The modern world stands on a cairn built by energy conversions in the past. Just as it took many loaves of bread and nosebags of hay to build Salisbury Cathedral, so it took many cubic metres of gas or puffs of wind to power the computer and develop the software on which I write these words. The Industrial Revolution was founded on the discovery of how to convert heat into work, initially via steam. Before that, heat (wood, coal) and work (oxen, people, wind, water) were separate worlds.
To be valuable, any conversion technology must produce reliable, just-in-time power that greatly exceeds — by a factor of seven and upwards — the amount of energy that goes into its extraction, conversion and delivery to a consumer. It is this measure of productivity, EROEI (energy return on energy invested), that limits our choice.
By the EROEI criterion, biofuel is a disastrous choice, requiring about as much tractor fuel to grow as you get out in ethanol or biodiesel. Wind power has a low energy return, because its vast infrastructure is energetically costly and needs replacing every two decades or so (sooner in the case of the offshore turbines whose blades have just expensively failed), while backing up wind with batteries and other power stations reduces the whole system’s productivity. Geothermal too may struggle, because turning warm water into electricity entails waste. Solar power with battery storage also fails the EROEI test in most climates. In the deserts of Arabia, where land is nearly free, sunlight abundant and gas cheap, solar power backed up with gas at night may be cheap.
Fossil fuels have amply repaid their energy cost so far, but the margin is falling as we seek gas and oil from tighter rocks and more remote regions. Nuclear fission passes the EROEI test with flying colours but remains costly because of ornate regulation.
Matt Ridley, “Nuclear Fusion Could Provide Unlimited Energy”, HumanProgress, 2018-04-09.
July 9, 2020
QotD: Energy return on energy invested
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