Why clean energy is far from secure in the future

While the investments are largely aimed at providing feedstock for petrochemical processing at Grangemouth, the development paves the way for onshore gas production, in part to fuel electrical energy generation via gas turbines.

Then there is the sad demise of Pelamis, the Scottish wave power pioneer whose expertise may yet survive through a new Government-backed body, Wave Energy Scotland. While these developments appear to be unconnected, they are in fact both driven by the underlying physics of energy, a topic that is seldom aired in relation to policy making.

Hydrocarbons, such as methane extracted from shale, are energy dense while wave energy is dilute.

The net result of this empirical fact is that modern gas turbines are highly-efficient, compact machines with low capital costs.

In contrast, extracting energy from waves requires vast arrays of large machines with high capital costs due to the sheer scale of engineering required.

Furthermore, while the output of gas turbines can be promptly ramped up or down to meet changing consumer demand, the output from renewable generators is intermittent.

So, in the absence of industrial-scale energy storage, renewable capacity needs to be largely matched by that from responsive plants such as gas turbines. Renewables therefore become a fuel-saver for thermal plants, rather than a direct replacement for them.

The limitations of renewable energy have of course been long known. James Watt's business partner Matthew Boulton was an early adopter of steam power, frustrated at the diminished output of the millwheel at his Birmingham factory when stream flows weakened. Indeed on his success in selling James Watt's new steam engine he boasted to James Boswell: "I sell here, sir, what all the world desires to have, power."

Boulton was indeed selling power, the ability to do useful work where and when required, rather than when the weather allowed. Indeed Watt's innovations largely led to the demise of wind and water as a source of industrial power. This key distinction between the physics of energy and power is one which has largely been forgotten in debates on energy policy.

As Scotland's output of intermittent renewable energy grows, so will the need for responsive gas plants that can deliver power as and when required.

It is therefore surprising that many of those most enthused with renewable energy are also aghast at the prospect of shale gas exploration in Scotland.

Intermittent renewable energy is enabled by gas turbines, and indeed locks in the use of methane to fuel them well into the future.

Worse still, opposition to new nuclear plants at Hunterston and Torness will ultimately see the replacement of significant low carbon baseload nuclear capacity with a mix of intermittent renewable energy backed-up by fossil fuels.

And indeed it will see the replacement of compact nuclear plants using energy dense uranium with diffuse renewables requiring vast quantities of steel, concrete and land per unit of energy actually produced.

Finally, while the physics of energy and power is largely ignored in our policy deliberations, debates on nuclear power itself are even more partisan. For example the Scottish Green Party claim that nuclear is not low carbon, and is in fact no cleaner than an efficient gas plant.

However, taking the median estimates of carbon intensity for gas and nuclear from the International Panel on Climate Change, it is clear that nuclear is some 40 times cleaner than gas and about the same as wind.

That Scotland will see future growth in renewable energy is not in doubt, but if we can't get our thinking on energy straight, then we have little hope of delivering a balanced supply of low cost, secure and clean energy into the far future.

Colin McInnes is Professor of Engineering Science, and Paul Younger is Professor of Energy Engineering, both at the University of Glasgow.