this study, there is no need for biomass, biofuel, nuclear or CCS; which lead to negative consequences such as nuclear waste and competition for arable land. Instead, they suggest a combination of wind, water and sun can meet the intermittent, peak and base load electricity demand.

Around the world, this scenario would require:

  • 3.8 million wind turbines (19000 GW)
  • 49,000 concentrated solar power plants (14,700 GW)
  • 40,000 solar photovoltaic plants (12,000 GW)
  • 1.7 billion rooftop solar photovoltaic systems (5,100 GW)
  • 900 hydroelectric plants (1170 GW)
  • 720,000 wave turbines (540 GW)
  • 5,350 geothermal plants (535 GW)
  • 490,000 tidal turbines (490 GW)

All these gigawatt (GW) values are installed capacity, which is the potential or peak power of all the installed turbines combined.

If you’re interested in climate solutions, you should check out the Solutions Project which was founded by Mark Jacobson, one of the two authors of this paper.

So, how are we doing so far?

Unfolding the map

Taking solar as an example, let’s take a look at what’s currently installed, and the rate at which we would need to install each technology to reach the numbers set out by Jacobson and Delucchi.

The growth of solar power on a global scale has consistently doubled every two years for the past 15 years. Behind the drama of policy U-turns and industry difficulties is a very smooth, steep curve. The same consistent growth is true for other renewable energy technologies

As of 2015, 237 GW of solar technology is up and running. This is 0.9 per cent of the WWS target of 26,700 GW in 2030.

Figure 2. On a global scale solar has been growing at consistently high rate for 15 years Source (years 2000–2013): Global Market Outlook for Photovoltaics 2014-2018 (EPIA, 2014), Source (year 2014): Global Market Outlook for Solar Power 2015-2019 (SSE, 2014), *based on prediction by Mercom.

There may be a long way to go, but at its current growth rate of 140.6 per cent (2000-2015) solar would reach its target by 2029. Even a slightly slower growth rate of 137 per cent would see solar reach the target in 2030.


Keeping track

The WWS scenario puts almost all the onus on wind and solar to achieve the cleanest possible energy mix. However, it seems unlikely that the nuclear industry will grind to a halt any time soon. So any increase in nuclear, biomass, biofuel or CCS capacity, whilst arguably being less preferential options, would reduce the need for quite so much wind and solar.

Regardless of the exact path that we take, emissions reductions targets are abstract and difficult to follow. Conversely, following the installed capacity of wind and solar is relatively straight forward and provides a simple check for global progress towards clean electricity.

Time will tell if renewable capacity in the coming years will tally with the roadmaps, giving scientists, government and industry an idea of progress in the most significant technological transition since the industrial revolution.

Charlie Cook has a MEng Civil Engineering from the University of Nottingham and spent two years working at CERN before starting at Imperial this week on the first cohort of the new MSc in Climate Change, Management and Finance.

Read more:

Charlie Cook’s blog: Charlie on energy

Blog: Why subsidise renewable energy?
Ajay Gambhir addresses some of the criticisms often levelled against efforts to mitigate climate change.

Blog: Apollo has landed: the role of the private sector in completing the race for 100% renewables
Dr Charles Donovan and Christopher Corbishley discuss the falling cost of renewables.

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