Energy density is the amount of energy stored in a given system per unit volume—and it is also the main reason why renewables have taken so long to disrupt the energy industry, and move things away from oil- and gas-based energy.
Of course, there are also issues about consumption, power usage and energy management, plus the economics of de-centralization of power generation and consumption—but energy density is crucial. The energy density equation dictates where and how you can extract, store and consume energy. It also limits the type of energy (for example, chemical, mechanical or electrical). It is therefore an essential part of supporting the energy needs of industry, mobility and consumers.
Understanding energy density
The highest energy density platforms are currently chemical- or nuclear-based. In other words, they depend on chemical or nuclear reactions to generate energy—for example, nuclear fusion or fission, chemical combustion, or fuel cells. All of these provide a continuous and predictable energy output as long the source is available. Renewables, however, only provide energy intermittently—for example, when the wind blows or the sun shines. They depend on external forces, including wind, water and light. To enable useful energy distribution and consumption, they therefore require an additional energy storage platform.
Historically, the scale of hydrocarbon extraction and processing has propelled industrialisation, and In relatively recent history, the Ford Model T and Honda Cub fueled the industrialization of the US and Asia. Coal-based factories drove the UK’s Industrial Revolution. Economic activity and industrialization increased as the energy density of energy sources improved. For example, as the world moved from coal-powered trains through diesel/electric to fully electric, speed moved from Stephenson’s Rocket’s 12mph to the 217mph seen on China’s Beijing to Shanghai line this century. However, there is a price. The consumption of coal has increased by an order of magnitude for the same energy density profile.
The world in 2021
The world is currently heavily dependent on hydrocarbon sources and exposed to the associated climate and pollution risks. The transition to renewables and Net Zero targets has already taken a while. Based on current forecasts, it will take another 30-odd years to achieve Net Zero. The simple reason for this slow progress is the challenge of balancing the energy density and power distribution equation.
Renewables will only disrupt hydrocarbons when parity is achieved for energy density storage technology. Current battery technology is still in its infancy and heavily dependent on rare earth elements and mining. Batteries are not yet anywhere near the energy density profile of hydrocarbon materials. If you look at electric cars like the Tesla and Porsche Taycan, the battery pack weighs around 600kg. Compare that with the weight of 80 liters of petrol: just 60kg.
The economics, portability and convenience of hydrocarbons is therefore hard to beat, but conversion is not impossible. Renewables now supply 27% of Germany’s electricity, up from 9% a decade ago. Eventually they will crowd out coal, although Germany plans to switch off its nuclear plants first. However, this has come at a cost. Germany has the second-highest consumer prices for electricity in Europe, a wealthy eco-friendly population, and a legacy of rapid industrialization. I am not sure India or China will be able to afford renewables in the same way.
A turning point?
Research has shown that the global response to the Covid-19 pandemic and reduced economic activity has driven the biggest annual fall in CO2 emissions since World War Two. Emissions have declined by around 7% this year. Delhi and Beijing had their first smog-free days in decades. However, this is not a sustainable model. The world population in 2020 was 7.8 billion and this is expected to increase to 9.9 billion by 2050, an increase of 25%. At the same time, we want to achieve a Net Zero carbon footprint by 2050. It is, frankly, difficult to see how this will be achieved.
I believe that energy density is the key driver to addressing Net Zero and climate change challenges. However, we also have to recognise that the price of Net Zero may be slower economic growth. The two are intrinsically linked. The question is whether we are ready to accept slower growth until renewables have achieved energy density parity with hydrocarbo