One of the defining features of the twenty-first century will be a transition from fossil fuels to other energy sources. To try to understand how this process might unfold, scholars have turned to past energy transitions for clues.

The main historical transitions were from biomass energy resources – such as wood, animal dung and agricultural waste – to fossil fuels: coal, oil and, most recently, natural gas. Another related transition was from thermal energy carriers (chiefly wood and coal) to electricity, itself generated from a wide variety of sources, beginning with coal and hydropower, then nuclear fission reactors and, more recently, wind, solar and geothermal energy.

A number of lessons about energy transitions have been distilled from historical research and published in a recent volume of the journal Energy Policy as well as some books and other academic articles.

First, the ways in which energy services are used – rather than the raw sources of energy as such – have often been key drivers of energy transitions. In a study of transitions for various British energy services and sectors, analyst Roger Fouquet found that the “main economic drivers identified for energy transitions were the opportunities to produce cheaper or better energy services”. For example, the shift from wood to coal as a household fuel source in eighteenth-century Britain was motivated mainly by growing scarcity – and hence rising prices – of wood; coal was much dirtier and more harmful to health when burned in the home. On the other hand, electrification was driven in the early stages mainly by demand for lighting – electric lighting was far superior to that derived from oil or gas lamps or candles.

The second insight from history – highlighted by Canadian professor Vaclav Smil, in his book, Energy transitions: history, requirements, prospects – is that past energy transitions were very gradual, taking several decades at least and in some cases over a century. However, Fouquet argues that the information and communication technology revolution could facilitate more rapid transitions in the future, since technologies can be copied and diffused more easily in the digital age.

The third major insight concerns the way new energy technologies are diffused. Charlie Wilson, of the University of East Anglia, has found some consistent patterns in the life cycles of different energy technologies – each seems to go through three stages.

First, in a formative stage that can last up to several decades, energy technologies undergo a period of experimentation and learning at relatively small unit and industry scales.

Second, in an upscaling stage, the unit size of an energy technology – such as the size and generation capacity of a coal-fired boiler, nuclear reactor or wind turbine – increases. The time taken for each technology to mature to its maximum scale varies. Nuclear power was one of the fastest, while natural-gas-fired power plants were much slower to mature.

Third, there is a growth phase for energy industries, an example being the number of wind turbines produced by factories in a year – which can occur up to two decades after the increase in unit size.

When plotted over time, these three stages together trace out familiar technology ‘S’ curves: growing gradually at first, then accelerating rapidly and finally slowing down as they approach technological efficiencies or market saturation.

These historical lessons suggest that the world has a long road to travel in its transition from fossil fuels to renewable energy. Current world primary energy supply is dominated by oil (33%), coal (27%) and gas (21%), with an additional 6% contributed by nuclear power derived from finite and depleting uranium supplies. Renewable energy makes up just 13% of primary energy: 2% from hydroelectricity, 10% from biomass and a paltry 1% from solar, wind and geothermal power combined.

The burning questions are how quickly these renewable technologies will reach optimum unit scales, and then how long it will take the industries to become large enough to produce meaningful aggregate energy capacity.

Some of the drivers for this next energy transition are similar to those identified earlier. Although there is a big debate about how long fossil fuel reserves will last, the rising trend in oil prices is definitely a major factor spurring the development of alternatives. Another driver is rising demand for modern energy services for the quarter of the world’s population that has no access to electricity, especially by the emerging middle classes in countries like China and India that are buying vehicles and household appliances en masse.

A novel driver is pollution and climate change concerns, although these have yet to translate into substantial global action to shift away from dirty fossil fuels.

The trouble is, as Smil points out, renewables have some major drawbacks: low energy density (joules per kilogram), low power density (watts per land area), intermittency, and limited geographical distribution.

It remains to be seen whether the transition from fossil fuels can be negotiated smoothly.