Can renewables meet public and political expectations?

The actual growth rate of Australia's EP over the past decade has been around 1.8% per annum.

In 2013 Australia's EP was $166/gigajoule (GJ), ranking it 11^th in the 34 OECD economies, 9% below the OECD average and 9% above the world average. A 40% increase would have taken Australia to $232/GJ, between Austria and Spain but 27% short of the 2013 leader, Ireland ($316/GJ). These EP figures come from International Energy Agency data for total primary energy supply and GDP in constant US dollars, 2005, purchasing power parity.

What do all these numbers tell us about the current 40% EP target? Frankly I doubt whether anyone knows. A recent rigorous economic analysis of 99 countries over 40 years showed no general decoupling and cautioned against policies aiming to reduce energy intensity (reciprocal of EP) faster than historical norms. Similarly, a recent critical review examined 17 scenarios for 'deep decarbonisation' in the energy sector (e.g. 80% reduction of emissions by 2050) andconcluded that all the scenarios rested on historically unprecedented rates of EP improvement.

For reasons that are unclear, EP growth and associated energy demand reduction seem to attract a unique degree of optimism. A sensible policy stance would be to accept the likelihood of future diminishing returns instead of indefinite EP growth, and account for the observation that EP improves at around the same rate regardless of government policies.

Energy productivity cannot be raised by proclamation.

Energy Return on Investment

The concept of Energy Return on Investment, also called Energy Returned on Energy Invested, originated in the 1970s in the biological discipline of ecology (specifically, migrating fish). It was largely forgotten for three decades, but returned to prominence with rising interest in 'peak oil'.

EROI is the ratio of the energy gained from an energy-obtaining effort to the energy expended in that effort, i.e. energy out : energy in. If it is greater than unity then the effort is, or might be, worthwhile. If it's less than unity the effort is usually pointless.

The idea is simple and important but the analysis needed to account for every component is complex. Results differ and are contentious. To make things worse there is no agreement on the significance of EROI values. Unity is obviously the barest minimum; five has been suggested as the lowest value to make an energy source sustainable. Oil has an EROI as high as 30 but it has been declining to its present 10-20. This is the expected pattern for all earth resources as grades decline and discovery and extraction require more effort.

With renewable energy systems, and especially biofuels, the EROI can be much lower. A recent dramatically low result of 0.83 for solar PV has attracted much debate but is consistent with the commonplace observation that no renewable energy system has been manufactured using only renewable energy. Inclusion of storage or backup for intermittent renewables will likely have the effect of lowering EROI further.

EROI studies do prompt caution about the future role of renewables. I feel confident that, once differences in EROI methodology and results have been resolved, they will eventually provide the objective evidence-based data needed for sound energy policy.

Let me leave the last word to eminent physicist, the late Sir David MacKay FRS, renowned for his advocacy of "numbers, not adjectives" in his book Sustainable Energy – without the hot air. In hislast interview he said that the ideathat renewable energy can power the UK is an "appalling delusion".

The odds are that Australians who expect 100% renewables will be disappointed.