A whirlwind of claim and counter-claim met last week's provocative piece in New Scientist, on a physicist's paper that indicates that perhaps wind power isn't so renewable after all. The paper, by Axel Kleidon, from the Max Planck Institute in Jena, Germany, certainly took an intriguing look at the limits of clean energy's poster-children of wind and wave power. But sadly, overly simplistic readings of the paper seem to have sparked inflated stories, along the lines of 'going green may halt winds'.
Kleidon's paper, to be published in Philosophical Transactions of the Royal Society comes at a fresh angle to the familiar issues around global warming - that of the laws of thermodynamics. He sought to look at the global energy budget of the earth, how much of that could be exploited for our power needs - and then whether massive conversion to wind, wave and solar may themselves have unintended negative consequences for the planet's energy balance - and possibly for climate change.
He concluded that the amount of 'free energy' that humans have to play with - from the planet's sun-driven tumult of wind, wave, solar and organic life - is quite small. The number for 'free energy' is around 1000 terawatts (tW) - but of that only 120 tW is usable by humans, as the rest is either over the oceans, or is lost during power production. Given that humans are currently pulling 17 tW from the earth, as fossil fuels, and using another 30 tW for energy from food, our current needs are already a big proportion of the total 'free energy' available.
Kleidon also sees our energy needs as only ever being on an upward arc - and so concludes that we will need to bump up the 17 tW of fossil fuel energy with ever higher numbers from future renewable sources. Focusing in on wind power, he calculates the most that we can harvest from the wind's 'free energy' is 70 tW. But at that exceptionally high-level, his climate modeling suggests that wind power would be as damaging for some aspects of the climate as doubling CO2.
It was this claim that had news headlines boldly proclaiming that wind power as a dead end for stopping climate change. But leading climate scientists quickly poured cold-water on many of the calculations, and modeling assumptions. For example, the extra heat from wind turbines is tiny compared to the heat already being produced directly from coal, nuclear and gas electricity generation.
Not only that, but the level of wind power Kleidon tested is some 350 times higher than the amount of energy from wind turbines installed now - and no-one is suggesting that all future energy should come only from wind power. That said, this line of inquiry is important. All attempts to extract energy from the earth will affect the energy flows is some way, and we need to get a good handle on those effects.
But a bigger issue is being missed. Human society is already using massive amounts of energy in very wasteful ways, producing goods which ultimately end in land-fill. Perhaps we should really be questioning the assumption of an endless thirst for energy, not taking it as a given. Renewables may have limits, but does our society really need to be pushing so hard towards them?