Colin McInnes and Ken Ledingham: Era of cheap energy is only over if we chose to make it so

YOU MAY be surprised to learn this but the substitution of coal for wood during the Elizabethan era was the first transition which was made to a low carbon economy.

Coal is a low carbon fuel since, per unit of energy produced, it releases less carbon than wood. This decarbonising of energy production continued through transitions from coal to oil, gas and now nuclear fission. Each new fuel has a higher energy density and lower carbon content than the last, particularly so for carbon-free nuclear energy. Over 400 years, these improvements in energy density have led to better energy utility, falling energy costs and, wonderfully, greater energy use.

During the Elizabethan era wood for fuel became scarce near major population centres. Some advocated simply growing more trees, a diffuse source of energy, to avoid the use of coal. Such a policy would no doubt have led to a sustainable wood burning society, but would never have led to the marvels of the industrial revolution. With the advent of coal-driven steam power, energy costs fell while prosperity rose as carbohydrate fuelled human labour was replaced with hydrocarbon fuelled machines. This is human progress.

In a strong parallel to the Elizabethan aversion to coal, some now advocate avoiding the use of uranium by returning almost entirely to diffuse and intermittent sources of energy, such as wind. This ignores huge improvements in energy density which have successfully delivered a growing supply of low cost, lower carbon energy.

While the wind, waves and sun are of course free, the massive infrastructure to turn it into concentrated electrical energy is not. If we're serious about displacing carbon from energy production we would be well advised to continue along the path of improving energy density. Natural gas has a carbon content about half that of coal. While many worry about the depletion of oil reserves, world utilisation of low carbon gas is likely to grow as high carbon oil prices eventually rise. Large new 'shale gas' fields are being tapped using advances in drilling technology. Compressed gas can be an almost direct substitute for oil in transportation, and is particularly useful for fleet vehicles such as public transport.

Moving to higher energy density again, the use of nuclear fuels can grow to provide carbon-free energy for the long-term future. Some dismiss nuclear energy as unsustainable since uranium is seen as a finite resource. In fact, nuclear energy has the almost magical quality that it can breed its own fuel, while spent nuclear fuel (wrongly classified as waste) still has copious quantities of latent energy which needs to be extracted rather than buried.

Nuclear energy is often claimed to be yesterday's technology. In fact, it is one of the key energy technologies of tomorrow, with compact high temperature reactors co-generating electricity and hydrogen for industry, or desalinating sea water in developing nations. We have only scratched the surface of what is possible with energy dense uranium, and later vast untapped global reserves of thorium, to help deliver a growing supply of clean energy.

While it is widely assumed that the era of cheap energy is over, the last 400 years of energy transitions have seen falling energy costs relative to incomes and growing energy use. The era of cheap energy is only over if we chose so. If we use technical innovation to accelerate, rather than supplant transitions towards greater energy density, we will ensure a supply of energy which becomes both cheaper and more abundant. And, as a useful side effect, we will de-carbonise our economy.

l Colin McInnes is Professor of Engineering Science and Ken Ledingham is William Penny Professor of Laser Nuclear Physics, both at the University of Strathclyde