Sunshine, wind, tides and worldwatts

A review of Renewable Energy: Ten Short Lessons

Also published on Resilience

Fun physics fact: water carries so much more kinetic energy than air that “A tidal current of 3 knots has the same energy density as a steady wind stream at 29 knots (a fair old blow).”

And consider this: “Ninety-nine per cent of planet Earth is hotter than 1,000 °C (1,832 °F). The earth is, in fact, a giant leaky heat battery.”

Stephen Peake uses these bits of information and many more to lucidly outline the physical bases of renewable energy sources, including solar and wind energy, geothermal energy, wave energy and tidal current energy. But the book also touches on the complex relationship between the physics of renewable energy, and the role energy plays in human society – and the results aren’t always enlightening.

Peake takes on a formidable task in Renewable Energy: Ten Short Lessons. The book is part of the “Pocket Einstein” series from Johns Hopkins University Press (or from Michael O’Mara Books in Britain). He has less than 200 small-format pages in which to cover both the need for and the prospects for a transition to 100% renewable energy.

Key to his method is the concept of a “worldwatt” – “the rate at which the world uses all forms of primary energy.” Peake estimates the rate of energy flow around the world from various potential renewable energy sources. Not surprisingly, he finds that the theoretically available renewable energy sources are far greater than all energy currently harnessed – primarily from fossil fuels – by the global economy.

But how do we get from estimates of theoretically available energy, to estimates of how much of that energy is practically and economically available? Here Peake’s book isn’t much help. He asks us to accept this summation:

“Taking a conservative mid-estimate of the numbers in the literature, we see that the global technical potential of different renewable sources adds up to 46 worldwatts. There is a definite and reasonable prospect of humans harnessing 1 worldwatt from 100 per cent renewable energy in the future.” (page 31)

But he offers no evidence or rationale for the conclusion that getting 1 worldwatt from renewable sources is a “reasonable prospect”, nor how near or far “in the future” that might occur.

A skeptic might well dismiss the book as renewable energy boosterism, noting a cheery optimism from the opening pages: “There is an exciting, renewable, electric, peaceful, prosperous, safer future just up ahead.” Others might say such optimism is the most helpful position one can take, given that we have no choice but to switch to a renewable energy way of life, ASAP, if we want human presence on earth to last much longer.

Yet a cheerfully pro-renewable energy position can easily shade into a cheerful pro-consumptionist stance – the belief that renewable energies can quickly become the driving force of our current industrial economies, with little change in living standards and no end to economic growth.

Peake briefly introduces a key concept for assessing which renewable energy sources will be economically viable, and in what quantities: Energy Return On Energy Invested (EROEI). He explains that as we exploit more difficult energy sources, the EROEI goes down:

“As wind turbines have become larger and moved offshore, the EROEI ratio for wind over a twenty-year lifetime has declined from around 20:1 in the early 2000s to as low as 15:1 in recent years for some offshore wind farms.” (page 84)

Affordable renewable energy, in other words, doesn’t always “scale up”. The greater the total energy demanded by society, the more we will be impelled to site wind turbines and solar panels in areas beyond the “sweet spots” for Energy Return On Energy Invested. Peake’s book would be stronger if he used this recognition to give better context to statements such as “Renewable electricity is now cheaper than fossil electricity …” (in the book’s opening paragraph), and “solar is now the cheapest electricity in history” (page 70).

While Peake expresses confidence that a prosperous renewable energy world is just ahead, he doesn’t directly engage with the issue of how, or how much, affluent lifestyles may need to change. The closest he comes to grappling with this contentious issue is in his discussion of energy waste:

“We need to stop wasting all forms of energy, including clean renewable sources of heat and electricity. The sooner we shrink our total overall demand for energy, the sooner renewables will be able to provide 100 per cent of the energy we need to power our zero-carbon economies.” (page 141)

Near the end of the book, in brief remarks about electric cars, Peake makes some curious statements about EVs:

“Millions of [electric vehicles] will need charging from the network. This presents both a challenge and an opportunity in terms of managing the network load.” (page 130, emphasis mine)

And a few pages later:

“In the future, new fleets of electric vehicles parked overnight could become another mass source of electricity storage and supply.” (page 134 emphasis mine)

In my next post I’ll take up this concept of the electric vehicle as energy storage, supply and load management resource.

In conclusion, Renewable Energy: Ten Short Lessons is a valuable primer on the physics of renewable energy, but isn’t a lot of help in establishing whether or not the existing world economy can be successfully transitioned to zero-carbon energy.

Photo at top of page: Wind Turbines near Grevelingenmeer, province of Zeeland, Netherlands